JP2012061398A - Catalyst for producing hydrogen, method for manufacturing the catalyst, and method for producing hydrogen by using the catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for producing hydrogen having long-term durability to poisoning caused by a sulfur-containing compound included in a fuel hydrocarbon compound, or to catalyst compound deterioration or coking caused by a temperature or a change of an atmosphere resulting from repetition of operation stop of a fuel cell system.SOLUTION: In this hydrogen production catalyst for producing hydrogen by reforming of a hydrocarbon compound, a catalyst composition containing alumina, a cerium-nickel tightly mixed oxide, a platinum group metal and a basicity imparting compound is carried on a honeycomb carrier.

Description

  The present invention relates to a hydrogen production catalyst for producing a hydrogen-containing gas by reforming a hydrocarbon compound, and a method for producing the catalyst.

Hydrogen-containing gas is widely used as a reducing gas in addition to hydrogen gas production, and also as a raw material for various chemical products. Recently, practical research has been conducted as a fuel for fuel cells. It is known that such a hydrogen-containing gas can be obtained by steam reforming of a hydrocarbon compound. The steam reforming reaction when methane, the main component of natural gas, is used as a raw material is shown in the following equation.
CH ₄ + H ₂ O → CO + 3H ₂
In a domestic fuel cell system, the system is frequently shut down in response to power and heat demand conditions. At this time, if the system is stopped while water and unreformed fuel remain in the reformer, problems such as catalyst deterioration, deterioration of restartability, and fuel leakage may occur. Therefore, when the fuel cell system is stopped, a method is employed in which the fuel is stopped and an inert gas is circulated to purge the interior of the reformer and then stop. Nitrogen and argon are known as inert gases, but they are not suitable for home use. Therefore, although steam is used as a purge gas, it is known that nickel-based catalysts that are industrially proven as hydrogen production catalysts are oxidized and deactivated by oxidation of nickel in a high-temperature steam atmosphere. Accordingly, a platinum group ruthenium-based catalyst is generally used as a hydrogen production catalyst for household fuel cells. However, ruthenium is also known to be easily sintered in an oxidizing atmosphere, and development of a hydrogen production catalyst that has excellent oxidation resistance and uses a small amount of expensive platinum group metal is desired.

  Hydrocarbon compounds used as fuel for reforming reactions include methanol, LP gas, natural gas, gasoline, light oil, kerosene, etc., but especially as a hydrogen source for household fuel cells in terms of infrastructure. Preference is given to using city gas, LP gas and kerosene. However, city gas, LP gas, and kerosene contain sulfur-containing compounds such as mercaptans as odorants and impurities, and these sulfur-containing compounds are present only in trace amounts, so that steam reforming catalysts and subsequent CO conversion catalysts are present. It becomes a catalyst poison substance. Therefore, as a means to avoid deterioration of the catalyst for hydrogen production due to sulfur-containing compounds contained in the fuel, a pretreatment desulfurization device is installed in front of the reformer, and the sulfur content is removed from the fuel gas before reforming. Preventive measures such as use for reaction have been implemented.

  On the other hand, a catalyst containing platinum and rhodium has been proposed as a catalyst capable of suppressing catalyst deterioration due to sulfur poisoning in a reforming reaction of a fuel containing a sulfur-containing compound (Patent Document 1). This document discloses that rhodium is particularly effective in improving sulfur poisoning resistance. Similarly, a steam reforming catalyst containing rhodium in addition to ruthenium has been proposed as a means of ensuring long-term catalyst stability even when a sulfur compound is contained in a hydrocarbon compound fuel in a certain concentration or more. (Patent Document 2). A rhodium-containing catalyst is excellent in sulfur poisoning resistance and oxidation resistance. However, rhodium is the most expensive noble metal among platinum group metals, and therefore a large amount of supported leads to a significant increase in catalyst price.

In addition, it is known that carbon precipitation is likely to occur at the acidic point of the carrier in the steam reforming reaction of hydrocarbons. For example, as a component for neutralizing the acidic point of the carrier component, an oxide of lanthanum, alkali metal or alkaline earth metal There has been proposed a hydrocarbon reforming catalyst that suppresses carbon deposition by adding (Patent Document 3). In this document, it is disclosed in Examples that carbon precipitation is suppressed by neutralizing the solid acid sites of a composite oxide carrier such as ZrO ₂ —Al ₂ O ₃ .

Japanese Patent Laid-Open No. 04-281845 Japanese Patent Publication No. 42277779 JP 2002-126522 A

  Since the catalyst for hydrogen production is used under high-temperature and high-humidity conditions, thermal deterioration due to sintering of catalyst components and poisoning deterioration due to sulfur-containing compounds contained in the raw material gas occur, so that improvement in durability is desired. Further, the catalyst life depends on the reaction temperature at the time of reforming, and if the reforming reaction proceeds efficiently at a low temperature, the catalyst life can be extended significantly.

  The present invention has been made in view of the above circumstances, and its purpose is to change the temperature and atmosphere by repeated poisoning due to sulfur-containing compounds contained in hydrocarbon-based compounds, which are fuels, and shutdown of the fuel cell system. It is to provide a catalyst for hydrogen production having long-term durability against catalyst component alteration or coking by the above, and a method for producing the catalyst.

  As a result of detailed investigations on the reforming reaction of hydrocarbon compounds, the present inventors have developed a catalyst composition containing alumina, a cerium-nickel intimate mixed oxide, a platinum group metal, and a basicity-imparting compound as a honeycomb. By using a catalyst for hydrogen production, which is supported on a carrier and the basicity-imparting compound is at least one element selected from the group consisting of magnesium, calcium, strontium, barium, yttrium, lanthanum, praseodymium and neodymium. The present inventors have found that the sulfur poisoning is improved and the thermal load is suppressed by the improvement of the low temperature activity, so that the catalyst life can be greatly extended, and the present invention has been completed.

  According to the hydrogen production catalyst of the present invention, even when the fuel gas contains a sulfur-containing compound, the reforming reaction can be performed at a low temperature, and poisoning deterioration due to the sulfur-containing compound can be suppressed. For this reason, the catalyst for hydrogen production of the present invention is suitable for household fuel cells, for example, suitable for incorporation into solid polymer fuel cells and solid oxide fuel cells.

  The catalyst for hydrogen production of the present invention comprises a catalyst composition containing alumina, a cerium-nickel intimate mixed oxide, a platinum group metal, and a basicity-imparting compound supported on a honeycomb carrier, wherein the basicity-imparting compound is A hydrogen production catalyst characterized by being at least one element selected from the group consisting of magnesium, calcium, strontium, barium, yttrium, lanthanum, praseodymium and neodymium. The cerium-nickel homogeneous mixed oxide is a complex oxide of cerium and nickel, a solid solution, a mixed oxide, or a mixture thereof (hereinafter, these are collectively referred to as a dense mixed oxide). . The present hydrogen production catalyst can generate hydrogen from a hydrocarbon compound by a reforming reaction. Details of the present invention will be described below.

As the alumina which is the catalyst composition of the hydrogen production catalyst of the present invention, γ-alumina, η-alumina, δ-alumina, θ-alumina, α-alumina and the like can be used. It is preferable to use activated alumina having a specific surface area of 20 to 300 m ² / g, more preferably 60 to ²⁰⁰ m ² / g, particularly preferably 80 to 180 m ² / g, δ-alumina or γ-alumina. Is preferred. When amorphous alumina having a specific surface area exceeding 300 m ² / g is used, the specific surface area is significantly reduced when exposed to a high temperature of 600 ° C. or higher during the reforming reaction, and a catalyst component such as a platinum group metal or a promoter component. Performance degradation may occur due to aggregation. Alumina having a specific surface area of less than 20 m ² / g is excellent in thermal stability, but is not preferable because dispersibility of initial catalyst components and promoter components becomes insufficient. As the alumina, various aluminum oxide powders commercially available can be used. Also, alumina hydrate containing boehmite or pseudoboehmite, alumina obtained by calcining precipitates obtained by hydrolyzing aluminum salts such as aluminum hydroxide and aluminum nitrate and alkoxides such as aluminum isopropoxide are used. You may do it. Further, it may be added as a precursor of alumina such as boehmite, aluminum nitrate or alumina sol to the catalyst composition and supported on the honeycomb carrier, and then calcined to be converted into alumina.

  Next, the cerium-nickel homogeneous mixed oxide which is the catalyst composition of the catalyst for hydrogen production of the present invention is more preferably 10-200 parts by mass of cerium-nickel homogeneous mixed oxide with respect to 100 parts by mass of alumina. Is preferably added to the catalyst composition at a ratio of 30 to 180 parts by mass, particularly preferably 50 to 150 parts by mass. When the content of the cerium-nickel homogeneous mixed oxide is less than 10 parts by mass with respect to 100 parts by mass of alumina, the initial performance and durability of the hydrogen production catalyst are insufficient, exceeding 200 parts by mass. However, the performance improvement effect commensurate with the cost cannot be obtained. The cerium-nickel homogeneous mixed oxide is partly reduced to nickel metal under the conditions for using the reforming reaction of the catalyst for hydrogen production. Presumed to be involved.

  The cerium-nickel intimate mixed oxide of the present invention is any one of a complex oxide, a solid solution and a mixed oxide of cerium and nickel, and particularly preferably a complex oxide or a solid solution. The molar ratio of cerium and nickel in the cerium-nickel dense mixed oxide is preferably in the range of 1:99 to 99: 1. In general, it is known that cerium and nickel single oxides are rapidly crystallized by a high-temperature heat treatment at 600 ° C. or higher, and are easy to sinter. Growth is suppressed and heat resistance is remarkably improved. In addition, cerium-nickel intimate mixed oxides have a stable crystal structure against catalyst poisoning components such as sulfur-containing compounds contained in fuel, and can suppress the transformation to inactive metal sulfides. it can. The crystal structure of the cerium-nickel dense mixed oxide is confirmed by measuring the lattice spacing (d value) by powder X-ray diffraction analysis. For example, when cerium and nickel form a composite oxide, the peak of the oxide with the smaller content ratio is not detected or is a very amorphous peak even if detected. When cerium and nickel form a solid solution, the X-ray diffraction peak position slightly shifts from the intrinsic value of cerium oxide or nickel oxide. The cerium-nickel homogeneous mixed oxide of the present invention may be a mixed oxide in which a single cerium oxide or nickel oxide peak is detected in addition to the X-ray diffraction peak of the composite oxide or solid solution. The preparation method of the cerium-nickel dense mixed oxide will be described later, but it is prepared by a solid-phase reaction method, a coprecipitation method, a deposition method, a chemical solution mixing method, an impregnation method and the like of a cerium compound and a nickel compound.

  Moreover, as a platinum group metal which is a catalyst composition of the catalyst for hydrogen production of the present invention, at least one metal selected from the group consisting of platinum, palladium, rhodium, ruthenium and iridium can be added. It is preferable to use any of rhodium, ruthenium, and iridium that can impart excellent steam reforming performance to various fuels at low temperatures. Ruthenium is particularly preferred because it can be used in combination with the cerium-nickel intimate mixed oxide of the present application, since it can provide reforming performance at low temperature and excellent durability performance. The platinum group metal is preferably added to the catalyst composition at a ratio of 0.1 to 15 parts by mass, more preferably 1 to 12 parts by mass, and particularly preferably 5 to 10 parts by mass with respect to 100 parts by mass of alumina. . If the platinum group metal content in the catalyst composition is less than 0.1 parts by mass with respect to 100 parts by mass of alumina, sufficient conversion performance may not be obtained, or sulfur poisoning and coking may easily occur. Sufficient durability performance cannot be obtained. Further, when 15 parts by mass or more of a platinum group metal is added to 100 parts by mass of alumina, the dispersibility is lowered, so that the performance improvement corresponding to the price increase cannot be obtained. Examples of platinum group metal source compounds include chloroplatinic acid aqueous solution, dinitrodiaminoplatinum nitric acid aqueous solution, palladium nitrate aqueous solution, palladium chloride aqueous solution, ruthenium chloride aqueous solution, ruthenium nitrate aqueous solution, rhodium chloride aqueous solution, rhodium nitrate aqueous solution, iridium chloride aqueous solution and nitric acid. An iridium aqueous solution or the like can be used.

  Two or more platinum group metals may be contained in the catalyst composition. Ruthenium is mentioned as a particularly preferable platinum group metal, and heat resistance and sulfur poisoning resistance are improved by adding ruthenium and another platinum group metal in combination. It is preferable that the addition ratio of ruthenium to other platinum group metal is such that the ruthenium metal is 1, and the total amount of other platinum group metals is 0.01 to 3 in weight ratio.

  The platinum group metal may be supported on any one of alumina, a cerium-nickel dense mixed oxide, and a basicity-imparting compound. For example, a platinum group metal previously supported on alumina and / or a cerium-nickel intimate mixed oxide is wet crushed and coated on a honeycomb carrier, or an aqueous platinum group metal solution is added to the slurry during wet pulverization. May be added to the catalyst composition to coat the honeycomb carrier, or the honeycomb carrier may be coated with alumina, a cerium-nickel intimate mixed oxide, or the like, and then the platinum group metal may be supported.

  Moreover, at least one element selected from the group consisting of magnesium, calcium, strontium, barium, yttrium, lanthanum, praseodymium and neodymium is added as a basicity-imparting compound which is a catalyst composition for the hydrogen production catalyst of the present invention. . The basicity-imparting compound is preferably added to the catalyst composition at a ratio of 0.5 to 20 parts by mass, particularly preferably 1 to 10 parts by mass with respect to 100 parts by mass of alumina. When the content of the basicity-imparting compound is less than 0.5 parts by mass with respect to 100 parts by mass of alumina, the reforming performance at low temperatures and the durability are degraded, and when the content exceeds 20 parts by mass, the carrier This is not preferable because the components and catalyst components are altered or the pores of the catalyst layer are clogged to impair gas diffusion and cause performance degradation. As the raw material for the basicity-imparting compound, oxides, carbonates, hydroxides, nitrates, acetates, chlorides, sulfates, and the like of the respective elements can be used. In the catalyst composition, oxides, carbonates, It is preferably contained in the form of a hydroxide or the like. Among the basic imparting substances, it is preferable to add compounds of barium, lanthanum, praseodymium and neodymium. In particular, barium, lanthanum, praseodymium and neodymium not only impart basicity but also have the effect of suppressing the crystal transition of activated alumina to α-alumina even when exposed to high temperature conditions of 800 ° C. or higher. Is greatly improved.

  As described above, the catalyst for hydrogen production of the present invention supports the catalyst composition containing alumina, the cerium-nickel intimate mixed oxide, the platinum group metal and the basicity-imparting compound on the honeycomb carrier. The catalyst composition is preferably supported at a supported amount of 100 to 300 g / L (mass per liter of catalyst, hereinafter the same) per unit volume of the honeycomb carrier, and the content ratio of each component of the catalyst composition is alumina. The cerium-nickel homogeneous mixed oxide is 10 to 200 parts by mass, the platinum group metal is 0.1 to 15 parts by mass, and the basicity-imparting compound is 0.5 to 20 parts by mass with respect to 100 parts by mass. preferable. When the supported amount of the catalyst composition is less than 100 g / L per unit volume of the honeycomb carrier, the thickness of the catalyst coat layer becomes thin, gas diffusion becomes insufficient, and the reaction efficiency is lowered. It is not preferable. On the other hand, if it exceeds 300 g / L, it is difficult to produce the catalyst, and there is a possibility that problems such as an increase in pressure loss due to cell blockage and carbon deposition during use are likely to occur. A more preferable loading amount of the catalyst composition is 150 to 250 g / L.

As the honeycomb carrier used in the present invention, a ceramic honeycomb carrier such as cordierite or mullite having a cell number of 100 to 600 cells / inch ² (number of cells per square inch), a metal honeycomb made of stainless steel, or the like. Can be used. When the number of cells of the honeycomb carrier is 100 cells / inch ² or less, the contact area with the gas per unit volume is small, so that it is difficult to obtain a sufficient reaction rate. When the number of cells exceeds 600 cells / inch ² , the catalyst composition It is not preferable because clogging is likely to occur when a product is loaded. The steam reforming reaction is an endothermic reaction, and it is necessary to raise the catalyst temperature to 500 ° C or higher by external heating, but the fuel cell system can be started in a short time by using a lightweight and good heat transfer metal honeycomb carrier Is possible. In particular, it is preferable to use a metal honeycomb carrier in which flat plates and corrugated plates made of a ferritic stainless steel (Fe—Cr—Al) thin steel sheet containing aluminum are alternately stacked and stacked in a spiral shape. The number of cells of the metal honeycomb carrier is 100 to 600 cells / inch ² (number of cells per square inch), and the foil thickness of the stainless steel sheet is preferably 10 to 50 μm. More preferably, the number of cells is 200 to 400 cells / inch ² , and the foil thickness of the stainless steel sheet is 20 to 30 μm. Further, when the foil thickness of the stainless steel sheet is less than 10 μm, the mechanical strength of the honeycomb may be lowered, and when it exceeds 50 μm, the catalyst weight becomes heavy, which is not preferable.

(Preparation example of cerium-nickel dense mixed oxide)
A method for preparing a cerium-nickel dense mixed oxide, which is one of the features of the present invention, will be described below. As described above, the cerium-nickel intimate mixed oxide can be prepared by mixing various cerium compounds and nickel compounds by a solid phase reaction method, a coprecipitation method, a deposition method, a chemical solution mixing method, an impregnation method, or the like. Below, a specific preparation example is shown.
(1) After mixing cerium oxide and nickel oxide, firing at a high temperature.
(2) After mixing a cerium salt aqueous solution and a nickel salt aqueous solution, the powdered powder is fired by spray drying.
(3) A cerium salt aqueous solution and a nickel salt aqueous solution are mixed, an alkaline compound such as aqueous ammonia is added and coprecipitated by hydrolysis, and then dried and fired.
(4) The nickel salt aqueous solution is immersed and mixed in cerium oxide and then dried and fired, or the nickel oxide aqueous solution is immersed in and mixed with nickel oxide and then dried and fired.
(5) After immersing the nickel salt aqueous solution in the cerium oxide precursor, mixing, drying, and firing, or immersing the cerium salt aqueous solution in the nickel oxide precursor, and then mixing, drying, and firing.

  In this case, as a raw material for the cerium compound, in addition to commercially available cerium oxide, a water-soluble cerium salt compound such as cerium nitrate, cerium chloride, cerium sulfate, cerium acetate, a cerium oxide sol that is a precursor of the cerium oxide, hydroxide Cerium or cerium carbonate can be used. As a raw material for the nickel compound, water-soluble nickel salt compounds such as nickel chloride, nickel sulfate, nickel ammonium sulfate, nickel nitrate, nickel acetate, nickel oxalate and nickel citrate can be used in addition to commercially available nickel oxide. Further, carbonates such as nickel carbonate, basic nickel carbonate, nickel hydroxide and partial hydrolysis products can be used as the precursor of the nickel oxide.

  The firing in the above (1) to (5) is carried out, for example, in air at 500 to 1000 ° C., preferably 600 to 800 ° C. for about 5 to 10 hours, so that the cerium-nickel leveling used in the present invention is performed. A dense mixed oxide can be obtained. The cerium-nickel intimate mixed oxide thus obtained is thermally stable and retains a high specific surface area after heat treatment as compared with each single oxide, thereby suppressing crystal growth at high temperatures. It has excellent physical properties. In particular, by using the cerium-nickel intimate mixed oxide obtained by the coprecipitation method (3) and the impregnation method (4) and (5), a highly active and durable catalyst for hydrogen production is obtained. Can be manufactured. In particular, the method (5) is preferable because a complex oxide or a solid solution having excellent characteristics can be easily prepared with a simple production facility.

  In a more preferred embodiment of the present invention, the content of nickel in the cerium-nickel intimate mixed oxide that is the catalyst composition of the hydrogen production catalyst is less than 50 mol%. The cerium-nickel dense mixed oxide contains 10 to 50 mol% of nickel, and a crystal peak is detected at the position of the fluorite-type structure of cerium dioxide by powder X-ray diffraction measurement, which is derived from nickel oxide. It is preferable that the crystal peak is not detected, or even if it is detected, the intensity of the main peak is less than 1/10 of the main peak intensity of the cerium dioxide. When the nickel content in the cerium-nickel dense mixed oxide is less than 10 mol%, the content of nickel in the catalyst composition is reduced and the reforming performance is insufficient, and the nickel content is 50 mol. If it exceeds 50%, nickel particles are likely to grow and sulfur poisoning and sintering occur under the conditions of catalyst use, making it difficult to obtain the effects of the present invention. The molar ratio of cerium and nickel and the crystal structure in the cerium-nickel homogeneous mixed oxide can be identified by directly analyzing the cerium-nickel homogeneous mixed oxide by using a catalyst composition from a catalyzed hydrogen production catalyst. It can also be confirmed by analyzing the collected sample as a sample.

  As described above, in the powder X-ray diffraction measurement of the above cerium-nickel dense mixed oxide, crystal peaks are mainly detected at positions similar to the cerium dioxide fluorite structure, and crystal peaks derived from nickel oxide are detected. Even if detected, the main peak has a peak intensity less than 1/10 of the main peak of the cerium dioxide. Thus, by setting the nickel content in the cerium-nickel dense mixed oxide within a specific range, nickel is easily compounded or solidified in the crystal structure of cerium oxide, and the effect of the present invention is maximized. To be demonstrated. The measurement conditions of X-ray diffraction in the examples of the present invention were a CuKα ray source, a voltage of 45 KV, a current of 40 mA, a scanning range of 10 to 90 °, and a scanning speed of 0.198 ° / min. Under the above X-ray diffraction measurement conditions, the cerium-nickel intimate mixed oxides shown in the examples all have a main peak d value in the range of 3.07 to 3.15, and JCPDS (Joint Committee of Powder Diffusion Standards). It was detected at a position almost coincident with the d value 3.12 of the cerium dioxide fluorite structure described on the card. When the solid solution is formed as described above, the d value is slightly shifted, but the deviation is preferably in the range of d value ± 0.05. Moreover, the d value of cerium dioxide described on the card is 3.12, 1.91, 1.63, 2.71 (hereinafter, omitted) in descending order of the relative intensity, and the positions substantially coincide with other than the main peak. A crystal peak is detected at (d value ± 0.05), and the crystal structure of the cerium-nickel dense mixed oxide of the present invention forms a complex oxide or solid solution almost similar to the cerium dioxide fluorite structure. it is conceivable that.

More preferably, the nickel content in the cerium-nickel homogeneous mixed oxide is 20 to 40 mol%, and the crystal peak derived from nickel oxide is not detected in the powder X-ray diffraction measurement, or the main peak is detected even if it is detected. Is preferably less than 1/15 of the main peak intensity of cerium dioxide. The specific surface area of the cerium-nickel dense mixed oxide is preferably 20 to 100 m ² / g, more preferably 30 to 70 m ² / g. If also a specific surface area of 20 m 2 / ^g less than, the contact efficiency with the reaction gas decreases not obtained sufficient initial activity, if more than 100 m 2 / ^g sharp by using easily sintering at high temperature reaction There is a possibility of performance degradation.

The cerium-nickel dense mixed oxide of the present invention may further contain an oxide of a transition metal such as chromium, manganese, iron, cobalt, copper, zinc, yttrium, zirconium, molybdenum, lanthanum, and tungsten. For example, cerium-nickel-manganese dense mixed oxide, cerium-nickel-iron dense mixed oxide, cerium-nickel-cobalt dense mixed oxide, cerium-nickel-yttrium dense mixed oxide, cerium-nickel-lanthanum A homogeneous mixed oxide can be used.
(Method for producing a catalyst for hydrogen production)
A typical production method of the hydrogen production catalyst of the present invention will be described below.

<Catalyst production method 1>
In a method for producing a catalyst for hydrogen production in which a catalyst composition containing alumina, a cerium-nickel intimate mixed oxide, a platinum group metal, and a basicity-imparting compound is supported on a honeycomb carrier, alumina and cerium-nickel intimate mixing A method for producing a catalyst for hydrogen production, which includes a step of coating a honeycomb carrier with a slurry obtained by mixing oxides and wet pulverizing, is preferable. A cerium-nickel intimate mixed oxide and alumina prepared in advance by the above preparation method are supplied to a pulverizer such as a ball mill, and an appropriate amount of water is added and wet pulverized to prepare a slurry. It is to coat. The basicity-imparting compound and the platinum group metal may be supported on alumina or a cerium-nickel intimate mixed oxide in advance, or may be added as a water-soluble salt during wet pulverization, as described later. The slurry may be supported on the honeycomb carrier after impregnation. When preparing the slurry, in addition to the catalyst composition, in order to adjust the viscosity of the slurry and improve the stability of the slurry, acidic compounds such as hydrochloric acid, sulfuric acid, nitric acid, acetic acid, oxalic acid, ammonia, tetraammonium hydroxide, etc. Basic compounds and polymer compounds such as polyacrylic acid and polyvinyl alcohol may be added as necessary. The average particle size of the slurry is preferably 0.5 to 10 μm. More preferably, the average particle diameter is 1 to 5 μm. Even if the average particle diameter of the slurry is smaller than 0.5 μm or exceeds 10 μm, the adhesion to the honeycomb carrier is lowered, and the coated catalyst composition is easily peeled off.

  The method for coating the honeycomb carrier with the slurry is not particularly limited, and methods such as an impregnation method, a suction method, a wet adsorption method, a spray method, and a coating method can be applied. The slurry coating operation can be performed under atmospheric pressure, under pressure, or under reduced pressure. The slurry temperature at the time of slurry coating is not particularly limited, and may be heated if necessary, and can be performed within a range from room temperature to 90 ° C. In the case of using a metal honeycomb carrier, the suction impregnation method is preferably used because the catalyst component can be uniformly supported when the slurry is sucked and impregnated under reduced pressure. After the slurry coating, it is preferable to remove excess slurry (for example, slurry remaining in the cells) adhering to the honeycomb carrier by a method such as air blowing and then drying under ventilation.

  There is no restriction | limiting in particular also about the drying method, As long as the conditions which can remove the water | moisture content of a slurry, all can be used. Drying may be performed by passing hot air at room temperature or 50 to 200 ° C. into the cell. After drying, the catalyst composition can be firmly fixed to the honeycomb carrier by firing at 400 to 800 ° C. in the air. For example, when a required amount of the catalyst composition cannot be supported by a single operation, the above slurry coating-drying-firing operation may be repeated.

  After coating the honeycomb carrier with alumina and a cerium-nickel intimate mixed oxide by the above process, the honeycomb catalyst is immersed and supported in an aqueous solution of a platinum group metal or a basicity-imparting compound, and the remaining catalyst composition is supported on the honeycomb carrier. . The platinum group metal and the basicity-imparting compound may be supported at the same time or separately impregnated, but preferably, the platinum-group metal is first supported by impregnating and supporting the basicity-imparting compound, followed by drying and firing. Provides excellent performance and durability. Regarding the firing conditions after the impregnation support, for example, the firing may be performed at 400 to 800 ° C. in air or in a reducing atmosphere. In this production method, the slurry coating step and the impregnation supporting step are separate steps, and after forming a strong coating layer of alumina and a cerium-nickel dense mixed oxide, the basicity-imparting compound and the platinum group metal are increased. Can be carried in dispersion.

<Catalyst production method 2>
The catalyst production method 2 includes a step of coating the honeycomb carrier with a slurry obtained by mixing and wet-grinding the basic imparting compound in addition to the alumina and the cerium-nickel intimate mixed oxide in the catalyst production method 1. It is what you have. In the same manner as in the catalyst production method 1, the slurry was coated on the honeycomb carrier, dried, fired, immersed in an aqueous solution of a platinum group metal and impregnated to carry all the catalyst composition on the honeycomb carrier. To do. In this production method, since the platinum group metal can be supported on the honeycomb carrier in the final step, the product can be processed by processing under the optimum conditions for the activation of the platinum group metal. Further, by supporting the platinum group metal on the outermost surface of the coating layer so as to be rich, excellent catalytic activity can be obtained even if the amount of platinum group metal supported is reduced.

(Method for reforming hydrocarbon compounds)
Next, the hydrogen production method using the hydrogen production catalyst of the present invention will be described below. In the hydrogen production method for producing hydrogen by a fuel reforming reaction using the hydrogen production catalyst, the fuel is a hydrogen production method in which the fuel is a hydrocarbon compound containing a sulfur-containing compound.

  Examples of the hydrocarbon compounds used as fuel for the reforming reaction include light hydrocarbons such as methane, ethane, propane, butane, heptane, and hexane, and petroleum hydrocarbons such as gasoline, light oil, and naphtha. , LPG, city gas, kerosene, and other industrially available fuels can be used. However, even if hydrocarbon compounds are refined such as desulfurization treatment, a small amount of sulfur-containing compounds remain, or sulfur-containing compounds such as mercaptans, thiophenes, and sulfides as odorants in general household LPG and city gas Is added. These sulfur-containing compounds are known to be poisons of the catalyst, but the hydrogen production catalyst of the present invention uses a hydrocarbon-based compound containing these sulfur-containing compounds as a fuel. By installing a desulfurizer to remove sulfur-containing compounds contained in the fuel and then carrying out the reforming reaction with the hydrogen production catalyst of the present invention, the catalyst can be used over a long period of time and the fuel cell system is maintained. Needless to say, management becomes easier.

  In the hydrogen production method of the present invention, a hydrocarbon compound serving as a fuel and water vapor are mixed. The ratio of the number of moles of water vapor to the number of moles of carbon atoms contained in the hydrocarbon compound (S / C ratio) is 1 to 5. , Preferably 2 to 4, more preferably 2.5 to 3.5. When the S / C ratio is smaller than 1, coke is likely to precipitate, and when it is larger than 5, the energy cost increases, which is not preferable.

The pressure is normal pressure or more and 5 MPa or less, preferably 3 MPa or less. Gas space velocity (SV) is 500~100,000H ^-1, and it is preferably a 1,000~30,000H ^-1. In order to perform an efficient reforming reaction, the reaction temperature should be such that the catalyst layer temperature is in the range of 500 to 1,000 ° C., preferably 600 to 900 ° C.
The hydrogen production catalyst of the present invention is excellent in oxidation resistance, and a trace amount of oxygen may be added if necessary. By adding oxygen, the hydrocarbon compound generates heat due to the partial oxidation reaction, and the temperature of the catalyst can be raised to a predetermined temperature without heating from the outside. Regarding the ratio of the hydrocarbon-containing gas and the oxygen-containing gas, the ratio of the number of moles of oxygen molecules to the number of moles of carbon atoms (oxygen / carbon ratio) is preferably 0 to 0.75.

  The reformed gas obtained by the hydrogen production catalyst of the present invention mainly contains hydrogen and carbon monoxide, and can be used as a raw material for fuel cells and chemical industries. For example, molten carbonate fuel cells and solid oxide fuel cells, which are classified as high-temperature operation fuel cells, can use carbon monoxide and hydrocarbons as fuel, so the reformed gas can be used as fuel for fuel cells. A preferred application that can be made.

  In addition, the reformed gas can be reduced in carbon monoxide concentration by CO modification reaction, or impurities can be removed by cryogenic separation method, PAS method, hydrogen storage alloy or palladium membrane diffusion method, etc. It can be gas. For example, the CO modification reaction is a reaction in which carbon monoxide and water are converted into hydrogen and carbon dioxide, and the carbon monoxide concentration can be reduced to about 1%. As the catalyst used for the CO modification reaction, for example, a known catalyst mainly composed of copper or iron may be used. When it is necessary to further reduce the carbon monoxide concentration, such as the fuel of a low-temperature operation type solid polymer fuel cell, it is oxidized to carbon dioxide by a CO selective oxidation catalyst installed at the subsequent stage of the CO modification catalyst, or CO selective methane It is desirable that the carbon monoxide concentration be 10 ppm or less by converting it to methane using a catalyst.

  Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited to the examples without departing from the spirit of the present invention.

Example 1
Cerium-nickel homogeneous mixed oxide: While stirring a mixed aqueous solution in which 291 g of nickel nitrate hexahydrate and 434 g of cerium nitrate hexahydrate are dissolved in 5 L of pure water, aqueous ammonia is gradually added dropwise to cause coprecipitation and pH. Was allowed to stand overnight. Next, after filtration and washing with sufficient water, the precipitate is dried at 150 ° C. for 12 hours, and then calcined in an air atmosphere at 600 ° C. for 5 hours to cerium-nickel dense mixed oxide (molar ratio Ce: Ni = 50: 50) was obtained. In the obtained cerium-nickel homogeneous mixed oxide, each peak was detected in the range of ± 0.5 with respect to the d value of fluorite-type cerium dioxide described in the JCPDS card in the powder X-ray diffraction measurement. The derived peak had an intensity of 1/15 or less of the main peak of cerium dioxide. Table 1 shows the mixing ratio of the cerium-nickel dense mixed oxide and the measured physical properties.

Metal honeycomb carrier: Fe-Cr-Al heat-resistant stainless steel plate having a foil thickness of 30 μm as a honeycomb carrier, 400 cells per square inch of cross-sectional area, an outer diameter of 20 mm, and a length of 66 mm (Geometric surface area of about 3000 m ² / m ³ ) was used.

Preparation of slurry: 100 g of activated alumina (γ-alumina) having a specific surface area of 155 m ² / g, 100 g of the cerium-nickel homogeneous mixed oxide, pure water and nitric acid are supplied to a ball mill and wet pulverized to obtain an aqueous slurry. Prepared. When the obtained slurry was observed with a particle size distribution analyzer (laser diffraction scattering type), the average particle size was 4.3 μm.

  Catalyst production: The lower part of the metal honeycomb carrier is immersed in the slurry, sucked from the upper part under reduced pressure, the slurry is filled into the cell, the carrier is taken out, and then the compressed air is blown to leave the excess slurry remaining in the cell. Was removed. The metal honeycomb carrier thus coated with the slurry was dried at 150 ° C. and then fired in air at 500 ° C. for 2 hours. Next, it is impregnated with an aqueous magnesium nitrate solution, dried, calcined in air at 600 ° C. for 2 hours, cooled, impregnated with an aqueous ruthenium nitrate solution and dried at 150 ° C., and then in a hydrogen stream (5% hydrogen / nitrogen balance) The finished catalyst (A) was obtained by reduction treatment at 600 ° C. for 2 hours. Table 2 shows the composition ratio and supported amount of the catalyst composition of the finished catalyst (A).

(Examples 2-3)
Production of catalyst: The finished catalysts (B) and (C) were obtained in the same manner as in Example 1 except that instead of magnesium nitrate as the basicity-imparting compound in Example 1, calcium nitrate or strontium nitrate was used. Table 2 shows the composition ratios and supported amounts of the catalyst compositions of the finished catalysts (B) and (C).

(Examples 4 to 6)
Preparation of slurry: An aqueous slurry was prepared in the same manner as in Example 1, except that 150 g of activated alumina (γ-alumina) and 75 g of cerium-nickel intimate mixed oxide were wet-ground. The average particle diameter of the obtained slurry was 4.8 μm.

  Production of catalyst: The obtained slurry was coated on a metal honeycomb carrier, dried at 150 ° C., and then fired in air at 500 ° C. for 2 hours. Thereafter, finished catalysts (D) to (F) were obtained in the same manner as in Example 1 except that the nitrate of the basicity-imparting compound was impregnated with the composition ratio shown in Table 2. The composition ratios and supported amounts of the catalyst compositions of the finished catalysts (D) to (F) are shown in Table 2.

(Examples 7 to 9)
Cerium-nickel intimate mixed oxide: Using cerium carbonate powder as a cerium source and an aqueous solution of nickel nitrate hexahydrate as a nickel source, each raw material so that the molar ratio is the ratio shown in Examples 7 to 9 in Table 1 After weighing and mixing uniformly, the mixture was sufficiently dried at 150 ° C. to remove moisture, and then calcined at 600 ° C. for 5 hours in an air atmosphere. A mixed oxide was obtained. In the X-ray diffraction measurement, a peak was detected only at a position similar to fluorite-type cerium dioxide in any cerium-nickel dense mixed oxide, and no crystal peak derived from nickel oxide was observed.

Preparation of slurry: 100 g of activated alumina (γ-alumina) having a specific surface area of 155 m ² / g, 150 g of each cerium-nickel dense mixed oxide, 25.6 g of barium nitrate, pure water and nitric acid are supplied to the ball mill. An aqueous slurry was prepared by wet pulverization. The slurry was prepared by adjusting the pulverization time so that the average particle size of each slurry was in the range of 3 to 5 μm.

  Production of catalyst: In the same manner as in Example 1, the metal honeycomb carrier was coated with the slurry, dried at 150 ° C, and then fired in air at 600 ° C for 2 hours. Next, it was impregnated with an aqueous ruthenium nitrate solution and dried at 150 ° C., and then subjected to reduction treatment at 600 ° C. for 2 hours in a hydrogen stream (hydrogen 5% / nitrogen balance) to obtain finished catalysts (G) to (I). . The composition ratio of the finished catalysts (G) to (I) and the supported amount of the catalyst composition are shown in Table 2.

(Comparative Example 1)
Preparation of slurry: 200 g of activated alumina (γ-alumina) having a specific surface area of 155 m ² / g, 73.6 g of magnesium nitrate, pure water and nitric acid were supplied to a ball mill and wet pulverized to prepare an aqueous slurry. When the obtained slurry was observed with a particle size distribution analyzer, the average particle size was in the range of 1.8 μm.

  Production of catalyst: In the same manner as in Example 1, the above-mentioned slurry was coated on a metal honeycomb carrier, dried at 150 ° C, and then fired in air at 600 ° C for 2 hours. Next, it was impregnated with an aqueous solution of nickel nitrate hexahydrate, dried and then calcined in air at 600 ° C. for 2 hours to obtain a comparative catalyst (a). The composition ratio and supported amount of the catalyst composition of the comparative catalyst (a) are shown in Table 2.

(Comparative Example 2)
Production of catalyst: A slurry obtained in the same manner as in Comparative Example 1 was coated on a metal honeycomb carrier, dried at 150 ° C, and then fired in air at 600 ° C for 2 hours. Next, it was impregnated with an aqueous ruthenium nitrate solution and dried at 150 ° C., and then subjected to reduction treatment at 600 ° C. for 2 hours in a hydrogen stream (5% hydrogen / nitrogen balance) to obtain a comparative catalyst (b). The composition ratio and supported amount of the catalyst composition of the comparative catalyst (b) are shown in Table 2.

(Comparative Example 3)
Preparation of slurry: 200 g of activated alumina having a specific surface area of 155 m ² / g, 100 g of commercially available cerium oxide having a specific surface area of 20 m ² / g, pure water and nitric acid were supplied to a ball mill and wet pulverized to prepare an aqueous slurry. . When the obtained slurry was observed with a particle size distribution analyzer, the average particle size was 2.5 μm.

  Production of catalyst: The above-mentioned slurry was coated on a metal honeycomb carrier, dried at 150 ° C, and then fired in air at 600 ° C for 2 hours. Next, it is impregnated with an aqueous solution of lanthanum nitrate hexahydrate, dried, calcined in air at 600 ° C. for 2 hours, cooled, impregnated with an aqueous ruthenium nitrate solution and dried at 150 ° C., and then in a hydrogen stream (hydrogen 5 % / Nitrogen balance) at 600 ° C. for 2 hours to obtain a comparative catalyst (c). The composition ratio and supported amount of the catalyst composition of the comparative catalyst (c) are shown in Table 2.

(Examples 10 to 11)
Production of catalyst: The slurry obtained in the same manner as in Examples 7 to 9 was coated on a metal honeycomb carrier, dried at 150 ° C, and then fired in air at 600 ° C for 2 hours. Next, it was impregnated with two kinds of platinum group metal mixed aqueous solutions in the ratios shown in Table 2 and dried at 150 ° C., followed by reduction treatment at 600 ° C. for 2 hours in a hydrogen stream (5% hydrogen / nitrogen balance). Completed catalysts (J) to (K) were obtained. The composition ratio of the finished catalysts (J) to (K) and the supported amount of the catalyst composition are shown in Table 2.

（水熱加速エージング）
実施例及び比較例の各触媒試料を以下の条件で水熱加速エージングを実施した。
処理温度：８００℃
処理時間：１００時間
処理ガス：２Ｌ／ｍｉｎ １０％Ｈ_２Ｏ／Ｎ_２バランス
（触媒性能試験）
水熱加速エージング後の試料を水素気流中で５００℃にて１時間還元してから、ラボ活性試験装置を用いて以下の試験条件で水素製造用触媒の性能試験を実施した。水素燃料ガスとして都市ガス１３Ａを脱硫処理せずにそのまま使用し、触媒出口温度７００℃、ＧＨＳＶ＝１０，０００Ｈ^−１でスチーム／カーボン（Ｓ／Ｃ）比＝２．５の条件にて改質反応を実施した。ガスクロマトグラフィー（島津製作所：ガスクロマトグラフＧＣ−８Ａ）を用いて生成ガスの各濃度を測定し、反応開始４８時間後のメタン転化率を下記式（１）により算出した。

(Hydrothermal accelerated aging)
Hydrothermal accelerated aging was performed on the catalyst samples of Examples and Comparative Examples under the following conditions.
Processing temperature: 800 ° C
Processing time: 100 hours Processing gas: 2 L / min 10% H ₂ O / N ₂ balance (catalyst performance test)
The sample after hydrothermal acceleration aging was reduced in a hydrogen stream at 500 ° C. for 1 hour, and then a performance test of the catalyst for hydrogen production was performed under the following test conditions using a laboratory activity test apparatus. The city gas 13A is used as hydrogen fuel gas without desulfurization, and reformed under the conditions of a catalyst outlet temperature of 700 ° C., a GHSV = 10,000 H ⁻¹ and a steam / carbon (S / C) ratio of 2.5. The reaction was carried out. Each concentration of the product gas was measured using gas chromatography (Shimadzu Corporation: gas chromatograph GC-8A), and the methane conversion 48 hours after the start of the reaction was calculated by the following formula (1).

なお、上記式において、ＣＯ濃度、ＣＯ_２濃度およびＣＨ_４濃度は、それぞれ生成ガス（触媒出口）における一酸化炭素、二酸化炭素およびメタンのガス濃度を表す。

In the above formula, the CO concentration, the CO ₂ concentration, and the CH ₄ concentration represent the gas concentrations of carbon monoxide, carbon dioxide, and methane in the product gas (catalyst outlet), respectively.

  The performance test results of the catalysts for hydrogen production in Examples 1 to 9 and Comparative Examples 1 to 3 are shown in Table 2.

  The present invention is a hydrogen production catalyst with little performance deterioration over a long period of time when hydrogen is generated by reforming a raw material gas composed of a hydrocarbon-based compound, and can be suitably applied particularly to a fuel gas containing a sulfur-containing compound.

Claims (7)

A catalyst for hydrogen production that generates hydrogen by a reforming reaction, comprising a catalyst composition comprising alumina, a cerium-nickel intimate mixed oxide, a platinum group metal, and a basicity imparting compound supported on a honeycomb carrier. And the basicity-imparting compound is at least one element selected from the group consisting of magnesium, calcium, strontium, barium, yttrium, lanthanum, praseodymium and neodymium. The catalyst composition is supported at a supported amount of 100 to 300 g / L (mass per liter of catalyst) per unit volume of the honeycomb carrier, and the content ratio of each component of the catalyst composition is 100 parts by mass of alumina. The cerium-nickel dense mixed oxide is 10 to 200 parts by mass, the platinum group metal is 0.1 to 15 parts by mass, and the basicity-imparting compound is 0.5 to 20 parts by mass. catalyst. The cerium-nickel dense mixed oxide contains 10 to 50 mol% of nickel, and a crystal peak is detected at the position of the fluorite-type structure of cerium dioxide by powder X-ray diffraction measurement, which is derived from nickel oxide. The catalyst for hydrogen production according to any one of claims 1 and 2, wherein a crystal peak is not detected, or even if it is detected, the intensity of the main peak is less than 1/10 of the main peak intensity of the cerium dioxide. The method for producing a catalyst for hydrogen production according to claims 1 to 4, wherein a catalyst composition comprising alumina, a cerium-nickel homogeneous mixed oxide, a platinum group metal and a basicity-imparting compound is supported on a honeycomb carrier. A method for producing a catalyst for hydrogen production, comprising a step of coating a honeycomb carrier with a slurry obtained by mixing alumina and a cerium-nickel-based dense mixed oxide and wet-grinding. 5. The hydrogen production method according to claim 4, further comprising the step of coating a honeycomb carrier with a slurry obtained by mixing and wet-pulverizing a basicity-imparting compound in addition to alumina and a cerium-nickel based mixed oxide. For producing a catalyst for use. 6. The method for producing a catalyst for hydrogen production according to claim 4 or 5, further comprising a step of supporting a platinum group metal by an impregnation method after supporting alumina, a cerium-nickel based mixed oxide and a basicity-imparting compound on a honeycomb carrier. . A hydrogen production method for producing hydrogen by a fuel reforming reaction using the hydrogen production catalyst according to claim 1, wherein the fuel is a hydrocarbon compound containing a sulfur-containing compound.