JP2005034778A - Monolithic catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a monolithic catalyst which has an excellent activity per amount of noble metal element used in the catalyst and, thereby, has the effectively utilizable noble metal element. <P>SOLUTION: The monolithic catalyst has two or more layers of cover layers formed by covering monolithic carrier, at least one of them is a catalyst layer formed by covering the monolithic carrier with catalyst active powder containing the noble metal element and carriers and the other layer of them is a cover layer having a different function from that of the catalyst layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a monolith catalyst, and more particularly to a shift catalyst having an activity of promoting a shift reaction for generating hydrogen and carbon dioxide from carbon monoxide and water vapor, and a fuel cell system equipped with the catalyst.

  Hydrogen-oxygen fuel cells are classified into various types depending on the type of electrolyte, the type of electrode, etc., and representative types include alkaline type, phosphoric acid type, molten carbonate type, solid electrolyte type, and solid polymer type. is there. Among them, a polymer electrolyte fuel cell that can operate at a low temperature (usually 100 ° C. or less) has attracted attention, and in recent years, development and practical application as a low-pollution power source for automobiles is progressing.

  In the polymer electrolyte fuel cell, it is most preferable in terms of energy efficiency to use pure hydrogen as a fuel source. However, at the present stage, in consideration of safety and infrastructure, etc., a method of using methanol, natural gas, gasoline, etc. as a fuel source and using these as hydrogen-rich reformed gas in the reformer is being sought. . However, for example, when methanol is used as a raw material, a methanol reforming reaction represented by the following formula (2)

Carbon monoxide is generated by this, and this CO acts as a catalyst poison for the platinum-based catalyst of the electrode of the fuel cell. For this reason, it is necessary to convert this CO into CO ₂ which is harmless to the platinum electrode catalyst, and the shift reaction represented by the following formula (1)

Is used to reduce the CO concentration contained in the reformed gas to about 1% by volume.

  Conventionally, Cu catalysts such as a Cu / Zn-based catalyst, a Cu / Zn / Al-based catalyst, and a Cu / Cr-based catalyst have been used as the shift catalyst for promoting the shift reaction. Here, for example, when the amount of hydrogen-rich gas supplied to the shift reaction increases rapidly, the amount of water vapor required to reduce the increased CO in the hydrogen-rich gas by the shift reaction also increases at the same time. In some cases, the necessary water vapor could not be sufficiently supplied, and the shift reaction did not proceed sufficiently.

  In order to solve this problem, for example, Patent Document 1 discloses a shift reaction catalyst comprising a catalytic metal having an activity for promoting a shift reaction and a water vapor adsorbing substance capable of adsorbing water vapor. Yes. According to the catalyst of Reference 1, when the water vapor partial pressure around the water vapor adsorbing material is low compared to the equilibrium state, the water vapor adsorbing material releases water vapor, and this water vapor is used to perform a shift reaction. It is said that the shift reaction activity can be maintained sufficiently high even when the amount of water vapor used for the shift reaction is insufficient. In Reference 1, zeolite is exemplified as the water vapor adsorbing substance. Moreover, as a preferable aspect, the aspect which has two layers of a catalyst layer and a zeolite layer is illustrated.

  However, in general, the Cu catalyst has a problem that if the catalyst is not placed in a reducing atmosphere when the operation is stopped, the catalyst itself is oxidized and its activity is lowered. In addition, the CO reduction rate may suddenly decrease as the space velocity SV (Space Velocity) increases.

In order to solve these problems, noble metal catalysts such as Pt / Al ₂ O ₃ have been developed as shift catalysts other than the Cu catalyst. This noble metal-based catalyst has characteristics that heat resistance is higher than that of the Cu catalyst, and a decrease in shift activity when the space velocity SV increases is relatively small. However, the noble metal catalyst has a problem of high cost and low absolute shift activity compared to the Cu catalyst.

Therefore, as a shift catalyst with improved shift activity, for example, Patent Document 2 discloses that an oxide porous body composed of at least one of titanium oxide, aluminum oxide, zirconium oxide, magnesium oxide, and cerium oxide, platinum, There has been disclosed a shift catalyst comprising a predetermined substance having a function of weakening the bonding force between platinum and carbon monoxide by coexisting with the platinum. According to the document 2, the catalyst performance is improved by adding a predetermined substance to change the electronic state of platinum and lowering the electron density, thereby weakening the bonding force between platinum and carbon monoxide. It is presumed that this is partly due. As the predetermined substance, at least one of molybdenum, rhenium, and niobium is exemplified.
JP 2002-66326 A JP 2002-273227 A

  In recent years, the shift catalyst is generally used as a monolith catalyst in which a catalytically active powder is supported on a monolith support. This is because the catalyst filling portion of the shift reactor can be easily filled with the catalyst, and the air permeability of the hydrogen-rich gas used for the shift reaction can be secured by the structure of the catalyst. Further, by adopting a monolithic catalyst form, when the hydrogen-rich gas is supplied, the catalyst can be prevented from being heated and calcined, and the catalyst life and catalytic activity can be improved.

  However, the shift catalyst of the above-mentioned document 2 is an invention made by paying attention exclusively to the composition of the obtained catalyst, and the catalyst is generally used as a monolith catalyst supported on a monolith support. It was not done.

  Therefore, for example, when the catalyst of Document 2 is supported on a monolith support and used as a shift catalyst, the same problem as that of a conventional monolith catalyst occurs. That is, heat is likely to be dissipated from the surface of the catalyst layer coated on the monolith support, and the catalyst activity may be reduced due to a decrease in the temperature around the catalytically active metal.

  Therefore, the object of the present invention is made in view of such problems of the prior art, and is excellent in activity per amount of the noble metal element used in the catalyst, thereby effectively utilizing the noble metal element. The object is to provide an available monolith catalyst.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have applied a catalyst layer formed by coating a catalytically active powder containing a noble metal element and a carrier when producing a noble metal-containing monolith catalyst. In addition, by coating a coating layer having a function different from that of the catalyst layer to form two or more coating layers, in particular, by forming a non-catalytic layer not containing a noble metal element, the amount per noble metal element used It has been found that the catalytic activity increases. Furthermore, when the non-catalyst layer is a heat insulating layer, it has been found that heat dissipation from the catalyst layer is suppressed, thereby preventing a decrease in catalyst activity, and the present invention has been completed.

  That is, the present invention has two or more coating layers formed by coating on a monolithic carrier, and has a function different from that of the catalytic layer formed by coating at least a catalytically active powder containing a noble metal element and a carrier. A monolithic catalyst having a coating layer is provided.

  The present invention also provides a shift catalyst using the monolith catalyst described above, a shift reactor in which the catalyst is disposed, a fuel reforming hydrogen generation system, a fuel cell system or a fuel equipped with the catalyst or the reactor. A reforming fuel cell moving body is provided.

  According to the present invention, in a monolithic catalyst containing a noble metal element, in addition to the catalyst layer, a coating layer having a function different from that of the catalyst layer is coated to form two or more coating layers, particularly containing a noble metal element. By forming a non-catalytic layer that does not, the activity per amount of noble metal element used increases. That is, it is possible to effectively use catalytic metal elements, particularly noble metal elements. Furthermore, when the non-catalytic layer is a heat insulating layer, heat dissipation from the surface of the coating layer is suppressed, and a decrease in catalytic activity can be prevented.

  The first aspect of the present invention is a catalyst layer having at least two coating layers formed by coating on a monolithic carrier, coated with a catalytically active powder containing at least a noble metal element and a carrier, and the function of the catalyst layer. Are monolithic catalysts having different coating layers.

  Conventionally, in a noble metal-based monolith catalyst containing a noble metal element and using a monolith support as a support, there has been a problem of more effectively using the noble metal element due to the structural characteristics of the monolith support. That is, heat easily dissipates from the surface of the coating layer coated by passing the raw material gas through the monolith, and accordingly, the temperature around the noble metal element which is a catalytically active metal is lowered, and the catalytic activity is lowered. That was a problem. In addition, when the catalytic active powder is coated on the monolithic carrier, the corner of the monolithic carrier is easily covered with the catalytically active powder, and the catalytic metal element, particularly the noble metal element, present in the deep part of the coating layer at the corner is effective. In other words, the catalytic activity per the amount of the precious metal element used is reduced and the cost is increased. On the other hand, according to the monolith catalyst of the present invention, in addition to the catalyst layer as described above, the catalyst activity per amount of the noble metal element used can be obtained by having a coating layer having a function different from that of the catalyst layer. As a result, the catalytic metal element, particularly the noble metal element, can be used effectively.

  In the monolith catalyst of the present invention, two or more coating layers are formed on the monolith support, at least one layer is a catalyst layer formed by coating a catalytically active powder containing a noble metal element and a support, and further the catalyst layer It has a feature in that it has a coating layer (also referred to as a “functional layer” in the present specification) having a different function. Here, the function of the functional layer is not particularly limited as long as it is different from the function of the catalyst layer. Further, “different from the function of the catalyst layer” means that the function of the catalyst layer is not exactly the same. For example, when the function of the catalyst layer is a function (A + B), The function possessed may be only a part of the function of the catalyst layer (A) or (B), or may be only the function not possessed by the catalyst layer (C) or (D), and (A + C ) Or (A + B + C) or the like, the function of the catalyst layer may be combined with the function of the catalyst layer. Here, as a function which the said functional layer has, it is preferable that the catalytic activity of the monolith catalyst of this invention, such as a heat insulation function, can be raised, for example. Note that the functional layer may have only one of these functions or a plurality of these functions.

  The present invention is characterized in that it has a catalyst layer formed by coating a catalytically active powder containing a noble metal element and a carrier, and a functional layer having a function different from that of the catalyst layer. The content of the noble metal element and other components contained in is not particularly limited, and may be the same or different in each coating layer.

Here, the noble metal element contained in the catalytically active powder is not particularly limited, and an element conventionally used as a catalytically active metal can be used. In addition, as the carrier on which the noble metal element is supported, those generally used as a catalyst carrier can be preferably used. Preferably, the carrier is an oxide carrier, more preferably the oxide carrier is heat stable. This is because when a thermally unstable component is contained, it collapses during the catalytic reaction and is inappropriate as a catalyst. Examples of the heat-stable oxide carrier include zirconium oxide (ZrO ₂ ), cerium oxide (CeO ₂ ), uranium oxide (UO ₂ ), thorium oxide (ThO ₂ ), and aluminum oxide (Al ₂ O _3). ), Calcium oxide (CaO), magnesium oxide (MgO), beryllium oxide (BeO), silicon oxide (SiO ₂ ), niobium oxide (Nb ₂ O), iron (III) oxide (Fe ₂ O ₃ ), manganese oxide ( Examples thereof include oxides such as MnO ₂ ) diphosphorus pentoxide (P ₂ O ₅ ) and divanadium pentoxide (V ₂ O ₅ ), and nitrides and composite oxides thereof. Here, one of these may be used alone, but two or more may be used in combination. The BET specific surface area of the carrier is preferably 40 m ² / g or more, more preferably 60 m ² / g or more, and particularly preferably 80 m ² / g or more.

  In this specification, when calculating the content of each component in the catalyst layer and the non-catalyst layer, the total mass of necessary additives such as metal elements, carriers, and organic binders forming each layer is 100% by mass. It shall be calculated as

  Here, the catalytically active powder may contain various other metal elements in addition to the noble metal element. However, the catalytically active powder may be a cerium element and / or a group 4 or group in the periodic table. It preferably contains an element belonging to Group 5 (also referred to as “Group 4 or Group 5 element” in this specification). More preferably, the catalytically active powder contains both a cerium element and a Group 4 or Group 5 element in addition to the noble metal element. As will be described later, the inclusion of these elements results in excellent catalytic performance when the monolith catalyst of the present invention is used as a shift catalyst. Furthermore, in the present invention, the noble metal element contained in the catalytically active powder is preferably one or more elements selected from the group consisting of platinum, rhodium, palladium, ruthenium, iridium and osmium elements. Examples of the Group 4 or Group 5 element include titanium, zirconium, vanadium, niobium and tantalum elements. Among these elements, one kind may be used alone, or two or more kinds may be used in combination. Here, the noble metal element is particularly preferably a platinum element, and the Group 4 or Group 5 element is preferably a niobium element. By containing these elements, the monolith catalyst of the present invention is particularly excellent in catalytic activity when used as a shift catalyst.

  In the monolith catalyst of the present invention, the functional layer is preferably a non-catalytic layer that does not contain a noble metal element. By setting it as this structure, the catalyst activity per the amount of noble metal elements used increases, and it becomes possible to use a noble metal element effectively. Here, as the non-catalyst layer, the composition and the like are not particularly limited as long as it is a layer made of a composition containing no noble metal element. Moreover, it does not prevent containing a metal element other than a noble metal element. Furthermore, with respect to the function of the non-catalyst layer, the effect of the present invention can be obtained, that is, it is possible to effectively use the noble metal element by improving the activity per amount of the noble metal element used in the catalyst. If it becomes, it will not specifically limit.

  Here, as a preferable configuration for obtaining the above effect in the present invention, for example, as described above, the non-catalyst layer is a heat insulating layer, and a surface treatment for disturbing the gas flow is exemplified. Is done. The catalyst layer may have only one of these functions or a plurality of these functions. Among them, the non-catalytic layer as a heat insulating layer suppresses heat dissipation from the surface of the coating layer, which has been a problem in the conventional monolith catalyst, and the temperature around the noble metal element is stably maintained at a high temperature. As a result, the catalyst activity is prevented from being lowered, so that the precious metal element can be effectively used, which is particularly preferable. Hereinafter, an embodiment in which the non-catalytic layer is a heat insulating layer will be described in detail.

The composition of the powder forming the heat insulating layer is not particularly limited as long as it contains a simple substance or a compound having a heat insulating action or a mixture thereof (also referred to as “heat insulating material” in the present specification). . As the heat insulating material, for example, zirconium oxide (ZrO ₂ ), cerium oxide (CeO ₂ ), uranium oxide (UO ₂ ), thorium oxide (ThO ₂ ), aluminum oxide (Al ₂ O ₃ ), calcium oxide ( CaO), magnesium oxide (MgO), beryllium oxide (BeO), silicon oxide (SiO ₂ ), niobium oxide (Nb ₂ O), iron (III) oxide (Fe ₂ O ₃ ), manganese oxide (MnO ₂ ), etc. Examples thereof include oxides, nitrides or composite oxides thereof. These heat insulating materials include compounds exemplified as the carrier, but it is more preferable that the heat insulating material is the same as the compound used as the carrier because preparation is simple. Among these, zirconium oxide, cerium oxide, and composite oxides thereof are particularly preferable as the heat insulating material in that the thermal conductivity is low and the heat insulating effect is large. Here, the content of the heat insulating material in the heat insulating layer is preferably 50 to 100% by mass.

  The powder forming the heat insulating layer may contain a component other than the heat insulating material, for example, may contain a metal component having catalytic activity other than the noble metal element. The heat insulating layer preferably contains a simple substance or a compound capable of adsorbing water vapor or a mixture thereof (also referred to as “water vapor adsorbing substance” in the present specification). As described above, in the conventional shift catalyst, for example, when the amount of hydrogen-rich gas supplied to the shift reaction increases rapidly, the water vapor necessary for reducing the increased CO in the hydrogen-rich gas by the shift reaction. Since the amount also increases at the same time, water vapor necessary for the reaction cannot be sufficiently supplied, and the shift reaction may not sufficiently proceed. Therefore, in the present invention, when the heat insulating layer contains a water vapor adsorbing substance, it is possible to stably supply water vapor to the catalyst metal even when the amount of water vapor necessary for the shift reaction increases rapidly. Become. Here, the water vapor adsorbing substance is not particularly limited, and examples thereof include zeolite. In addition, only 1 type may be used independently among these, and 2 or more types may be used together.

  From the above, one of the preferred embodiments of the present invention is a catalyst layer having at least two coating layers formed by coating on a monolithic carrier and coated with a catalytically active powder containing at least a noble metal element and a carrier, It can also be said to be a monolith catalyst having a coating layer (also referred to as “oxide layer” in this specification) formed by coating a powder containing a heat-stable oxide. In the above aspect, more preferably, the heat-stable oxide is the heat insulating substance, and the oxide layer contains the water vapor adsorbing substance. As described above, particularly preferably in this embodiment, the heat-stable oxide is one or more selected from cerium oxide, zirconium oxide, and cerium-zirconium composite oxide. In the present invention, an even more preferred embodiment is one in which the heat-stable oxide contained in the oxide layer is used as a carrier in the catalyst layer at the same time.

  The monolith carrier is not particularly limited and conventionally known ones can be used. Examples thereof include metal honeycombs, ceramic honeycombs, metal foams, ceramic foams, and the like.

  In the present invention, the number of coating layers formed on the monolith carrier is not particularly limited as long as it is 2 or more, and for example, the catalyst layer and the functional layer may be 3 or more in total. In this invention, Preferably a coating layer is 2-5 layers. In the present invention, the coating layer may be formed by coating the same composition a plurality of times when the coating layer is formed. In this case, the layers having exactly the same composition are counted as one layer.

  In the present invention, the order in which the monolithic carrier is coated with the catalyst layer and the non-catalyst layer, that is, which is the upper layer and the lower layer, is not particularly limited. Hereinafter, preferred arrangements of the catalyst layer and the non-catalyst layer in the present invention will be described by taking a heat insulating layer as an example, but the present invention is not limited to this.

  For example, in the present invention, when the non-catalytic layer, particularly the heat insulating layer, is coated on the lower layer of the catalytic layer, the following advantages are obtained. That is, in general, in a monolith catalyst, the catalytically active powder is easily thickly coated on the corner portion of the monolith support during coating, and a catalytic metal element, particularly a noble metal element, existing deep in the coating layer of the corner portion is effective. There is a problem that the catalytic activity per amount of noble metal element used is lowered and the cost is increased. However, according to the above aspect, by disposing the non-catalytic layer containing no precious metal in the lower layer, the coating of the catalytically active powder on the corner portion of the monolith support can be avoided, and the above problems can be solved. It is.

  On the other hand, when the non-catalyst layer, particularly the heat insulating layer, is coated on the upper layer of the catalyst layer, there are the following advantages. That is, in general, when a monolith catalyst is used, heat is easily dissipated from the surface of the coating layer formed on the monolith support by passing the raw material gas through the monolith, and accordingly, the temperature around the noble metal element is increased. In some cases, the catalytic activity may decrease. On the other hand, when a non-catalytic layer that does not contain a noble metal is disposed in the upper layer as in the above embodiment, the non-catalytic layer suppresses heat release from the catalyst layer, and the periphery of the noble metal element is maintained at a high temperature. It is possible to prevent the decrease.

  Here, for example, when the monolith catalyst of the present invention has n coating layers, the following embodiments are more preferable. That is, in this case, it is preferable that the concentration of the noble metal element in each of the coating layers is constantly increasing or constantly decreasing from the lower layer to the upper layer. In this case, the first layer to the n-th layer are referred to from the side closer to the surface of the monolith carrier, the first layer is the bottom layer, and in the adjacent coating layer, other than the noble metal element concentration When the composition is different but the concentration of the noble metal element is equal, it is included in the “increase” or “decrease”.

In other words, according to one preferable aspect of the present invention, the monolith catalyst of the present invention has n coating layers (n ≧ 2), and the noble metal element concentration in the k-th layer is C _k mass%. Always

It is preferable that In this way, when the concentration of the noble metal element in the coating layer is constantly increasing from the lower layer to the upper layer, as described above, by reducing the amount of the noble metal element contained in the lower layer, the monolith support It is possible to solve the problem that the noble metal element existing in the deep part of the corner is not effectively used. In this case, C ₁ = 0, that is, the lowermost layer is a non-catalytic layer.

On the other hand, according to another preferred embodiment of the present invention, the monolith catalyst of the present invention has n coating layers (n ≧ 2), and the noble metal element concentration in the k-th layer is C _k mass%. Always when

It is preferable that In this way, when the concentration of the noble metal element in the coating layer is constantly decreasing from the lower layer to the upper layer, as described above, by reducing the amount of the noble metal element contained in the upper layer, it is possible to cover the upper layer. As a result of the heat radiation from the coating layer being suppressed by the layer, the periphery of the noble metal element is maintained at a high temperature, and it is possible to prevent a decrease in the catalytic activity. In this case, C _n = 0, that is, the uppermost layer is a non-catalytic layer.

  It does not specifically limit as a method to manufacture the monolith catalyst of this invention, A conventionally well-known method can be used. For example, a composition containing a precious metal element, a carrier and other necessary additives is calcined and pulverized in advance to prepare a catalytically active powder. After adding water and necessary additives to this, stirring and pulverizing are performed to obtain catalytic activity. It can be produced by preparing a powder slurry, coating this onto a monolith carrier to form a coating layer, and drying and firing the monolith carrier.

  In the present invention, when the functional layer is a non-catalytic layer, the ratio of the coating amount of the non-catalytic layer to the coating amount of the catalyst layer is preferably 0.5 to 2. When this value is 0.5 or more, the amount of the non-catalytic layer is sufficiently secured, and the effect obtained by arranging the non-catalytic layer is sufficiently obtained. On the other hand, when this value is 2 or less, a sufficient amount of the catalyst layer is secured, and excellent catalyst performance is obtained. Here, the “coating amount” represents the coating amount of the powder forming each coating layer coated on the monolithic carrier in terms of the mass per liter of the monolithic carrier.

  Moreover, the value of the ratio of the coating thickness of the non-catalyst layer to the coating thickness of the catalyst layer is preferably 0.5-2. This range is preferable for the same reason as described above.

  The second of the present invention is a shift catalyst having an activity of promoting the shift reaction represented by the following formula (1),

This is a shift catalyst using the monolith catalyst of the present invention. Hereinafter, embodiments in which the monolith catalyst of the present invention is applied to a shift catalyst will be described in detail, but the present invention is not limited to the following embodiments.

  First, the shift reaction for producing hydrogen and carbon dioxide from carbon monoxide and water vapor can be understood by being decomposed into the following formulas (i) and (ii).

Here, if the active oxygen (O) generated simultaneously when H ₂ is generated from H ₂ O by the reaction represented by the above formula (i) moves to the oxidation active point on the catalyst metal that oxidizes CO, The oxidation reaction represented by formula (ii) also proceeds efficiently. Therefore, in order in the shift catalyst of the present invention to proceed efficiently shift reaction represented by the formula (1), the active species which can be taken out of H ₂ from the H _{2 O} in the catalyst layer (A), the CO It is preferable that an active species (B) having an oxidizing ability and an active species (C) having an excellent oxygen carrying ability are present. Due to the presence of the three active species, a catalyst having excellent shift reactivity can be obtained even at low temperatures. Here, if the active species (A), (B) and (C) are present in the catalyst, H ₂ can be produced from gaseous H ₂ O, and the dispersion of these components in the catalyst It doesn't matter about sex. This is because even when the active species (A) and (B) are not adjacent to each other, the active oxygen (O) is transported through the active species (C), and a smooth reaction can be ensured. In addition, the presence of the active species (A) exhibits excellent CO conversion even at a low temperature of 300 ° C. unlike conventional catalysts, and the above mechanism promotes water and CO adsorption.

  In the present invention, the noble metal element is the active species (B). Therefore, when the monolith catalyst of the present invention is used as a shift catalyst, it is preferable that the active species (A) and (C) are further present in the coating layer in addition to the noble metal element. Here, examples of the active species of (A) include the Group 4 or Group 5 elements. Moreover, a cerium element is illustrated as an active species of (C). As described above, in the shift catalyst of the present invention, platinum element is particularly preferable as the noble metal element contained in the catalytically active powder forming the coating layer, and niobium as the Group 4 or Group 5 element. Elements are particularly preferred. This is because when these elements are present in the catalyst layer, a high CO conversion rate is obtained, and when a platinum element is present, an effect of suppressing a methane formation reaction as a side reaction is also obtained.

  In the monolith catalyst of the present invention, when the catalytically active powder contains a cerium element, the content of the cerium element in the catalytically active powder is preferably 5 to 95 mol%, more preferably 30 to 90, in terms of metal. Mol%. Sufficient catalytic activity is obtained when the content of the cerium element is 5 mol% or more. On the other hand, when it is 95 mol% or less, the balance with other components is good and excellent catalytic activity is obtained.

  Furthermore, in the monolith catalyst of the present invention, when the catalytically active powder contains a Group 4 or Group 5 element, the content of the Group 4 or Group 5 element in the catalytically active powder is preferably in terms of metal. 5 to 50 mol%. Sufficient catalytic activity can be obtained when the content of the Group 4 or Group 5 element is 5 mol% or more. On the other hand, at 50 mol% or less, a good balance with other components and excellent catalytic activity can be obtained. In addition, when using together 2 or more types of elements, it calculates with the total amount.

  Here, conventionally, as the monolith-supported shift catalyst having the active species (A), (B) and (C), for example, zirconium oxide which is a raw material of the active species (A), and a raw material of the active species (C) A shift catalyst is known in which a cerium oxide is mixed to form a slurry, a monolith substrate is coated with the slurry, dried and fired, and then a platinum element as an active species (B) is supported on the coating layer. It has been. However, in the shift catalyst, the active species (A), (B) and (C) are close to each other and can act in cooperation in the vicinity of the surface of the coating layer on which platinum element is supported. Therefore, it is presumed that shift activity decreases under high space velocity conditions. On the other hand, in the shift catalyst of the present invention, the active species (A), (B) and (C) are uniformly present in the catalytically active powder forming the coating layer. For this reason, it is considered that the active species can work in cooperation not only on the surface of the coating layer but also on the entire coating layer, and a high shift activity can be maintained even under high space velocity conditions.

  When the monolith catalyst of the present invention is applied to a shift catalyst, the coating layer of the monolith catalyst can contain various components in addition to the above for the purpose of enhancing the shift activity. For example, as described in Japanese Patent Application Laid-Open No. 2002-273227, a substance having a function of weakening the bonding force between a noble metal element and carbon monoxide, such as molybdenum and a rhenium element, may be further included. By containing these metals, the shift activity can be further improved.

In the present invention, the catalytically active powder forming the coating layer contains a noble metal element such as platinum, rhodium, palladium, ruthenium, iridium and osmium elements. Examples of the raw material compound used for containing the noble metal element include dinitrodiamine platinum and platinum chloride as the raw material compound of platinum element, and dinitrodiamine platinum is particularly preferable. This is because the dispersibility in the catalytically active powder is excellent. In addition, in order to use chloride, when manufacturing a catalyst industrially on a large scale, air pollution caused by the calcined exhaust gas must be considered, and chlorine corrosion of the exhaust pipe has a great adverse effect. Similarly, as a raw material compound such as rhodium, palladium, ruthenium, iridium and osmium, nitrates, ammonium salts and the like are preferably used. The cerium element material compound is preferably cerium oxide or a cerium-zirconium composite oxide. This is because these compounds are compounds having a redox ability capable of moving oxygen atoms in the crystal, so that the use of these compounds can suppress the so-called methanation reaction that consumes H ₂ generated in the shift reaction. Further, as a raw material compound of Group 4 or Group 5 elements such as titanium, zirconium, vanadium, niobium and tantalum elements, cerium oxide, zirconium oxide, titanium oxide, niobium oxide and divanadium pentoxide, and nitrides thereof Examples of the compound used as a carrier in the present invention, such as composite oxides. Among them, a compound used as a carrier in the present invention is preferably used in terms of easy production, and cerium-zirconium composite oxide is particularly preferably used for the above reasons.

By storing the shift catalyst of the present invention in a reaction vessel and allowing the reformed gas to flow into the vessel, CO contained in the reformed gas can be efficiently converted to CO ₂ . That is, it can be used as a shift reactor. Moreover, it can be set as a shift reactor also by using directly the shift catalyst of this invention which is a monolith catalyst, without using such a reaction container. That is, the third of the present invention is a reactor for performing a shift reaction represented by the following formula (1),

It is the shift reactor by which the shift catalyst of this invention is arrange | positioned. As described above, since the shift catalyst of the present invention is excellent in CO conversion even when used at a space velocity of 10,000 h ⁻¹ or more, the shift reactor can be miniaturized and is particularly advantageous.

The shift catalyst and shift reactor of the present invention can be mounted and used in a fuel reforming hydrogen generation system, a fuel cell system, or a fuel reforming fuel cell vehicle. FIG. 1 shows a system flow diagram of a fuel reforming hydrogen generation system mounted on a vehicle. Referring to the drawings, first, fuel such as methanol, gasoline, hydrocarbons, etc. is supplied to the fuel tank. The fuel is vaporized in the vaporizer, and if necessary, sulfur contained in the desulfurizer is removed. In the reforming section, the fuel is reformed into a hydrogen-rich reformed gas, usually by steam reforming using steam. Also, a hydrogen-rich reformed gas can be obtained by autothermal reforming in which a gas containing oxygen is simultaneously supplied in addition to water vapor and a partial oxidation reaction is also performed. Next, the reformed gas is sent to the shift unit, and CO contained in the reformed gas is converted to CO ₂ to reduce the CO concentration to about 1% by volume. The reformed gas with the CO concentration reduced to about 1% by volume is subsequently transferred to the CO selective oxidation unit, and the CO concentration is reduced to the ppm order. A reformed gas and an oxidant (usually air) whose CO concentration is reduced to the order of ppm are supplied to the fuel cell, and the power generation reaction proceeds. Note that spent fuel and oxidant are discharged from the fuel cell. The fuel reforming hydrogen generation system preferably further includes a hydrogen extractor having a hydrogen separation membrane or the like. This is because the generated hydrogen gas can be easily separated and purified.

  The monolith catalyst of the present invention can exhibit an excellent CO conversion rate when applied to a shift catalyst as described above. By using the shift catalyst having such characteristics for CO conversion in the fuel reformed gas, it is possible to efficiently reduce the CO concentration in the fuel gas supplied to the fuel cell. In particular, since the CO concentration can be reduced to a very low concentration even when the space velocity is high, it can be used effectively even in a moving body such as an automobile in which the mounting range is limited.

  The embodiment of the monolith catalyst of the present invention has been described above by taking the shift catalyst as an example, but the monolith catalyst of the present invention is not limited to this and can be applied to various catalysts.

  Next, the present invention will be described in detail using examples.

Comparative Example 1
12. Dinitrodiamine platinum complex salt containing 8.451% by mass of platinum element in terms of metal, using cerium-zirconium composite oxide (BET specific surface area 70 m ² / g) of Ce / Zr = 68/32 (molar ratio) as a carrier. After making 2 g into an aqueous solution having a total liquid volume of 1.0 L, the carrier is added, impregnated with platinum element, sufficiently stirred, dried for one day, and then calcined at 400 ° C. for 1 hour to obtain a catalytically active powder. Got.

  A catalytically active powder slurry was prepared by adding alumina sol (equivalent to 4 g in terms of alumina) as a coating aid to 200 g of the catalytically active powder, and further adding 1.0 L of water and wet grinding. The pulverization is performed for 1 hour using a commercially available ball-type vibration mill. At this time, the average particle diameter is adjusted to 1.0 to 5.0 μm by adjusting the ball diameter, pulverization time, amplitude, and vibration frequency. did. The platinum element content in the catalytically active powder was 0.5% by mass.

  A 0.12 L cordierite honeycomb monolith support (400 cells / inch) was coated with the catalyst active powder slurry prepared above, dried at 200 ° C., and fired at 500 ° C. in air to obtain a shift catalyst. . Here, the coating amount of the catalytically active powder on the monolith support was 24 g (200 g / L), and the content of platinum element in the total volume of the shift catalyst was 1.0 g / L.

Comparative Example 2
The same amount of the cerium-zirconium composite oxide used in Comparative Example 1 was added to 100 g of the catalytically active powder prepared in Comparative Example 1, and a catalytically active powder slurry was prepared in the same manner as in Comparative Example 1.

  Furthermore, a shift catalyst was obtained by the same method as in Comparative Example 1 except that the amount of the coated catalytically active powder was 24 g. Here, the content of platinum element in the total volume of the shift catalyst was 1.0 g / L.

Example 1
A non-catalytic layer was formed by coating 12 g of the cerium-zirconium composite oxide used in Comparative Example 1 on a honeycomb monolith by the same method as in Comparative Example 1, drying and firing.

  Then, the catalyst active powder slurry prepared in Comparative Example 1 was coated on the upper layer by the same method as in Comparative Example 1, dried and calcined to form a catalyst layer, and a shift catalyst was obtained. Here, the amount of catalytically active powder in the coated catalyst layer was 12 g, and the content of platinum element in the total volume of the shift catalyst was 1.0 g / L.

Example 2
A shift catalyst was obtained in the same manner as in Example 1 except that the catalyst layer and non-catalyst layer in Example 1 were coated in reverse. The platinum element content in the total volume of the shift catalyst was 1.0 g / L.

Activity Test A shift activity test was performed on the shift catalysts prepared in Comparative Examples 1 and 2 and Examples 1 and 2.

First, for each 40 mL of the catalyst, a 2% hydrogen-containing nitrogen atmosphere was passed at a space velocity (GHSV) of 30,000 h ⁻¹ , and an activation treatment was performed at 400 ° C. for 1 hour. Next, the catalyst was cooled to 200 ° C. in a nitrogen atmosphere, and the outlet gas was analyzed by gas chromatography while raising the temperature. At this time, the space velocity was 30,000 h ⁻¹ . In all shift catalyst activity tests, the input gas composition was 2.5 / 24/35/15 / 23.5% by volume of CO / H ₂ O / H ₂ / CO ₂ / N ₂ and the reaction The gas flow rate was 20 L / min.

  Using the outlet CO concentration obtained by analyzing the outlet gas, the CO conversion rate was calculated by the following formula. The results are shown in Table 1.

As can be seen from Table 1, in Examples 1 and 2, both showed a CO conversion rate of 28%, which was higher than the 25% of Comparative Examples 1 and 2. In Examples 1 and 2, this has a non-catalyst layer in addition to the catalyst layer. Further, since the non-catalyst layer contains a heat insulating material, heat from the coating layer surface of the monolith catalyst is reduced. It is considered that the emission was suppressed, and as a result, the decrease in catalytic activity was suppressed. In Examples 1 and 2, since both showed the same activity, in the monolith catalyst of the present invention, the catalyst layer and the non-catalyst layer can be obtained if the number of coating layers formed on the monolith support is two or more. It was shown that a high catalytic activity can be obtained even under a high space velocity condition of 30,000 h ⁻¹ regardless of the arrangement of. Furthermore, this makes it possible to obtain a monolith catalyst that has excellent activity per amount of noble metal element used in the catalyst and can effectively use the noble metal element.

FIG. 1 is a diagram showing a system flow diagram of a fuel reforming hydrogen generation system mounted on a vehicle.

Claims (16)

  It has two or more coating layers formed by coating on a monolithic carrier, and has at least a catalyst layer formed by coating a catalytically active powder containing a noble metal element and a carrier, and a coating layer having a function different from that of the catalyst layer. Monolith catalyst.   The monolithic catalyst according to claim 1, wherein the coating layer having a function different from that of the catalyst layer is a non-catalytic layer not containing a noble metal element.   The monolith catalyst according to claim 2, wherein the non-catalytic layer functions as a heat insulating layer.   The monolith catalyst according to claim 2 or 3, wherein the non-catalytic layer is coated on a lower layer of the catalyst layer.   The monolith catalyst according to claim 2 or 3, wherein the non-catalytic layer is coated on an upper layer of the catalyst layer.   The monolith catalyst according to any one of claims 2 to 5, wherein a value of a ratio of a coating amount of the non-catalyst layer to a coating amount of the catalyst layer is 0.5 to 2.   The monolith catalyst according to any one of claims 2 to 5, wherein a value of a ratio of the coating thickness of the non-catalyst layer to the coating thickness of the catalyst layer is 0.5 to 2.   The monolithic catalyst according to any one of claims 2 to 7, wherein the non-catalytic layer contains a substance having water vapor adsorption ability.   The monolithic catalyst according to any one of claims 1 to 8, wherein the catalytically active powder further contains a cerium element and a Group 4 or Group 5 element.   The monolith catalyst according to claim 9, wherein the noble metal element is a platinum element.   The monolith catalyst according to claim 9 or 10, wherein the Group 4 or Group 5 element is a niobium element.   A composition comprising at least two coating layers formed by coating on a monolithic carrier, coated with a catalytically active powder containing at least a noble metal element and a carrier, and a composition containing a heat-stable oxide A monolithic catalyst having a coating layer formed by coating. A shift catalyst having an activity of promoting a shift reaction represented by the following formula (1),

The shift catalyst using the monolith catalyst of any one of Claims 1-12. A reactor for performing a shift reaction represented by the following formula (1),

A shift reactor in which the shift catalyst according to claim 13 is arranged.   A fuel reforming type hydrogen generation system, a fuel cell system, or a fuel reforming type fuel cell moving body equipped with the shift catalyst according to claim 13 or the shift reactor according to claim 14.   16. The fuel reforming hydrogen generation system, fuel cell system, or fuel reforming fuel cell moving body according to claim 15, wherein a hydrogen extractor is mounted.

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