JP2015167887A - Co selection methanation catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extend service life of a CO selection methanation catalyst, enhance a CO removal ratio of the CO selection methanation catalyst for making outlet CO density a low value in a wide temperature range, and enhance steam tolerance of the CO selection methanation catalyst.SOLUTION: There is provided the CO selection methanation catalyst comprising: a carrying metal catalyst for performing methanation of CO in hydrogen-rich gas including CO and COselectively; and a coating layer for covering a surface of the carrying metal catalyst. The coating layer has a mesoporous structure and formed of an oxide including a non-Si metal.

Description

  The present invention relates to a CO selective methanation catalyst that can be widely applied to a CO removal step of a domestic solid polymer fuel cell fuel reformer and a catalytic reaction process accompanied by a decrease in activity due to accumulation of reactants.

  Since the polymer electrolyte fuel cell is operated at a low temperature of about 80 ° C., if the hydrogen rich gas as the fuel contains carbon monoxide at a certain level or more, the power generation performance is reduced due to CO poisoning of the anode platinum catalyst. There will be a problem that it will drop or eventually no power can be generated at all.

In order to avoid this CO poisoning, in a domestic polymer electrolyte fuel cell power generation system that uses city gas, LP gas, kerosene or the like after being converted to hydrogen-rich gas by a fuel reformer, CO in the fuel cell anode inlet gas It is desirable to always keep the concentration below 10 ppm. Many actual systems employ a CO selective oxidation catalyst that mixes air with the product gas at the final stage of the fuel reforming process and oxidizes CO contained in the gas to CO ₂ .
CO + 1/2 O ₂ = CO ₂ (Scheme 1)

  In this catalyst, as shown in Reaction Formula 1, since it is necessary to constantly take in air from the outside, an air blower, its control system, and a complicated gas mixing structure for uniformly mixing the supplied air with the reaction gas are provided. It is necessary to install it in the fuel reformer.

  Recently, a CO selective methanation catalyst has attracted attention as a new method to replace this CO selective oxidation catalyst (for example, Patent Documents 1 and 2).

In Patent Document 1, a non-stoichiometric Ni-Al composite oxide precursor produced by a spray plasma method is impregnated with a ruthenium salt and subjected to a reduction treatment. _A CO selective methanation catalyst capable of selectively causing a CO methanation reaction even in a high temperature region where a _2- methanation reaction and a reverse aqueous shift reaction proceed predominantly is disclosed.

  In Patent Document 2, at least one selected from halogen, an inorganic acid, and a metal oxyacid, which are carbon dioxide reaction inhibitors, is adsorbed or bonded to an active component of a catalyst for methanating carbon monoxide, A CO selective methanation catalyst excellent in the selectivity of the CO methanation reaction is disclosed.

WO2010 / 122855 WO2011 / 142481

  The catalysts disclosed in Patent Documents 1 and 2 are excellent in the selectivity of the CO methanation reaction. However, when further research was carried out for practical use of such a catalyst, the catalysts of these documents were used. When used, it was found that the catalyst is likely to deteriorate (catalytic activity decreases) particularly when the reaction gas has a high superficial velocity. In addition, when the CO selective oxidation catalyst was used, the CO concentration of the outlet gas (hereinafter referred to as “outlet CO concentration”) was easy to be 10 ppm or less, but when the CO selective methanation catalyst was used, Only in a very narrow temperature range, the outlet CO concentration could be reduced to 10 ppm or less.

  The present invention has been made in view of such circumstances, and the first problem is to extend the life of the CO selective methanation catalyst, and the second problem is to remove CO from the CO selective methanation catalyst. The third problem is to increase the steam resistance of the CO selective methanation catalyst by increasing the rate and lowering the outlet CO concentration over a wide temperature range.

According to a first aspect of the present invention, there is provided a supported metal catalyst that selectively methanates CO in a hydrogen-rich gas containing CO and CO ₂ , and a coating layer that covers a surface of the supported metal catalyst, The layer is provided with a CO selective methanation catalyst having a mesoporous structure and made of an oxide containing a non-Si metal.

  The present inventors have found that by providing a coating layer on a supported metal catalyst, it is possible to extend the life of the CO selective methanation catalyst and improve the CO removal rate. Further, various studies were made on the structure and material of the coating layer, and as a result, it was found that the life of the catalyst was dramatically increased by using mesoporous silica as the coating layer.

  However, as a result of further research, the coating layer made of mesoporous silica has excellent stability under normal operating conditions in which the water vapor concentration in the hydrogen rich gas is about 20%, but the water vapor concentration in the hydrogen rich gas is 60%. It was found that the rate of decrease in catalyst activity was greatly increased under conditions of about%. Since the water vapor concentration in the hydrogen-rich gas can reach 60% when the fuel cell system is started or stopped or abnormally stopped, it is important that the rate of decrease in catalyst activity is low even under such conditions.

  As a result of further research, it was found that the deterioration of the catalytic activity in a high-concentration steam environment was caused by the collapse of the structure of the coating layer made of mesoporous silica when exposed to high-concentration steam. It was. And based on this knowledge, when research was conducted on a method for suppressing the structural collapse of the coating layer, it was found that the structural collapse hardly occurs when the coating layer having a mesoporous structure is made of an oxide containing a non-Si metal, The present invention has been completed.

  Further investigations have shown that when the coating layer is made of zirconia, the structural stability of the coating layer is significantly increased. According to such a viewpoint, the coating layer does not necessarily have a mesoporous structure. Therefore, according to the second aspect of the present invention, CO in the hydrogen-rich gas containing CO and CO2 is selectively methanated. There is provided a CO selective methanation catalyst comprising a supported metal catalyst and a coating layer covering a surface of the supported metal catalyst, wherein the coating layer is made of zirconia.

It is a block diagram which shows schematic structure of the whole hydrogen production system. (A)-(B) is a perspective view which shows the example of a honeycomb base material, (C) is a top view of one cell of a honeycomb base material. (A) shows a TEM image of the core catalyst of Production Example 1, and (B) shows a TEM image of the mesoporous silica-coated catalyst of Production Example 2. 4 is a graph showing changes in catalytic activity of the mesoporous silica-coated catalyst of Production Example 2 by high-concentration steam treatment. (B) is the graph which expanded the vertical axis | shaft of (A). (A)-(B) are SEM images which show the fine structure of the coating layer of the mesoporous zirconia-coated catalyst of Production Example 3. The STEM-EDS measurement result of the mesoporous zirconia-coated catalyst of Production Example 3 is shown. (A)-(F) are TEM images of the mesoporous zirconia-coated catalyst of Production Example 4 produced by changing the blending amounts of water and zirconium alkoxide. 6 is a graph showing changes in catalytic activity of the mesoporous zirconia-coated catalyst of Production Example 3 by high-concentration steam treatment. (B) is the graph which expanded the vertical axis | shaft of (A). (A)-(D) is a graph which shows the catalyst activity before and behind the steam treatment of the catalyst obtained by coat | covering a core catalyst with mesoporous silica, mesoporous titania, mesoporous alumina, and mesoporous zirconia, respectively. (A)-(B) is a graph which shows the result of the long-term durability test about a mesoporous zirconia coating catalyst and a mesoporous alumina coating catalyst, respectively.

  Hereinafter, embodiments of the present invention will be described.

1. 1 is a flow diagram for producing and purifying a high-concentration hydrogen gas supplied from a raw fuel (city gas, etc.) to a fuel cell (for example, a polymer electrolyte fuel cell (PEFC stack)) and an outline of the entire system. The configuration is shown. A portion surrounded by a broken line corresponds to the fuel reforming device (fuel processing device) 14, in which the raw fuel supplied from the raw fuel supply system 4 flows and passes through each catalyst layer. It performs the removal of CO (10 ppm or less) high concentration of hydrogen gas (reformed gas: _{H 2} to about 75%, CO ₂ 20%) obtained.

The raw fuel is first removed from the sulfur component by the desulfurizer 5, and then hydrogen (H ₂ ) and carbon monoxide (CO) are generated by the reforming reaction in the reformer 7 including the reforming catalyst layer (steam generator 6). CO is converted to CO ₂ by a CO converter 8 including a CO conversion catalyst layer.

A gas containing about 0.5 to 1.0% of CO (H ₂ , CO _2, etc.) is in the CO selective methanation reactor 11 including a selective methanation catalyst layer of CO using the CO selective methanation catalyst according to the present invention. In the course of passing through the catalyst layer, the H ₂ gas (reformed gas) having a CO concentration of 10 ppm or less is supplied to the PEFC stack 13.

  The CO selective methanation catalyst is preferably used as a granular catalyst. Further, the CO selective methanation catalyst may be used by coating on a honeycomb substrate. An example of the honeycomb substrate is shown in FIGS. 2 (A) and 2 (B). 2A is an example of a cordierite honeycomb substrate, and FIG. 2B is an example of a metal honeycomb substrate. In any case, a large number of vertical, horizontal, diagonal, corrugated partition plates (partitions) arranged along the longitudinal direction of the cylinder (cylindrical, rectangular tube, etc.) are provided in an intersecting manner. A gas passage is provided between the partition plates. The entire surface of these partition plates is coated with a CO selective methanation catalyst. A honeycomb structure having not only a hexagonal cross section but also gas passages (flow paths) (cells) having a quadrangular shape, a sinusoidal waveform, or other shapes is simply referred to as a honeycomb or a honeycomb substrate in this specification.

  Moreover, as a method of coating the honeycomb base material with the CO selective methanation catalyst, a method of coating the honeycomb base material with a coating layer formed on the powder, or a catalyst powder as shown in FIG. A method of forming the catalyst layer 3 by coating the honeycomb substrate 1 on the honeycomb substrate 1 and then forming the coating layer 5 can be mentioned.

2. Configuration of CO Selective Methanation Catalyst A CO selective methanation catalyst according to an embodiment of the present invention includes a supported metal catalyst that selectively methanates CO in a hydrogen-rich gas containing CO and CO ₂ , and the supported metal catalyst. A coating layer covering the surface is provided.

<Supported metal catalyst>
The type of the support metal catalyst and the active metal is not particularly limited as long as it has a CO methanation ability as described in Patent Documents 1 and 2. Specifically, for example, Ni, Ru, Fe, Co, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, and a composite thereof can be used as the active metal. Oxides, nitrides, and carbides composed of at least one of Al, V, Ti, Zr, Si, Mg, and Ce can be used. Specific examples include zeolite and silica alumina. Such a supported metal catalyst preferably contains a methanation reaction inhibitor that selectively suppresses the methanation reaction of CO ₂ . As the methanation reaction inhibitor, a material that brings the surface charge of the active metal to the δ + side or various materials that have an effect of suppressing CO ₂ methanation activity can be applied, and in particular, F, Cl, Br, I Or any one or more of inorganic acids such as halogen, HCl, HNO ₃ , H ₂ SO ₄ , H ₃ PO ₄ , and metal oxygen acids such as boric acid, vanadate acid, tungstic acid, chromic acid, etc. desirable. Since the existence form on the catalyst depends on the production process, it is not limited to the above compound, but may be a precursor, a reaction product, or a decomposition product thereof. In one embodiment, the active metal is Ni, or an alloy or mixture of Ni and V, and the support is an Al oxide containing V oxide (ie, the V oxide is supported in the matrix of Al oxide or A state of being dispersed and mixed). This is because it became clear from the experiment described in Patent Document 1 that the supported metal catalyst having such a structure can selectively methanate CO over a long period of time.

<Coating layer>
The catalyst of this embodiment is characterized in that a coating layer having a function of reducing the CO concentration is formed on the supported metal catalyst. As described above, the reaction gas flowing into the CO selective methanation reactor 11 usually contains about 0.5 to 1.0% of CO, and the supported metal catalyst is long in CO having such a concentration. When exposed to time, carbon species gradually deposit on the supported metal catalyst and its activity gradually decreases, but according to the present embodiment, a coating layer is formed on the supported metal catalyst, thereby supporting the supported metal catalyst. Since the CO concentration on the catalyst is reduced as compared with the CO concentration in the reaction gas, deterioration of the supported metal catalyst is suppressed. According to the experiments by the present inventors, it was found that the higher the CO concentration, the greater the rate of deterioration of the supported metal catalyst, and when the CO concentration was 0.2% or less, the deterioration of the supported metal catalyst was extremely slow. Therefore, it is preferable that the CO concentration on the surface of the supported metal catalyst is 0.2% or less by forming a coating layer on the supported metal catalyst.

  The principle of reducing the CO concentration on the surface of the supported metal catalyst by providing the coating layer usually involves at least one of a concentration gradient due to diffusion resistance and a concentration gradient due to methanation reaction. Since the concentration gradient due to diffusion resistance is limited in the diffusion of CO in the pores in the coating layer, the CO supply rate to the surface of the supported metal catalyst is higher than the CO consumption rate due to methanation on the surface of the supported metal catalyst. Is a concentration gradient formed when. The concentration gradient due to the methanation reaction is a concentration gradient formed when CO is methanated by the coating layer metal supported on the wall surfaces of the pores.

  In the present embodiment, the coating layer has a mesoporous structure. In the present specification, the “mesoporous structure” is a structure having a large number of pores (mesopores) having a diameter of 1 to 50 nm. The structure of the pores is not limited, and may be a regular structure or a random structure. Whether or not it has a mesoporous structure can be determined by whether or not the diameter of the pores observed in the electron microscope image is in the range of 1 to 50 nm. In another aspect, whether or not the mesoporous structure is determined by whether or not a peak exists in the pore diameter range of 1 to 50 nm in the pore diameter distribution measured according to JIS Z 8831-2: 2010. Also good. Specifically, the peak position of the pore diameter in the pore diameter distribution is, for example, 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50 nm, and may be within a range between any two of the numerical values exemplified here. In another aspect, the mesoporous structure is determined by the mesopore defined by (pore diameter 1 to 50 nm pore volume) / (pore diameter 1 to 100 nm pore volume) in the pore size distribution. It may be determined depending on whether the pore ratio is 0.1 or more. Specifically, this mesopore ratio is, for example, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0,. 55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1 and between any two of the numerical values illustrated here It may be within the range.

  The coating layer is made of an oxide containing a non-Si metal. According to experiments by the present inventors, it has been found that a mesoporous structure composed of an oxide containing a non-Si metal has high structural stability in a high-concentration water vapor environment. The non-Si metal is preferably made of at least one selected from aluminum, titanium, vanadium, strontium, yttrium, zirconium, niobium, lanthanum, and tantalum. In one example, the mesoporous structure can be formed by hydrolyzing a metal alkoxide in the presence of an alkyltrimethylammonium salt. However, since the metals listed above tend to form a reasonably stable alkoxide, the mesoporous structure is There is an advantage that it is easy to form. The non-Si metal preferably contains aluminum, and the coating layer is more preferably made of mesoporous alumina. In this case, the catalyst activity is improved by the high-concentration steam treatment. Moreover, as a non-Si metal, it is preferable that a zirconium is included and it is further more preferable that a coating layer consists of mesoporous zirconia. In this case, the structural stability of the coating layer is particularly high.

  The coating layer may or may not contain Si, but preferably does not substantially contain Si. The atomic ratio of Si / non-Si metal is preferably 1 or less, more preferably 0.2 or less, specifically, for example, 0, 0.1, 0.2, 0.3, 0 .4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 and may be within a range between any two of the numerical values exemplified here.

  The thickness of the coating layer is, for example, 1 to 200 nm, specifically, for example, 1, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, and 200 nm, and may be within a range between any two of the numerical values exemplified here.

  By the way, from the viewpoint that the structural stability of the coating layer becomes extremely high when the coating layer is made of zirconia, the coating layer does not necessarily have a mesoporous structure, a dense thin film having no mesoporous structure, or an integrated structure of particles Or a network structure. In this case, a CO selective methanation catalyst having a coating layer with high structural stability in a high-concentration steam environment can be obtained.

  In order to demonstrate the effect of the present invention, various experiments shown below were conducted.

1. Production Example 1 (Preparation of core catalyst)
An AlVOx catalyst powder as a catalyst carrier was prepared by the following method. 0.60 g of ammonium vanadate (NH ₄ ) ₂ VO ₃ was placed in 61 mL of pure water and heated to dissolve. In addition, 44.1 g of aluminum nitrate was dissolved in 235 mL of pure water. After mixing these two solutions, the solution was transferred to a 2 L beaker, and an aqueous ammonium carbonate solution was added dropwise so that pH = 8 in about 15 minutes while stirring at 2500 rpm. Thereafter, stirring was continued for 30 minutes. The deposited precipitate was filtered through a 0.2 μm membrane filter and washed with 1 L of pure water. The obtained precipitate was dried under reduced pressure at room temperature for half a day and then dried in a drying furnace at 110 ° C. for 12 hours. The obtained gel was ground and then fired in air at 500 ° C. for 3 hours. As a result, an oxide carrier having a molar ratio of Al: V = 0.96: 0.04 was obtained.

6.26 g of the AlVOx catalyst powder was added to 50 mL of pure water to prepare a suspension. The dissolved nickel nitrate _{Ni (NO 3) 2 · 6H} 2 O ( Kanto Chemical) 12.8 g of pure water 50 mL. While stirring the suspension of the oxide carrier, a total amount of nickel nitrate aqueous solution was added using a burette in about 20 minutes. The mixture was stirred at room temperature for 30 minutes and in a 45 ° C. water bath for 30 minutes, and then cooled to room temperature once. Then, it was applied to an evaporator in a hot water bath at 35 to 50 ° C. to remove all moisture. The obtained powder was dried at 110 ° C. for 12 hours and then calcined at 500 ° C. for 3 hours to obtain a core catalyst made of Ni / AlVOx supporting Ni 30 wt% in terms of metal.

2. Production Example 2 (construction of mesoporous silica layer on core catalyst)
A mesoporous silica layer was constructed on the core catalyst prepared in Production Example 1 by the following method.
5.00 g of the core catalyst and 2.00 g of 28% ammonia water (manufactured by Kanto Chemical Co., Inc.) were added to 150 mL of ultrapure water to prepare a suspension. Further, 0.6 g of hexadecyltrimethylammonium bromide (manufactured by Acros) was dissolved in a mixed solution of 40 mL of ethanol (manufactured by Kanto Chemical Co., Ltd.) and 6 mL of ultrapure water. Next, 1.20 g of tetraethyl orthosilicate (manufactured by Kanto Chemical Co., Inc.) was added to 8 mL of ethanol to obtain an alkoxide solution. While stirring the suspension of the core catalyst, the whole amount of hexadecyltrimethylammonium bromide solution was added using a pipette in 1 minute, and the suspension was stirred at room temperature for 30 minutes. Next, while stirring the suspension, the entire amount of the alkoxide solution was added using a pipette in 1 minute, followed by stirring at room temperature for 16 hours. Thereafter, the suspension was filtered, and the residue was washed with 400 mL of ethanol. The obtained residue was dried at room temperature under reduced pressure, further dried at 250 ° C. for 1.5 hours, then calcined at 550 ° C. for 4 hours, and a mesoporous silica layer having a thickness of 15 nm was built on the surface of the core catalyst. A mesoporous silica-coated catalyst was obtained. FIG. 3 shows TEM images before and after the formation of the coating layer made of mesoporous silica.

3. Water vapor resistance test of mesoporous silica-coated catalyst The water-resistant property of the mesoporous silica-coated catalyst obtained in Production Example 2 was examined.
The mesoporous silica-coated catalyst was pressurized under a pressure of 10 MPa for 10 minutes to obtain a disk-shaped molded body having a diameter of 20 mm. This was pulverized and sized to 1 mm to 2 mm and filled with 2.1 mL of a quartz tube having a diameter of 1/2 inch. This sample was subjected to a reduction treatment under a flow of hydrogen at 500 ° C. for 1 hour, and then the temperature characteristics for the CO selective methanation reaction were measured. Next, the temperature characteristics of this sample were measured after flowing nitrogen gas containing 60% water vapor at 200 ° C. for 12 hours. Thereafter, the water vapor treatment for 12 hours and the temperature characteristic measurement were further repeated. The obtained results are shown in FIG. In FIG. 4, the treatment time 0h indicates the temperature characteristic before the steam treatment. As shown in FIG. 4, when the mesoporous silica-coated catalyst was treated in a steam / nitrogen atmosphere at 200 ° C. and 60%, the catalytic activity significantly decreased. From the nitrogen adsorption measurement and electron microscope observation, it was found that this decrease in activity was caused by the structural collapse of the mesoporous silica layer.

4). Production Example 3 (construction of mesoporous zirconia layer on core catalyst)
On the core catalyst produced in Production Example 1, a mesoporous zirconia layer was constructed by the following method.
5.00 g of the core catalyst was added to 150 mL of dehydrated ethanol (manufactured by Kanto Chemical Co.) to prepare a suspension. Further, 0.6 g of hexadecyltrimethylammonium bromide (manufactured by Acros) was dissolved in 48 mL of ethanol (manufactured by Kanto Chemical Co., Ltd.) and 5.3 mL of ultrapure water. Next, 2.12 g of zirconium tetra-n-butoxide (manufactured by Kanto Chemical Co., Inc.) was added to 10 mL of ethanol to obtain an alkoxide solution. While stirring the suspension of the core catalyst, the whole amount of hexadecyltrimethylammonium bromide solution was added using a pipette in 1 minute, and the suspension was stirred at room temperature for 30 minutes. Next, while stirring the suspension, the entire amount of the alkoxide solution was added using a pipette in 1 minute, followed by stirring at room temperature for 16 hours. Thereafter, the suspension was filtered, and the residue was washed with 400 mL of ethanol. The obtained filtrate was dried under reduced pressure at 50 ° C. for 3 hours, further dried at 250 ° C. for 1.5 hours, and then calcined at 550 ° C. for 4 hours to form a mesoporous zirconia layer on the surface of the core catalyst. A mesoporous zirconia-coated catalyst was obtained. An SEM image of the obtained catalyst is shown in FIG. Referring to FIG. 5, it can be seen that pores of about 2 to 50 nm are randomly formed in the mesoporous zirconia layer. These pores realize good diffusion of the reaction gas to the core catalyst. The obtained catalyst was subjected to elemental analysis by scanning transmission electron microscope energy dispersive X-ray spectroscopy (STEM-EDS). The result is shown in FIG. Referring to FIG. 6, it can be seen that Zr is distributed almost uniformly. This result shows that the mesoporous zirconia layer is formed substantially uniformly.

5. Production Example 4 (construction of a mesoporous zirconia layer on the core catalyst, change of the raw material composition)
A mesoporous zirconia-coated catalyst was obtained by constructing a mesoporous zirconia layer in the same manner as in Production Example 3, except that the addition amount of water and zirconium alkoxide (zirconium tetra n-butoxide) (ZB) to 5 g of the core catalyst was changed. . A TEM image of the catalyst obtained under each condition is shown in FIG.
As shown in FIG. 7, the structure of the zirconia layer varies depending on the amount of water added for hydrolysis used for zirconia coating and the amount of zirconium alkoxide as a zirconia source, and the amount of water added is about 5 g relative to 5 g of the core catalyst. In this case, a good zirconia layer was formed. In addition, the thickness of the mesoporous zirconia layer could be adjusted by the amount of zirconium alkoxide added.

6). Water vapor resistance test of mesoporous zirconia-coated catalyst The water resistance property of the mesoporous zirconia-coated catalyst obtained in Production Example 3 was examined in the same manner as in “3. Water vapor resistance test of mesoporous silica-coated catalyst”. The obtained result is shown in FIG. As shown in FIG. 8, the mesoporous zirconia-coated catalyst showed no change in activity even when subjected to a steam treatment for 72 hours at 200 ° C. in a 60% steam / nitrogen atmosphere. As a result, it became clear that the mesoporous zirconia coating layer has excellent water vapor resistance unlike the mesoporous silica coating layer.

7). Steam Resistance Tests of Various Metal Oxide Coated Catalysts FIGS. 9 (A) to (D) show the steam for the catalysts obtained by coating the core catalyst with mesoporous silica, mesoporous titania, mesoporous alumina, and mesoporous zirconia, respectively. The result of a tolerance test is shown. As shown in FIG. 9, it can be understood that the water vapor resistance of the coated catalyst is improved when the core catalyst is coated with any of mesoporous titania, mesoporous alumina, and mesoporous zirconia. Further, as shown in FIG. 9C, a surprising result was obtained that the catalytic activity of the mesoporous alumina-coated catalyst was improved by the steam treatment.

  In addition, the mesoporous silica-coated catalyst produced in Production Example 2 was used, and the mesoporous zirconia-coated catalyst produced in Production Example 3 was used. As the mesoporous titania-coated catalyst and mesoporous alumina-coated catalyst, those produced by the following method were used.

(Mesoporous titania-coated catalyst)
On the core catalyst produced in Production Example 1, a mesoporous titania layer was constructed by the following method.
5.00 g of the core catalyst was added to 150 mL of dehydrated ethanol (manufactured by Kanto Chemical Co.) to prepare a suspension. Further, 0.6 g of hexadecyltrimethylammonium bromide (manufactured by Acros) was dissolved in 48 mL of ethanol (manufactured by Kanto Chemical Co., Ltd.) and 5.3 mL of ultrapure water. Next, 1.57 g of titanium tetraisopropoxide (manufactured by Kanto Chemical Co., Inc.) was added to 10 mL of ethanol to obtain an alkoxide solution. While stirring the suspension of the core catalyst, the whole amount of hexadecyltrimethylammonium bromide solution was added using a pipette in 1 minute, and the suspension was stirred at room temperature for 30 minutes. Next, while stirring the suspension, the entire amount of the alkoxide solution was added using a pipette in 1 minute, followed by stirring at room temperature for 16 hours. Thereafter, the suspension was filtered, and the residue was washed with 400 mL of ethanol. The obtained filtrate was dried under reduced pressure at 50 ° C. for 3 hours, further dried at 250 ° C. for 1.5 hours, and then calcined at 550 ° C. for 4 hours to form a mesoporous titania layer on the surface of the core catalyst. A mesoporous titania-coated catalyst was obtained.

(Mesoporous alumina-coated catalyst)
A mesoporous alumina layer was constructed on the core catalyst produced in Production Example 1 by the following method.
5.00 g of the core catalyst was added to 150 mL of dehydrated ethanol (manufactured by Kanto Chemical Co.) to prepare a suspension. Further, 0.6 g of hexadecyltrimethylammonium bromide (manufactured by Acros) was dissolved in 48 mL of ethanol (manufactured by Kanto Chemical Co., Ltd.) and 5.3 mL of ultrapure water. Next, 1.12 g of aluminum triisopropoxide (manufactured by Kanto Chemical Co., Inc.) was added to 15 mL of toluene to obtain an alkoxide solution. While stirring the suspension of the core catalyst, the whole amount of hexadecyltrimethylammonium bromide solution was added using a pipette in 1 minute, and the suspension was stirred at room temperature for 30 minutes. Next, while stirring the suspension, the entire amount of the alkoxide solution was added using a pipette in 1 minute, followed by stirring at room temperature for 16 hours. Thereafter, the suspension was filtered, and the residue was washed with 400 mL of ethanol. The obtained filtrate was dried under reduced pressure at 50 ° C. for 3 hours, further dried at 250 ° C. for 1.5 hours, and then calcined at 550 ° C. for 4 hours to form a mesoporous alumina layer on the surface of the core catalyst. A mesoporous alumina-coated catalyst was obtained.

8). Next, a long-term durability test was performed on the mesoporous zirconia-coated catalyst and the mesoporous alumina-coated catalyst.
The long-term evaluation conditions and procedure of the catalyst will be described below. Prior to the activity evaluation, the catalyst sample was subjected to hydrogen reduction. This is to reduce the catalytically active component. For reduction, 500 mL / min of H ₂ gas was allowed to flow through the reaction tube, the temperature was raised to 500 ° C. at 20 ° C./min, and the temperature was maintained for 1 hour. After the reduction, the gas was switched from H ₂ to N ₂ for 5 minutes to purge H ₂ . After completion of the reduction, the temperature was lowered to a temperature at which the activity of the catalyst was evaluated (197 ° C. for mesoporous zirconia-coated catalyst and 203 ° C. for mesoporous alumina-coated catalyst). Steam was introduced into the reaction tube, and the reaction gas was introduced after 5 minutes. The water vapor supply rate was set to a value corresponding to water vapor / CO = 34 (molar ratio), ion exchange water was sent to a vaporizer maintained at 200 ° C. with a micropump, and the generated water vapor was introduced into the reaction tube with N ₂ carrier. Each reaction gas was introduced into the reaction tube by a mass flow controller, and the composition was CO 0.5 vol%, H ₂ 80 vol%, and CO ₂ 19 vol% on a dry basis. The superficial velocity SV was 4800h- ¹ . A quartz tube having an outer diameter of 13 mm was used as the reaction tube. 2.1 mL of granular catalyst adjusted to 1.1 mm to 2 mm was packed in a predetermined position in the center of the reaction tube. The temperature of the catalyst layer was measured by inserting the tip of the sheath thermocouple at a position of about 2 mm from the upper end of the catalyst layer. The gas from the reaction tube outlet was quantified with a non-dispersive infrared analyzer (manufactured by Horiba, Ltd.).
The obtained result is shown in FIG. As shown in FIG. 10, it can be seen that both catalysts maintain high activity over a long period of time.

9. Measurement of pore size distribution of various mesoporous metal oxide-coated catalysts Next, pore size distribution measurement was performed on mesoporous zirconia-coated catalyst, mesoporous alumina-coated catalyst, mesoporous titania-coated catalyst, and mesoporous silica-coated catalyst.
The conditions and procedures for measuring the pore size distribution of the catalyst will be described below. Prior to the measurement of the pore size distribution, the catalyst sample was heated and degassed. This is for removing components in the air adsorbed on the catalyst. The catalyst was filled with 0.5 g of a Pyrex glass sample tube, heated to 300 ° C. at 10 ° C./min while being evacuated, and then maintained for 30 minutes. After completion of heating and degassing, the temperature is lowered to room temperature while evacuated, quickly attached to a capacity method adsorption amount measuring device (Bell Soap Max, manufactured by Nippon Bell), and then subjected to ultra-high vacuum evacuation and then measuring the nitrogen adsorption isotherm at liquid nitrogen temperature Went. Next, the obtained adsorption isotherm was analyzed using the BJH method (Barrett, Joyner, Hallender method) to obtain a pore size distribution.
Next, in this pore size distribution, the mesopore ratio defined by (pore size 1 to 50 nm pore volume) / (pore size 1 to 100 nm pore volume) was measured. , Both were 0.2 or more. Moreover, the peak positions in the pore size distribution were all in the range of 1 to 50 nm.

Claims (7)

Comprises a supported metal catalyst which selectively methanation of CO in the hydrogen-rich gas containing CO and CO _2, a coating layer covering the surface of the supported metal catalyst,
The CO selective methanation catalyst, wherein the coating layer has a mesoporous structure and is made of an oxide containing a non-Si metal. The catalyst according to claim 1, wherein the non-Si metal is made of at least one selected from aluminum, titanium, vanadium, strontium, yttrium, zirconium, niobium, lanthanum, and tantalum. The catalyst according to claim 2, wherein the non-Si metal includes at least one of aluminum and zirconium. The catalyst according to any one of claims 1 to 3, wherein an atomic ratio of Si / non-Si metal is 1 or less. The catalyst according to any one of claims 1 to 4, wherein the coating layer is made of mesoporous alumina or mesoporous zirconia. Comprises a supported metal catalyst which selectively methanation of CO in the hydrogen-rich gas containing CO and CO _2, a coating layer covering the surface of the supported metal catalyst,
The coating layer is a CO selective methanation catalyst made of zirconia. The catalyst according to any one of claims 1 to 6, wherein the coating layer has a thickness of 1 to 200 nm.