TWI740982B - Precious metal catalyst for hydrogen peroxide production and hydrogen peroxide production method - Google Patents

Abstract

The present invention provides a precious metal catalyst capable of producing high-concentration hydrogen peroxide, and a method for producing hydrogen peroxide. A noble metal catalyst used in a method of directly reacting hydrogen and oxygen to obtain hydrogen peroxide. It contains palladium, gold, oxygen atoms, and bromine atoms, and the aforementioned oxygen atoms and bromine atoms are present on the outermost surface of the noble metal catalyst . A method for producing hydrogen peroxide, including the following steps: introducing a gas containing hydrogen and oxygen into a reaction medium; contacting the introduced hydrogen and oxygen in the reaction medium with the noble metal catalyst at a pressure of 0.1 MPa or more. Hydrogen oxide.

Description

Precious metal catalyst for hydrogen peroxide production and hydrogen peroxide production method

The present invention relates to a noble metal catalyst used in a method of directly reacting hydrogen and oxygen to obtain hydrogen peroxide, and a method for producing hydrogen peroxide using the noble metal catalyst.

Hydrogen peroxide has oxidizing power and strong bleaching and bactericidal effects, so it is used as a bleaching agent and bactericide for paper, pulp, fiber, etc., and it is widely used in oxidation reactions based on epoxidation and hydroxylation. Important industrial products.

In addition, hydrogen peroxide is used in the semiconductor industry for cleaning the surfaces of semiconductor substrates, chemical polishing of copper, tin and other copper alloy surfaces, and etching of electronic circuits. In addition, the decomposition products of hydrogen peroxide are water and oxygen, so from the viewpoint of environmentally friendly chemicals, it is in an important position, and it is also valued as a substitute for chlorine-based bleaching agents.

In the past, hydrogen peroxide production methods are known as anthraquinone method, electrolysis method, and oxidation method using isopropanol, etc. The anthraquinone method is mainly used in industry. However, the anthraquinone method is a multi-stage method such as hydrogenation of anthraquinone, oxidation by air, hydrogen peroxide generated by water extraction, and further purification and concentration. Therefore, this method requires high equipment investment, uses a large amount of energy, and may release the organic solvent used to dissolve anthraquinone into the atmosphere, and cannot be said to be an ideal hydrogen peroxide production method.

As a method to solve the above problems, there is a method of directly producing hydrogen peroxide from oxygen and hydrogen by using a catalyst in the reaction medium. For example, someone has proposed a method for producing hydrogen peroxide by contacting a solid catalyst containing gold, platinum or palladium as a metal component in the liquid phase with hydrogen and oxygen in the presence of water, acid, and non-acidic oxygen-containing organic compounds. It is known that a certain degree of hydrogen peroxide is generated (Patent Document 1).

Patent Document 2 discloses a method for producing hydrogen peroxide by contacting hydrogen and oxygen in a reaction medium, in which a platinum group metal catalyst supported on an oxide support is used. The literature reports that the reaction medium is usually water, and in order to suppress the decomposition of the generated hydrogen peroxide, aqueous hydrochloric acid, hydrobromic acid, phosphoric acid, sulfuric acid, etc. can be used, especially hydrochloric acid and hydrobromic acid aqueous solutions are ideal. It is also described that the aqueous solution of hydrochloric acid can be appropriately replaced with a combination of a mixed aqueous solution of sodium chloride, potassium chloride, etc., which are chloride ion components, and sulfuric acid, phosphoric acid, etc., which are hydrogen ion components. Furthermore, it is also described that the aqueous solution of hydrobromic acid can be appropriately replaced with a combination of a mixed aqueous solution of sodium bromide, potassium bromide, etc., which are bromide ion components, and sulfuric acid, phosphoric acid, etc., which are hydrogen ion components.

Patent Document 3 proposes a method of directly producing hydrogen peroxide aqueous solution from hydrogen and oxygen in a stirred reactor. The hydrogen and oxygen are respectively made into the form of small bubbles, the inorganic acid is added to make it acidic in advance, and the introduction of hydrogen and oxygen is set. The amount is a certain molar ratio method. The document also states that the aforementioned aqueous reaction medium may contain a stabilizer for hydrogen peroxide (for example, phosphonate or tin) and a decomposition inhibitor (for example, halide). The aforementioned documents also record that bromide among halides is a particularly ideal decomposition inhibitor, and it is advantageous to use it in combination with _{bromine (Br 2) in a free state.}

Patent Document 4 discloses a method for producing an organic hydrogen peroxide solution or an organic hydrogen peroxide aqueous solution by a direct synthesis method. In this case, a non-explosive gaseous mixture containing hydrogen and oxygen and a liquid reaction medium are connected to a catalyst containing noble metal. The fixed bed composed of the mixture. The document also discloses that the aforementioned liquid reaction medium contains strong acids and halides.

Patent Document 5 discloses a method of directly synthesizing an aqueous solution of hydrogen peroxide from hydrogen and oxygen using the heterogeneous catalyst in the three-phase system. In the reaction, the catalyst is composed of a metal compound selected from pure palladium or a combination of palladium and at least one other noble metal. The document also discloses: In this method, the aforementioned metal compound is supported on a support containing at least one compound selected from the group consisting of zirconium dioxide and superacidic zirconium dioxide, and the liquid water phase is 0.05 to 3 mmol relative to the water phase. The concentration per liter contains bromide ions and its pH is in the range of 0~4.

Patent Documents 6 and 7 disclose a method for producing hydrogen peroxide that does not use halogen ions as a decomposition inhibitor, but reacts hydrogen and oxygen in the presence of a noble metal catalyst and a radical scavenger in a reaction medium. [Prior Technical Documents] [Patent Documents]

[Patent Document 1] Japanese Patent Publication No. 40-19006 [Patent Document 2] Japanese Patent Publication No. 3394043 [Patent Document 3] Japanese Patent Publication No. 2002-503617 [Patent Document 4] Japanese Patent Application Publication No. 2007-537119 [Patent Document 5] Japanese Patent Application Publication No. 05-213607 [Patent Document 6] Japanese Patent Application Publication No. 2014-15353 [Patent Document 7] International Publication No. 2014/01372

(Problem to be solved by the invention) However, none of the conventional direct production methods of hydrogen peroxide can obtain high-concentration hydrogen peroxide, which has become one of the practical problems. (The way to solve the problem)

The inventors of the present case studied hard and found that by using a noble metal catalyst with a specific composition to directly react hydrogen and oxygen to obtain hydrogen peroxide, the production of high-concentration hydrogen peroxide can be achieved. invention.

That is, a specific method for solving the aforementioned problems is as follows.

The first embodiment of the present invention is a noble metal catalyst used in a method of directly reacting hydrogen and oxygen to obtain hydrogen peroxide. It contains palladium, gold, oxygen atoms, and bromine atoms. The aforementioned oxygen atoms and bromine atoms are present in The most surface of precious metal catalyst.

The second embodiment of the present invention is a method for producing hydrogen peroxide, including the following steps: introducing a gas containing hydrogen and oxygen into the reaction medium; contacting the introduced hydrogen and oxygen in the reaction medium at a pressure of 0.1 MPa or more The noble metal catalyst of the above-mentioned first embodiment obtains hydrogen peroxide. (Effects of the invention)

By using the precious metal catalyst of the present invention, it is possible to produce high-concentration hydrogen peroxide in a method of directly reacting hydrogen and oxygen to obtain hydrogen peroxide. In addition, by the method for producing hydrogen peroxide of the present invention, high-concentration hydrogen peroxide can be produced.

The following is a detailed description of the method for producing the precious metal catalyst and hydrogen peroxide of the present invention. In addition, in this specification, high-concentration hydrogen peroxide refers to, for example, 5% by weight or more, more preferably 10% by weight or more of hydrogen peroxide.

Embodiment 1: Noble metal catalyst The precious metal catalyst of the present invention contains palladium, gold, oxygen atoms, and bromine atoms, and the aforementioned oxygen atoms and bromine atoms are present on the outermost surface of the precious metal catalyst.

The precious metal catalyst of the present invention contains palladium and gold in terms of precious metals. The molar ratio of palladium to gold (palladium/gold) is preferably 0.1-10, more preferably 1-5. In addition to palladium and gold, the precious metal catalyst of the present invention may also contain other precious metals such as platinum or silver. In addition, in this specification, the noble metal containing palladium and gold in a state that does not contain oxygen atoms and bromine atoms is also referred to as a noble metal catalyst precursor.

In order to improve catalyst efficiency and reaction efficiency, precious metals can also be supported on supports such as carbon, silica, alumina, silica alumina, titania or zirconia. It is better to use rutile titanium oxide as the support.

The method for supporting the above-mentioned noble metal on the support may be a conventionally known method without any particular limitation, but an impregnation method or an ion exchange method is preferred. The aforementioned impregnation method can adopt evaporation dry solid method, equilibrium adsorption method, pore filling method, etc.

The amount of the aforementioned precious metal to the support is preferably 0.01-10 parts by weight, and more preferably 0.05-5 parts by weight, relative to 100 parts by weight of the support. In addition, in the method for producing hydrogen peroxide of the present invention, the amount of precious metal catalyst (supported catalyst when supported on a support) is preferably 1 to 100 g relative to 1L of the reaction medium, and 1 relative to 1L ~40g is more ideal.

The noble metal can also be used as a monomer without being supported. For example, it can be used in the form of a nanocolloid in which the noble metal is dispersed in a dispersant such as polyvinylpyrrolidone.

The noble metal catalyst of the present invention has oxygen atoms and bromine atoms on its outermost surface. "The presence of oxygen atoms and bromine atoms on its outermost surface" refers to the presence of oxygen atoms and bromine atoms on the outermost surface of the noble metal catalyst, but it does not exclude the presence of oxygen atoms and bromine atoms on the outermost surface of the noble metal catalyst The existence of the atoms, and the presence of oxygen atoms and bromine atoms inside the precious metal catalyst. Since the noble metal catalyst of the present invention has oxygen atoms and bromine atoms on its outermost surface, high concentration hydrogen peroxide can be produced in the method for producing hydrogen peroxide using the noble metal catalyst. In the conventional method of directly producing hydrogen peroxide from oxygen and hydrogen using a noble metal catalyst, the aforementioned catalyst also serves as a decomposition catalyst for hydrogen peroxide, and therefore the decomposition of the generated hydrogen peroxide occurs at the same time. Therefore, in such a method, certain compounds are often used in order to suppress decomposition. It is known that in the conventional technology, halogen ions such as chloride ions and bromide ions are present in the liquid phase of the reaction medium. However, it has not been known in the past that the noble metal catalyst itself has oxygen atoms and bromine atoms like the noble metal catalyst of the present invention. The inventors of the present invention found out the structure of the precious metal catalyst of the present invention for the first time, and found that the production of high-concentration hydrogen peroxide was achieved under the presence of the precious metal catalyst of the present invention. The mechanism is not yet known, but it is speculated that the presence of oxygen atoms and bromine atoms on the outermost surface of the noble metal catalyst of the present invention can inhibit the hydrogen peroxide produced from being re-adsorbed on the noble metal catalyst, and the decomposition of hydrogen peroxide is inhibited. As a result, The production concentration of hydrogen peroxide has increased.

The existence of oxygen atoms and bromine atoms on the outermost surface of precious metal catalysts can be confirmed by Low Energy Ion Scattering (LEIS) analysis. Low-energy ion scattering (LEIS) analysis method is a method of irradiating a solid surface with an ion beam of rare gas or alkali element from several 100eV to several keV, and measuring the energy spectrum and angle spectrum of the scattered ions to analyze the sample. Qualitative and quantitative top-level atoms. A low energy ion scattering spectrometer (LEIS), for example, Qtac100 manufactured by ION-TOF can be used.

In the precious metal catalyst of the present invention, the ratio of the detected amount of bromine atoms to the detected amount of palladium measured by low energy ion scattering (LEIS) analysis is preferably 0.10 or more, more preferably 0.15 or more, and still more preferably 0.3 or more. In addition, the ratio of the detection amount of bromine atoms to the detection amount of palladium measured by low energy ion scattering (LEIS) analysis is preferably 0.45 or less, and more preferably 0.40 or less. The ratio of the detection amount of bromine atoms to the detection amount of palladium measured by low energy ion scattering (LEIS) analysis should be kept at a fixed value during the process of the production method of hydrogen peroxide described later. The amount of change between the start of the reaction and the end of the reaction is preferably Δ0.5 or less, more preferably Δ0.30 or less, and even more preferably Δ0.25 or less. The presence of this specific amount of bromine on the outermost surface of the noble metal catalyst can produce high-concentration hydrogen peroxide.

In the precious metal catalyst of the present invention, the ratio of oxygen atoms to palladium measured by low energy ion scattering (LEIS) analysis is preferably 1.5 or more, more preferably 1.7 or more. In addition, the ratio of oxygen atoms to palladium measured by low energy ion scattering (LEIS) analysis is preferably 4.0 or less, and more preferably 3.5 or less. When oxygen atoms are present on the outermost surface of the noble metal catalyst in this amount, palladium becomes an oxidized state. As a result, it is believed that bromine atoms become easy to exist on the outermost surface of the noble metal catalyst. The ratio of the detected amount of oxygen atoms to palladium measured by low energy ion scattering (LEIS) analysis should be unchanged or slightly increased during the process of the production method of hydrogen peroxide described later, preferably, it is 0 every 1 hour. The change of ~0.25 is better, the change of Δ0~0.1 every 1 hour is better, and the change of Δ0~0.05 every 1 hour is better. During the period from the beginning of the direct reaction of hydrogen and oxygen to the end of the reaction, the amount of oxygen atoms on the outermost surface of the noble metal catalyst does not change or slightly increases, and the decomposition inhibition of hydrogen peroxide can be maintained even in the late stage of the reaction. Produce high-concentration hydrogen peroxide. A similar effect can be obtained by adding an excessive amount of bromine to the reaction medium, but it is believed that by making the surface of the noble metal catalyst an oxidized state, the adsorption amount of bromine atoms can be maintained with good efficiency.

The noble metal catalyst of the present invention can be produced by contacting the noble metal catalyst precursor with an oxygen component and a bromine component in a medium. For example, by introducing an oxygen-containing gas into a liquid medium containing bromine components, and bringing the bromine component, the introduced oxygen, and the precious metal catalyst precursor in the liquid medium into contact at a pressure above 0.1 MPa, the precious metal catalyst can be obtained. Media. The oxygen partial pressure in the introduced gas should be 20% or more, preferably 30% or more, 40% or more, 50% or more, more preferably 60% or more, more preferably 70% or more, 80% The above is better. The upper limit of the oxygen partial pressure in the introduced gas is 95%, 90%, etc., which can be set appropriately considering the partial pressure of other gas components. In addition to oxygen, the introduced gas can also contain hydrogen, nitrogen, argon, helium or carbon dioxide. Examples of the liquid phase medium include water, alcohols such as methanol and ethanol, ketones such as acetone, and mixed solvents thereof. Among these, water and alcohol are preferred. Examples of the bromine component include bromides such as bromic acid, bromate, and sodium bromide. Among these, sodium bromide is preferred. The amount of bromine used in the reaction medium is preferably 0.01 mM to 10 mM, more preferably 0.02 mM to 5 mM, and even more preferably 0.02 mM to 1 mM. The reaction pressure is preferably 0.1 MPa to 10 MPa, more preferably 0.5 MPa to 5 MPa, and still more preferably 1 MPa to 2 MPa. In addition, the reaction time is usually 0.01 to 100 hours, preferably 0.5 to 10 hours.

The noble metal catalyst of the present invention can be manufactured on the spot by using the hydrogen peroxide manufacturing method of Embodiment 2 described later. For example, by adding the above-mentioned precious metal catalyst precursor to the reaction medium containing the bromine component, the oxygen introduced into the reaction medium can be brought into contact with the precious metal catalyst precursor at a pressure of 0.1 MPa or more to produce precious metals in the reaction system. catalyst. In addition, it can be used directly as a noble metal catalyst for obtaining hydrogen peroxide by directly reacting hydrogen and oxygen in the production step of hydrogen peroxide.

In addition, the precious metal catalyst of the present invention, by being carried on a support, has a high effect of inhibiting the decomposition of high-concentration hydrogen peroxide in the late stage of the reaction, so it is ideal.

Embodiment 2: The manufacturing method of hydrogen peroxide The manufacturing method of hydrogen peroxide of the present invention includes the following steps: introducing a gas containing hydrogen and oxygen into the reaction medium; making the introduced hydrogen and oxygen into the reaction medium and the first The noble metal catalyst of the embodiment is contacted under a pressure of 0.1 MPa or more to obtain hydrogen peroxide. According to the method for producing hydrogen peroxide of the present invention, high-concentration hydrogen peroxide can be produced.

The noble metal catalyst used in the method for producing hydrogen peroxide of the present invention is the noble metal catalyst of the first embodiment described above. Therefore, the description that overlaps with the above is appropriately omitted and not described. In the method for producing hydrogen peroxide of the present invention, the amount of precious metal catalyst (supported catalyst when supported on a support) is preferably 1~100g with respect to 1L of the reaction medium, and 1~ with respect to 1L. 40g is more ideal.

In the method for producing hydrogen peroxide of the present invention, the oxygen partial pressure in the introduced gas is preferably 20% or more, more preferably 30% or more, more preferably 40% or more, more preferably 50% or more, and more preferably 60% or more. Even better, more than 70% is better, more than 80% is better. The upper limit of the oxygen partial pressure in the introduced gas is 95%, 90%, etc., which can be set appropriately considering the partial pressure of other gas components. The oxygen partial pressure in the introduced gas can increase the concentration of hydrogen peroxide produced by the above ratio. The mechanism is unknown, but it is believed that the increase in the amount of oxygen on the surface of the precious metal catalyst can increase the rate of hydrogen peroxide generation.

In addition, when the oxygen partial pressure in the introduced gas is in the above ratio, the precious metal catalyst precursor can be added to the reaction medium containing the bromine component, and the hydrogen and oxygen introduced into the reaction medium can be contacted with the precious metal. The precursor of the medium is contacted at a pressure of 0.1 MPa or more, and the precious metal catalyst of the first embodiment is prepared in the reaction system on the spot. The hydrogen and oxygen can be directly combined with the precious metal catalyst of the first embodiment. The step of obtaining hydrogen peroxide by contacting at a pressure of 0.1 MPa or more is ideal.

The partial pressure of hydrogen in the introduced gas should avoid the explosion range and be an excess ratio of oxygen to hydrogen (for example, the volume ratio of the flow rate of hydrogen and oxygen becomes such as 1:2~1:10). For example, 5-20%, preferably 10-15%. Furthermore, from a safety point of view, in order to further reduce the risk of explosion, hydrogen and oxygen should preferably be diluted. The diluent gas that can be used at this time is a passive gas that does not affect the reaction of hydrogen and oxygen. For example, nitrogen, argon, and helium can be used. Considering the cost point of view, nitrogen is preferable. In addition, oxygen may be diluted with compressed air and used as an oxygen mixed gas. In addition, the gas may also contain carbon dioxide. In this case, the partial pressure of carbon dioxide in the gas is, for example, 0.01 to 5%, preferably 1 to 2%.

A gas system containing hydrogen and oxygen is introduced into the reaction medium, but from the viewpoint of reaction efficiency, it is usually introduced into the liquid phase, that is, the reaction solution.

In the method for producing hydrogen peroxide of the present invention, the reaction medium preferably contains a bromine component. Examples of the bromine component include bromides such as bromic acid, bromate, and sodium bromide. Among these, sodium bromide is preferred. When the reaction medium contains a bromine component, by adding the above-mentioned precious metal catalyst precursor to the reaction medium, the oxygen with a partial pressure of 20% or more introduced into the reaction medium is brought into contact with the precious metal catalyst precursor at a pressure of 0.1 MPa or more. The noble metal catalyst of the first embodiment can be produced in the reaction system by the method of preparation on the spot, and hydrogen and oxygen can be directly contacted with the noble metal catalyst of the first embodiment at a pressure of 0.1 MPa or more to obtain hydrogen peroxide. Steps, it is ideal.

The amount of bromine component used in the reaction medium is preferably 0.01 mM to 10 mM, preferably 0.02 mM to 5 mM, and even more preferably 0.02 mM to 1 mM.

In the method for producing hydrogen peroxide of the present invention, in order to suppress the decomposition of hydrogen peroxide, a halogen or halide ion (for example, chlorine or chloride ion) other than bromine used in the past can also be used.

The method for producing hydrogen peroxide of the present invention is usually implemented in a liquid phase reaction medium. The reaction medium can be used without any special restrictions as long as it does not hinder the reaction of hydrogen and oxygen. Such a reaction medium is well known to those having ordinary knowledge in the technical field.

The aforementioned reaction medium includes, for example, alcohols such as water, methanol and ethanol, ketones such as acetone, and mixed solvents thereof. Among them, water and alcohol are preferred. In addition, hydrocarbon solvents such as heptane, hexane, and pentane with water solubility of 0.1 g/L or less, and fluorine-based liquids with a perfluorocarbon structure can also be used as auxiliary solvents.

In addition, these reaction media may contain additives for pH adjustment, stabilizer effect, or enhancement of gas solubility. For example, acids such as phosphoric acid and sulfuric acid, fluorine-based inactive liquids, and the like may also be contained. When the reaction medium contains these additives, the weight of the reaction medium is the weight of the additives already contained.

These reaction media may also contain free radical scavengers. The free radical scavenger can be one that has the function of scavenging free radicals, such as carbon dioxide, nitrone compounds, nitrone compounds, and dithiocarbamate derivatives such as those exemplified in Japanese Unexamined Patent Application Publication No. 2014-15353 And ascorbic acid derivatives. These free radical scavengers may be in the form of salts, or in the form of hydrates, or in this form. Examples of the aforementioned salt include sodium salt and potassium salt.

In the present invention, the introduced hydrogen and oxygen are brought into contact with the noble metal catalyst of the first embodiment described above in a reaction medium at a pressure of 0.1 MPa or more to obtain hydrogen peroxide.

This reaction can increase the hydrogen concentration and oxygen concentration soluble in the water by setting the pressure to a high level, and can increase the yield of hydrogen peroxide. Therefore, it is usually carried out using a pressure-resistant autoclave and other reaction devices.

The aforementioned reaction device can be any type such as a stirred tank type, bubble column type, fixed bed type, micro reactor, etc., and the reaction can be carried out in a batch type or a continuous type. The aforementioned reaction device includes a gas introduction part and a gas discharge part, and is usually equipped with a thermometer, a pressure gauge, and the like.

In addition, the reaction of the present invention sometimes uses corrosive halogen. Therefore, the reaction device should be made of stainless steel lined with Teflon (registered trademark), Inconel or Hastelloy. By. Reaction devices formed with stainless steel or glass lining can also be used.

In the present invention, during the synthesis of hydrogen peroxide, the reaction temperature of hydrogen and oxygen is preferably 0-100°C, and more preferably the range of 5-50°C. The reaction pressure is preferably 0.1 MPa or more, preferably 0.1 MPa to 10 MPa, more preferably 0.5 MPa to 5 MPa, and still more preferably 1 MPa to 2 MPa. In addition, the reaction time is usually 0.01 to 100 hours, preferably 0.5 to 50 hours.

The method for producing hydrogen peroxide of the present invention includes the aspect of the method for producing hydrogen peroxide including the following steps: A gas containing hydrogen and oxygen is introduced into a reaction medium containing a bromine component to have an oxygen partial pressure of 20% The above method is introduced; the introduced oxygen is brought into contact with the noble metal catalyst precursor in the reaction medium at a pressure above 0.1 MPa to obtain the noble metal catalyst; the introduced hydrogen, oxygen, and The noble metal catalyst obtained in the above steps is contacted under a pressure of more than 0.1 MPa to obtain hydrogen peroxide. According to this aspect, the noble metal catalyst of the first embodiment can be manufactured in the reaction system by the on-site preparation method, and the second step of obtaining hydrogen peroxide can be carried out directly under the existing conditions of the noble metal catalyst, so it is ideal. In this aspect, the reaction conditions such as the amount of bromine component, oxygen partial pressure, and reaction pressure are as defined above.

In the method for producing hydrogen peroxide of the present invention, in the precious metal catalyst, the ratio of the detected amount of bromine atoms measured by low energy ion scattering (LEIS) analysis and the detected amount of palladium is preferably 0.10 or more, more preferably 0.15 or more , And more preferably 0.3 or more. In addition, the ratio of the detection amount of bromine atoms to the detection amount of palladium measured by low energy ion scattering (LEIS) analysis is preferably 0.45 or less, and more preferably 0.40 or less. Here, the ratio of the detection amount of bromine atoms to the detection amount of palladium measured by low energy ion scattering (LEIS) analysis should be kept at a fixed value during the production method of hydrogen peroxide. From hydrogen to oxygen The amount of change between the start of the direct reaction and the end of the reaction is preferably Δ0.5 or less, more preferably Δ0.3 or less, and even more preferably Δ0.25 or less. The specific amount of bromine is present on the outermost surface of the noble metal catalyst during the period from the beginning of the direct reaction of hydrogen and oxygen to the end of the reaction, so that high-concentration hydrogen peroxide can be produced.

In the method for producing hydrogen peroxide of the present invention, the ratio of oxygen atoms to palladium measured by low-energy ion scattering (LEIS) analysis in the noble metal catalyst is preferably 1.5 or more, more preferably 1.7 or more. In addition, the ratio of oxygen atoms to palladium measured by low energy ion scattering (LEIS) analysis is preferably 4.0 or less, and more preferably 3.5 or less. Since oxygen atoms are present on the outermost surface of the noble metal catalyst in this amount, palladium becomes an oxidized state. As a result, it is believed that bromine atoms become easy to exist on the outermost surface of the noble metal catalyst. The ratio of oxygen atoms to palladium measured by low energy ion scattering (LEIS) analysis should be unchanged or slightly increased during the process of the hydrogen peroxide production method, preferably 0~0.25 per hour It is better to increase the amount of change, and it is even better to increase the amount of change of Δ0~0.1 every 1 hour, and it is better to increase the amount of change of Δ0~0.05 every 1 hour. During the period from the beginning of the direct reaction of hydrogen and oxygen to the end of the reaction, the amount of oxygen atoms on the outermost surface of the noble metal catalyst does not change or slightly increases, and the decomposition inhibition of hydrogen peroxide can be maintained even in the late stage of the reaction. Get high concentration of hydrogen peroxide. A similar effect can be obtained by adding an excessive amount of bromine to the reaction medium. It is believed that by making the surface of the noble metal catalyst into an oxidized state, the adsorbed amount of bromine atoms can be maintained with good efficiency. [Example]

Hereinafter, the present invention will be described in more detail based on examples and comparative examples, but the present invention is not limited to the following examples.

(Example 1) (1) Manufacture of precious metal catalyst carried on a support 200 ml of a mixed solvent of ethanol and water (water:ethanol=1:1) was added with 2g of oxalic acid and stirred. 10 g of titanium oxide (rutile type titanium oxide (IV)) manufactured by Sakai Chemical Co., Ltd., _{0.05 g of HAuCl 4} and 0.12 g of PdCl ₂ were added thereto, and reflux was performed at 80° C. for 1 hour while using a Liebig cooler.

After 1 hour, the suspended solution was transferred to a 300ml beaker and heated to remove the solvent. Then, the obtained solid was dried in a dryer at 85° C. for one day to obtain a precious metal catalyst precursor (Pd-Au/TiO ₂ ) supported on the support.

Then, in a 270ml autoclave lined with Teflon (registered trademark) equipped with a stirring device and a gas blowing tube, add the precious metal catalyst precursor (Pd-Au/TiO ₂ ) 1.125 made above and carried on the support. g. 270 ml of reaction solution (containing 0.5 mM phosphoric acid and 0.05 mM sodium bromide, the reaction medium is water).

While adjusting the temperature in the autoclave to 25℃, blow the gas into the autoclave at a rate of 250ml/min (hydrogen 10%, oxygen 80%, nitrogen 10%) (oxygen partial pressure in the gas 80%), and adjust the pressure It is 1M Pascal, and it is reacted while stirring at 1000 rpm to prepare a precious metal catalyst. During this reaction, hydrogen peroxide is also produced. After the reaction solution is introduced into the precious metal catalyst precursor, the precious metal catalyst is taken out from the reaction solution at regular intervals, and low energy ion scattering (LEIS) analysis is used to measure the surface of the precious metal catalyst at each reaction time. In addition, in Table 1, the reaction time of 0 hours refers to the state in which the precious metal catalyst is taken out immediately after the precious metal catalyst precursor is introduced into the reaction solution.

(Surface analysis of precious metal catalyst) The surface analysis of precious metal catalyst is carried out in the following way. Using a low-energy ion scattering spectrometer (LEIS) Qtac100 (manufactured by ION-TOF), the elemental analysis on the surface of the precious metal catalyst is carried out under the conditions of 2KeV~5KeV helium ion or neon ion beam irradiation. Identify each element in the energy spectrum obtained. Calculate the detection amount (integration value) of each element, and calculate the ratio of the detection amount of bromine atoms to the detection amount of palladium (Br/Pd) and the ratio of oxygen atoms to the detection amount of palladium (O/Pd). The ratio of these detection amounts is shown in Table 1.

(Example 2) The gas composition of Example 1 was changed to a gas composition of 10% hydrogen, 18% oxygen, and 72% nitrogen (the oxygen partial pressure in the gas was 18%), except for this, the same procedure as in Example 1 was carried out. The precious metal catalyst is analyzed and measured on the surface of the precious metal catalyst at each reaction time by low-energy ion scattering (LEIS). The results are shown in Table 1. The reaction process also produces hydrogen peroxide.

【Table 1】

From the results shown in Table 1, it is confirmed that oxygen atoms and bromine atoms are present on the outermost surface of the noble metal catalyst. Furthermore, when the ratio of the detected amount of bromine atoms to the detected amount of palladium is 0.10 or more, and the ratio of oxygen atoms to palladium is 1.5 or more, a higher concentration of hydrogen peroxide is produced in the reaction.

(Example 3) (1) The precious metal catalyst precursor carried on the support was manufactured in 200 ml of a mixed solvent of ethanol and water (water: ethanol = 1:1), and 2 g of oxalic acid was added and stirred. 10 g of titanium oxide (rutile type titanium oxide (IV)) manufactured by Sakai Chemical Co., Ltd., _{0.05 g of HAuCl 4} and 0.12 g of PdCl ₂ were added thereto, and reflux was performed at 80° C. for 1 hour while using a Liebig cooler.

After 1 hour, the suspended solution was transferred to a 300ml beaker and heated to remove the solvent. Then, the obtained solid was dried in a dryer at 85° C. for one day to obtain a precious metal catalyst precursor (Pd-Au/TiO ₂ ) supported on the support.

(2) The production experiment of hydrogen peroxide was carried out in a 270ml autoclave lined with Teflon (registered trademark) equipped with a stirring device and a gas blowing tube, and added the precious metal catalyst precursor produced above on a support. (Pd-Au/TiO ₂ ) 1.125 g, reaction solution 270 ml (containing 0.5 mM phosphoric acid and 0.05 mM sodium bromide, the reaction medium is water).

While adjusting the temperature in the autoclave to 25℃, blow the gas into the autoclave at a rate of 250ml/min (hydrogen 10%, oxygen 25%, nitrogen 64%, carbon dioxide 1%) (the oxygen partial pressure in the gas is 25%) ), adjust the pressure to 1M Pascal, and react while stirring at 1000 rpm. After introducing the precious metal catalyst precursor into the reaction solution, at regular intervals, use a hydrogen peroxide automatic titration device (equipment name: HP-300, manufacturing company: Hiranuma Sangyo, using the iodine coulometric titration method) for the concentration of hydrogen peroxide After quantification, it is confirmed that the concentration of hydrogen peroxide starts to decrease, and the reaction is terminated. A peak of the concentration of hydrogen peroxide was observed 30 hours after the start of the reaction, which was 6.0 wt%. The results are shown in Table 2. The above-mentioned hydrogen peroxide production process also produces the precious metal catalyst carried on the support.

(Example 4) The gas composition of Example 3 was changed to a gas composition of 10% hydrogen, 30% oxygen, 59% nitrogen, and 1% carbon dioxide (the partial pressure of oxygen in the gas was 30%). Proceed in the same way to produce hydrogen peroxide. The peak of the hydrogen peroxide concentration was observed 45 hours after the start of the reaction, which was 7.7% by weight.

(Example 5) The gas composition of Example 3 was changed to a gas composition of 10% hydrogen, 50% oxygen, 39% nitrogen, and 1% carbon dioxide (the partial pressure of oxygen in the gas was 50%). Proceed in the same way to produce hydrogen peroxide. The peak of hydrogen peroxide concentration was observed 30-40 hours after the reaction started, which was 9.0wt%.

(Example 6) Change the gas composition of Example 3 to a gas composition of 10% hydrogen, 70% oxygen, 19% nitrogen, and 1% carbon dioxide (the partial pressure of oxygen in the gas is 70%). Proceed in the same way to produce hydrogen peroxide. The peak of hydrogen peroxide concentration was observed 40 hours after the reaction started, which was 11.0 wt%.

(Example 7) The gas composition of Example 3 was changed to a gas composition of 10% of hydrogen, 89% of oxygen, and 1% of carbon dioxide (the oxygen partial pressure in the gas was 89%), except that it was carried out in the same manner as in Example 3. hydrogen peroxide. The peak of hydrogen peroxide concentration was observed 45 hours after the start of the reaction, which was 11.5 wt%.

(Comparative Example 1) The gas composition of Example 3 was changed to a gas composition of 10% hydrogen, 19.2% oxygen, 69.8% nitrogen, and 1% carbon dioxide (the oxygen partial pressure in the gas was 19.2%). Otherwise, the same as in Example 3. Proceed in the same way to produce hydrogen peroxide. A peak of hydrogen peroxide concentration was observed 25 hours after the start of the reaction, which was 4.7% by weight.

(Example 8) (1) Preparation of nano colloidal precious metal catalyst precursor Using polyvinylpyrrolidone (PVP) as a dispersant, PdCl ₂ and HAuCl _{4 were} reduced with oxalic acid to prepare nano colloidal precious metal catalyst precursor ( Pd-Au nano colloid). (2) In the production experiment of hydrogen peroxide, a 270ml autoclave lined with Teflon (registered trademark) equipped with a stirring device and a gas blowing tube was added to the nano colloidal precious metal catalyst precursor (Pd- Au nanocolloid) 74.52mg, 130ml reaction solution (containing 0.5mM phosphoric acid and 2.0mM sodium bromide, reaction medium is water and ethanol).

While adjusting the temperature in the autoclave to 20℃, blow the gas into the autoclave at a rate of 600ml/min (hydrogen 10%, oxygen 30%, nitrogen 60%) (oxygen partial pressure in the gas 30%), and adjust The pressure was 1M Pascal, and the reaction was made while stirring at 1000 rpm. After the precious metal catalyst precursor is introduced into the reaction solution, the hydrogen peroxide automatic titration device (equipment name: HP-300, manufacturing company: Hiranuma Sangyo, using the iodine coulometric titration method) is used to measure the hydrogen peroxide concentration at regular intervals. Quantitatively, the reaction was terminated after confirming that the concentration of hydrogen peroxide started to decrease. The peak of hydrogen peroxide concentration was observed 8 hours after the start of the reaction, which was 7.0 wt%. The results are shown in Table 3.

(Example 9) The gas composition of Example 8 was changed to a gas composition of 10% hydrogen, 60% oxygen, 29% nitrogen, and 1% carbon dioxide (the oxygen partial pressure in the gas was 60%). Otherwise, the same as in Example 8. Proceed in the same way to produce hydrogen peroxide. The peak of hydrogen peroxide concentration was observed 8 hours after the start of the reaction, which was 8.0 wt%.

(Example 10) The gas composition of Example 8 was changed to a gas composition of 10% hydrogen, 80% oxygen, 9% nitrogen, and 1% carbon dioxide (the partial pressure of oxygen in the gas was 80%). Otherwise, the same as in Example 8. Proceed in the same way to produce hydrogen peroxide. A peak of hydrogen peroxide concentration was observed 14 hours after the start of the reaction, which was 10.0 wt%.

【Table 2】

【table 3】

From the results shown in Table 2 and Table 3, it can be seen that the method for producing hydrogen peroxide of the present invention can produce high-concentration hydrogen peroxide. In addition, it can be seen that by controlling the oxygen partial pressure in the gas introduced in the hydrogen peroxide production method, the noble metal catalyst of the present invention can be obtained, and hydrogen peroxide can be carried out in the presence of the noble metal catalyst of the present invention. The manufacture can obtain high concentration of hydrogen peroxide.

Claims (4)

A noble metal catalyst used in the method of directly reacting hydrogen and oxygen to obtain hydrogen peroxide. It contains palladium, gold, oxygen atoms, and bromine atoms, and the bromine atoms measured by low energy ion scattering (LEIS) analysis The ratio of the detected amount of palladium to the detected amount of palladium is 0.10 or more, and the ratio of oxygen atoms to palladium is 1.5 or more. A method for producing hydrogen peroxide, including the following steps: introducing a gas containing hydrogen and oxygen into a reaction medium; contacting the introduced hydrogen and oxygen with a noble metal catalyst in the reaction medium at a pressure above 0.1 MPa to obtain peroxide Hydrogen; The precious metal catalyst is the precious metal catalyst as claimed in claim 1. For example, the method for producing hydrogen peroxide in item 2 of the scope of patent application, wherein the oxygen partial pressure in the introduced gas is 20% or more and 95% or less. For example, the method for producing hydrogen peroxide in item 2 or 3 of the scope of patent application, wherein the reaction medium contains bromine.