WO2025002620A1 - Conversion of carbon dioxide to value-added chemicals using zeolite-based catalysts - Google Patents

Abstract

The present invention relates to the field of carbon dioxide (CO₂) utilization and more specifically the conversion of CO₂ into value-added chemicals through hydrogenation. The present invention thus provides methods and catalysts for efficient and selective conversion of CO₂ into value-added chemicals through hydrogenation, as well as systems implementing both of these.

Description

Conversion of carbon dioxide to value-added chemicals using zeolite-based catalysts

Technical field

The present invention relates to the field of carbon dioxide (CO2) utilization and more specifically the conversion of CO2 into value-added chemicals through hydrogenation. The present invention thus provides methods and catalysts for efficient and selective conversion of CO2 into value-added chemicals through hydrogenation, as well as systems implementing both of these.

Background

The accumulation of carbon dioxide (CO2) in the Earth's atmosphere has reached alarming levels, leading to severe environmental consequences such as climate change and global warming. To address this pressing issue, there is an urgent need for innovative approaches that can effectively reduce CO2 emissions and mitigate its impact on the planet. Additionally, the utilization of CO2 plays a crucial role in carbon cycling for the advancement of the circular economy and has gathered significant research attention worldwide due to its potential to mitigate greenhouse gas emissions and contribute to sustainable development.

In this context, zeolites have emerged as highly promising candidates for addressing the challenges associated with CO2 capture and conversion. Zeolites are crystalline, macro-/meso-/ and microporous materials with well-defined structures, characterized by a network of interconnected channels and cages. These unique structures provide an ideal platform for catalytic processes, making zeolites exceptionally versatile in a wide range of applications.

In recent years, there has been substantial research focused on the conversion of CO2 into methanol (CH3OH), which is considered the primary product of interest. However, the synthesis of ethanol or higher-value C2+OH compounds through CO2 hydrogenation has received comparatively limited attention. Ethanol is an attractive target product due to its non-toxic nature and its versatility for further conversion into valuable chemicals, such as ethylene, which has numerous industrial applications. Thus there is a need in the field for further developments of evermore stable and efficient catalysts suitable for CO2 conversion to value-added chemicals and the implementation of such catalysts in catalytic systems which are industrially scalable.

For the practical application of CO2 hydrogenation to ethanol, several challenges have hindered its widespread adoption, such as low selectivity, slow reaction kinetics, undesirable reaction intermediates and poor cost-effectiveness. Thus there remains as need in the field for the development of new catalyst- and/or process designs that can achieve high ethanol selectivity as well as a high CO2 conversion.

Summary

The present invention aims to address at least some of the aforementioned limitations and challenges associated with synthesis of ethanol from CO2 in catalytic hydrogenation reactions.

It is thus a first aspect of the present invention to provide a method for the catalytic hydrogenation of CO2 into ethanol, the method comprising contacting a feed stream containing CO2 and H₂ with a solid heterogeneous catalyst in a reaction chamber, wherein the H2/CO2 volume ratio in the feed stream is from 1 :1 to 10:1.

A second aspect of the present invention is to provide a system for the catalytic conversion of CO2 into ethanol in a hydrogenation reaction, the system comprising: a. a reaction chamber equipped with a zeolite catalyst; b. a reaction chamber inlet for CO2, H₂ and optionally H₂O provided together or separately; c. a heating source; and d. a product outlet; wherein the reaction chamber is a plug-flow reactor and wherein the zeolite catalyst is a gmelinite (GME) based catalyst.

A third aspect of the present invention is to provide a solid zeolite catalyst selected from the group consisting of gmelinite potassium (K-GME), gmelinite sodium (Na- GME), and gmelinite calcium (Ca-GME), characterized in comprising 1-2 wt% (based on total catalyst weight) of at least one auxiliary non-noble transition metal. The present inventors have surprisingly found that all of the above mentioned aspects can aid in providing solutions to the challenge of converting harmful greenhouse gas CO2 into value-added chemicals such as ethanol.

Definitions

As used herein the term “GME” refers to a crystalline synthetic form of the mineral compound gmelinite. Gmelinite is a zeolite with an aluminosilicate framework comprising the repeating unit {(SisAI₄)O24- 11 H₂O}^4-. The structure of the interconnected tetrahedra results in channels and pores within the framework with exposed active sites that can be targeted either for the purpose of catalysis, or for adsorbing a chemical entity such as a metal ion into the channel structure. The negative charge of the aluminosilicate framework may be in principle be balanced by any cationic material or metal. Within the present disclosure, in particular potassium, calcium and sodium forms of GME are highlighted, and referred to as K-GME, Ca-GME and Na-GME respectively. Exemplary K-GME refers to K^SisADOs^l 1 H₂O, while Ca-GME refers to Ca2(Si8Al4)O24-11 H2O. The identifier (K-Ca)-GME refers to mixtures of K-GME and Ca- GME, such as those obtained by ion exchange of Na-GME using both K and Ca as exchange ions. Other zeolite abbreviations used herein which are well known to those skilled in the art include CHA (Chabazite), FAU (Faujasite), and ANA (analcime).

As used herein, the symbols 7’ such as used in relation to zeolites, e.g., in H-Cu/FAU or K-Cu/GME refers to the situation where Cu (or another metal) was added in the zeolite structure by an adsorption process like incipient wetness impregnation or ion exchange. On the other hand, the term

such as used for K-Cu@GME refers to the situation where a zeolite which already contained Cu was transformed and/or recrystallized (such as by inter-zeolite transformation) into another framework/structure which now also contains Cu adsorbed and/or doped and/or incorporated into the pores of the zeolite framework as an auxiliary metal framework without affecting the aluminosilicate structure. The same terminology may be used for other metals and other zeolite structures.

As used herein, the symbol ‘V such as used in relation to silylated zeolites 0.5h₄\K- Cu@GME refers to a catalyst obtained by the reaction between silylating agent h₄ and the zeolite K-Cu@GME. Further herein, the ‘0.5h4’ in 0.5h4\K-Cu@GME refers to the reaction stoichiometry between silylating agent h₄ and K-Cu@GME, and identifies that 0.5 mmol h4 per gram K-Cu@GME zeolite was employed in the reaction. The same nomenclature may be used for other silylating agents and zeolite systems.

As used herein the term “AFI” refers to a zeolite of a specific structural type. The AFI- framework is originally identified in the material abbreviated ‘AIPO-5’ which is an aluminophosphate known to those skilled in the art of heterogeneous catalysis. The AFI framework resembles the GME framework in the crystallographic ab-plane with big 12-membered channels with an aperture of 7.3 A, but only has these parallel nonintersecting channels as opposed to the GME framework which also features intersecting 8-membered channels.

As used herein, the term “one-pot” or “one-step” in relation to catalytic hydrogenation reaction refers to a process wherein successive chemical reaction steps are performed in one reaction chamber or reaction vessel without isolation, separation or purification of any intermediates. In such reactions, the only separation of the intermediate and/or product mixture is performed in isolation of the final desired product. One-pot reactions are particularly advantageous for scale-up as they require less physical interventions. The term “one-pot reaction” and/or “one-step reaction” is a well-known term in the field of chemicals synthesis.

Description of Drawings

Figure 1 : The effect of water addition in the CO2 conversion and selectivity of the CO2 hydrogenation catalyzed by the K-Cu@GME zeolite as prepared following Example 1 . Testing was performed in a temperature range from 200°C to 350 °C under H2/CO2 volume ratio of 5 and a pressure of 2.0 MPa. The H2O/CO2 molar ratio was varied as being A) 0, B) 0.35, C) 0.5 and D) 0.4. The shown data is for a Cu-loading of 1 wt% in K-Cu@GME.

Figure 2: The influence of pressure in the CO2 hydrogenation towards ethanol production under H2/CO2 volume ratio of 5 and a H2O/CO2 molar ratio of 0.4 at 250°C. The shown data is for a Cu-loading of 1 wt% in K-Cu@GME as prepared following Example 1 . Figure 3: The effect of the Cu loading in the direct synthesis of ethanol from CO2 under H2/CO2 ratio of 5 and a H2O/CO2 ratio of 0.4 at 250°C and 2.0 MPa using the catalyst system K-xCu@GME, x referring to the wt% of Cu (based on total catalyst weight) as illustrated on the principal axis and prepared following Example 1 .

Figure 4: Selectivity and CO2 conversion from the stability test of Ca-Cu@GME under H2/CO2 volume ratio of 5 and a H2O/CO2 molar ratio of 0.4 at 250°C and 2.0 MPa. The shown data is for a Cu-loading of 1 wt% in K-Cu@GME as prepared following Example 1.

Figure 5: X-ray d iff ractog rams of K-Cu@GME reacted with varying amounts of the silylating agent trichloromethylsilane (hi). Obtained at room temperature using Cu-Ka radiation.

Figure 6: X-ray d iff ractog rams of K-Cu@GME reacted with 0.5 mmol of silylating agent per 1 gram of zeolite. Employed silylating agents are trimethylchlorosilane (h₂), trimethoxymethylsilane (h₃) and hexadecyltrimethoxysilane (h₄). Obtained at room temperature using Cu-Ka radiation.

Figure 7: Structural and catalytic investigation of mixed (K-Ca)-Cu@GME catalyst. A: Selectivity and CO2 conversion from the stability test of (K-Ca)-Cu@GME under H2/CO2 volume ratio of 5 and a H2O/CO2 molar ratio of 0.4 at 250°C and 2.0 MPa. The shown data is for a nominal Cu-loading of 1 wt% in (K-Ca)-Cu@GME. The dotted line represents CO2 conversion as indicated on the right y-axis, while the bar charts display selectivities on the left y-axis.

B: comparative X-ray diffractograms of Na-GME, (K-Ca)-GME, (K-Ca)-Cu@GME and (K-Ca)-Cu@GME reacted with 0.5 mmol of hexadecyltrimethoxysilane (h₄) per 1 gram of zeolite. The diffractograms illustrate the structural similarity between all four samples. Obtained at room temperature using Cu-Ka radiation.

Figure 8: Selectivity and CO2 conversion from the stability test of silylated xh K- Cu@GME (x = 0.5, 2.5, 7.5 or 10) under H2/CO2 volume ratio of 5 and a H2O/CO2 molar ratio of 0.4 at 250°C and 2.0 MPa. The shown data is for a nominal Cu-loading of 1 wt%. The dotted line represents CO2 conversion as indicated on the right y-axis, while the bar charts display selectivities on the left y-axis. A: 0.5hi\K-Cu@GME; B: 2.5hi\K-Cu@GME; C: 7.5hi\K-Cu@GME; D: 10hAK- Cu@GME.

Figure 9: Selectivity and CO2 conversion from the stability test of silylated 0.5h_x\K- Cu@GME (x = 2, 3 or 4) under H2/CO2 volume ratio of 5 and a H2O/CO2 molar ratio of 0.4 at 250°C and 2.0 MPa. The shown data is for a nominal Cu-loading of 1 wt%. The dotted line represents CO2 conversion as indicated on the right y-axis, while the bar charts display selectivities on the left y-axis.

A: 0.5h₂\K-Cu@GME; B: 0.5h₃\K-Cu@GME; C: 0.5h₄\K-Cu@GME.

Figure 10: Selectivity and CO2 conversion from the stability test of silylated 0.5h₄\(K- Ca)-Cu@GME under H2/CO2 volume ratio of 5 and a H2O/CO2 molar ratio of 0.4 at 250°C and 2.0 MPa. The shown data is for a nominal Cu-loading of 1 wt%. The dotted line represents CO2 conversion as indicated on the right y-axis, while the bar charts display selectivities on the left y-axis. Stable operation and ethanol production is observed for the full 50 hours duration of the test.

Figure 11 : Selectivity and CO2 conversion from the test of silylated 0.5hi\K-Cu@GME where water is added periodically every three hours of operation. H2/CO2 volume ratio of 5; T = 250°C; P = 2.0 MPa. The shown data is for a nominal Cu-loading of 1 wt%. The dotted line represents CO2 conversion as indicated on the right y-axis, while the bar charts display selectivities on the left y-axis. Water was added continuously for the first hour at a H2O/CO2 molar ratio of 0.4, then cut off for the subsequent two hours. This cycle was repeated for the duration of the test. Catalyst lifetime was improved drastically by this methodology.

Detailed description

The present invention is directed to a new method for catalytic hydrogenation of CO2 which involves chemical manipulation of CO2 and H₂ by solid heterogeneous catalysts into value-added chemicals such as ethanol, thereby allowing for utilization of CO2 in carbon cycling for the advancement of circular economy.

One embodiment of the present disclosure is to provide a method for the catalytic hydrogenation of CO2 into ethanol, the method comprising contacting a feed stream containing CO2 and H₂ with a solid heterogeneous catalyst in a reaction chamber, wherein the H2/CO2 volume ratio in the feed stream is from 1 :1 to 10:1 . The feed stream may preferably be a gaseous feed stream. The hydrogenation may preferably be operated continuously or in cycles. An advantage of the disclosed method is however that it can be operated in a single reactor unit and thereby enables easier scale-up and maintenance.

The present inventors have surprisingly identified a catalyst composition and process method which when subjected to appropriate feed stream compositions and reaction parameters produce value-added chemicals such as ethanol with sufficiently high selectivity and conversion rate to be industrially relevant.

In one embodiment of the presently disclosed method, the H2/CO2 volume ratio in the feed stream is from 1 :1 to 10:1 , such as 1 :1 , such as 2:1 , such as 3:1 , such as 4:1 , such as 5:1 , such as 6:1 , such as 7:1 , such as 8:1 , such as 9:1 , such as 10:1 or any 0.5 increment therein between. Preferably, the molar ratio of H2 and CO2 in the feed stream is from 4:1 to 6:1 , such as 4.5:1 to 5.5:1 , such as 5:1 .

In one embodiment of the presently disclosed method, the reaction chamber is selected from the group consisting of plug-flow reactor, multi-tubular reaction, fluidised bed reactor and void reactor. In one embodiment, the reaction chamber is a plug-flow reactor. The examples of the present disclosure makes use of a plug-flow reactor comprising a stainless steel reactor with an inner diameter of 4 mm, wherein the active catalyst is fixed between two sections of quartz wool. It will be immediately apparent to the skilled person that other types of plug-flow reactors of different type and dimensions would be equally suitable for use in the method of the present disclosure, thus it is also within the scope of the present disclosure to cover such embodiments.

The majority of solid heterogeneous catalysts employed industrially are solid acid catalysts. Thus, in one embodiment, the solid heterogeneous catalyst is an acidic catalyst.

Solid acid catalyst is generally considered as any type of acid which is not soluble in the reaction medium. This may for some reactions include organic acids such as oxalic acid, tartaric acid, but for most purposes refer to metal oxides such as titania, zirconia, alumina, niobia and mixed silicoaluminates (or aluminosilicates) including zeolites. Thus in one embodiment of the presently disclosed method, the catalyst is a zeolitebased catalyst.

One of the key advantages of zeolites lies in their exceptional catalytic properties. The inherent porosity of zeolites allows for high surface areas, providing numerous active sites for catalytic reactions. This enables efficient adsorption and activation of CO2 molecules, facilitating subsequent conversion reactions. The well-defined and uniform pore sizes of zeolites also contribute to their selectivity, allowing for precise control over reaction pathways and product distributions.

Furthermore, the chemical composition of zeolites can be tailored and modified to enhance their catalytic performance. Through the incorporation of different metal ions or organic functional groups, zeolites can be customized to exhibit specific catalytic properties, such as improved CO2 adsorption capacity, enhanced stability, and increased reaction rates. This tunability makes zeolites adaptable to various CO2 conversion processes and enables the optimization of reaction conditions to achieve desired product yields and selectivities.

In one embodiment of the presently disclosed method, the catalyst is a zeolite-based catalyst selected from the group consisting of gmelinite (GME), chabazite (CHA), faujasite (FAU), and analcime (ANA), preferably, the zeolite-based catalyst is based on gmelinite (GME).

Gmelinite (GME) is a naturally occurring sodium-calcium zeolite, and the framework has a three-dimensional micropore system. These multipore frameworks are especially interesting for catalysis, since the pores of different sizes could allow unique catalytic activities. Compared to many other zeolite frameworks, the GME framework has not implemented industrially in catalysis so far. This is thought to be due to frequently occurring stacking faults, which both synthetic and natural occurring gmelinite is prone to display, wherein chabazite (CHA) intergrowths block the main GME channel. As a result of this, entire layers of a GME zeolite can consists of CHA, which drastically limits the porosity of the zeolite, and thus its potential applications.

The presently disclosed method, however, is suitable to produce GME structures of very high purity, such as of more than 90% purity, such as substantially devoid and/or free of any CHA. In one embodiment of the presently disclosed method, the catalyst has a Si/AI ratio between 2.0 and 4.0, such as between 2.0 and 2.5, such as between 2.5 and 3.0, such as between 3.0 and 3.5, such as between 3.5 and 4.0, preferably between 3.0 and 4.0, such as 3.1 , 3.2, 3.3, 3.4, 3.5, 3,6, 3.7, 3.8, 3.9, 4.0, or any 0.01 increment therein between.

Gmelinite zeolites are sometimes referred to by their cation constituents, such as gmelinite potassium being characterized by the repeating unit K₄(Si₈AI₄)O2₄-11 H₂O. It will be apparent to the skilled person that other cationic species can be used in combination with the aluminosilicate, and may in some embodiments be one or more elements selected from main group 1 or 2 of the periodic table, ie the cation of gmelinite may in some embodiments be one or more selected from the group consisting of lithium, sodium, potassium, rubidium, caesium, francium, beryllium, magnesium, calcium, strontium, barium and radium. In one embodiment of the presently disclosed method, the catalyst is preferably selected from the group consisting of gmelinite sodium (Na-GME), gmelinite potassium (K-GME) and gmelinite calcium (Ca-GME) or a gmelinite wherein the cation is a mixture of at least two cations selected from sodium, potassium and calcium. In one embodiment, the at least two cations are potassium and calcium. In one embodiment, the gmelinite catalyst always comprise potassium, alone or in combination with another cation.

In one embodiment of the presently disclosed method, the catalyst unit cell comprises a repeating unit selected from the group consisting of Na₄(Si₈AI₄)O2₄-1 1 H₂O, K₄(Si₈AI₄)O₂₄- 11 H₂O, and Ca₂(Si₈AI₄)O₂₄-1 1 H₂O.

Potassium and calcium cations have higher ionic radii than sodium cations, therefore, they are expected to be more strongly linked to the zeolite framework. As a result, the structure is more stable and can resist greater temperatures without collapsing or losing crystallinity. Furthermore, the presence of these exchangeable cations can result in a more rigid structure, which improves the zeolite's thermal stability. As a result, K- GME and Ca-GME zeolites are preferred over Na-GME zeolites for high-temperature applications including catalysis and gas separation as in the present disclosure. The inventors of the present application have surprisingly found that the operando and/or in situ lifetime of the hydrogenation catalyst can be significantly improved by reaction with silylating agents bearing hydrophobic groups. Without wishing to be bound by theory, this improved stability is believed to arise as a result of a hydrophobic layer protecting the zeolite framework from highly hydrophilic molecules during reaction, allowing with preference less polar molecules such as hydrogen, carbon dioxide, alkanes and alcohols to pass the layer. As such, deactivation of the catalyst is postponed evidenced in a stable product mixture for a longer period of continuous operation, such as of more than 20, 30 or even 50 hours. Even more surprising is also that the silylating agent can be added in only very small quantities of approximately 0.5 mmol pr gram of zeolite in order to obtain the effect, and likely also with even lower loadings. This could not be predicted based on the available prior art where usually up to 10 mmol (20 timers higher silylation loading) is needed for a significant improvement in stability and substrate conversion.

In an embodiment of the present disclosure, the catalyst comprises a hydrophobic layer, such as a hydrophobic layer obtained by silylation of zeolite OH-groups using a silylating agent. Preferably, the catalyst is a silylated heterogenous catalyst such as a silylated zeolite-based catalyst, or is a catalyst having been subjected to a step of silylation using a silylating agent.

In an embodiment of the present disclosure, the catalyst is a silylated Cu-doped gmelinite based catalyst such as silylated K-GME, Ca-GME or (K-Ca)-GME, obtained by the reaction with a silylating agent selected from the group consisting of trichloromethylsilane (hi), trimethylchlorosilane (hs), trimethoxymethylsilane (hs) and hexadecyltrimethoxysilane (h₄).

In one embodiment, the silylating agent is trichloromethylsilane (hi). In one embodiment, the silylating agent is trimethylchlorosilane (hs) - In one embodiment, the silylating agent is trimethoxymethylsilane (h₃). In one embodiment, the silylating agent is hexadecyltrimethoxysilane (h₄).

In one embodiment of the present disclosure, the catalyst is a silylated Cu-doped gmelinite based catalyst such as K-GME, Ca-GME or (K-Ca)-GME obtained by the reaction with hexadecyltrimethoxysilane (h4), preferably in an amount of 0.5 mmol silylating agent per gram of zeolite.

In one embodiment of the present disclosure, the catalyst is a silylated Cu-doped gmelinite based catalyst obtained by the reaction of Cu-doped K-GME or (K-Ca)-GME with hexadecyltrimethoxysilane (h4).

In one embodiment of the present disclosure, the silylated zeolite catalyst comprise and/or is obtained by reaction with 0.1 mmol to 20 mmol silylating agent per gram of zeolite, such as 0.5 mmol to 10 mmol silylating agent per gram of zeolite, such as 0.5 mmol silylating agent per gram of zeolite, such as 1 .0 mmol silylating agent per gram of zeolite, such as 2.5 mmol silylating agent per gram of zeolite, such as 5.0 mmol silylating agent per gram of zeolite, such as 7.5 mmol silylating agent per gram of zeolite, such as 10.0 mmol silylating agent per gram of zeolite. In one embodiment, the silylated catalyst comprise 0.4 mmol to 0.6 mmol silylating agent per gram of zeolite, such as 0.5 mmol silylating agent per gram of zeolite.

In one embodiment, the catalyst denoted 0.5h₄\(K-Ca)-Cu@GME is characterized by Si/AI = 3.6; Cu/AI = 0.030; K/AI = 0.29; Ca/AI = 0.59; Cu (wt%) = 0.82, as determined by XRF analysis.

In one embodiment of the presently disclosed method, the catalyst further comprises at least one auxiliary transition metal, such as a non-noble transition metal. The catalyst may in some embodiments comprise from 0.5 to 5.0 wt% (based on total catalyst weight) of at least one auxiliary transition metal, such as non-noble transition metal. Preferably, the at least one auxiliary transition metal is present in an amount (based on total catalyst weight) from 0.5 wt% to 2.5 wt%, such as from 0.5 wt% to 2.0 wt%, such as from 0.8 wt% to 2.2 wt%, such as from 0.5 wt% to 1 .5 wt%, such as from 1 .0 wt% to 1 .5 wt%, such as from 1 .0 wt% to 2.0 wt%.

In one embodiment of the presently disclosed method, the catalyst may comprise 0.8 wt% to 2.2 wt% (based on total catalyst weight) of at least one auxiliary non-noble transition metal, such as selected from Cu, Fe, Co, Mn, Cr or any two-element mixture thereof, such as 0.8 wt% to 0.9 wt%, such as 0.9 wt% to 1 .0 wt%, such as 1 .0 wt% to 1.1 wt%, such as 1 .1 wt% to 1 .2 wt%, such as 1 .2 wt% to 1 .3 wt%, such as 1 .3 wt% to 1 .4 wt%, such as 1 .4 wt% to 1 .5 wt%, such as 1 .5 wt% to 1 .6 wt%, such as 1 .6 wt% to

1 .7 wt%, such as 1 .7 wt% to 1 .8 wt%, such as 1 .8 wt% to 1 .9 wt%, such as 1 .9 wt% to

2.0 wt%, such as 2.0 wt% to 2.1 wt%, such as 2.1 wt% to 2.2 wt% (based on total catalyst weight) of at least one auxiliary non-noble transition metal, such as selected from Cu, Fe, Co, Mn, Cr or any two-element mixture thereof.

In one embodiment of the presently disclosed method, the non-noble transition metal is selected from the group consisting of Cu, Fe, Ni, Co, Mn, Cr, or any two-element mixture thereof, but is preferably comprising Cu, such as consisting essentially of Cu, more preferably zero-valent Cu.

One embodiment of the presently disclosed method further comprises a step of introducing water into the reaction chamber. Water may be introduced together with H₂ and CO₂ in the feed stream or separately through a dedicated water-inlet using a pump, such as an HPLC pump. Water may in one embodiment be introduced so as to provide a H2O/CO2 molar ratio between 0.1 and 1 .0.

The introduction of water may have an impact on the selectivity and yield of the intended alcohols through modification of the reaction pathways. Water, as a reactant, participates in the well-known water-gas shift reaction (WGSR), by reacting with CO to produce H₂ and CO₂. This exothermic reaction is thermodynamically favored at elevated temperatures, typically exceeding 400°C, and requires a catalyst, such as copper or iron, to proceed to great extent. Without wishing to be bound by theory, the present inventors contemplated that by facilitating the conditions for the water-gas shift reaction, the production of CO (observed e.g., in Fig. l a when no water is added) could be avoided because the produced CO is further reacted in the process, thereby increasing the ethanol yield and selectivity. Indeed, at a H2O/CO2 value of 0.35, the CO selectivity has greatly decreased, and at a value of 0.4 no CO is identified in the product stream. Instead, a markedly higher ethanol selectivity is observed. The implementation of water at high temperatures in reactions involving zeolite-based materials is however non-trivial because water is a known degrader of zeolites, in particular by hydrolysis of AI-0 and Si-0 bonds and removal of Al from its tetrahedral positions and creation of extra framework Al species (EFAI). It is therefore surprising that the zeolite is stable for any significant amount of time at the elevated temperatures of more than 200 °C in the presence of water. Thus, in one embodiment of the presently disclosed method, the molar ratio of H2O and CO2 is between 0.1 and 1 .0, such as 0.1 , such as 0.2, such as 0.3, such as 0.4, such as 0.5, such as 0.6, such as 0.7, such as 0.8, such as 0.9, such as 1 .0 but is preferably 0.4 or 0.5, more preferably the molar ratio of H₂O and CO2 0.4.

In one embodiment of the presently disclosed method, the H2O/CO2 molar ratio is between 1 :10 and 1 :1 , such as 1 :10, such as 2:10, such as 3:10, such as 4:10, such as 5:10, such as 6:10, such as 7:10, such as 8:10, such as 9:10, such as 1 :1 but is preferably 4:10 or 5:10, more preferably H2O/CO2 molar ratio is 4:10.

One embodiment of the present disclosure is to provide a method for the catalytic hydrogenation of CO2 into ethanol in the presence of a zeolite catalyst, the method comprising contacting a feed stream containing CO2 and H₂ with the catalyst and a source of water such as to achieve a H2O/CO2 ratio of from 0.4 to 0.5, wherein the source of water is provided periodically for one every three consecutive hours; preferably wherein the zeolite catalyst is a silylated Cu-doped GME catalyst, such as obtained by the reaction between Cu-doped GME and a silylating agent.

The feed stream may in some embodiments comprise other reagents and/or molecules than only carbon dioxide and hydrogen, that is to say the feed stream may in one embodiment comprise CO2, H₂ and at least one further reagent such as carbon monoxide. Without wishing to be bound by theory, it is believed that the combination of CO2 and CO with H2 will generally result in higher conversion of CO2, thereby increasing the yield of value-added chemicals produced from the reaction.

Thus in one embodiment of the presently disclosed method, the CO/CO2 molar ratio is between 1 :10 and 1 :1 , such as 1 :10, such as 2:10, such as 3:10, such as 4:10, such as 5:10, such as 6:10, such as 7:10, such as 8:10, such as 9:10, such as 1 :1. More preferably the CO/CO2 molar ratio is below 4:10, such as below 3:10, such as below 2:10, such as between 5:100 and 2:10.

Like water, pressure, and in particular high pressure also plays a crucial role in this disclosed method, as it can significantly influence the conversion rate and selectivity of the reaction. Therefore, in one embodiment of the presently disclosed method, the catalytic hydrogenation is carried out at non-ambient pressure. In one embodiment, the catalytic hydrogenation is carried out at a pressure between 0.5 MPa and 5 MPa, such as between 1 .0 MPa and 4 MPa, such as between 1 .5 MPa and 3 MPa, such as between 1 .5 MPa and 2.5 MPa, such as between 1 .7 MPa and 2.3 MPa, such as between 1 .8 MPa and 2.2 MPa, such as between 1 .9 MPa and 2.1 MPa, such as 2.0 MPa

As shown in Fig. 2, the conversion rate of CO2 gradually increases with pressure, ranging from approximately 6.1 % at 1 .5 MPa to approximately 8.5% at 3.0 MPa. Surprisingly, the selectivity towards ethanol production does not follow the same trend and instead displays an optimum at 2.0 MPa of pressure. Starting from only a few percent at 1 .5 MPa, ethanol selectivity increases to a significant 63% at 2.0 MPa (corresponding to 7.33% CO2 conversion) before again dropping down to modest but still relevant 44% and 39% at 2.5 MPa and 3.0 Mpa respectively.

In one embodiment, the catalytic hydrogenation is carried out at a pressure a or above 1 .8 MPa, such as at or above 1 .9 MPa, such as at or above 2.0 MPa.

In one embodiment of the presently disclosed method, the catalyst is brought into contact with the feed stream at a temperature of at least 200 °C, such as at least 250 °C, such as at least 300 °C, such as at least at least 350 °C.

In one embodiment of the presently disclosed method, the catalyst is brought into contact with the feed stream at a temperature from 200 °C to 500 °C, such as from 200 °C to 400 °C, such as from 250 °C to 350 °C, such as from 275 °C to 325 °C, but preferably at a temperature ranging from 250 °C to 300 °C.

In one embodiment of the present disclosure, the method provides continuous CO2 conversion above 6.0 % for at least 8 hours of continuous operation and/or hydrogenation, such as for at least 15 hours, such as for at least 25 hours, such as for at least 40 hours, such as for at least 50 hours.

In one embodiment of the present disclosure, the method provides continuous CO2 conversion above 7.0 % for at least 8 hours of continuous operation and/or hydrogenation, such as for at least 15 hours, such as for at least 25 hours, such as for at least 40 hours, such as for at least 50 hours.

In one embodiment of the present disclosure, the method provides continuous CO2 conversion above 8.0 % for at least 8 hours of continuous operation and/or hydrogenation, such as for at least 15 hours, such as for at least 25 hours, such as for at least 40 hours, such as for at least 50 hours.

In one embodiment of the present disclosure, the method is for catalytically producing ethanol from CO2 hydrogenation reaction with a selectivity of at least 30% during continuous operation for at least 8 hours, such as for at least 15 hours, such as for at least 25 hours, such as for at least 40 hours, such as for at least 50 hours.

In one embodiment of the present disclosure, the method provides continuous ethanol selectivity is above 30 % for at least 8 hours of continuous operation and/or hydrogenation, such as for at least 15 hours, such as for at least 25 hours, such as for at least 40 hours, such as for at least 50 hours.

In one embodiment of the present disclosure, the method is for catalytically producing ethanol from CO2 hydrogenation reaction with a selectivity of at least 40% during continuous operation for at least 8 hours, such as for at least 15 hours, such as for at least 25 hours, such as for at least 40 hours, such as for at least 50 hours.

In one embodiment of the present disclosure, the method provides continuous ethanol selectivity is above 40 % for at least 8 hours of continuous operation and/or hydrogenation, such as for at least 15 hours, such as for at least 25 hours, such as for at least 40 hours, such as for at least 50 hours.

In one embodiment of the present disclosure, said method provides ethanol selectivity which is stable or which does not decrease for at least 8 hours of continuous operation, such as for at least 15 hours, such as for at least 25 hours, such as for at least 40 hours, such as for at least 50 hours.

One embodiment of the present disclosure is a method for catalytically producing ethanol through the direct hydrogenation of CO2 using a solid heterogeneous catalyst, comprising providing a solid heterogeneous catalyst in a reaction chamber, heating said reaction chamber to a temperature of at least 150 °C, such as to a temperature from 250 °C to 300 °C, and simultaneously or subsequently contacting said solid catalyst with a feed stream having a H₂/CC>2=5 volume ratio and a H₂O/CO2=0.4 molar ratio, optionally wherein said solid heterogeneous catalyst is gmelinite potassium (K- GME) or gmelinite calcium (Ca-GME) further comprising Cu as an auxiliary transition metal in an amount from 0.5 wt% to 2.5 wt% (based on total catalyst weight), such as from 0.8 wt% to 2.2 wt%, such as from 0.5 wt% to 2.0 wt%, such as from 1 .0 wt% to 2.0 wt%.

It is also within the present disclosure to provide a system for the catalytic conversion of CO2 into ethanol in a hydrogenation reaction, the system comprising: a. a reaction chamber equipped with a zeolite catalyst; b. a reaction chamber inlet for CO2, H₂ and optionally H₂O provided together or separately; c. a heating source; and d. a product outlet; wherein the reaction chamber is a plug-flow reactor and wherein the zeolite catalyst is a gmelinite (GME) based catalyst.

In one embodiment of the presently disclosed system, the catalyst is selected from the group consisting of gmelinite sodium (Na-GME), gmelinite potassium (K-GME) and gmelinite calcium (Ca-GME), and/or the catalyst unit cell comprises a repeating unit selected from the group consisting of Na₄(Si8AI₄)O₂₄-11 H₂O, K₄(Si8AI₄)O2₄-11 H₂O, and Ca2(Si8AI₄)O24- 11 H2O.

In one embodiment of the presently disclosed system, the catalyst is a mixed gmelinite potassium/calcium catalyst (K-Ca)-GME. Preferably the potassium and calcium is present in K/Ca ratio ranging from 0.4 to 4, more preferably ranging from 0.5 to 2.0, more preferably from 1 .0 to 1 .5.

In one embodiment of the presently disclosed system, the catalyst may be a silylated catalyst obtained by the reaction between a gmelinite or Cu-doped gmelinite catalyst and a silylating agent, such as selected from the group consisting of trichloromethylsilane (hi), trimethylchlorosilane (h₂), trimethoxymethylsilane (hs) and hexadecyltrimethoxysilane (h₄). Also within the scope of the present disclosure is use of such silylated catalysts (catalysts obtained by said reaction), for catalytic hydrogenation of CO2 into value-added chemicals, such as ethanol.

In one embodiment of the presently disclosed system, the catalyst may further comprise at least one auxiliary transition metal, such as comprise from 0.5 to 5 wt% (based on total catalyst weight) of at least one auxiliary transition metal. The transition metal is preferably a non-noble transition metal and may in one embodiment be selected from the group consisting of Cu, Fe, Ni, Co, Mn, Cr, or any two-element mixture thereof, but is preferably comprising Cu, such as consisting essentially of Cu, more preferably zero-valent Cu.

The catalyst of the disclosed system may in some embodiments comprise from 0.5 to 5.0 wt% (based on total catalyst weight) of the at least one auxiliary transition metal, such as non-noble transition metal. Preferably, the at least one auxiliary transition metal is present in an amount (based on total catalyst weight) from 0.5 wt% to 2.5 wt%, such as from 0.8 wt% to 2.2 wt%, such as from 0.5 wt% to 2.0 wt%, such as from 0.5 wt% to 1 .5 wt%, such as from 1 .0 wt% to 1 .5 wt%.

It is also within the scope of the present disclosure to provide a solid zeolite catalyst selected from the group consisting of gmelinite potassium (K-GME), gmelinite sodium (Na-GME), and gmelinite calcium (Ca-GME), characterized in comprising 0.5 wt% to 2.5 wt% (based on the total catalyst weight) of at least one auxiliary non-noble transition metal. In one embodiment, the at least one auxiliary non-noble transition metal is present in an amount (based on total catalyst weight) from 0.8 wt% to 2.2 wt%, such as from 1 .0 wt% to 2.0 wt%, such as from 1 .0 wt% to 1 .5 wt%.

The auxiliary non-noble transition metal of the presently disclosed zeolite catalyst is preferably a non-noble transition metal, and may in one embodiment be selected from the group consisting of Cu, Fe, Ni, Co, Mn, Cr, or any two-element mixture thereof, but is preferably comprising Cu, such as consisting essentially of Cu, more preferably zero- valent Cu.

It is also within the scope of the present disclosure to encompass the use of the catalyst as provided hereinabove for the catalytic hydrogenation of CO2 into a value- added chemical, such as wherein the chemical is selected from the group consisting of ethanol, methanol, methane, methanal, and ethanal (CH₃CHO), preferably ethanol.

In one embodiment, the use is of a Cu-doped zeolite catalyst obtained by reaction such as K-GME, Ca-GME or (K-Ca)-GME obtained by the reaction with a silylating agent selected from the group consisting of trichloromethylsilane (hi), trimethylchlorosilane (hs), trimethoxymethylsilane (hs) and hexadecyltrimethoxysilane (h₄).

In one embodiment of the present disclosure, the use is of a silylated catalyst obtained by the method comprising: a. providing a gmelinite based zeolite selected from potassium gmelinite, sodium gmelinite, calcium gmelinite or a mixture thereof such as mixed potassium/calcium gmelinite; b. dispersing said zeolite into an organic non-polar solvent, preferably toluene to provide a first solution; c. preparing a second solution by dissolving a silylating agent in an organic non-polar solvent, preferably toluene; d. mixing the first solution with the second solution and stirring the resulting mixture for at least 8 hours, more preferably 24 hours; and e. recovering the silylated gmelinite-based catalyst from the mixture.

It is preferred that said gmelinite based zeolite is doped with from 0.8 to 2.2 wt% Cu (based on total catalyst weight before silylation) in order to ensure sufficient catalytic hydrogenation properties of the resulting catalyst.

Examples

In the following, unless specified otherwise, catalysts referred to as H-Cu/FAU, K- Cu@GME, Na-Cu@GME and Ca-Cu@GME refer to zeolites with a 1 wt% (based on the total catalyst weight) Cu-loading. For catalysts having been subjected to reaction with a silylating agent, the Cu-loading (unless specified otherwise) also refers to 1 wt% (based on the total catalyst weight) prior to reaction with the silylating agent.

Materials

All reagents used in the procedures were of reagent grade and used without further purification. These included CBV400 (H-FAU, Zeolyst, Si/AI = 2.6), NaOH (>98.7%, VWR Chemicals, 1310-73-2), KNO₃ (>99%, Sigma-Aldrich, 7757-79-1 ), Ca(NO₃)₂-4H₂O (99%, Sigma-Aldrich, 13477-34-4), Cu(NO₃)₂-xH₂O (>99.999%, Sigma-Aldrich, 13778-31 -9), Toluene (99%, Sigma Aldrich, 108-88-3), Trichloromethylsilane (CH₃SiCI₃, 99%, Sigma Aldrich, 75-79-6), Trimethylchlorosilane ((CH₃)₃SiCI, 99%, Sigma Aldrich, 75-77-4), Trimethoxymethylsilane (CH₃Si(OCH₃)₃, 95%, Sigma Aldrich, 1185-55-3), Hexadecyltrimethoxysilane (H₃C(CH₂)i₅Si(OCH₃)₃, > 85%, Sigma Aldrich, 16415-12-6).

Methods

X-

was carried out by using a HUBER G670 Gionier camera in transmission mode with Cu-Ka radiation. The powders were measured with 0.005° steps for 1 hour.

N₂

measurements were performed at 77 K with a Micromeritics 3Flex.

Prior to the measurements, the powders were degassed at 400 °C overnight under vacuum. The Brunauer-Emmett-Teller (BET) method was used to estimate the surface area. The pore volume of the materials was estimated by a single point adsorption at 0.95 relative pressure. The t-plot method (Galarneau, A. et al.) was used to calculate the micropore volume, an alternative methodology could follow ASTM D4365. The Barrett-Joyner-Halenda (BJH) method on the desorption brand was used for the pore size distribution.

Transmission electron

was performed on the calcined Cu-containing zeolites on a FEI Tecnai T20 G2 microscope with 200 kV acceleration voltage.

analysis was conducted on a ThermoFischer

Scientific K-Alpha™ with a monochromated Al Ka X-ray source. The elemental spectra were measured with a pass energy of 50 eV and step size of 0.1 eV, at an operating vacuum of about 2- 10⁷ mbar.

Scanninq electron

(SEM) was done on a Quanta 200 ESEM FEG operated at 20 kV. The samples were loaded on carbon tape and coated with gold for 60 seconds at 20 nA current in argon atmosphere.

was performed on a micromeritics ASAP 2020. Initially, the samples were heated to 500 °C in a flow of N₂. The temperature was then decreased to 150 °C and subsequently, the gas was changed to an NH₃ flow for 30 minutes to get the NH₃ to chemisorp on the catalyst, before the catalyst was flushed with N₂ for 3 hours to remove physically adsorbed NH₃. The desorption of NH₃ took place when the temperature was increased at 600 °C with a ramp of 5°C/min.

X-ray Fluorescence

was done in a PANanalytical Epsilon 3X. Prior to the measurement, the powders (250 mg) were mixed with the non-wetting agent Li Br (0.60 g) and Lithium Borate Flux (10.5 g). A Claisse LaNEO FLuxer was used to melt the mixture at 1050 °C and poured into a mold to create glass discs for the XRF measurements.

Solid state NMR

for ²⁷AI and ²⁹Si was performed in the Broker AVANCE III

HD spectrometer operating at a 14.05 T magnetic field, coupled with a 4 mm CP/MAS BBFO probe. The ²⁷AI-MAS-NMR spectra were obtained using one-pulse experiments with a 0.5 ps TT/1 2 excitation pulse, an interscan delay of 0.5 s, and a spinning frequency of 8 kHz. The ²⁹Si-MAS-NMR spectra were obtained using one-pulse experiments with a 4.75 ps TT/2 excitation pulse, an interscan delay of 60 s, and a spinning frequency of 5 kHz. High-power 1 H decoupling was applied during the acquisition of both ²⁷AI- and ²⁹Si-MAS-NMR. The Solids Lineshape Analysis module in Topspin was used to simulate the peaks. The chemical shifts for ²⁷AI were referenced to a 0.1 M AI(CI)₃.6H₂O solution at 0.0 ppm, while those for ²⁹Si were referenced to TMS solution at 0.0 ppm.

Electron

resonance (EPR) spectroscopy was done using an ER 4102ST resonance cavity, at a microwave frequency of 9.46 GHz and microwave power of 6.67 mW on a Broker CW X-band EMX spectrometer. Electromagnets consisting of two large water-cooled copper coils were utilized to generate magnetic fields ranging from 220 mT to 300 mT. The EPR spectra had a modulation frequency of 100 kHz and a modulation amplitude of 5.2 G.

Fourier Transform Infrared

dehydration experiments were conducted using a Thermo Fischer Nicolet iS50 FT-IR instrument. Initially, a pellet was formed by compressing between 12 and 15 mg of the sample. This pellet was then placed into a Harrick Scientific Cell, which was connected to both a vacuum pump and a heater. Vacuum was applied for a brief duration before the initial measurement. Subsequently, the cell was gradually heated to 350°C at a rate of 10°C per minute and maintained at this temperature for one hour. The cell was then allowed to cool back to room temperature. Throughout the process, measurements were taken approximately every 100°C. These measurements were conducted in transmission mode.

Example 1 -catalyst synthesis

Synthesis of parent Na-GME was done based on modifications to the protocol of Mielby, J. et al. (2001).

Initially, 1 wt% of Cu was encapsulated in the parent zeolite H-FAU, by incipient wetness impregnation.

2.5 g of commercial H-FAU (CBV400, Si/AI=2.6, 2.8 wt% Na₂O) was added to a plastic flask with a cross-shaped magnetic stirring bar. To reach a concentration of 1wt% Cu/CBV400, a solution of 3 wt% Cu (anhydrous based) was prepared from CU(NO3)2‘XH₂O, in 808 pL demineralized water, which corresponds to 90% of the total pore volume of the H-FAU (V_totai = 0.36 cm³/g, see Table 1).

The CU(NO₃)₂ aqueous solution was added drop-wise to the plastic bottle while stirring, and was subsequently left stirring for a minimum of 8 hours.

Thereafter, the light blue powder was washed with deionized H₂O, dried at 80 °C for a minimum of 8 hours, and was calcined at 550 °C for 5 hours with a temperature ramp of 3 hours to form the material denoted as H-Cu/FAU.

A total of 1 .2 g H-Cu/FAU, was meticulously ground with 0.29 g of NaOH pellets using a 160 mL agate mortar and pestle. The resulting material was transferred to a 65 mL teflon beaker and placed in a 220 mL teflon-lined autoclave containing 15 mL of demineralized water. The mixture was crystallized for 24 hours at 140 °C, and the product was washed with demineralized water until neutral pH, and then dried for 72 hours at 80°C, resulting in the material denoted as Na-Cu@GME.

In order to form a more thermally stable form of GME, the sodium ions were exchanged with potassium ions, calcium ions or a mix of both. For this purpose (regarding K-ion exchange), 1 .0 g Na-Cu@GME was added to a beaker containing an 80 mL solution of KNO3 in demineralized H₂O. The beaker with a magnetic stirrer, was then placed in an oil bath and maintained at 80°C for at least 8 hours. The amount of potassium ions in the KNO3 solution was three times that of the sodium ions in the sample Na-Cu@GME, assuming that all the sodium from the added NaOH came to be in the zeolite.

After the ion-exchange, the powder was isolated by centrifugation. The resulting precipitate was washed with demineralized H₂O and placed in a drying oven at 80°C for at least 8 hours. Finally, the precipitate was calcined for 5 hours at 550 °C (with a ramp time of 3 hours) to result the material denoted as K-Cu@GME.

A sample denoted Ca-Cu@GME was synthesized in an analogous way from Na- Cu@GME employing Ca(NO3)2 in the ion-exchange reaction rather than KNO3. A sample denoted (K-Ca)-Cu@GME was also synthesized in an analogous way from Na- Cu@Gme employing a mix of K and Ca nitrates. For this, the amount of potassium and calcium ions in the aqueous nitrate solution was three times that of the sodium ions in the sample Na-GME, i.e. (n_K + n_Ca)/nNa equal to 3, assuming that all the sodium from the added NaOH came to be in the Na-GME zeolite. The specific distribution of K and Ca is not very important for the final product, as ion exchange will be governed by ionic radii of the exchanged ions, allowing potassium to preferentially migrate and exchange within larger channels, while calcium due to it’s smaller size can exchange in the smaller zeolite channels of GME.

Thus the K:Ca ratio may vary from 10:1 to 1 :10 in the solution used for ion exchange.

A variety of Cu-loadings can be achieved by varying the amount of Cu which is impregnated on the commercial H-FAU zeolite in the first step of the synthesis. Using this approach, GME catalysts with Cu-loadings of 0 (K-GME), 0.5 wt%, 1 .0 wt%, 1 .5 wt%, 2.0 wt% and 2.5 wt% were produced.

Synthesis of the zeolites of the present invention may be done via different methodologies.

Alternatively to the methodology presented above, the catalyst presented herein may be prepared by initially converting H-FAU to Na-GME via interzeolite conversion using NaOH and subsequently ion-exchanged with K and/or Ca and/or Cu to achieve Cu- doped gmelinite type catalysts. The skilled person can produce catalysts following this alternative methodology following the procedure outlined in Mielby, J. et al. (2001 ) without undue burden. Prior to testing of synthesized samples in the catalytic reaction, the powder samples were reduced under a flow of 5 vol.% H₂/N₂ at 350 °C for 2 hours with a temperature ramp of 5 °C/min in a plug flow reactor.

Sample characterization

All samples were subjected to a plethora of characterization techniques to verify the zeolite framework of the synthesized sample. A combination of XRD, SEM, TEM, and XPS was utilized for the macro- and microscopic structural characterization.

Surface area and pore volume was determined by N₂ physisorption and NH₃-TPD. These results are presented in Table 1 here below.

The parent zeolite H-Cu/FAU exhibited a considerably higher surface area at around 549 m²/g and a total pore volume of 0.36 cm³/g, while the daughter zeolite Na- Cu@GME displayed lower surface area and total pore volume (42 m²/g, and 0.051 cm³/g, respectively). Several factors are known to cause zeolites synthesized via interzeolite transformation to exhibit a lower pore volume and surface area than those synthesized via the conventional hydrothermal route.

During the interzeolite transformation, the original zeolite framework is initially dissolved, and then recrystallized to another structure, leading to the formation of crystals with reduced surface area and pore volume. In contrast, conventional hydrothermal synthesis typically yields crystals with a greater surface area and pore volume that are larger and better defined. Furthermore, the interzeolite transformation process involves the migration of cations between the parent and daughter zeolites, which can potentially lead to changes in the crystal structure and pore size distribution, resulting in a decrease in the final product's overall surface area and pore volume. Presumably due to the ionic radii of potassium (0.135 nm) being larger than the sodium ionic radii (0.95 nm), the surface area (14 m²/g) and total pore volume (0.037 cm³/g ) of K-Cu@GME is lower than the corresponding Na-Cu@GME.

Table 1 - Surface area and pore volumes for various zeolites of the present invention calculated from N₂-physisorption at 77 K. Numbers in sample name indicate Cu- loadings in the range of 0.1 to 2.5 wt% as achieved by incipient wetness impregnation of H-FAU followed by interzeolite transformation as described here above. ^a Estimated by the t-plot method, ^b estimated from a single point adsorption of 0.95 relative pressure, ^c estimated by the BET method.

Silylation experiments

For this example, the synthesis procedure is exemplified using K-Cu@GME wherein the FAU to GME interzeolite transformation was performed in a calcination step at 400 °C for 5 with a ramp time of 4 hours. The K-Cu@GME may however also be calcined at other temperatures in the range of 300 to 550 °C without significantly impacting the resulting properties.

1g of the K-Cu@GME catalyst was dispersed in 20 ml of toluene. The dispersion of the catalyst was achieved with the use of an ultrasonic bath for approximately 30 minutes. Subsequently, another solution was prepared containing the respective silylating agent and 20 ml toluene. Varying amounts of the silylating agent were assessed, ranging from a minimum of 0.5 mmol per gram of zeolite to a maximum of 10 mmol per 1 gram of zeolite. The solution with the silylating agent was combined with the dispersed zeolite in toluene solution and the mixture was left to stir for 24 hours at room temperature while covered with aluminum foil. Following this, the catalysts were isolated by centrifugation and rinsed twice with ethanol prior to storing them in a drying oven at 80 °C overnight. Four distinct silylating agents were investigated trichloromethylsilane (hi), trimethylchlorosilane (h₂), trimethoxymethylsilane (hs), and hexadecyltrimethoxysilane (h₄).

XRD was employed to verify the success of silylation. The X-ray diffractograms in Fig. 5 depict K-Cu@GME and xhi\K-Cu@GME, (silylated with x = 0.5 to 10 mmol trichloromethylsilane pr gram zeolite). The diffractogram of 0.5hi\K-Cu@GME closely resembles non-silylated K-Cu@GME, with well-defined GME peaks. However, the zeolites silylated with more than 2.5 mmol of trichloromethylsilane pr 1 gram zeolite exhibit two significantly more intense peaks, indicating altered signals and a reduction in the GME signal intensity. Silylation involves the reaction of silane compounds with zeolite surface hydroxyl groups. Without wishing to be bound by theory, this process is believed to potentially introduce organic moieties, modifying the structure to make it more hydrophobic and potentially impacting the crystal lattice. The degree of impact on the diffractograms of Fig. 5 appear to be proportional to the concentration of the silylating agent.

In Fig. 6, the four investigated silylating agents are reacted with K-Cu@GME in the lowest evaluated concentration (0.5 mmol per 1 gram zeolite). It can be seen that the specific silylating agent employed had no discernible effect on the catalysts structure. The diffractograms of the materials silylated with 0.5 mmol of different silylating agents, closely mirror the diffraction pattern observed in non-silylated K-Cu@GME.

N₂ physisorption provided estimates of surface area and total pore volume for the silylated catalysts, with results detailed in Table 2. Surprisingly, silylation consistently increased both BET surface area and pore volume compared to non-silylated K- Cu@GME contradicting what has generally been known in the art such as in Vu et.,(2018) where post-synthetic silylation methods lead to a reduction in pore volume. Notably, the increase was particularly pronounced when the concentration of the silylating agent trichloromethylsilane (hi) was increased, leading to significant enhancements in both parameters. For instance, the surface area increased from 14 m² g ¹ in K-Cu@GME to 95.18 m² g ¹ in 7.5hi\K-Cu@GME. Without wishing to be bound by theory, it is speculated that this increase be attributed to the interaction of chlorine in trichloromethylsilane with zeolite OH groups, resulting in HCI production during silylation. This presence of HCI could potentially induce dealumination, creating additional micropores and boosting overall porosity. The treatment also enriched silicon in the zeolite framework, fostering the development of new silica domains and further enhancing porosity. When various silylating agents were employed, the BET surface area and pore volume still increased, albeit less prominently for trimethoxymethylsilane (h₃) and hexadecyltrimethoxysilane (h₄), lacking Cl, compared to trichloromethylsilane (hi) and trimethylchlorosilane (h₂). In Table 2, 0.5h₃\K-Cu@GME and 0.5h₄\K-Cu@GME displayed surface areas of 17.88 m² g^-1 and 20.56 m² g^-1 , while trichloromethylsilane (hi) and trimethylchlorosilane (h₂) exhibited nearly double values at 32.67 m² g^-1 and 29.19 m² g^-1 , respectively.

Table 2 - N₂ physisorption data for silylated Cu-doped GME catalysts

FTIR spectroscopy (data not shown) confirmed the presence of C-H vibration frequencies in the range of 2800-3000 cm^-1 supporting the notion that the surface of the zeolite is made more hydrophobic with the silylation. The above silylated catalysts (Table 2) are investigated further for their stability and CO2 hydrogenation properties in Examples 5 and 6 here below.

Example 2 - initial catalytic testing for production of ethanol from CO2

Catalytic reaction

The catalysts as produced above were tested under flow conditions, by using the Micromeritics plug flow reactor FR-50. The stainless steel reactor had an inner diameter of 4 mm, and it was loaded with 100 mg of the fractionated catalyst (150-355 pm) mixed with roughly 900 mg of fractionated quartz (150-355 pm). The solids were fixed between two pieces of quartz wool. The temperature of the reaction was regulated using a thermocouple placed in the middle of the reactor.

Exemplary, K-Cu@GME was first reduced in situ at 350 °C under a flow of H₂ (5 mL/min) and N₂ (45 mL/min) for 120 min. The reduced K-Cu(1 )@GME was in a first setup tested under 2.0 MPa and at the temperature range 200 °C to 350 °C. The reactant gas flow volume ratios (H₂/CO₂) varied from 4:1 to 6:1 . Subsequently, the effect of H₂O was investigated in the reactant gas mixture by adding H₂O to the reaction chamber with an HPLC pump. The H₂O/CO₂ molar ratio varied from 0.35 to 0.7 while CO₂ was fed in the reactor with a constant flow of 10 mL/min, and H₂ with a constant flow of 50 mL/min. The catalysts exemplified in the tables above were all subjected to the same testing regime including a prolonged stability test to evaluate the continuous operation performance of the catalyst. Exemplary for Ca-Cu@GME, this data can be seen in Fig. 4. The catalyst displays are very high stability, maintaining CO₂ conversion above 10% and ethanol selectivity above 45% for the first 8 hours of continuous operation. For the mixed potassium/calcium gmelinite catalyst (denoted (K- Ca)-Cu@GME) data obtained under similar conditions can be seen in Fig. 7A. Also in Fig. 7B is XRD data showing that the structure of the zeolite does not change with mixing potassium and calcium, the shown diffractograms are essentially superimposable with parent Na-GME except for intensity differences.

The mixed gmelinite catalyst displays a good CO₂ conversion above 10% with stable and high production (selectivity of approximately 60%) of EtOH for the first 13 hours of continuous operation. The quantification of products was done using an online GC with an FID detector equipped with PoraBond U polar column, and a TCD detector equipped with two DB-1 non-polar capillary column. Calibration of the GC was performed by creating standard curves through direct injection of commercial analogues of the analytes with known concentrations. From the constructed calibration curves, a calibration equation was determined for each analyte. Unless specified otherwise, the catalytic results shown in Table 3 to Table 9 here below were quantified based on GC measurements performed after 1 hour of operation under the specified conditions.

Results

The results, as shown in Fig. 1 a, indicated the production of carbon monoxide, methane (CH₄), methanol (CH₃OH), formaldehyde (CH₂O), and ethanol (EtOH) at 350°C. However, the CO₂ conversion rate (3.16%) and ethanol selectivity (1 1%) were observed to be too low for feasible industrial applications. Conversely, the selectivity towards CO at 350°C was notably high (70%). Fig. 1 b shows the experimental results when adding water to the feed stream at a H₂O/CO₂ ratio of 0.35. The addition of water resulted in a reduction in CO production and an increase in ethanol production, which was observed at 250°C with higher conversion and selectivity. Figs. 1 c and 1 d display the results obtained at H₂O/CO₂ molar ratios of 0.5 and 0.4, respectively. At both of these latter ratios, the selectivity towards ethanol was found to be highest at 250°C, with values of 61% and 58% and higher conversion rates of 7.44% and 5.07%, respectively.

Importantly, no CO was detected in the product stream, indicating that by increasing the water ratio, the formation of CO was eliminated, while the conversion and selectivity towards ethanol were significantly improved.

A tabular summary of the data presented in Fig. 1 as well as additional data is presented below in Table 3 through Table 7. Table 3 - Catalytic results for K-Cu@GME at 2.0 Mpa, H2/CO2 at 5, H2O/CO2 at 0.5

Table 4 - Catalytic results for K-2.0Cu@GME at 2.0 Mpa, H2/CO2 at 5, H2O/CO2 at 0.4

Table 5 - Catalytic results for K-Cu@GME at 2.0 Mpa, H2/CO2 at 5, H2O/CO2 at 0.4

Table 6 - Catalytic results for K-Cu@GME at 2.0 Mpa, H2/CO2 ratio of 4, and a H2O/CO2 ratio of 0.4.

Table 7 - Catalytic results for K-Cu@GME at 2.0 Mpa, H2/CO2 ratio of 6, and a H2O/CO2 ratio of 0.4.

The optimal conditions for the CO2 hydrogenation using K-Cu@GME were determined to be a H2/CO2 ratio of 5 and a H2O/CO2 ratio of 0.4 at 250°C and 2.0 Mpa. A H2O/CO2 at 0.5 was also found to perform very well for this system.

Example 3 - effects of pressure on CO2 conversion and ethanol selectivity.

The effect of pressure on CO2 hydrogenation for ethanol production was examined at a temperature of 250°C, a H2/CO2 ratio of 5 and a H2O/CO2 ratio of 0.4 by varying the pressure between 1 .5 and 3.0 Mpa. High pressure plays a crucial role in this process, as it can significantly influence the conversion rate and selectivity of the reaction. As shown graphically in Fig. 2 (also in Table 8 below), conversion rate of CO2 gradually increases with pressure from approximately 6.1% at 1 .5 Mpa to approximately 8.5% at 3.0 Mpa. The selectivity towards ethanol production surprisingly however does not follow the same trend and instead exhibits an optimum at 2.0 Mpa of pressure.

From only a few percent at 1 .5 Mpa, ethanol selectivity increases to a significant 63% at 2.0 Mpa (7.33% conversion) before again dropping down to modest 44% and 39% at 2.5 Mpa and 3.0 Mpa respectively.

Table 8 - Catalytic results showing the influence of pressure in the CO2 hydrogenation for K-Cu@GME at 2.0 Mpa, 250 °C, H2/CO2 ratio of 5, and H2O/CO2 ratio of 0.4.

Example 4 - effects of Cu-loading on CO2 conversion and ethanol selectivity.

The Cu loading, referring to the amount or concentration of copper (Cu) in the catalyst, has a significant impact on the CO2 hydrogenation process for ethanol production. Fig. 3 presents the CO2 conversion and selectivities of methane, methanol and ethanol at 250 °C, 2.0 Mpa, with a H2/CO2 ratio of 5 and H2O/CO2 ratio of 0.4 with varying the Cu- loading in the catalyst between 0 and 2.5 wt% (see also Table 9).

Increasing the Cu-loading was found generally to enhance the activity of the catalyst. Cu serves as an active site for the hydrogenation reaction, facilitating the conversion of CO2 to ethanol. This is demonstrated in Fig. 3, where the absence of Cu loading (K- GME) results in the production of methane as the only detectable product, while the conversion of CO2 remains low, measuring only 1.29%. Higher Cu loading is expected to provide more available active sites, leading to increased reaction rates and improved ethanol production.

Observing Fig. 3, it becomes apparent that increasing the Cu loading within the range of 0.1 wt% to 1 wt% follows the expected trend and leads to an enhanced selectivity towards ethanol production and an improved CO2 conversion.

Cu loading can however also influence the reaction mechanism of CO2 hydrogenation and this is evident when the Cu loading increases at 2 wt% and 2.5 wt%. The presence of Cu modifies the adsorption and activation of CO2 and H₂, influencing the reaction intermediates and subsequent steps. Higher Cu loading can alter the reaction pathways and favor the formation of specific products, like methanol and methane. At a Cu loading of 2 wt%, both the CO2 conversion rate and the selectivity towards ethanol reach 7.49% and 59% respectively. These values are comparable to the CO2 conversion rate of 7.33% and the selectivity towards ethanol of 63% observed at a Cu loading of 1 wt%.

However, with an increase in Cu loading to 2.5 wt%, both the CO2 conversion and ethanol selectivity experience a drastic decline, measuring only 5.54% and 33% respectively for a catalyst with this Cu-loading. Consequently, Fig. 3 illustrates that a loading between 1 and 2 wt% of Cu in this type of zeolites constitutes a surprising optimum.

Table 9 - Catalytic results for K-Cu@GME with different Cu loadings at 2.0 Mpa, H2/CO2 ratio of 5, and a H2O/CO2 ratio of 0.4. K-GME is also included for reference.

Example 5 - effects of silylation on CO2 conversion, ethanol selectivity and stability.

The catalytic experiments were conducted using the respective silylated catalysts under identical reaction conditions as the standard K-Cu@GME catalysts namely 20 bar and 250 °C, with a volumetric H2/CO2 ratio of 5, and a molar H2O/CO2 ratio of 0.4.

The results illustrating the performance variations of catalysts silylated by different amounts of trichloromethylsilane (hi) are shown in Fig. 8A-8D, while Fig. 9A-9C illustrates the performance of K-Cu@GME catalysts silylated using 0.5 mmol of various silylating agents (h₂, h₃ and h₄) per 1 gram zeolite. From both sets of figures it is clear to see that the in situ stability and/or operando lifetime is drastically increased for all systems, generally increasing from 8 hours of stable operation up to 20 hours and above. In particular silylation using 0.5 mmol h₄ per 1 gram zeolite stands out as being very stable for the duration of the experiment (30 hours) with no appreciative change in conversion or selectivity and with a CO2 conversion at 6.55% and 35% selectivity to ethanol throughout the entire test. Methane selectivity remained constant at around 30%, methanol selectivity at 11 %, and carbon monoxide selectivity at 23%. A selection of these data (quantified as previously described) is presented here below in Table 10 to Table 15, however this selection should not be seen as limiting on the invention, and all data may be directly evaluated from the figures filed with this application.

Table 10 - Stability test for (K-Ca)-Cu@GME at 2.0 MPa, H2/CO2 ratio of 5, and a H2O/CO2 ratio of 0.4.

Table 11 - Stability test for 0.5hi\K-Cu@GME at 2.0 MPa, H2/CO2 ratio of 5, and a H2O/CO2 ratio of 0.4.

Table 12 - Stability test for 0.5h₂\K-Cu@GME at 2.0 MPa, H2/CO2 ratio of 5, and a H2O/CO2 ratio of 0.4.

Table 13 - Stability test for 0.5h₃\K-Cu@GME at 2.0 MPa, H2/CO2 ratio of 5, and a H2O/CO2 ratio of 0.4.

Table 14 - Stability test for 0.5h₄\K-Cu@GME at 2.0 MPa, H2/CO2 ratio of 5, and a H2O/CO2 ratio of 0.4.

Table 15 - Stability test for 0.5h₄\(K-Ca)-Cu@GME at 2.0 MPa, H2/CO2 ratio of 5, and a H2O/CO2 ratio of 0.4.

From these data it appears that the hydrophobic nature of the silylated catalyst played a pivotal role in governing reactant adsorption and diffusion processes. Trichloromethylsilane (hi), with its chlorinated functional group, introduced a unique hydrophobic character distinct from that associated with trimethylchlorosilane (h₂). This divergence in hydrophobic properties potentially influenced how the catalyst interacted with both water and reactants during the catalytic process, ultimately leading to the formation of ethane and acetic acid rather than ethanol as the C2 product.

It's crucial to emphasize that, despite the aspiration for a hydrophobic catalyst to protect the zeolite GME, it should still continue to facilitate the participation of water as a reactant. Therefore 0.5 mmol silylating agent per 1 gram zeolite is a preferred reaction stoichiometry to form a sufficiently thin hydrophobic layer around the zeolite core.

For the silylated mixed ion catalyst (0.5h₄\(K-Ca)-Cu@GME), the catalytic data is presented in Fig. 10, obtained under the same reaction conditions as described here above in the beginning of Example 5.

This catalytic system exhibited a unique behavior demonstrating continuous operation stability for over 50 hours (the entire lifetime of the experiment). Ethanol selectivity consistently remained at around 40% , while CO2 conversion surpassed other silylated materials, reaching approximately 8.2%.

Example 6 - effects of cycled water addition on operation stability.

In this experiment, water was periodically introduced into the reactor during continuous operation using the catalyst 0.5hi\K-Cu@GME. Aside from the addition of water, all other reaction conditions were kept constant and as in Example 5.

Specifically, water was supplied to the reactor for a duration of 1 hour (at a ratio of H2O/CO2 of 0.4), with the water supply subsequently cut off at the end of each hour and maintained off for a duration of 2 hours. This cycle repeated, with water added again in the fourth hour, seventh hour, and so forth for the entire duration of the 60 hours experiment. The objective of this experiment was to evaluate if by periodically supplying water, the catalyst’s operando lifetime could be extended. Initially lasting 21 hours before any decrease in conversion could be observed, the catalyst’s lifespan was increased to 46 hours by applying this simple manipulation, and EtOH selectivity was constant around 40% for 55 hours (see Fig. 11).

Water played a crucial role as a reactant in the experiment. Without wishing to be bound by theory, the present inventors speculate that as water was produced during the reaction within the pores of the zeolite, its exit was hindered by the hydrophobic layer surrounding the zeolite formed by the reaction with the silylating agent. Consequently, the water produced could be utilized in the channels to react with CO2 and generate a stable stream of ethanol in the product without needed additional water for reagent. References

Mielby, J. et aL, - A shortcut to high-quality gmelinite through steam-assisted interzeolite transformation, Micoporous and Mesoporous Materials (2022) https://doi.Org/10.1016/j.micromeso.2021.1 11606

Galarneau, A. et aL, - Validity of the t-Plot Method to Assess Microporosity in Hierarchical Micro/Mesoporous Materials, Langmuir, American Chemical Society, 2014, doi:10.1021/la5026679.

Vu, H.-T. et aL, - Silylated Zeolites With Enhanved Hydrothermal Stability for the Aqueous-Phase Hydrogenation of Levulinic Acid to y-Valerolactone, Front. Chem., 2018, vol 6, 143, doi:10.3389/fchem.2018.00143

Items

1 . A method for the catalytic hydrogenation of CO2 into at least one value-added chemical, comprising contacting a feed stream containing CO2 and H₂ with a solid heterogeneous catalyst in a reaction chamber, wherein the H2/CO2 volume ratio in the feed stream is from 1 :1 to 10:1 .

2. The method according to item 1 , wherein the H2/CO2 volume ratio in the feed stream is from 1 :1 to 10:1 , such as 1 :1 , such as 2:1 , such as 3:1 , such as 4:1 , such as 5:1 , such as 6:1 , such as 7:1 , such as 8:1 , such as 9:1 , such as 10:1 or any 0.5 increment therein between.

3. The method according to any one of the preceding items, wherein the H2/CO2 volume ratio in the feed stream is from 4:1 to 6:1 , such as 4.5:1 to 5.5:1 , such as 5:1.

4. The method according to any one of the preceding items, wherein the at least one value-added chemical is one or more selected from the group consisting of ethanol, methanol, methane, methanal, and ethanal.

5. The method according to any one of the preceding items, wherein the reaction chamber is a plug-flow reactor 6. The method according to any one of the preceding items, wherein the catalyst is an acidic catalyst.

7. The method according to any one of the preceding items, wherein the catalyst is a zeolite-based catalyst.

8. The method according to any one of the preceding items, wherein the catalyst is a zeolite-based catalyst selected from the group consisting of gmelinite (GME), chabazite (CHA), faujasite (FAU), and analcime (ANA).

9. The method according to any one of the preceding items, wherein the catalyst has a Si/AI ratio between 2.0 and 4.0, such as between 2.0 and 2.5, such as between 2.5 and 3.0, such as between 3.0 and 3.5, such as between 3.5 and 4.0, preferably between 3.0 and 4.0, such as 3.1 , 3.2, 3.3, 3.4, 3.5, 3,6, 3.7, 3.8, 3.9, 4.0, or any 0.01 increment therein between.

10. The method according to any one of the preceding items, wherein the catalyst is a gmelinite (GME) based catalyst.

11 . The method according to any one of the preceding items, wherein the catalyst is selected from the group consisting of gmelinite sodium (Na-GME), gmelinite potassium (K-GME) and gmelinite calcium (Ca-GME).

12. The method according to any one of the preceding items, wherein the catalyst unit cell comprises a repeating unit selected from the group consisting of Na₄(Si₈AI₄)O₂₄-11 H₂O, K₄(Si₈AI₄)O₂₄- 11 H₂O, and Ca₂(Si₈AI₄)O₂₄-11 H₂O.

13. The method according to any one of the preceding items, wherein the catalyst further comprises at least one auxiliary transition metal.

14. The method according to any one of the preceding items, wherein the catalyst comprises from 0.5 to 5.0 wt% (based on total catalyst weight) of at least one auxiliary transition metal, such as from 0.5 to 2.5 wt%, from 0.8 to 2.2 wt%, from 1 .0 to 2.0 wt%. 15. The method according to any one of items 13 to 14, wherein the at least one auxiliary transition metal is a non-noble transition metal.

16. The method according to any one of the preceding items, wherein the catalyst comprises 1 .0 wt% (based on total catalyst weight) of at least one auxiliary non- noble transition metal.

17. The method according to any one of items 1 to 15, wherein the catalyst comprises 2.0 wt% (based on total catalyst weight) of at least one auxiliary non- noble transition metal.

18. The method according to any one of items 15 to 17, wherein the non-noble transition metal is selected from the group consisting of Cu, Fe, Ni, Co, Mn, and Cr.

19. The method according to any one of items 13 to 18, wherein the transition metal is Cu.

20. The method according to item 19, wherein the Cu is in the form of zero-valent Cu.

21 . The method according to any one of the preceding items, wherein the method further comprises a step of introducing water into the reaction chamber.

22. The method according to any one of the preceding items, wherein the amount of water provides a H2O/CO2 molar ratio between 0.1 and 1 .0.

23. The method according to any one of the preceding items, wherein the molar ratio of H₂O and CO2 is between 0.1 and 1 .0, such as 0.1 , such as 0.2, such as 0.3, such as 0.4, such as 0.5, such as 0.6, such as 0.7, such as 0.8, such as 0.9, such as 1 .0 but is preferably 0.4 or 0.5, more preferably the molar ratio of H₂O and CO20.4. The method according to any one of the preceding items, wherein the catalytic hydrogenation is carried out at non-ambient pressure The method according to any one of the preceding items, wherein the catalytic hydrogenation is carried out at a pressure between 0.5 MPa and 5 MPa, such as between 1 .0 MPa and 4 MPa, such as between 1 .5 MPa and 3 MPa, such as between 1 .5 MPa and 2.5 MPa, such as between 1 .7 MPa and 2.3 MPa, such as between 1 .8 MPa and 2.2 MPa, such as between 1 .9 MPa and 2.1 MPa, such as 2.0 MPa. The method according to any one of the preceding items, wherein the catalyst is brought into contact with the feed stream at a temperature of at least 200 °C, such as at least 250 °C, such as at least 300 °C, such as at least at least 350 °C. The method according to any one of items 1 to 25, wherein the catalyst is brought into contact with the feed stream at a temperature from 200 °C to 500 °C, such as from 200 °C to 400 °C, such as from 250 °C to 350 °C, such as from 275 °C to 325 °C. The method according to any one of the preceding items, wherein the catalyst is brought into contact with the feed stream at a temperature ranging from 250°C to 300°C. A system for the catalytic conversion of CO2 into ethanol in a hydrogenation reaction, the system comprising: a. a reaction chamber equipped with a zeolite catalyst; b. a reaction chamber inlet for CO2, H₂ and optionally H₂O provided together or separately; c. a heating source; and d. a product outlet; wherein the reaction chamber is a plug-flow reactor and wherein the zeolite catalyst is a gmelinite (GME) based catalyst. 30. The system according to item 29, wherein the catalyst is selected from the group consisting of gmelinite sodium (Na-GME), gmelinite potassium (K-GME) and gmelinite calcium (Ca-GME).

31 . The system according to any one of items 29 to 30, wherein the catalyst unit cell comprises a repeating unit selected from the group consisting of Na₄(Si₈AI₄)O₂₄-11 H₂O, K₄(Si₈AI₄)O₂₄- 11 H₂O, and Ca₂(Si₈AI₄)O₂₄-1 1 H₂O.

32. The system according to any one of items 29 to 31 , wherein the catalyst further comprises at least one auxiliary transition metal.

33. The system according to any one of items 29 to 32, wherein the catalyst comprises from 0.5 to 5 wt% (based on total catalyst weight) of at least one auxiliary transition metal, such as from 0.5 to 2.5 wt%, from 0.8 to 2.2 wt%, from 1 .0 to 2.0 wt%.

34. The system according to any one of items 29 to 33, wherein the at least one auxiliary transition metal is a non-noble transition metal.

35. The system according to any one of items 29 to 34, wherein the catalyst comprises 1 .0 wt% (based on total catalyst weight) of at least one auxiliary non- noble transition metal.

36. The system according to any one of items 29 to 34, wherein the catalyst comprises 2.0 wt% (based on total catalyst weight) of at least one auxiliary non- noble transition metal.

37. The system according to any one of items 29 to 36, wherein the non-noble transition metal is selected from the group consisting of Cu, Fe, Ni, Co, Mn, and Cr.

38. The system according to any one of items 29 to 37, wherein the transition metal is Cu. The system according to item 38, wherein the Cu is in the form of zero-valent Cu. A solid zeolite catalyst selected from the group consisting of gmelinite potassium (K-GME), gmelinite sodium (Na-GME), and gmelinite calcium (Ca- GME), characterized in comprising 0.5-2.5 wt% (based on total catalyst weight) of at least one auxiliary non-noble transition metal, such as from 0.8 to 2.2 wt%, from 1 .0 to 2.0 wt%. The catalyst according to item 40, wherein the at least one non-noble transition metal is selected from the group consisting of Cu, Fe, Ni, Co, Mn, and Cr. The catalyst according to any one of items 40 to 41 , wherein the catalyst comprises 1 .0 wt% (based on total catalyst weight) of at least one auxiliary non- noble transition metal. The catalyst according to any one of items 40 to 41 , wherein the catalyst comprises 2.0 wt% (based on total catalyst weight) of at least one auxiliary non- noble transition metal. The catalyst according to any one of items 40 to 43, wherein the non-noble transition metal is Cu. The catalyst according to item 44, wherein the Cu is in the form of zero-valent Cu. Use of the catalyst according to any one of items 40 to 45, for the catalytic hydrogenation of CO2 into a value-added chemical. The use according to item 46, wherein the value-added chemical is selected from the group consisting of ethanol, methanol, methane, methanal, and ethanal. Items 2

1 . A method for the catalytic hydrogenation of CO2 into at least one value-added chemical selected from the group consisting of ethanol, methanol, methane, methanal, and ethanal, the method comprising contacting a feed stream containing CO2 and H₂ with a solid heterogeneous catalyst in a reaction chamber, wherein the H2/CO2 volume ratio in the feed stream is from 4:1 to 6:1 .

2. The method according to any one of the preceding items, wherein the at least one value-added chemical is ethanol.

3. The method according to any one of the preceding items, wherein the reaction chamber is a plug-flow reactor.

4. The method according to any one of the preceding items, wherein the catalyst is a gmelinite (GME) based catalyst selected from the group consisting of gmelinite sodium (Na-GME), gmelinite potassium (K-GME) and gmelinite calcium (Ca-GME).

5. The method according to any one of the preceding items, wherein the catalyst unit cell comprises a repeating unit selected from the group consisting of Na₄(Si₈Al4)O24-11 H₂O, K₄(Si₈Al4)O24-11 H₂O, and Ca₂(Si₈AI₄)O24-1 1 H₂O.

6. The method according to any one of the preceding items, wherein the catalyst further comprises at least one auxiliary transition metal.

7. The method according to any one of the preceding items, wherein the catalyst comprises from 0.8 wt% to 2.2 wt% (based on total catalyst weight) of at least one non-noble transition metal selected from the group consisting of Cu, Fe, Ni, Co, Mn, and Cr .

8. The method according to any one of items 6 to 7, wherein the transition metal is Cu. 9. The method according to any one of the preceding items, wherein the method further comprises a step of introducing water into the reaction chamber, wherein the amount of water provides a H2O/CO2 molar ratio between 0.4 and 0.5.

10. The method according to any one of the preceding items, wherein the catalytic hydrogenation is carried out at a pressure between 1 .9 MPa and 2.1 MPa, such as 2.0 MPa.

11 . The method according to any one of items 1 to 10, wherein the catalyst is brought into contact with the feed stream at a temperature from 200 °C to 300 °C.

12. A system for the catalytic conversion of CO2 into ethanol in a hydrogenation reaction, the system comprising: a. a reaction chamber equipped with a zeolite catalyst; b. a reaction chamber inlet for CO2, H₂ and optionally H₂O provided together or separately; c. a heating source; and d. a product outlet; wherein the reaction chamber is a plug-flow reactor and wherein the zeolite catalyst is a gmelinite (GME) based catalyst selected from the group consisting of gmelinite sodium (Na-GME), gmelinite potassium (K-GME) and gmelinite calcium (Ca-GME),

13. The system according to item 12, wherein the catalyst further comprises from 0.8 to 2.2 wt% (based on total catalyst weight) of Cu.

14. A solid zeolite catalyst selected from the group consisting of gmelinite potassium (K-GME), gmelinite sodium (Na-GME), and gmelinite calcium (Ca- GME), characterized in comprising 1 .0-2.0 wt% (based on total catalyst weight) of Cu.

15. Use of the catalyst according to item 14, for the catalytic hydrogenation of CO2 into a value-added chemical selected from the group consisting of ethanol, methanol, methane, methanal, and ethanal.

Claims

Claims

1 . A method for the catalytic hydrogenation of CO2 into at least one value-added chemical selected from the group consisting of ethanol, methanol, methane, methanal, and ethanal, the method comprising contacting in a reaction chamber, a feed stream containing CO2 and H₂ with a solid gmelinite (GME) based heterogeneous catalyst comprising 0.8 wt% to 2.2 wt% Cu, wherein the H2/CO2 volume ratio in the feed stream is from 4:1 to 6:1 and wherein the catalytic hydrogenation is carried out at a pressure at or above 1 .8 MPa, further wherein the method comprises a step of introducing water into the reaction chamber, wherein the water provides a H2O/CO2 molar ratio between 0.4 and 0.5.

2. The method according to the preceding claim, wherein the H2/CO2 volume ratio in the feed stream is from 4.5:1 to 5.5:1 , such as 5:1 .

3. The method according to any one of the preceding claims, wherein the reaction chamber is selected from the group consisting of plug-flow reactor, multi-tubular reaction, fluidised bed reactor and void reactor.

4. The method according to any one of the preceding claims, wherein the value- added chemical is ethanol.

5. The method according to any one of the preceding claims, wherein the catalyst is selected from the group consisting of gmelinite sodium (Na-GME), gmelinite potassium (K-GME) and gmelinite calcium (Ca-GME) or a mixture thereof.

6. The method according to any one of the preceding claims, wherein the catalyst unit cell comprises a repeating unit selected from the group consisting of Na4(SisAl4)O24- 11 H2O, K₄(Si₈Al4)O24-11 H2O, and Ca2(Si8Al4)O24‘1 1 H2O or a mixture thereof.

7. The method according to any one of the preceding claims, wherein the catalyst is a mixed gmelinite potassium/calcium catalyst ((K-Ca)-GME).

8. The method according to claim 7, wherein the catalyst comprise potassium and calcium in a K/Ca ratio ranging from 0.4 to 4, more preferably ranging from 0.5 to 2.0, more preferably from 1 .0 to 1 .5.

9. The method according to any one of the preceding claims, wherein the Cu is in the form of zero-valent Cu.

10. The method according to any one of the preceding claims, wherein the catalyst comprises a hydrophobic layer, such as a hydrophobic layer obtained by silylation of zeolite OH-groups using a silylating agent.

11 . The method according to any one of the preceding claims, wherein the catalyst is a silylated heterogenous catalyst such as a silylated zeolite-based catalyst, or is a catalyst having been subjected to a step of silylation using a silylating agent.

12. The method according to claim 11 , wherein the silylated zeolite-based catalyst comprise and/or is obtained from the reaction with a silylating agent selected from the group consisting of trichloromethylsilane (hi), trimethylchlorosilane (h₂), trimethoxymethylsilane (h₃) and hexadecyltrimethoxysilane (h₄).

13. The method according to any one of claims 10 to 12, wherein the silylating agent is selected from the group consisting of trichloromethylsilane (hi), trimethylchlorosilane (h₂), trimethoxymethylsilane (h₃) and hexadecyltrimethoxysilane (h₄).

14. The method according to any one of claims 10 to 13, wherein the silylating agent is trichloromethylsilane (hi).

15. The method according to any one of claims 10 to 13, wherein the silylating agent is trimethylchlorosilane (h₂).

16. The method according to any one of claims 10 to 13, wherein the silylating agent is trimethoxymethylsilane (h₃).

17. The method according to any one of claims 10 to 13, wherein the silylating agent is hexadecyltrimethoxysilane (h₄).

18. The method according to any one of claims 10 to 17, wherein the silylated catalyst comprise and/or is obtained by reaction with 0.1 mmol to 20 mmol silylating agent per gram of zeolite.

19. The method according to any one of claims 10 to 18, wherein the silylated catalyst comprise and/or is obtained by reaction with 0.5 mmol to 10 mmol silylating agent per gram of zeolite, such as 0.5 mmol silylating agent per gram of zeolite, such as 1 .0 mmol silylating agent per gram of zeolite, such as 2.5 mmol silylating agent per gram of zeolite, such as 5.0 mmol silylating agent per gram of zeolite, such as 7.5 mmol silylating agent per gram of zeolite, such as 10.0 mmol silylating agent per gram of zeolite.

20. The method according to any one of claims 10 to 19, wherein the silylated catalyst comprise and/or is obtained by reaction with 0.4 mmol to 0.6 mmol silylating agent per gram of zeolite, such as 0.5 mmol silylating agent per gram of zeolite.

21 . The method according to any one of claims 10 to 20, wherein the silylating agent is hexadecyltrimethoxysilane (h₄), and wherein the silylated catalyst comprise and/or is obtained by reaction with 0.4 mmol to 0.6 mmol silylating agent per gram of zeolite, such as 0.5 mmol silylating agent per gram of zeolite.

22. The method according to any one of the preceding claims, wherein the water is periodically introduced into the reaction chamber in sequential steps.

23. The method according to any one of the preceding claims, wherein the water is periodically introduced into the reaction chamber in sequential steps, such as for 1 hour every 2 hours, for 1 hour every 3 hours, or for 1 hour every 4 hours.

24. The method according to any one of the preceding claims, wherein the water is periodically introduced into the reaction chamber for 1 hour every 3 hours.

25. The method according to any one of the preceding 1 to 21 , wherein the water is introduced into the reaction chamber, in continuous or periodical additions, for the duration of the catalytic hydrogenation.

26. The method according to any one of the preceding claims, wherein the catalytic hydrogenation is carried out at a pressure between 1 .8 MPa and 3 MPa.

27. The method according to any one of the preceding claims, wherein the catalytic hydrogenation is carried out at a pressure between 1 .9 MPa and 2.1 MPa, such as 2.0 MPa.

28. The method according to any one of the preceding claims, wherein the catalyst is brought into contact with the feed stream at a temperature of at least 200 °C, such as at least 250 °C, such as at least 300 °C, such as at least at least 350 °C.

29. The method according to any one of the preceding claims, wherein the catalyst is brought into contact with the feed stream at a temperature from 200 °C to 500 °C, such as from 200 °C to 400 °C, such as from 250 °C to 350 °C, such as from 275 °C to 325 °C.

30. The method according to any one of the preceding claims, wherein the catalyst is brought into contact with the feed stream at a temperature ranging from 250°C to 300°C.

31 . The method according to any one of the preceding claims, wherein CO2 conversion is above 6.0 % for at least 8 hours of continuous operation and/or hydrogenation, such as for at least 15 hours, such as for at least 25 hours, such as for at least 40 hours, such as for at least 50 hours.

32. The method according to any one of the preceding claims, wherein CO2 conversion is above 7.0 % for at least 8 hours of continuous operation and/or hydrogenation, such as for at least 15 hours, such as for at least 25 hours, such as for at least 40 hours, such as for at least 50 hours.

33. The method according to any one of the preceding claims, wherein CO2 conversion is above 8.0 % for at least 8 hours of continuous operation and/or hydrogenation, such as for at least 15 hours, such as for at least 25 hours, such as for at least 40 hours, such as for at least 50 hours.

34. The method according to any one of the preceding claims, wherein ethanol selectivity is above 30 % for at least 8 hours of continuous operation and/or hydrogenation, such as for at least 15 hours, such as for at least 25 hours, such as for at least 40 hours, such as for at least 50 hours.

35. The method according to any one of the preceding claims, wherein ethanol selectivity is above 40 % for at least 8 hours of continuous operation and/or hydrogenation, such as for at least 15 hours, such as for at least 25 hours, such as for at least 40 hours, such as for at least 50 hours.

36. The method according to any one of the preceding claims, wherein catalytic hydrogenation is performed in a one-step reaction or one-pot reaction.

37. A system for the catalytic conversion of CO2 into ethanol in a hydrogenation reaction, the system comprising: a. a reaction chamber equipped with a solid gmelinite (GME) based heterogeneous catalyst comprising 0.8 wt% to 2.2 wt% Cu; b. a reaction chamber inlet for CO2, H₂ and optionally H₂O provided together or separately; c. a heating source; and d. a product outlet; wherein the reaction chamber is selected from the group consisting of plug-flow reactor, multi-tubular reaction, fluidised bed reactor and void reactor.

38. The system according to claim 37, wherein the reaction chamber is a plug-flow reactor.

39. The system according to any one of claims 37 to 38, wherein the zeolite catalyst and the CO2, H₂ and optionally H₂O is provided in the same reaction chamber.

40. The system according to any one of claims 37 to 39, wherein the system is comprise only a single reaction chamber.

41 . The system according to any one of claims 37 to 40, wherein the system is configured for a one-pot and/or one-step hydrogenation of CO2 into ethanol.

42. The system according to any one of claims 37 to 41 , wherein the catalyst is selected from the group consisting of gmelinite sodium (Na-GME), gmelinite potassium (K-GME) and gmelinite calcium (Ca-GME) or a mixture thereof.

43. The system according to any one of claims 37 to 42, wherein the catalyst unit cell comprises a repeating unit selected from the group consisting of Na₄(Si₈AI₄)O₂₄-11 H₂O, K₄(Si₈AI₄)O₂₄- 11 H₂O, and Ca₂(Si₈AI₄)O₂₄-1 1 H₂O.

44. The system according to any one of claims 37 to 43, wherein the catalyst is a mixed gmelinite potassium/calcium catalyst ((K-Ca)-GME).

45. The system according to claim 44, wherein the potassium and calcium is present in K/Ca ratio ranging from 0.4 to 4, more preferably ranging from 0.5 to 2.0, more preferably from 1 .0 to 1 .5.

46. The system according to any one of claims 37 to 45, wherein the Cu is in the form of zero-valent Cu.

47. The system according to any one of claims 37 to 46, wherein the catalyst is a silylated catalyst.

48. The system according to claim 47 wherein the silylated catalyst obtained by the reaction between the gmelinite catalyst and a silylating agent, such as selected from the group consisting of trichloromethylsilane (hi), trimethylchlorosilane (h₂), trimethoxymethylsilane (h₃) and hexadecyltrimethoxysilane (h₄).

49. The system according to any one of claims 47 to 48, wherein the silylated catalyst comprise or is obtained from reaction with 0.5 mmol to 10 mmol silylating agent per 1 gram of zeolite.

50. The system according to any one of claims 47 to 49, wherein the silylated catalyst comprise or is obtained from reaction with 0.5 mmol silylating agent per 1 gram of zeolite.

51 . The system according to any one of claims 47 to 50, wherein the silylated catalyst comprise or is obtained from reaction with 0.5 mmol hexadecyltrimethoxysilane (h₄) per 1 gram of zeolite.

52. A solid zeolite catalyst selected from the group consisting of gmelinite potassium (K-GME), mixed gmelinite potassium/calcium ((K-Ca)-GME), gmelinite sodium (Na-GME), and gmelinite calcium (Ca-GME) or a mixture thereof, characterized in comprising 0.5 to 2.5 wt% Cu (based on total catalyst weight), such as from 0.8 to 2.2 wt%(based on total catalyst weight).

53. The catalyst according to claim 52, wherein the catalyst comprises 1 .0 wt% (based on total catalyst weight) of Cu.

54. The catalyst according to claim 52, wherein the catalyst comprises 2.0 wt% (based on total catalyst weight) of Cu.

55. The catalyst according to any one of claims 52 to 54, wherein the Cu is in the form of zero-valent Cu.

56. The catalyst according to any one of claims 52 to 55, wherein the catalyst is a silylated catalyst.

57. The catalyst according to claim 56 wherein the silylated catalyst obtained by the reaction between the gmelinite catalyst and a silylating agent, such as selected from the group consisting of trichloromethylsilane (hi), trimethylchlorosilane (h₂), trimethoxymethylsilane (h₃) and hexadecyltrimethoxysilane (h₄).

58. The catalyst according to any one of claims 56 to 57, wherein the silylated catalyst comprise or is obtained from reaction with 0.5 mmol to 10 mmol silylating agent per 1 gram of zeolite.

59. The catalyst according to any one of claims 56 to 58, wherein the silylated catalyst comprise or is obtained from reaction with 0.5 mmol silylating agent per 1 gram of zeolite.

60. The catalyst according to any one of claims 56 to 59, wherein the silylated catalyst comprise or is obtained from reaction with 0.5 mmol hexadecyltrimethoxysilane (h₄) per 1 gram of zeolite.

61 . Use of the catalyst according to any one of claims 52 to 60, for the catalytic hydrogenation of CO2 into a value-added chemical.

62. Use of the catalyst according to any one of claims 56 to 60, for the catalytic hydrogenation of CO2 into a value-added chemical, wherein the catalyst is obtained by reaction with a silylating agent.

63. The use according to claim 62, wherein the value-added chemical is selected from the group consisting of ethanol, methanol, methane, methanal, and ethanal.

64. Use of a silylated gmelinite based catalyst obtained by the reaction between a silylating agent and a gmelinite-based zeolite for catalytic hydrogenation of CO2 into one or more value-added chemicals including at least ethanol.

65. The use according to claim 64, wherein the silylated catalyst is obtained by the method comprising: a. providing a gmelinite based zeolite selected from potassium gmelinite, sodium gmelinite, calcium gmelinite or a mixture thereof such as mixed potassium/calcium gmelinite; b. dispersing said zeolite into an organic non-polar solvent, preferably toluene to provide a first solution; c. preparing a second solution by dissolving a silylating agent in an organic non-polar solvent, preferably toluene; d. mixing the first solution with the second solution and stirring the resulting mixture for at least 8 hours, more preferably 24 hours; and e. recovering the silylated gmelinite-based catalyst from the mixture.

66. The use according to any one of claims 64 to 65, wherein the gmelinite-based zeolite is doped with 0.8 to 2.2 wt% (based on total catalyst weight prior to silylation) of a transition metal, such as Cu.

67. The use of any of claims 64 to 66, wherein the silylating agent is selected from the group consisting of trichloromethylsilane (hi), trimethylchlorosilane (h₂), trimethoxymethylsilane (h₃) and hexadecyltrimethoxysilane (h₄).

68. The use of any of claims 64 to 67 wherein the silylating agent is dissolved in the second solution in an amount corresponding to from 0.5 mmol to 10 mmol silylating agent per 1 gram of zeolite, preferably 0.5 mmol silylating agent per 1 gram of zeolite.