JP2008161742A - Catalyst for removing carbon monoxide in hydrogen gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-activity catalyst which carries a low content noble metal and is capable of efficiently decreasing the concentration of carbon monoxide in hydrogen gas in a water gas shift reaction. <P>SOLUTION: The catalyst for removing carbon monoxide in hydrogen gas is manufactured by subjecting a base catalyst, which is obtained by depositing platinum and molybdenum on a carrier consisting of a metal oxide, to reduction treatment with hydrogen. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a catalyst used in a water gas shift reaction, which is used to remove carbon monoxide (CO) contained in hydrogen gas such as reformed gas by converting it into carbon dioxide (CO ₂ ). About.

  In recent years, polymer electrolyte fuel cells have attracted attention. In the polymer electrolyte fuel cell, hydrogen (fuel) is supplied to the anode side, oxygen or air (oxidant) is supplied to the cathode side, and both are reacted through a solid electrolyte membrane (proton conductive membrane) to obtain electric power. Is. As an electrode catalyst, a catalyst in which platinum or platinum alloy is supported on platinum black or carbon powder is generally used for both the anode and the cathode. It is known that when the anode side electrode catalyst contains CO in hydrogen, it is poisoned even if it is in a very small amount, resulting in a decrease in battery performance. Therefore, it is desirable to remove CO in hydrogen as much as possible.

As a method for removing CO in hydrogen gas, oxygen is introduced into the reaction system in the presence of a catalyst, and CO is selectively oxidized and removed to CO ₂ (the following formula (1)), and in the reaction system There is known a method of removing water (H ₂ O) by adding water (H ₂ O) to cause a water gas shift reaction in the presence of a catalyst to convert CO to CO ₂ [the following formula (2)].
[CO oxidation reaction]
CO + 1 / 2O ₂ → CO ₂ (1)
[Water gas shift reaction]
CO + H ₂ O ＣＯ CO ₂ + H ₂ (2) ΔH = −41 kJ / mol
In the former method, when the hydrogen concentration in the reaction system is high, the oxygen introduced into the system reacts with a large amount of hydrogen present in the system as shown in the following formula (3). A high catalyst is required (see, for example, Patent Document 1).
H ₂ + 1 / 2O ₂ → H ₂ O (3)
On the other hand, the latter method using a water gas shift reaction is a method for producing hydrogen using a hydrocarbon such as methane as a raw material, after reacting the hydrocarbon and steam to obtain a reformed gas containing hydrogen and CO. It is widely known as a method for removing CO in the reformed gas (see, for example, Patent Document 2). This CO removal method by water gas shift reaction is generally performed by combining two steps with different reaction temperatures. Each reaction in the two-stage process is called a high temperature shift reaction or a low temperature shift reaction depending on the reaction temperature.

  As the catalyst suitable for the high temperature shift reaction, an iron-chromium-based catalyst is known, and as the catalyst suitable for the low temperature shift reaction, a copper-zinc based catalyst is conventionally known (for example, Patent Document 3 and Patent Document). 4). However, these catalysts have a problem that CO cannot be sufficiently reduced when the space velocity of the reaction gas is high, and the supported metal is oxidized when exposed to air (oxygen), and the activity is significantly reduced.

  In view of this, it has been proposed to use a catalyst containing a noble metal-based metal that has high activity and can sufficiently reduce CO even under conditions with a high space velocity and has oxidation resistance. As such a catalyst, for example, a catalyst whose activity is improved by adding rhenium, alkali metal, molybdenum or the like as an auxiliary active component to a catalyst in which platinum is supported on a metal oxide has been proposed (for example, a patent) (See Literature 5, Patent Literature 6, and Patent Literature 7).

However, since these noble metal catalysts require a large amount of expensive noble metal, their spread has been hindered from the viewpoint of cost. In order to solve such problems, it has been desired to develop a highly active noble metal catalyst even with a small amount of noble metal content.
British Patent 1,116,585 JP 2000-302405 A Japanese Patent Publication No.59-46883 JP-A-53-141191 Japanese Patent No. 3215680 JP-A-2005-246116 JP 2002-273227 A

  The subject of this invention is providing the highly active low noble metal carrying | support catalyst which can reduce the CO density | concentration in hydrogen gas efficiently in the said water gas shift reaction.

  In order to solve the above-mentioned problems, the present invention provides a carbon monoxide in hydrogen gas produced by hydrogen reduction treatment of a basic catalyst in which platinum and molybdenum are supported on a support made of a metal oxide ( A CO) removal catalyst is provided.

The catalyst for removing CO of the present invention maintains high catalytic activity when removing CO by converting it into CO ₂ by water gas shift reaction even if the amount of noble metal used is small. can do. The CO removal catalyst of the present invention is useful, for example, in the production of hydrogen gas for fuel in fuel cells.

The method for producing the CO removal catalyst of the present invention will be described in detail below.
[Carrier]
In the present invention, a carrier made of a metal oxide is used. As the carrier, usually a porous material having a particle size of about 2 to 4 mm, a pellet shape or the like is preferably used. When the metal oxide is a powder, it can be supported on a porous body.
Examples of the metal oxide include zirconia, titania, alumina, silica, silica / alumina, zeolite, rare earth oxides such as lanthanum oxide, ceria, and neodymium oxide. These metal oxides may be used alone, or a mixture or composite oxide of two or more of these may be used. Among these, zirconia, titania, alumina, rare earth element oxides, or mixtures or composite oxides thereof are preferable because the catalyst preparation is relatively easy. Particularly, zirconia or zirconia and rare earth element oxides are preferable. Mixtures or composite oxides are preferred.

[Supporting main active ingredient]
Platinum is supported on the carrier. Platinum is the main active component of the catalyst of the present invention.
The amount of platinum supported is generally 0.01 to 20.0% by weight, preferably in terms of platinum metal, with respect to the total weight of the carrier and platinum (in terms of platinum metal) contained in the catalyst of the present invention. Is an amount of 0.01 to 10.0% by weight, more preferably 0.1 to 5.0% by weight, particularly preferably 0.2 to 2.0% by weight. If the amount of platinum loaded is too small, it is difficult to obtain sufficient catalytic activity for removing CO by converting CO in hydrogen gas to CO ₂ by a water gas shift reaction. Not only can further improvement in activity be expected, it is also disadvantageous in terms of economy.
Platinum should just be carry | supported on the surface of the said support | carrier as a metal, an oxide, or these mixtures. In the production of the catalyst of the present invention, since the basic catalyst is reduced with hydrogen gas or the like, even if it contains platinum oxide, it can be made a platinum metal having catalytic activity. Absent.
There is no restriction | limiting in particular as a carrying | support method of platinum, A well-known method is employ | adopted. For example, a nitric acid solution of dinitrodiammine platinum [Pt (NO ₂ ) ₂ (NH ₃ ) ₂ ] or an aqueous solution such as chloroplatinic acid hexahydrate is added dropwise to the carrier, sufficiently impregnated, and then dried. Next, by baking at a temperature of 300 to 700 ° C., preferably 400 to 600 ° C. for about 30 minutes to 2 hours, platinum metal or the like can be supported on the carrier.

[Molybdenum support]
The catalyst of the present invention contains molybdenum as an auxiliary active component together with the main active component. Molybdenum may be contained in the basic catalyst in the form of an inorganic compound such as a metal, oxide, hydroxide, or a mixture thereof.
The supported amount of molybdenum is such that the amount of molybdenum relative to the total weight of the support and molybdenum (molybdenum metal equivalent) contained in the catalyst of the present invention is usually 0.01 to 20.0% by weight in terms of molybdenum metal, preferably The amount is 0.01 to 10.0% by weight, more preferably 0.1 to 10.0% by weight, and particularly preferably 0.1 to 5.0% by weight. If the amount of molybdenum loaded is too small, the effect of contributing to the improvement of the water gas shift reaction is not sufficient. Conversely, if the amount is too large, further improvement of the effect cannot be expected, and the water gas shift reaction is reduced.

[Preparation of basic catalyst]
When preparing the basic catalyst of the present invention, it is possible to employ a method in which platinum is first supported on the carrier as described above, and then molybdenum, which is an auxiliary active component, is supported. Molybdenum should just be carry | supported by the said support | carrier as inorganic compounds, such as a metal and an oxide, or these mixtures.
There is no restriction | limiting in particular as a loading method of molybdenum, A well-known method is employ | adopted. Examples of the precursor of molybdenum metal or molybdenum oxide include inorganic compounds such as hexaammonium heptamolybdate tetrahydrate and organic metal compounds such as acetylacetone molybdenyl. As the supporting method, for example, an aqueous solution of hexaammonium hexamolybdate tetrahydrate is dropped and impregnated on the main active ingredient supporting carrier, and then the supporting carrier is dried at a temperature of 100 to 110 ° C., and then 300 A method of baking at a temperature of ˜700 ° C., preferably 400 ° C. to 600 ° C. for 30 minutes to 2 hours can be mentioned. In addition, you may perform the hydrogen reduction process mentioned later directly after drying, without performing baking after dripping, impregnation, and drying of molybdenum-containing aqueous solution.

[Hydrogen reduction treatment]
The method for producing a catalyst of the present invention is characterized in that a basic catalyst comprising a carrier carrying the main active component and auxiliary active component is subjected to hydrogen reduction treatment at a high temperature. The high temperature reduction treatment is preferably performed in a reducing atmosphere at a temperature of 300 to 700 ° C., preferably 400 to 600 ° C., for 30 minutes to 5 hours. The reducing atmosphere includes an inert gas atmosphere such as nitrogen or argon containing 1 to 100% by volume, preferably 5 to 25% by volume of hydrogen.

[Characteristics of the catalyst of the present invention]
The catalyst of the present invention obtained as described above has platinum supported on a support made of a metal oxide, further supports molybdenum in the form of a metal or an inorganic compound as an auxiliary active component, and is further subjected to a high temperature reduction treatment. Thus, the catalytic activity of the conversion / removal of CO to CO ₂ by the water gas shift reaction of platinum can be improved.

[Example-1]
(Catalyst preparation)
990 g of a zirconia granular carrier (Daiichi Rare Element Chemical Co., Ltd .: RSC-HP) is put in a container, and 270 mL of dinitrodiammine platinum nitrate aqueous solution (concentration: 37 g / L (in terms of platinum metal)) is dropped and impregnated. Left for 1 hour. Then, it dried at 110 degreeC * 2 hours in the air using the dryer. Subsequently, in a firing furnace, the temperature is raised from room temperature to 500 ° C. in an air atmosphere in 1 hour, and a firing treatment is performed in air at 500 ° C. for 1 hour to support a zirconia granular carrier carrying platinum (platinum carrying amount: zirconia). 1% by weight of the total amount of support and platinum metal, 14 g / L) was prepared. This is referred to as “basic catalyst A”.
100 g of the basic catalyst A obtained above was put into a container, and 27 mL of molybdenum hexamolybdate tetrahydrate aqueous solution (molybdenum 0.33 g) having a molybdenum equivalent concentration of 0.13 mol / L was dropped and impregnated. Left for hours. Then, it dried in air at 110 degreeC for 2 hours using the dryer. Subsequently, the temperature was raised from room temperature to 500 ° C. in a firing furnace in 1 hour, and the firing treatment was performed at 500 ° C. for 1 hour. A zirconia granular carrier supporting 0.33% by weight) was prepared. This is referred to as “basic catalyst B”.
Further, the basic catalyst B obtained above was filled in a 15 ml reaction tube, and the temperature was raised from room temperature to 500 ° C. over 1 hour while flowing a mixed gas of H ₂ (20% by volume) and N ₂ (80% by volume). After that, hydrogen reduction treatment was performed while maintaining the same temperature for 1 hour.
(Catalyst evaluation)
Next, the mixed gas was switched to N ₂ gas, heating was stopped, and the temperature was lowered to 100 ° C. or lower. When the temperature drops below 100 ° C., the supply of N ₂ gas is stopped and then H ₂ (60% by volume), CO ₂ (9% by volume), CO (6% by volume), and water vapor (25% by volume) ) Was supplied under the condition of a space velocity of 5,000 h ⁻¹ . Gas analyzer (best) using the non-dispersive infrared method as the measurement principle, heating the catalyst and the mixed gas to be introduced to the specified temperature, and measuring the CO concentration (volume%) at the outlet of the reaction tube under the measurement conditions excluding water vapor It was measured using Sokki Co., Ltd. product: Bex-2201E). The evaluation of the CO removal performance was performed in the range of 180 ° C. to 250 ° C. at the inlet gas temperature. Further, the CH ₄ content (ppm) at the outlet of the reaction tube was measured using the same method and the same measuring device.

[Example-2]
In Example-1, the basic catalyst B was subjected to reduction treatment at 400 ° C. instead of the reduction treatment temperature of 500 ° C., and the CO removal performance was subsequently evaluated.

[Example-3]
In Example-1, the basic catalyst B was subjected to reduction treatment at 600 ° C. instead of the reduction treatment temperature of 500 ° C., and the CO removal performance was subsequently evaluated.

[Example-4]
Instead of the zirconia support in Example-1, zirconia composite oxide powder (Daiichi Rare Element Chemical Industries, Ltd .: NZI-01, composition (wt%): ZrO ₂ / CeO ₂ / Nd ₂ O ₃ = 65 / 25/10) was supported on a 600 cpsi cordierite honeycomb at 150 g / L, and the platinum loading was 14 g / L in the same manner as in Example 1 (8.3 wt% based on the total catalyst powder weight). ), A catalyst was prepared such that the amount of molybdenum loaded was 4.7 g / L (2.8% by weight based on the total weight of the catalyst powder), and the performance was evaluated.

[Comparative Example-1]
The hydrogen reduction treatment was not performed in the procedure described in Example 1, and the CO removal performance of the basic catalyst B was evaluated.
Table 1 summarizes the types of carriers and the hydrogen reduction treatment temperatures used in Examples 1 to 4 and Comparative Example 1.

[Measurement result]
The said measurement result about the catalyst of said Examples -1 to -4 and Comparative Example-1 is shown in FIG. From the result of FIG. 1, it was confirmed that hydrogen reduction treatment at a high temperature of 400 ° C. or higher, particularly 500 ° C. or higher has a great effect on improving CO removal performance. It was also confirmed that good CO removal performance was obtained even with a catalyst prepared using zirconia composite oxide powder.
The amount of CH ₄ produced by the CO methanation reaction, which is a side reaction, is 100 ppm or less regardless of which catalyst is used, and it has been confirmed that it does not contribute to the reduction of CO.

  Therefore, the method for producing a CO removal catalyst according to the present invention greatly improves the activity of the shift reaction in the water gas shift reaction.

It is a figure which shows CO removal performance in each inlet-gas temperature of the catalyst obtained in Example-1-Example-4 and Comparative Example-1.

Claims (7)

  A catalyst for removing carbon monoxide in hydrogen gas, which is produced by hydrogen reduction treatment of a basic catalyst in which platinum and molybdenum are supported on a metal oxide support.   The catalyst for removing carbon monoxide according to claim 1, wherein the temperature of the hydrogen reduction treatment is 300 ° C or higher and 700 ° C or lower.   The catalyst for removing carbon monoxide according to claim 1 or 2, wherein the support made of a metal oxide is zirconia, or a mixture or composite oxide composed of zirconia and an oxide of one or more rare earth elements.   The catalyst for removing carbon monoxide according to any one of claims 1 to 3, wherein the molybdenum supported on the carrier in the basic catalyst is in the form of a metal or an inorganic compound.   The removal amount of carbon monoxide according to any one of claims 1 to 4, wherein a supported amount of platinum is 0.01 to 20.0% by weight in terms of platinum metal with respect to a total weight of the support and platinum. catalyst.   The removal amount of carbon monoxide according to any one of claims 1 to 5, wherein the supported amount of molybdenum is 0.01 to 20.0 wt% in terms of molybdenum metal with respect to the total weight of the support and molybdenum. catalyst.   It is characterized in that platinum is supported on a support made of a metal oxide, then molybdenum is supported on the support to prepare a basic catalyst, and then the basic catalyst is subjected to hydrogen reduction treatment at a temperature of 300 ° C. to 700 ° C. A method for producing a catalyst for removing carbon monoxide in hydrogen gas.

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