WO2010136619A2 - METHOD FOR PREPARING NANOPARTICLES OF Ni-Sn ALLOYS AND THE USE THEREOF IN REFORMING REACTIONS - Google Patents

Abstract

The invention relates to a method for preparing Ni-Sn nanoparticles, consisting in: preparing a solution of a nickel carboxylate, in which said carboxylate has between 1 and 6 carbon atoms, and a tin halide in an organic solvent; adding polyvinylpyrrolidone (PVP); stirring same until a uniform solution is obtained; adding an inorganic reducing compound; refluxing same, thereby obtaining a colloidal solution; and adding an organic polar solvent to the previously produced colloidal solution, thereby causing the precipitation of a solid. The invention also relates to the use of these particles in reforming reactions.

Description

 Procedure for preparing nanoparticles of Ni-Sn alloys and their use in reforming reactions

Technical field

The present invention is encompassed in the field of obtaining catalysts for reforming reactions.

Background

The forecasts on fossil fuel reserves, together with the increase in their price and increasingly stringent environmental regulations, have led to the development of processes capable of generating energy without the use of fossil fuels. Within this field, the importance of the reactions of reforming products such as bioethanol or glycerin (byproduct of the biodiesel process) for obtaining synthesis gas is unquestionable.

These are catalytic processes that have been widely studied in recent years and on which it is known which are the most suitable metals to be used as active phases in such reactions on an industrial scale. In this selection both chemical and economic aspects have been taken into account. The products formed in the reforming reactions are normally controlled by thermodynamics. At low temperatures, the formation of methane is favored, while high temperatures are required to obtain high hydrogen productions, which can affect the stability of the catalyst or cause the sintering of the active particles. However, the most important problem, even without solution, is the poisoning of catalysts by carbonaceous deposits at these temperatures. This problem has been

REPLACEMENT SHEET (RULE 26) studied among others, by Trirran et al., which have proposed a series of reactions involved in the formation of coke during the methane reforming reaction:

(4-JC) CH ₄ + * <-> CH _x - * + ^ - ^ H ₂ (1)

CH _X - * OC- * + | H ₂ (2)

H ₂ O + * <-> 0 - * + H ₂ (3)

C - * + O- * <-> CO ₂ + 2 * (4)

Keep in mind that for chain hydrocarbons longer than methane, the amount of carbon formed will be more important.

In general, it can be said that the dissociation of hydrocarbons on the surface of a catalyst generates very reactive monocarbon species that can give rise to CO. However, when the concentration of these species becomes very important or their slow gasification, they can polymerize and give species that are much more difficult to oxidize and that will end up blocking the active particle.

As a possible solution is to prevent these monocarbon species ("carbide") from forming. Since this compound is formed by interaction of the 2p orbitals of the carbon with the d of the transition metal that acts as the active phase, it has been proposed to modify the catalyst so that orbitals d of the transition metal are in interaction with some other configuration element proper electronics in the original catalyst. This could be achieved by doping nickel catalysts (with a great tendency to form coke despite its high activity) with elements such as Sn, Pb, etc. If these

REPLACEMENT SHEET (RULE 26) Dopants become alloyed with the active metal in reforming, the formation of the "carbide" origin of more important carbonaceous deposits will be difficult with the reaction time. In this sense, work has been carried out in which bimetallic catalysts have been prepared and it has been shown that deactivation of the catalyst becomes considerably reduced at the cost of a loss of activity (the presence of Sn causes the formation of coke on the catalyst be smaller (and consequently also the deactivation of it.) However, the activity may decrease if the total amount of metal is kept constant because Sn is less active than nickel).

Taking into account the interest of the reforming processes, the design of catalysts capable of being active, stable and cheap enough to be used on an industrial scale, is a top priority in the current state of the energy sector.

For a catalyst to be active, it is necessary that the reagents are adsorbed on the surface with sufficient force so that the average life time of the species allows the reaction. This adsorption force cannot be too large either, since the desorption of the reaction products would be prevented, that is, by inhibiting the reaction, the active centers would be blocked.

This fundamental parameter that determines the activity of a catalyst is strongly influenced by the size and shape of the metal clusters on the surface. It has been established that the atoms in the corners and edges of a metal cluster, with a lower average coordination number than the atoms inside the cluster, are those that have the best properties to give a good

REPLACEMENT SHEET (RULE 26) activity. This means that the higher the number of metal atoms with low average coordination number in a cluster, the greater the activity of the catalyst. This number is maximized in the case that the active phase is in the form of nanoparticles.

On the other hand, it is known that nickel is very active in reforming reactions, but that it has a great tendency to form carbon. A good solution to the problem would be the synthesis of Ni nanoparticles alloyed with Sn: the loss of activity due to the presence of tin would be compensated by the presence of nanoparticles and the formation of the "carbide" would be very limited by the alloy of both metals . As a catalytic support, alumina may be suitable if its stability properties are considered.

With the present invention, the synthesis of Ni-Sn alloys of nanometric size, as well as supported Ni-Sn alloys of nanometric size, preferably on γ-alumina, has been achieved. Characterization analyzes have shown that both metals are alloyed, which will bring interesting stability properties to the catalyst in hydrocarbon reforming reactions.

Description of the invention

The present invention describes a process for preparing nanoparticles of a Ni-Sn alloy (Ni ₃ Sn) and of the same nanoparticles supported on γ-Al ₂ C> ₃ .

The present invention relates more specifically to a process for the preparation of Ni-Sn nanoparticles, characterized in that it comprises:

REPLACEMENT SHEET (RULE 26) - preparing a solution of a nickel carboxylate in which said carboxylate has between 1 and 6 carbon atoms, and a tin halide in an organic solvent

- add PVP, keep stirring until a homogeneous solution is obtained,

- add an inorganic reducing compound, preferably NaBH ₄

- Refluxing to obtain a colloidal solution, adding a polar organic solvent to the colloidal solution resulting above, causing the precipitation of a solid.

According to particular embodiments, the nickel carboxylate is nickel acetate, the tin halide is tin chloride and the organic solvent is ethylene glycol.

According to further particular embodiments, the polar organic solvent is a ketone of 3 to 6 carbon atoms, preferably acetone.

The process according to the present invention may comprise, in addition to the precipitation of the solid, steps of

- isolation, preferably by centrifugation,

- washing, preferably with one or more alcohols and one or more ketones,

- drying, preferably for at least 6 hours at 100 ° C.

According to particular embodiments the virus is isolated by centrifugation, washing is performed with ethanol and acetone and drying at 100 ⁰ C for 12 hours.

REPLACEMENT SHEET (RULE 26) According to a particularly preferred embodiment, the procedure followed for the preparation of the nanoparticles is as follows:

• prepare a solution of nickel acetate (0.64 g) and tin chloride (0.16 g.) In ethylene glycol (70 mL of ethylene glycol),

• add the appropriate amount of PVP (this parameter determines the size of the nanoparticles) (tests done for 0, 0.5, 0.7 and 1 grams),

• keep stirring until a completely homogeneous solution is obtained,

• add NaBH ₄ (0.34 g.) Which acts as a reducing agent,

• reflux at 200 ° C for 2.5 hours and cool to room temperature,

• add acetone (25 mL of acetone) to the colloidal solution resulting above, which causes the precipitation of a solid,

• separate the solid by centrifugation,

• wash several times with acetone and ethanol and dry at 100 ° C for 12 hours.

According to a variant of the process of the invention, supported nanoparticles of a Ni-Sn alloy are prepared, adding after the preparation of the solution of nickel carboxylate and the tin halide in an organic solvent, an amount of a support substance, obtaining supported nanoparticles.

A further preferred embodiment of the process is characterized in that it comprises:

REPLACEMENT SHEET (RULE 26) - prepare a solution of nickel acetate (0.64 g) and tin chloride (0.16 g.) in ethylene glycol (70 mL of ethylene glycol), add an amount of a support substance, preferably alumina and more preferably, gamma - alumina (4.2 g. of γ-Al ₂ O ₃ )

- add PVP (0.5 g.), keep stirring until a completely homogeneous solution is obtained,

- add NaBH ₄ (0.34 g.) which acts as a reducing agent,

- refluxing at 200 ⁰ C for 2.5 hours and cool to room temperature, add acetone (25 mL of acetone) to the resulting colloidal solution above, causing precipitation of a solid,

- separate the solid by centrifugation,

- Wash repeatedly with acetone and ethanol and dry at 100 ° C for 12 hours.

A second object of the present invention is the use of the particles obtained by the process, in conversion reactions of organic compounds, and preferably in reforming reactions.

The present invention also relates to a method of reforming fuels comprising contacting a feed with a catalyst constituted by the Ni-Sn nanoparticles obtained by the described process.

REPLACEMENT SHEET (RULE 26) Example

The described procedure has been used by varying the amount of PVP added that acts as a protective agent and it has been found that the size of the nanoparticles obtained varies linearly with the amount of protective agent.

REPLACEMENT SHEET (RULE 26)

Claims

1. A procedure for the preparation of nanoparticles characterized in that it comprises: - preparing a solution of a nickel carboxylate in which said carboxylate has between 1 and 6 carbon atoms, and a tin halide in an organic solvent - add PVP, keep stirring until a homogeneous solution is obtained, - add an inorganic reducing compound, - reflux, obtaining a colloidal solution, - adding a polar organic solvent to the above colloidal solution, causing the precipitation of a solid. 2. A process for the preparation of nanoparticles according to claim 1, characterized in that the nickel carboxylate is nickel acetate, the tin halide is tin chloride and the organic solvent is ethylene glycol. 3. A process for the preparation of nanoparticles according to claim 1, characterized in that the inorganic reducer is NaBH ₄ . 4. A process for the preparation of nanoparticles according to claim 1, characterized in that the polar organic solvent is acetone. REPLACEMENT SHEET (RULE 26) 5. A process for the preparation of nanoparticles according to claim 1, characterized in that it further comprises after precipitation of the solid - isolation, - washed - drying 6. A process for the preparation of nanoparticles according to claim 5, characterized in that the isolation is carried out by centrifugation, the washing is carried out with acetone and ethanol and the drying is carried out at 100 ° C for 12 hours. 7. A method of preparing nanoparticles according to any one of the preceding claims characterized in that it comprises: - prepare a solution of nickel acetate and tin chloride in ethylene glycol, - add PVP, - keep stirring until a completely homogeneous solution is obtained, - add NaBH ₄ that acts as a reducing agent, - reflux at 200 ° C for 2.5 hours and cool to room temperature, add acetone to the resulting colloidal solution, causing a solid to precipitate, - separate the solid by centrifugation, - washing repeatedly with acetone and ethanol and dried at 100 ⁰ C for 12 hours. 8. A method of preparing nanoparticles according to any one of the preceding claims REPLACEMENT SHEET (Rule 26) characterized in that after the preparation of the solution of nickel carboxylate and tin halide in an organic solvent, add an amount of a support substance, obtaining supported nanoparticles. 9. A nanoparticle preparation process according to claim 8, characterized in that it comprises: - preparing a solution of nickel acetate and tin chloride in ethylene glycol, - add an amount of a support substance, - add PVP, keep stirring until a completely homogeneous solution is obtained, - add NaBH ₄ that acts as a reducing agent, - reflux at 200 ° C for 2.5 hours and cool to room temperature, add acetone to the resulting colloidal solution, causing a solid to precipitate, - separate the solid by centrifugation, - washing repeatedly with acetone and ethanol and dried at 100 ⁰ C for 12 hours. REPLACEMENT SHEET (Rule 26)