WO2018016359A1

WO2018016359A1 - Noble metal catalyst for manufacturing hydrogen peroxide, and method for manufacturing hydrogen peroxide

Info

Publication number: WO2018016359A1
Application number: PCT/JP2017/025067
Authority: WO
Inventors: 石原　達己; 英俊池田; 君塚　健一; 奥田　典和
Original assignee: 三菱瓦斯化学株式会社; 国立大学法人九州大学
Priority date: 2016-07-19
Filing date: 2017-07-10
Publication date: 2018-01-25
Also published as: JPWO2018016359A1; TW201829060A; CN109310998A; TWI740982B

Abstract

Provided are a noble metal catalyst and a method for manufacturing hydrogen peroxide, with which it is possible to manufacture high-concentration hydrogen peroxide. A noble metal catalyst used in a method for directly reacting hydrogen and oxygen to obtain hydrogen peroxide, the noble metal catalyst containing palladium, gold, oxygen atoms, and bromine atoms, the oxygen atoms and the bromine atoms being present on the outermost surface of the noble metal catalyst; and a method for manufacturing hydrogen peroxide, the method including introducing air containing hydrogen and oxygen into a reaction medium, bringing the hydrogen and oxygen introduced in the reaction medium into contact with the noble metal catalyst under a pressure of 0.1 MPa or more to obtain hydrogen peroxide.

Description

Noble metal catalyst for hydrogen peroxide production and method for producing hydrogen peroxide

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

Hydrogen peroxide is used as a bleaching agent and disinfectant for paper, pulp, fiber, etc. because it has an oxidizing power and a strong bleaching and disinfecting action. It also includes epoxidation and hydroxylation. It is an important industrial product used extensively in oxidation reactions.

Furthermore, hydrogen peroxide is used in the semiconductor industry for cleaning the surface of semiconductor substrates and the like, for chemical polishing of copper, tin and other copper alloy surfaces, and for etching electronic circuits. And since hydrogen peroxide is a decomposition product of water and oxygen, it is positioned as important from the viewpoint of green chemistry and attracts attention as an alternative material for chlorine bleach.

Conventionally, an anthraquinone method, an electrolytic method, a method using oxidation of isopropyl alcohol, and the like are known as methods for producing hydrogen peroxide, and the anthraquinone method is mainly employed industrially. However, the anthraquinone method is a multi-step method such as hydrogenation of anthraquinone, oxidation with air, extraction of hydrogen peroxide produced with water, and further purification and concentration. Therefore, this method is not necessarily an ideal method for producing hydrogen peroxide because it requires high capital investment, uses a large amount of energy, and releases an organic solvent for dissolving anthraquinone to the atmosphere. I can't say that.

As a method for solving the above problems, there is a method of directly producing hydrogen peroxide from oxygen and hydrogen using a catalyst in a reaction medium. For example, hydrogen peroxide is produced by bringing hydrogen and oxygen into contact with a solid catalyst containing gold, platinum or palladium as a metal component in the liquid phase in the presence of water, an acid, and a non-acidic oxygen-containing organic compound. A method has been proposed, and it is known that a certain amount of hydrogen peroxide is generated (Patent Document 1).

Patent Document 2 discloses a method for producing hydrogen peroxide using a platinum group metal catalyst supported on an oxide support in a method for producing hydrogen peroxide catalytically from hydrogen and oxygen in a reaction medium. . In this document, water is usually suitable as the reaction medium, and hydrochloric acid aqueous solution, hydrobromic acid aqueous solution, phosphoric acid aqueous solution, sulfuric acid aqueous solution, etc., particularly hydrochloric acid aqueous solution, It has been reported that an aqueous hydrogen acid solution can be suitably used. Further, it is described that a mixed aqueous solution of sodium chloride, potassium chloride or the like as a chloride ion component and sulfuric acid or phosphoric acid as a hydrogen ion component can be suitably employed instead of the hydrochloric acid aqueous solution. Furthermore, it is described that a combination of a mixed aqueous solution of sodium bromide, potassium bromide or the like as the bromide ion component and sulfuric acid, phosphoric acid or the like as the hydrogen ion component can be suitably employed instead of the hydrobromic acid aqueous solution. Has been.

Patent Document 3 is a method for producing an aqueous hydrogen peroxide solution directly from hydrogen and oxygen in a stirred reactor, in which hydrogen and oxygen are separately made into small bubbles, made acidic by adding an inorganic acid in advance, and hydrogen and oxygen. A method has been proposed in which the amount of oxygen introduced is a constant molar ratio. The document also states that the aqueous reaction medium may include a stabilizer against hydrogen peroxide (eg, phosphonate or tin) and a decomposition inhibitor (eg, halide). Furthermore, the document states that bromides are particularly preferred decomposition inhibitors among the halides, and are advantageously used in combination with free bromine (Br ₂ ).

Patent Document 4 is a method for producing an organic hydrogen peroxide solution or an organic hydrogen peroxide aqueous solution by a direct synthesis method, in which a non-explosive gaseous mixture containing hydrogen and oxygen and a liquid reaction medium are used. A production process is disclosed for passing through a fixed bed comprising a mixture containing a noble metal catalyst. The document also discloses that the liquid reaction medium contains a strong acid and a halide.

Patent Document 5 is a method for directly synthesizing an aqueous solution of hydrogen peroxide from hydrogen and oxygen by heterogeneous catalysis in a three-phase system, which is a solid heterogeneous catalyst suspended in a granular state in a liquid aqueous phase. Wherein the catalyst reacts directly on the surface of the catalyst and the catalyst comprises a pure compound of palladium or a combination of metal and at least one other noble metal. Further, the document discloses that in this method, the metal compound is supported on a carrier containing at least one compound selected from zirconium dioxide and superacid zirconium dioxide, and the liquid aqueous phase is 0.1% relative to the aqueous phase. It discloses that it contains bromide ions at a concentration of 05-3 mmol / l and its pH is in the range of 0-4.

Patent Documents 6 and 7 disclose a method for producing hydrogen peroxide in which hydrogen and oxygen are reacted in a reaction medium in the presence of a noble metal catalyst and a radical scavenger without using a halogen ion as a decomposition inhibitor. .

Japanese Patent Publication No. 40-19006 Japanese Patent No. 3394043 JP-T-2002-503617 Special Table 2007-537119 Japanese Patent Laid-Open No. 05-213607 JP 2014-15353 A International Publication No. 2014/01372

However, none of the conventional methods for directly producing hydrogen peroxide can provide high-concentration hydrogen peroxide, which is one of the problems for practical application.

As a result of intensive studies, the present inventors have achieved the production of high-concentration hydrogen peroxide by using a noble metal catalyst having a specific configuration in a method for obtaining hydrogen peroxide by directly reacting hydrogen and oxygen. As a result, the present invention has been completed.

That is, specific means for solving the above-described problems are 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 is a noble metal catalyst containing palladium, gold, oxygen atoms and bromine atoms, wherein the oxygen atoms and bromine atoms are present on the outermost surface of the noble metal catalyst.

The second embodiment of the present invention introduces a gas containing hydrogen and oxygen into the reaction medium;
A method for producing hydrogen peroxide, comprising bringing hydrogen and oxygen introduced in a reaction medium into contact with the noble metal catalyst of the first embodiment under a pressure of 0.1 MPa or more to obtain hydrogen peroxide. It is.

By using the noble metal catalyst of the present invention, hydrogen peroxide having a high concentration can be produced in a method in which hydrogen and oxygen are directly reacted to obtain hydrogen peroxide. Moreover, high concentration hydrogen peroxide can be manufactured with the manufacturing method of hydrogen peroxide of this invention.

Hereinafter, the noble metal catalyst and the method for producing hydrogen peroxide of the present invention will be described in detail. In the present specification, high concentration hydrogen peroxide refers to, for example, 5% by weight or more, more preferably 10% by weight or more.

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

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

The noble metal can be supported on a support such as carbon, silica, alumina, silica alumina, titanium oxide or zirconia in order to increase the catalyst efficiency and the reaction efficiency. As the carrier, rutile type titanium oxide is preferably used.

As a method of supporting the noble metal on the carrier, a conventionally known method can be employed without any particular limitation, but an impregnation method or an ion exchange method is preferable. As the impregnation method, an evaporation to dryness method, an equilibrium adsorption method, a pore filling method, or the like can be employed.

The amount of the noble metal supported on the carrier is preferably 0.01 to 10 parts by weight, more preferably 0.05 to 5 parts by weight with respect to 100 parts by weight of the carrier. In the method for producing hydrogen peroxide according to the present invention, the amount of the noble metal catalyst (supported catalyst when supported on a carrier) is preferably 1 to 100 g with respect to 1 L of the reaction medium, and 1 to 1 L with respect to 1 L. 40 g is more preferable.

The noble metal can be used without being supported alone, and 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 precious metal catalyst of the present invention has oxygen atoms and bromine atoms on the outermost surface. “Oxygen atoms and bromine atoms are present on the outermost surface” means that oxygen atoms and bromine atoms are present on the outermost surface of the noble metal catalyst, but other than oxygen atoms and bromine atoms are present on the outermost surface of the noble metal catalyst. It does not exclude the presence of atoms and the presence of oxygen and bromine atoms inside the noble metal catalyst. Since the noble metal catalyst of the present invention has an oxygen atom and a bromine atom on the outermost surface thereof, a high concentration of hydrogen peroxide can be produced in the method for producing hydrogen peroxide using the noble metal catalyst. In a conventional method for producing hydrogen peroxide directly from oxygen and hydrogen using a noble metal catalyst, the catalyst also functions as a decomposition catalyst for hydrogen peroxide, so that the generated hydrogen peroxide is simultaneously decomposed. For this reason, some compounds are often used to suppress decomposition in such a method, and it is known in the prior art that halogen ions such as chlorine ions and bromine ions are present in the liquid phase of the reaction medium. . However, a configuration in which an oxygen atom and a bromine atom are present in the noble metal catalyst itself as in the noble metal catalyst of the present invention has not been known. The present inventors have found the constitution of the noble metal catalyst of the present invention for the first time, and have found that production of hydrogen peroxide at a high concentration can be achieved under the conditions in which the noble metal catalyst of the present invention exists. Although it is not clear as the mechanism, in the noble metal catalyst of the present invention, due to the presence of oxygen atoms and bromine atoms on the outermost surface, resorption of the produced hydrogen peroxide to the noble metal catalyst is suppressed, It is considered that the decomposition of hydrogen peroxide is suppressed, and as a result, the production concentration of hydrogen peroxide increases.

The presence of oxygen atoms and bromine atoms on the outermost surface of the noble metal catalyst can be confirmed by low energy ion scattering (LEIS) analysis. Low energy ion scattering (LEIS) analysis is a method in which a solid surface is irradiated with a rare gas or alkali element ion beam of several hundred eV to several keV, and the sample is measured by measuring the energy spectrum and angular spectrum of the scattered ions. It is a method of analysis, and qualitative and quantitative determination of the outermost layer atoms is possible. As a low energy ion scattering spectrometer (LEIS), for example, Qtac100 manufactured by ION-TOF can be used.

In the noble metal catalyst of the present invention, the ratio of the detected amount of bromine atom to palladium, preferably measured by low energy ion scattering (LEIS) analysis, is 0.10 or more, more preferably 0.15 or more. More preferably, it is 0.3 or more. Further, the ratio of the detected amount of bromine atoms to 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 detected amount of bromine atoms to palladium, which is measured by this low energy ion scattering (LEIS) analysis, is preferably maintained at a constant value in the process of producing 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. Due to the presence of this specific amount of bromine on the outermost surface of the noble metal catalyst, a high concentration of hydrogen peroxide can be produced.

In the noble metal catalyst of the present invention, preferably, the ratio of oxygen atom to palladium, measured by low energy ion scattering (LEIS) analysis, is 1.5 or more, more preferably 1.7 or more. Further, the ratio of oxygen atom to palladium, measured by low energy ion scattering (LEIS) analysis, is preferably 4.0 or less, and more preferably 3.5 or less. It is considered that when oxygen atoms are present in this amount on the outermost surface of the noble metal catalyst, palladium is in an oxidized state, and as a result, bromine atoms are likely to be present on the outermost surface of the noble metal catalyst. The ratio of the detected amount of oxygen atoms to palladium, measured by this low energy ion scattering (LEIS) analysis, preferably remains unchanged or slightly increases in the course of the hydrogen peroxide production method described below. It is more preferable to increase at a change amount of 0 to 0.25 per hour, more preferable to increase at a change amount of Δ0 to 0.1 per hour, and a change of Δ0 to 0.05 per hour. It is preferable to increase the amount. From the start 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, so that the suppression of hydrogen peroxide decomposition is maintained even in the later stage of the reaction. A concentration of hydrogen peroxide can be produced. Although a similar effect can be obtained by adding a bromine component in excess to the reaction medium, it is considered that the adsorption amount of bromine atoms can be efficiently maintained by bringing the surface of the noble metal catalyst into an oxidized state.

The noble metal catalyst of the present invention can be produced by bringing a noble metal catalyst precursor into contact with an oxygen component and a bromine component in a medium. For example, a gas containing oxygen is introduced into a liquid phase medium containing a bromine component, and the bromine component in the liquid phase medium, the introduced oxygen, and the noble metal catalyst precursor are brought into contact under a pressure of 0.1 MPa or more. Thus, a noble metal catalyst can be obtained. The oxygen partial pressure in the introduced gas is preferably 20% or more, more preferably 30% or more, more preferably 40% or more, and more preferably 50% or more, It is more preferably 60% or more, more preferably 70% or more, and more preferably 80% or more. The upper limit of the partial pressure of oxygen in the introduced gas can be set as appropriate in consideration of the partial pressure of other gas components, such as 95% and 90%. The introduced gas may contain hydrogen gas, nitrogen gas, argon gas, helium gas or carbon dioxide in addition to oxygen gas. 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 alcohols are preferable. Examples of the bromine component include bromides such as bromic acid, bromate, and sodium bromide. Among these, sodium bromide is preferable. The amount of the bromine component used is preferably 0.01 mM to 10 mM, more preferably 0.02 mM to 5 mM, and further preferably 0.02 mM to 1 mM in the reaction medium. The reaction pressure is preferably 0.1 MPa to 10 MPa, more preferably 0.5 MPa to 5 MPa, and further preferably 1 MPa to 2 MPa. 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 also be prepared in use by the hydrogen peroxide production method of Embodiment 2 described later. For example, the above-mentioned noble metal catalyst precursor is added to a reaction medium containing a bromine component, and the oxygen introduced into the reaction medium is brought into contact with the noble metal catalyst precursor under a pressure of 0.1 MPa or more. Noble metal catalysts can be produced in the system. And in the manufacturing process of hydrogen peroxide as it is, it can be used as a noble metal catalyst for directly reacting hydrogen and oxygen to obtain hydrogen peroxide.

Further, the noble metal catalyst of the present invention is preferable because it is supported on a support because the effect of suppressing the decomposition of high-concentration hydrogen peroxide in the late stage of the reaction is enhanced.

Embodiment 2: Method for producing hydrogen peroxide The method for producing hydrogen peroxide of the present invention comprises introducing a gas containing hydrogen and oxygen into a reaction medium,
Contacting hydrogen and oxygen introduced in the reaction medium with the noble metal catalyst of the first embodiment under a pressure of 0.1 MPa or more to obtain hydrogen peroxide. By the method for producing hydrogen peroxide according to the present invention, high-concentration hydrogen peroxide can be produced.

The noble metal catalyst used in the method for producing hydrogen peroxide according to the present invention is the noble metal catalyst of the first embodiment. Therefore, the description overlapping with the above is omitted as appropriate. In the method for producing hydrogen peroxide of the present invention, the amount of the noble metal catalyst (supported catalyst when supported on a carrier) is preferably 1 to 100 g per 1 L of the reaction medium, and 1 to 40 g per 1 L. More preferred.

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, and more preferably 40% or more. 50% or more is more preferable, 60% or more is more preferable, 70% or more is more preferable, and 80% or more is more preferable. The upper limit of the partial pressure of oxygen in the introduced gas can be set as appropriate in consideration of the partial pressure of other gas components, such as 95% and 90%. When the oxygen partial pressure in the introduced gas is the above ratio, the concentration of the produced hydrogen peroxide can be increased. Although this mechanism is not clear, it is thought that the rate of hydrogen peroxide generation can be improved by increasing the amount of oxygen on the surface of the noble metal catalyst.

Further, when the oxygen partial pressure in the introduced gas is the above ratio, the above-mentioned noble metal catalyst precursor is added to the reaction medium containing the bromine component, and hydrogen and oxygen introduced into the reaction medium, and the noble metal By contacting the catalyst precursor with a pressure of 0.1 MPa or more, the noble metal catalyst of the first embodiment can be prepared in use in a reaction system, and hydrogen, oxygen and the first This is preferable because the step of obtaining hydrogen peroxide by bringing the noble metal catalyst of the embodiment into contact with a pressure of 0.1 MPa or more can be performed.

The hydrogen partial pressure in the introduced gas is such that the explosion range is avoided and oxygen is excessive with respect to hydrogen (for example, the volume ratio of the flow rate of hydrogen gas to oxygen gas is 1: 2 to 1:10). For example, 5 to 20%, preferably 10 to 15%. Furthermore, in order to further reduce the risk of explosion from the viewpoint of safety, it is preferable to dilute hydrogen and oxygen. The diluent gas that can be used in this case is an inert gas that does not affect the reaction between hydrogen and oxygen. For example, nitrogen gas, argon gas, and helium gas can be used. Nitrogen gas is preferable from the viewpoint of cost. Note that oxygen may be diluted with compressed air and used as an oxygen mixed gas. In addition, carbon dioxide may be contained in the gas. In this case, the partial pressure of carbon dioxide in the gas is, for example, 0.01 to 5%, preferably 1 to 2%.

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

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 preferable. When the reaction medium contains a bromine component, the above-mentioned noble metal catalyst precursor is added to the reaction medium, and oxygen having a partial pressure of 20% or more introduced into the reaction medium and the noble metal catalyst precursor is 0.1 MPa or more. In the reaction system, the noble metal catalyst of the first embodiment can be preparatively produced at the time of use, and hydrogen and oxygen and the noble metal catalyst of the first embodiment can be directly added in the reaction system in an amount of 0. 0. This is preferable because the step of obtaining hydrogen peroxide by bringing it into contact under a pressure of 1 MPa or more can be carried out.

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

In the method for producing hydrogen peroxide of the present invention, a halogen other than bromine or a halogen ion (for example, chlorine or chlorine ion) conventionally used for suppressing decomposition of hydrogen peroxide may be used.

The method for producing hydrogen peroxide of the present invention is usually carried out in a reaction medium that is in a liquid phase. The reaction medium can be used without particular limitation as long as it does not inhibit the reaction between hydrogen and oxygen. Such reaction media are well known to those skilled in the art.

Examples of the reaction medium include water, alcohols such as methanol and ethanol, ketones such as acetone, and mixed solvents thereof. Among these, water and alcohol are preferable. Further, a hydrocarbon solvent such as heptane, hexane or pentane having a water solubility of 0.1 g / L or less, or a fluorinated liquid having a perfluorocarbon structure may be used as an auxiliary solvent.

Further, these reaction media may contain additives for pH adjustment, stabilizer effect or gas solubility improvement, for example, acids such as phosphoric acid and sulfuric acid, and fluorine-based inert liquids. You may contain. When the reaction medium contains these additives, the weight of the reaction medium is the weight including the additives.

These reaction media may contain a radical scavenger. Any radical scavenger may be used as long as it has a radical scavenging function. Examples thereof include carbon dioxide, nitrone compounds, nitroso compounds, dithiocarbamate derivatives and ascorbic acid as exemplified in JP-A-2014-15353. Derivatives. These radical scavengers may be in the form of salts, or in the form of hydrates where possible. Examples of the salt include sodium salt and potassium salt.

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

In this reaction, by setting the pressure high, the hydrogen concentration and oxygen concentration that can be dissolved in water can be increased, and the yield of hydrogen peroxide can be increased. Therefore, a reaction device such as a pressure-resistant autoclave is usually used. Implemented.

The reactor can be of any type such as a stirring tank type, bubble column type, fixed bed type, microreactor, etc., and the reaction can be carried out either batchwise or continuously. The reaction apparatus includes a gas introduction part and a gas discharge part, and usually includes a thermometer and a pressure gauge.

Further, since corrosive halogen may be used in the reaction of the present invention, a reactor made of Teflon (registered trademark) lining stainless steel, Inconel or Hastelloy is preferably used. A reactor formed of stainless steel or glass lining may be used.

In the present invention, the reaction temperature of hydrogen and oxygen during the synthesis of hydrogen peroxide is preferably from 0 to 100 ° C., particularly preferably from 5 to 50 ° C. The reaction pressure is 0.1 MPa or more, preferably 0.1 MPa to 10 MPa, more preferably 0.5 MPa to 5 MPa, and further preferably 1 MPa to 2 MPa. 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 comprises:
Introducing a gas containing hydrogen and oxygen into a reaction medium containing a bromine component at an oxygen partial pressure of 20% or more in the introduced gas;
Contacting the introduced oxygen in the reaction medium with the above noble metal catalyst precursor under a pressure of 0.1 MPa or more to obtain a noble metal catalyst;
A method for producing hydrogen peroxide, comprising bringing hydrogen and oxygen introduced in a reaction medium into contact with the noble metal catalyst obtained in the above step under a pressure of 0.1 MPa or more to obtain hydrogen peroxide. Includes embodiments. According to this aspect, the noble metal catalyst of the first embodiment can be prepared in use in the reaction system, and the process of obtaining the next hydrogen peroxide can be carried out as it is under the condition that the noble metal catalyst is present. This is preferable because it is possible. In this embodiment, reaction conditions such as the amount of bromine component, oxygen partial pressure, reaction pressure and the like are as defined above.

In the method for producing hydrogen peroxide of the present invention, the noble metal catalyst preferably has a ratio of the detected amount of bromine atom to palladium as measured by low energy ion scattering (LEIS) analysis, preferably 0.10 or more, more preferably. Is 0.15 or more, more preferably 0.3 or more. Further, the ratio of the detected amount of bromine atoms to 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 detected amount of bromine atoms to palladium, which is measured by the low energy ion scattering (LEIS) analysis here, preferably keeps a constant value during the process of producing hydrogen peroxide, and direct reaction between hydrogen and oxygen The amount of change from the start to the end of the reaction is preferably Δ0.5 or less, more preferably Δ0.3 or less, and more preferably Δ0.25 or less. Since this specific amount of bromine is present on the outermost surface of the noble metal catalyst from the start of the direct reaction of hydrogen and oxygen to the end of the reaction, a high concentration of hydrogen peroxide can be produced.

In the method for producing hydrogen peroxide of the present invention, the noble metal catalyst preferably has a ratio of oxygen atom to palladium as measured by low energy ion scattering (LEIS) analysis of 1.5 or more, more preferably 1. 7 or more. Further, the ratio of oxygen atom to palladium, measured by low energy ion scattering (LEIS) analysis, is preferably 4.0 or less, and more preferably 3.5 or less. It is considered that when oxygen atoms are present in this amount on the outermost surface of the noble metal catalyst, palladium is in an oxidized state, and as a result, bromine atoms are likely to be present on the outermost surface of the noble metal catalyst. The ratio of the detected amount of oxygen atom to palladium, as measured by this low energy ion scattering (LEIS) analysis, is preferably unchanged or slightly increased during the process of producing hydrogen peroxide, and is preferably 0 to 0 per hour. It is more preferable to increase at a change amount of .25, more preferable to increase at a change amount of Δ0 to 0.1 per hour, and increase at a change amount of Δ0 to 0.05 per hour. It is preferable to continue. From the start 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, so that the suppression of hydrogen peroxide decomposition is maintained even in the latter stage of the reaction. Hydrogen peroxide can be produced. Although a similar effect can be obtained by adding a bromine component in excess to the reaction medium, it is considered that the adsorption amount of bromine atoms can be efficiently maintained by bringing the surface of the noble metal catalyst into an oxidized state.

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

Example 1
(1) Production of support-supported noble metal catalyst 2 g of oxalic acid was added to 200 ml of a mixed solvent of ethanol and water (water: ethanol = 1: 1) and stirred. There Sakai Chemical Co. titania (rutile type titanium oxide (IV)) 10 _g, added HAuCl 4 0.05 g and PdCl ₂ 0.12 g, was refluxed for 1 hour at 80 ° C. while using a Liebig condenser.

After 1 hour, the suspension was transferred to a 300 ml beaker and heated to remove the solvent. Thereafter, the obtained solid was dried with an oven at 85 ° C. for 1 day to obtain a support-supported noble metal catalyst precursor (Pd—Au / TiO ₂ ).

Next, in a 270 ml autoclave lined with Teflon (registered trademark) equipped with a stirrer and a gas blowing tube, 1.125 g of the carrier-supported noble metal catalyst precursor (Pd—Au / TiO ₂ ) produced above and 270 ml of the reaction solution (Containing 0.5 mM phosphoric acid and 0.05 mM sodium bromide, the reaction medium is water).

While adjusting the temperature inside the autoclave to 25 ° C., the gas was blown into the autoclave at a rate of 250 ml / min (hydrogen 10%, oxygen 80%, nitrogen 10%) (oxygen partial pressure in the gas 80%), and the pressure was 1M. The mixture was adjusted to Pascal and reacted with stirring at a rotational speed of 1000 rpm to produce a noble metal catalyst. In the course of this reaction, hydrogen peroxide was also produced. The noble metal catalyst was taken out from the reaction solution at regular intervals after the noble metal catalyst precursor was introduced into the reaction solution, and the surface of the noble metal catalyst at each reaction time was measured by low energy ion scattering (LEIS) analysis. In Table 1, the reaction time of 0 hour means a state in which the noble metal catalyst is taken out immediately after the noble metal catalyst precursor is introduced into the reaction solution.

(Surface analysis of precious metal catalysts)
The surface analysis of the noble metal catalyst was performed as follows.
Elemental analysis of the surface of the noble metal catalyst was performed using a low energy ion scattering spectrometer (LEIS) Qtac100 (manufactured by ION-TOF) under the conditions of 2 KeV to 5 KeV helium ion or neon ion beam irradiation. Each element was identified in the obtained energy spectrum. The detection amount (integral value) of each element was calculated, and the ratio of the detection amount of bromine atoms to palladium (Br / Pd) and the ratio of the detection amount of oxygen atoms to palladium (O / Pd) were determined. Table 1 shows the ratio of these detected amounts.

(Example 2)
A noble metal catalyst was produced in the same manner as in Example 1, except that the gas composition of Example 1 was changed to a gas composition of 10% hydrogen, 18% oxygen, and 72% nitrogen (partial oxygen pressure in gas 18%). The surface of the noble metal catalyst at each reaction time was measured by low energy ion scattering (LEIS) analysis. The results are shown in Table 1. In the course of the reaction, hydrogen peroxide was also produced.

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

(Example 3)
(1) Production of carrier-supported noble metal catalyst precursor 2 g of oxalic acid was added to 200 ml of a mixed solvent of ethanol and water (water: ethanol = 1: 1) and stirred. Thereto were added 10 g titania (rutile titanium oxide (IV)), 10 g HAUCl ₄ and 0.12 g PdCl _2, and the mixture was refluxed at 80 ° C. for 1 hour using a Liebig condenser.

(2) Production of hydrogen peroxide In the experiment, the carrier-supported noble metal catalyst precursor (Pd—Au / TiO) produced in the above was placed in a 270 ml autoclave lined with Teflon (registered trademark) equipped with a stirrer and a gas blowing tube. ₂ ) 1.125 g and 270 ml of reaction solution (containing 0.5 mM phosphoric acid and 0.05 mM sodium bromide, the reaction medium is water) were added.

While adjusting the temperature inside the autoclave to 25 ° C., the gas was blown into the autoclave at a rate of 250 ml / min (10% hydrogen, 25% oxygen, 64% nitrogen, 1% carbon dioxide) (25% oxygen partial pressure in the gas) ), The pressure was adjusted to 1 M Pascal, and the reaction was carried out with stirring at a rotational speed of 1000 rpm. Hydrogen peroxide concentration titration device (equipment name: HP-300, manufacturer: Hiranuma Sangyo, measurement method using iodine coulometric titration) at regular intervals after introducing the precious metal catalyst precursor into the reaction solution After confirming that the hydrogen peroxide concentration began to decrease, the reaction was terminated. The peak of hydrogen peroxide concentration was found 30 hours after the start of the reaction and was 6.0 wt%. The results are shown in Table 2.
In the process of producing hydrogen peroxide, a support-supported noble metal catalyst was also produced.

(Example 4)
Except for changing the gas composition of Example 3 to a gas composition of 10% hydrogen, 30% oxygen, 59% nitrogen, and 1% carbon dioxide (partial oxygen partial pressure in gas 30%), the same as in Example 3 Hydrogen peroxide was produced. The peak of hydrogen peroxide concentration was found 45 hours after the start of the reaction and was 7.7 wt%.

(Example 5)
Except for changing the gas composition of Example 3 to a gas composition of 10% hydrogen, 50% oxygen, 39% nitrogen, and 1% carbon dioxide (partial oxygen pressure in gas 50%), the same as in Example 3 Hydrogen peroxide was produced. The peak of the hydrogen peroxide concentration was found 30 to 40 hours after the start of the reaction and was 9.0 wt%.

(Example 6)
Except for changing the gas composition of Example 3 to a gas composition of 10% hydrogen, 70% oxygen, 19% nitrogen, and 1% carbon dioxide (oxygen partial pressure in gas 70%), the same as in Example 3 Hydrogen peroxide was produced. A peak of the hydrogen peroxide concentration was found 40 hours after the start of the reaction and was 11.0 wt%.

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

(Comparative Example 1)
Except that 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 (partial oxygen pressure in gas 19.2%). In the same manner as in Example 3, hydrogen peroxide was produced. The peak of the hydrogen peroxide concentration was found 25 hours after the start of the reaction, and was 4.7 wt%.

(Example 8)
(1) a PdCl ₂ and HAuCl ₄ was reduced with oxalic acid as a dispersing agent produced polyvinylpyrrolidone (PVP) of Colloidal noble metal catalyst precursor, were nanocolloidal noble metal catalyst precursor (Pd-Au nano colloid) was prepared.
(2) Production of hydrogen peroxide In the experiment, the nanocolloid noble metal catalyst precursor (Pd—Au nanocolloid) produced in the above was placed in a 270 ml autoclave lined with Teflon (registered trademark) equipped with a stirrer and a gas blowing tube. ) 74.52 mg, 130 ml of reaction solution (containing 0.5 mM phosphoric acid and 2.0 mM sodium bromide, the reaction medium is water and ethanol).

While adjusting the temperature inside the autoclave to 20 ° C., the gas was blown into the autoclave at a rate of 600 ml / min (hydrogen 10%, oxygen 30%, nitrogen 60%) (oxygen partial pressure in the gas 30%), and the pressure was 1M. The mixture was adjusted to Pascal and reacted while stirring at a rotation speed of 1000 rpm. Hydrogen peroxide concentration titration device (equipment name: HP-300, manufacturer: Hiranuma Sangyo, measurement method using iodine coulometric titration) at regular intervals after introducing the precious metal catalyst precursor into the reaction solution After confirming that the hydrogen peroxide concentration began to decrease, the reaction was terminated. The peak of the hydrogen peroxide concentration was observed 8 hours after the start of the reaction and was 7.0 wt%. The results are shown in Table 3.

Example 9
Except for changing the gas composition of Example 8 to a gas composition of 10% hydrogen, 60% oxygen, 29% nitrogen, and 1% carbon dioxide (partial oxygen pressure in gas 60%), the same as in Example 8. Hydrogen peroxide was produced. The peak of the hydrogen peroxide concentration was found 8 hours after the start of the reaction and was 8.0 wt%.

(Example 10)
Except that the gas composition of Example 8 was changed to a gas composition of 10% hydrogen, 80% oxygen, 9% nitrogen, and 1% carbon dioxide (oxygen partial pressure in the gas 80%), the same as in Example 8. Hydrogen peroxide was produced. The peak of the hydrogen peroxide concentration was found 14 hours after the start of the reaction, and was 10.0 wt%.

As is clear from the results shown in Tables 2 and 3, the method for producing hydrogen peroxide of the present invention can produce high-concentration hydrogen peroxide. In addition, by controlling the oxygen partial pressure in the gas introduced in the method for producing hydrogen peroxide, the noble metal catalyst of the present invention can be obtained, and at the same time, the hydrogen peroxide under the conditions in which the noble metal catalyst of the present invention exists. It was found that a high concentration of hydrogen peroxide was obtained.

Claims

A noble metal catalyst used in a method of directly reacting hydrogen and oxygen to obtain hydrogen peroxide,
A noble metal catalyst comprising palladium, gold, oxygen atoms and bromine atoms, wherein the oxygen atoms and bromine atoms are present on the outermost surface of the noble metal catalyst.
The noble metal catalyst according to claim 1, wherein the ratio of the detected amount of bromine atoms to palladium as measured by low energy ion scattering (LEIS) analysis is 0.10 or more.
3. The noble metal catalyst according to claim 1, wherein the ratio of oxygen atom to palladium as measured by low energy ion scattering (LEIS) analysis is 1.5 or more.
Introducing a gas containing hydrogen and oxygen into the reaction medium;
Peroxidation comprising contacting hydrogen and oxygen introduced in a reaction medium with the noble metal catalyst according to any one of claims 1 to 3 under a pressure of 0.1 MPa or more to obtain hydrogen peroxide. A method for producing hydrogen.
The production method according to claim 4, wherein the oxygen partial pressure in the introduced gas is 20% or more.
The method for producing hydrogen peroxide according to claim 4 or 5, wherein the reaction medium contains a bromine component.