WO2015151477A1

WO2015151477A1 - Steam reforming catalyst, steam reforming method using same, and steam reforming reaction apparatus

Info

Publication number: WO2015151477A1
Application number: PCT/JP2015/001739
Authority: WO
Inventors: 山崎　清; 瀬戸　博邦
Original assignee: 株式会社デンソー
Priority date: 2014-04-02
Filing date: 2015-03-26
Publication date: 2015-10-08
Also published as: JP2015196142A

Abstract

　This steam reforming catalyst is used for steam reforming of oxygen-containing hydrocarbons, and contains: a carrier that includes a compound oxide in which both ceria and alumina are dispersed at the nanometer scale; at least one first metallic element selected from the group consisting of the platinum group of metals, supported on the carrier; and at least one second metallic element selected from the group consisting of the alkali metals, alkaline earth metals, and rare earth elements, supported on the carrier. In so doing, coking is sufficiently unlikely to occur, even in environments devoid of oxygen gas, or under conditions of a low molar ratio (S/C) of steam to carbon; high activity is maintained even when exposed to high temperatures; and it is possible to more efficiently reform oxygen-containing hydrocarbons with steam.

Description

Steam reforming catalyst, steam reforming method using the same, and steam reforming reaction apparatus

Cross-reference of related applications

This application is based on Japanese Patent Application No. 2014-75975 filed on April 2, 2014, the contents of which are incorporated herein by reference.

The present disclosure relates to a steam reforming catalyst, a steam reforming method using the same, and a steam reforming reaction apparatus, and more specifically, a method of reforming an oxygen-containing hydrocarbon with steam, a catalyst used therefor, and the catalyst. The present invention relates to a reaction apparatus provided.

While reduction of carbon dioxide emissions from automobiles and the like is demanded, ethanol obtained from biomass is attracting attention as a carbon neutral fuel, particularly a CO ₂ neutral fuel. However, ethanol has a small calorific value, and in order to be used as a fuel for an internal combustion engine such as an automobile, it is desirable to use part or all of it reformed to hydrogen or carbon monoxide.

On the other hand, in an internal combustion engine such as an automobile, hydrogen or carbon monoxide is generated from part or all of the fuel by a steam reforming reaction, and these are supplied to the internal combustion engine to improve thermal efficiency and startability of the internal combustion engine. Technology is known. Since this steam reforming reaction is usually an endothermic reaction, it is possible to improve the thermal efficiency by performing the steam reforming reaction using exhaust heat from the internal combustion engine.

As a catalyst for reforming oxygen-containing hydrocarbons such as ethanol with water vapor, Japanese Patent Application Laid-Open No. 2005-185989 (Patent Document 1) discloses an active metal component containing a silver component and a noble metal component other than the silver component, and alumina. An oxygen-containing hydrocarbon reforming catalyst containing a solid acidic substance, and an oxygen-containing hydrocarbon reforming catalyst further containing at least one selected from an alkali metal component or an alkaline earth metal component are disclosed. Yes. However, the oxygen-containing hydrocarbon reforming catalyst disclosed in Patent Document 1 has sufficient suppression of coking in an environment where oxygen gas is not present or in a condition where the molar ratio (S / C) of water vapor to carbon is low. It wasn't.

Japanese Patent Laid-Open No. 2008-149313 (Patent Document 2) discloses one selected from the group consisting of platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), and ruthenium (Ru). From the group consisting of the above active ingredient A and molybdenum (Mo), vanadium (V), tungsten (W), chromium (Cr), rhenium (Re), cobalt (Co), cerium (Ce) and iron (Fe). A metal catalyst comprising one or more selected metals, an oxide thereof, an alloy thereof or an active component B which is a mixture thereof, and Al ₂ O ₃ , TiO ₂ , ZrO ₂ , SiO ₂ on which the metal catalyst is supported. _{_{_{, YSZ, Al 2 O 3 -SiO}}} 2, the fuel reforming reaction catalyst containing a one or more carriers selected from the group consisting of CeO _2, and further alkali metal and Al Fuel reforming reaction catalyst containing the one or more active component C is selected from among Li-earth metal is disclosed. However, even in the fuel reforming reaction catalyst disclosed in Patent Document 2, coking is not sufficiently suppressed in an environment where oxygen gas is not present or in a condition where the molar ratio (S / C) of water vapor to carbon is low. There wasn't.

Further, JP 2010-207782 A (Patent Document 3) discloses a carrier containing a composite oxide in which ceria and alumina are both dispersed on the nm scale, and a long-period periodic table 8 on the carrier. A steam reforming catalyst containing at least one metal element belonging to Groups 10 to 10 is disclosed. According to the description of the publication, coking is unlikely to occur even in an environment where oxygen gas is not present or in a condition where the molar ratio (S / C) of water vapor to carbon is low, and oxygen-containing hydrocarbons are efficiently reformed with water vapor. It is possible to generate hydrogen. However, in recent years, the required characteristics for the steam reforming catalyst have been increasing more and more, the environment where oxygen gas does not exist, the condition where the molar ratio (S / C) of steam and carbon is low, and further, the time or place of S Even under conditions where the S / C is low due to fluctuations in / C, coking is unlikely to occur sufficiently, high activity is maintained even when exposed to high temperatures, and oxygen-containing hydrocarbons are efficiently treated with steam There has been a demand for a steam reforming catalyst that can be reformed quickly.

JP 2005-185989 A JP 2008-149313 A JP 2010-207782 A

In the present disclosure, in the steam reforming reaction of an oxygen-containing hydrocarbon, coking sufficiently occurs even in an environment where the catalytic activity is high and the oxygen gas is not present or the molar ratio (S / C) of steam and carbon is low. An object of the present invention is to provide a steam reforming catalyst for oxygen-containing hydrocarbon which is difficult to perform, and a method for steam reforming oxygen-containing hydrocarbon using the same.

As a result of intensive research to achieve the above object, the present inventors have found that at least one member belonging to the platinum group is present in a support containing a composite oxide in which ceria and alumina and, if necessary, zirconia are dispersed in the nm scale. In the steam reforming reaction of oxygen-containing hydrocarbons, by supporting at least one second metal element selected from the group consisting of the first metal element and the alkali metal, alkaline earth metal and rare earth elements The present disclosure has been completed by finding that a steam reforming catalyst that exhibits catalytic activity and does not sufficiently cause coking can be obtained.

According to the first aspect of the present disclosure, the steam reforming catalyst includes a support containing a composite oxide in which ceria and alumina are both dispersed on the nm scale, and at least one member belonging to the platinum group supported on the support. And at least one second metal element selected from the group consisting of alkali metals, alkaline earth metals, and rare earth elements supported on the carrier, and oxygen-containing hydrocarbons by steam It is a catalyst for reforming.

According to the second aspect of the present disclosure, in the steam reforming catalyst according to the first aspect, the composite oxide further contains zirconia, and ceria, alumina, and zirconia are all in nm scale. Are distributed.

According to the third aspect of the present disclosure, in the steam reforming catalyst according to the first or second aspect, the first metal element supported on the carrier is rhodium.

According to the fourth aspect of the present disclosure, in the steam reforming catalyst according to any one of the first to third aspects, the second metal element supported on the carrier is sodium, potassium, cesium, magnesium, It is at least one selected from the group consisting of strontium, barium, lanthanum and neodymium.

According to the fifth aspect of the present disclosure, the steam reforming method of the oxygen-containing hydrocarbon is the steam reforming catalyst according to any one of the first to fourth aspects described above, in the presence of steam. In contact with

According to the sixth aspect of the present disclosure, in the steam reforming method according to the fifth aspect, the oxygen-containing hydrocarbon is ethanol.

According to a seventh aspect of the present disclosure, a steam reforming reaction apparatus is a catalytic reaction apparatus including the steam reforming catalyst according to any one of the first to fourth aspects, and the steam of the oxygen-containing hydrocarbon It can be suitably used for the reforming method.

Although the reason why the catalytic activity in the steam reforming reaction of oxygen-containing hydrocarbons is increased by the steam reforming catalyst is not necessarily clear, the present inventors speculate as follows. That is, in the steam reforming catalyst, even if at least one metal element selected from the platinum group metal elements that are the supported first metal elements is oxidized during the steam reforming reaction, the composite oxide Since ceria or ceria-zirconia solid solution is contained inside, it is presumed that oxygen on the catalyst surface is absorbed by these, and the metal element is reduced to a metal state exhibiting high catalytic activity, and the catalytic activity is increased. Is done. Also, by dispersing ceria, alumina, and zirconia on the nm scale, the adsorption sites on the surface of the composite oxide are increased as compared with the conventional steam reforming catalyst, and the water vapor adsorption capacity is improved. It is presumed that the catalytic activity is increased because water vapor efficiently contacts and reacts.

In addition, ceria and ceria-zirconia solid solution usually grows more easily in a reducing atmosphere such as a steam reforming reaction than in an oxidizing atmosphere, but in the steam reforming catalyst, ceria and alumina that do not form a solid solution with each other. Alternatively, the ceria-zirconia solid solution and alumina act as a barrier to suppress the grain growth of the composite oxide at high temperatures, and also suppress the grain growth of the metal element supported thereon, so that the catalytic activity is increased. Inferred. In particular, ceria and ceria-zirconia solid solutions are more likely to grow in a reducing atmosphere such as a steam reforming reaction than in an oxidizing atmosphere, and tend to grow at 600 ° C. or higher. Inferred.

Furthermore, although the reason why coking is difficult to occur in the steam reforming catalyst is not necessarily clear, the present inventors speculate as follows. In general, it is believed that coking in a steam reforming catalyst occurs at acid sites on the support. Therefore, the present inventors have focused on the catalyst deterioration due to coking, particularly that the catalyst deterioration becomes remarkable under the reaction conditions with low S / C (steam / carbon). The coking generated in the catalyst occurs because the dehydration reaction of oxygen-containing hydrocarbons such as ethanol proceeds on the strong acid point on the support, and the polymerization reaction of the generated olefins such as ethylene proceeds. I guessed it. The above carrier contains ceria as a basic carrier and alumina as a neutral carrier, and contains a complex oxide containing zirconium as a neutral carrier as necessary. There is a point. The second metal element contains at least one metal element selected from the group consisting of alkali metals, alkaline earth metals, and rare earth elements, which are basic components. It is possible to eliminate strong acid sites, and it is presumed that the above dehydration reaction and polymerization reaction, particularly the polymerization reaction is suppressed, and coking is less likely to occur. Thus, by including the support and the second metal element, it is presumed that coking is hardly caused in the steam reforming catalyst, and a decrease in catalytic activity is suppressed. The basicity of a metal oxide generally used as a catalyst carrier increases in the order of silica <titania <alumina <zirconia <ceria <magnesia.

According to the steam reforming catalyst, the steam reforming method, and the steam reforming reaction apparatus, coking occurs even in an environment where no oxygen gas is present or in a condition where the molar ratio (S / C) of steam to carbon is low. It is difficult to efficiently reform oxygen-containing hydrocarbons with steam to generate hydrogen.

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. In the drawing
6 is a graph showing the atomic ratio of Ce, Zr, and Al in a composite oxide obtained in Examples 1 to 10 in a minute range with a cross-sectional diameter of 0.5 nm. 6 is a graph showing the catalytic activity at the initial stage in the steam reforming reaction of ethanol for the monolith catalysts obtained in Examples 1 to 10 and Comparative Examples 1 to 8. 6 is a graph showing the catalytic activity after durability in the steam reforming reaction of ethanol for the monolith catalysts obtained in Examples 1 to 10 and Comparative Examples 1 to 8. 6 is a graph showing the rate of decrease in activity by an endurance test in a steam reforming reaction of ethanol for the monolith catalysts obtained in Examples 1 to 10 and Comparative Examples 1 to 8. 6 is a graph showing the amount of carbon deposited on a catalyst after an endurance test in a steam reforming reaction of ethanol for the monolith catalysts obtained in Examples 1 to 7, 9 and Comparative Example 1. 6 is a graph showing the results of measuring the amount of acid sites (NH ₃ desorption amount) by the ammonia temperature-programmed desorption (NH ₃ -TPD) method for the carrier of the monolith catalyst obtained in Examples 1 to 7, 9 and Comparative Example 1. is there. FIG. 3 is a view showing specifications of monolith catalyst samples of Examples 1 to 10 and Comparative Examples 1 to 8.

Hereinafter, the present disclosure will be described in detail according to the embodiment.

First, the steam reforming catalyst will be described. The steam reforming catalyst is a catalyst for reforming an oxygen-containing hydrocarbon with steam, a support containing a composite oxide in which both ceria and alumina are dispersed in nm scale, and a platinum group supported on the support. At least one first metal element selected from the group consisting of metals (hereinafter referred to as “first supported metal element”), and an alkali metal, alkaline earth metal and rare earth element supported on the carrier. It contains at least one second metal element selected from the group (hereinafter referred to as “second supported metal element”).

By using such a support containing a composite oxide in which ceria, alumina, and, if necessary, zirconia are dispersed in nm scale, the steam reforming catalyst is high in the steam reforming reaction of oxygen-containing hydrocarbons. It shows catalytic activity.

Here, “nm-scale dispersion” means that the composite oxide is divided into a plurality of microregions having a cross-sectional diameter of 1 nm or less and the composition is measured using a microanalyzer having high resolution. A state in which most of the minute region is formed by a plurality of components. As an apparatus capable of such microanalysis, for example, a field emission scanning transmission microscope (FE-STEM) such as “HD-2000” manufactured by Hitachi, Ltd. may be mentioned. Note that “a microscopic region having a cross-sectional diameter of 1 nm or less” means a region in a composite oxide through which the beam is transmitted when a beam having a diameter of 1 nm or less is irradiated to the composite oxide in a measurement using a microanalyzer. Means.

As the composite oxide, when the composite oxide is divided into a plurality of minute regions having a cross-sectional diameter of 1 nm or less, the cerium and aluminum contents in the minute regions are respectively charged ratios of cerium and aluminum ± 20% (Preferably ± 10%) and such a micro region is preferably 90% or more of the total micro region, and the zirconium content in the micro region is zirconium loading ratio ± 20 % (Preferably ± 10%) and such a micro region is more than 90% of the total micro region. Thus, the composite oxide in which the composition of most of the microregions is almost the same as the charged composition has a substantially uniform composition and tends to exhibit higher catalytic activity in the steam reforming reaction of oxygen-containing hydrocarbons. In addition, “the charging ratio of cerium, aluminum and zirconium” means the ratio (unit:%) of the charging amount of cerium, aluminum and zirconium to the total charging amount of the metal forming the composite oxide. Further, “within the range of the charging ratio ± 20%” means, for example, 50 to 90% when the charging ratio is 70%.

Steam reforming catalysts tend to exhibit high catalytic activity even in steam reforming reactions of oxygen-containing hydrocarbons at high temperatures. The reason for this is not necessarily clear, but the present inventors speculate as follows. That is, the composite oxide contains ceria or ceria-zirconia solid solution with low solid phase reactivity, and even if the first supported metal element is oxidized and exposed to a high temperature of 600 ° C. or higher, It is presumed that the catalytic activity is increased because the solid-phase reaction with the oxide is difficult to proceed and is reduced to a metal state exhibiting high catalytic activity without being stabilized in the state of oxide. In addition, the composite oxide and the first supported metal element exhibit a strong interaction, and grain growth of the first supported metal element on the support containing the composite oxide is suppressed even at a high temperature of 600 ° C. or higher. It is assumed that the catalytic activity is increased. Furthermore, ceria or ceria-zirconia solid solution usually grows more easily in a reducing atmosphere such as a steam reforming reaction than an oxidizing atmosphere, but ceria and alumina or ceria-zirconia solid solution and alumina, which do not form a solid solution with each other. It is presumed that the catalytic activity is enhanced because the composite oxide acts as a barrier to each other to suppress the grain growth of the complex oxide at a high temperature and the grain growth of the metal element supported thereon.

The action of reducing the first supported metal element from the oxide state to the metal state is also exhibited in ceria, but more effectively when ceria forms a solid solution with zirconia. Therefore, in the composite oxide, it is preferable that at least a part of each of ceria and zirconia forms a cubic ceria-zirconia solid solution.

Furthermore, the steam reforming catalyst can maintain a high pore volume of the mesopores of the composite oxide even after being exposed to a high temperature. This is presumably because sintering of the complex oxide at high temperatures is suppressed by the barrier action. In addition, the range of the pore diameter of a mesopore means the range from the lower limit 3.5nm to 100nm which can be measured using a mercury porosimeter in principle. In the case of the composite oxide, the pore volume having a pore diameter of 3.5 to 100 nm is 0.07 cm ³ / g or more after calcination at 600 ° C. for 5 hours and after calcination at 800 ° C. for 5 hours. in 0.04 cm ³ / is preferably g or more, 600 after firing for 5 hours at ° C. 0.13 cm ³ / g in the are and 800 ° C. or higher after calcination for 5 hours 0.10 cm ³ / g or more in More preferably, it is 0.19 cm ³ / g or more after calcination at 600 ° C. for 5 hours, and particularly preferably 0.15 cm ³ / g or more after calcination at 800 ° C. for 5 hours.

As the composite oxide, the ceria crystallite diameter calculated from the half width of the peak of CeO ₂ (220) by X-ray diffraction is 5 to 10 nm after baking at 600 ° C. for 5 hours, and at 800 ° C. for 5 hours. It is preferably 10 to 20 nm after firing, and 35 nm or less after firing at 1000 ° C. for 5 hours. When the ceria crystallite diameter is in the above range, sintering at high temperatures is further suppressed, and a sufficient pore volume tends to be ensured even after exposure to high temperatures.

When the first supported metal element and / or the second supported metal element is supported on the support containing the composite oxide having a sufficiently secured pore volume, the metal elements are highly dispersed in the mesopores. It is carried by. The mesopores are a reaction field in the steam reforming reaction of oxygen-containing hydrocarbons, and a sufficient pore volume is secured even at high temperatures. For this reason, it is surmised that the steam reforming catalyst exhibits high catalytic activity even in the steam reforming reaction of oxygen-containing hydrocarbons at high temperatures.

The composite oxide can be produced, for example, by the following method. First, a ceria precursor and an alumina precursor are deposited as a precipitate from an aqueous solution in which a cerium compound and an aluminum compound are dissolved or a solution containing water. At this time, if necessary, a zirconium compound can be dissolved in the aqueous solution or a solution containing water to precipitate the zirconia precursor as a precipitate. Moreover, when a ceria precursor and a zirconia precursor are simultaneously deposited as precipitates, at least a part thereof forms a solid solution.

As the cerium compound, aluminum compound and zirconium compound, salts such as sulfates, nitrates, chlorides and acetates are generally used. Examples of the solvent for dissolving the salt include water and alcohols. Furthermore, for example, a mixture of aluminum hydroxide, nitric acid and water can be used as an aqueous solution containing aluminum nitrate.

The precursor precipitate can be precipitated by adding an alkaline solution to the aqueous solution or a solution containing water to adjust the pH of the solution. At this time, each precursor is added by instantly adding an alkaline solution and stirring vigorously, or by adjusting the pH at which each precursor begins to precipitate by adding hydrogen peroxide or the like, and then adding an alkaline solution or the like. Body precipitates can be deposited almost simultaneously. On the other hand, the alkaline solution is added over time, for example, over 10 minutes to increase the neutralization time, or the pH of the solution is monitored and adjusted stepwise to the pH at which each precursor precipitates. Or by adding a buffer solution so that the pH of the solution is maintained at a pH at which the precipitate of each precursor precipitates (or Vice versa).

Examples of the alkaline solution include ammonia water, an aqueous solution in which ammonium carbonate, sodium hydroxide, potassium hydroxide, sodium carbonate and the like are dissolved, or an alcohol solution. Among them, ammonia water, an aqueous solution of ammonium carbonate or an alcohol solution is preferable because it volatilizes when the composite oxide is fired. Further, from the viewpoint of promoting the precipitation reaction of the precursor precipitate, the pH of the alkaline solution is preferably 9 or more.

Thereafter, the precursor precipitate thus obtained is aged and then fired to obtain a composite oxide.

In the method for producing a composite oxide, when the precursor precipitate is aged, dissolution and reprecipitation of the precipitate are promoted by heating heat, and the resulting composite oxide particles can be grown. A composite oxide composed of crystallites having high crystallinity and an appropriate particle size can be obtained. The aging temperature is preferably room temperature or higher, more preferably 100 to 200 ° C., and particularly preferably 100 to 150 ° C. When the aging temperature is less than the lower limit, the effect of aging is small, and the time required for aging tends to be long.On the other hand, when the upper limit is exceeded, the water vapor pressure becomes extremely high, so a pressure vessel is required and the production cost is high. Tend to be.

In the method for producing the composite oxide, the precipitate can be fired in the air. The firing temperature is preferably 300 to 800 ° C. When the firing temperature is less than the lower limit, the resulting composite oxide tends to lack stability as a carrier, and when the upper limit is exceeded, the specific surface area of the composite oxide tends to decrease.

As mentioned above, although the manufacturing method of complex oxide was demonstrated, the manufacturing method of the said complex oxide is not limited to the said embodiment. For example, the solution containing the precursor precipitate may be heated as it is to evaporate the solvent to dry the precipitate, and then fired. In this case, since the precipitate is aged during the drying of the precipitate, the drying of the precipitate is preferably performed at the aging temperature.

The carrier used for the steam reforming catalyst is not particularly limited as long as it contains such a complex oxide, and even if it is composed only of the complex oxide, the complex oxide and other porous oxides. It may consist of a mixture with a product. Examples of the other porous oxides include alumina, ceria, zirconia, titania, silica and the like. These oxides may be used alone or in combination of two or more. . In the mixture of the composite oxide and another porous oxide, the content of the composite oxide is preferably 50% by mass or more. When the content of the composite oxide is less than the lower limit, the catalytic activity in the steam reforming reaction of the oxygen-containing hydrocarbon tends to decrease.

The steam reforming catalyst includes a support containing such a composite oxide, at least one first metal element selected from the group consisting of platinum group metals supported on the support, and supported on the support. It contains at least one second metal element selected from the group consisting of alkali metals, alkaline earth metals and rare earth elements.

In such a steam reforming catalyst, a platinum group metal (ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir) and platinum (Pt)) supported on the carrier. It is necessary to contain at least one first metal element selected from the group consisting of:

Among the at least one first metal element selected from the group consisting of the platinum group metals, rhodium is more preferable from the viewpoint of showing high catalytic activity in the steam reforming reaction of oxygen-containing hydrocarbons. Moreover, the metal element which belongs to the said platinum group may be used individually by 1 type, or may use 2 or more types together.

The content of the first supported metal element in the steam reforming catalyst is preferably 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of the support. If the content of the first supported metal element is less than the lower limit, sufficient catalytic activity tends not to be obtained in the steam reforming reaction of the oxygen-containing hydrocarbon. It tends to grow and the catalytic activity does not improve.

Moreover, in such a steam reforming catalyst, alkali metals (lithium, sodium, potassium, rubidium and cesium), alkaline earth metals (beryllium, magnesium, calcium, strontium and barium) and rare earth elements supported on the carrier are supported. Contains at least one second metal element selected from the group consisting of (scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium) It is necessary to.

Of the at least one second metal element selected from the group consisting of alkali metals, alkaline earth metals and rare earth elements, sodium is used from the viewpoint of high catalytic activity and prevention of catalyst deterioration in the steam reforming reaction of oxygen-containing hydrocarbons. (Na), potassium (K), cesium (Cs), magnesium (Mg), strontium (Sr), barium (Ba), lanthanum (La) and at least one selected from the group consisting of neodymium (Nd) It is preferable that it is at least one selected from the group consisting of sodium (Na), potassium (K), magnesium (Mg) and lanthanum (La). In addition, at least one selected from the group consisting of the alkali metal, alkaline earth metal and rare earth element may be used alone or in combination of two or more.

The amount of the second supported metal element supported in the steam reforming catalyst is not particularly limited, but the ratio to the number of atoms of the first supported metal element is preferably 0.05 to 10, preferably 0.1 to 5 is more preferable. If the amount of the second supported metal element is less than the lower limit, sufficient catalytic activity or catalyst deterioration preventing effect tends to be not obtained in the steam reforming reaction of the oxygen-containing hydrocarbon. The supported metal element covers the first supported metal element and the catalytic activity tends to decrease.

As a method for supporting the first metal element and the second metal element, for example, the composite oxide is contained in a solution containing a compound of the metal element of the first metal element and the second metal element at a predetermined concentration. Examples include a method of immersing the carrier, impregnating the carrier with a solution containing a predetermined amount of metal element, and firing the carrier. In addition, the loading method of the first metal element and the second metal element is that after the first metal element is first supported and fired, the second metal element is supported and fired, or the second metal element is first supported and fired. The first metal element may be supported and fired, or may be performed simultaneously. At this time, the support containing the composite oxide may be used in the form of powder such as pellets, or the support containing the composite oxide is previously applied to a known base material such as a cordierite honeycomb base material by coating or the like. You may fix and use.

Calcination in such a supporting method can be performed in the atmosphere. The firing temperature is preferably 200 to 600 ° C. If the firing temperature is less than the lower limit, the compound of the first metal element is not sufficiently thermally decomposed and becomes difficult to be in a metal state, so that the activity tends to be low. The element grows and the catalytic activity in the steam reforming reaction of the oxygen-containing hydrocarbon tends to decrease. The firing time is preferably from 0.1 to 100 hours. When the firing time is less than the lower limit, the compound of the metal element is not sufficiently thermally decomposed and becomes difficult to be in a metal state, and therefore the activity tends to be low. This is not possible, leading to an increase in cost for preparing the catalyst.

The shape of the steam reforming catalyst is not particularly limited, and can be formed into various shapes such as a pellet shape, a monolith shape, a honeycomb shape, or a foam shape according to the application.

Such a steam reforming catalyst is used to reform an oxygen-containing hydrocarbon with steam, and exhibits high catalytic activity in the steam reforming reaction of the oxygen-containing hydrocarbon.

Next, a method for steam reforming of oxygen-containing hydrocarbon will be described. The steam reforming method for oxygen-containing hydrocarbons is a method for generating hydrogen by bringing oxygen-containing hydrocarbons into contact with the steam reforming catalyst in the presence of steam.

The steam reforming reaction apparatus used in such a steam reforming method is not particularly limited as long as it includes the steam reforming catalyst, and is conventionally known such as a fixed bed flow type reaction apparatus and a fluidized bed type reaction apparatus. Catalytic reactors can be used.

Examples of the oxygen-containing hydrocarbon include alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, s-butyl alcohol, and t-butyl alcohol, dimethyl ether, diethyl ether, ethyl methyl ether, And ethers. Among these oxygen-containing hydrocarbons, since it is liquid at room temperature, it is easy to handle, has high safety, has high affinity with water (steam), and is easily available. It is preferable to apply to ethanol and diethyl ether, and more preferable to apply to methanol and ethanol.

In the steam reforming method of the oxygen-containing hydrocarbon, the oxygen-containing hydrocarbon and the steam may be supplied independently to the reaction device, or may be supplied to the reaction device after mixing them in advance.

The mixing ratio of the oxygen-containing hydrocarbon and water vapor is not particularly limited. For example, when the oxygen-containing hydrocarbon is ethanol, the water vapor to carbon molar ratio (S / C) is 0.2 to 2. It is preferable that the ratio is 0.4 to 1. By using the steam reforming catalyst, the oxygen-containing hydrocarbon can be reformed even under low S / C conditions where coking has conventionally occurred. That is, the steam reforming method for oxygen-containing hydrocarbons is particularly suitable for reforming reactions under low S / C conditions of S / C = 0.2 to 0.6 (preferably 0.4 to 0.6). It is valid.

The temperature of the reforming reaction is preferably 250 to 650 ° C., more preferably 350 to 600 ° C. By using the steam reforming catalyst, it is possible to reform the oxygen-containing hydrocarbon even at a low temperature of 400 ° C. or lower, which has been conventionally low in catalytic activity and difficult to steam reform the oxygen-containing hydrocarbon. .

Hereinafter, the present disclosure will be described more specifically based on examples and comparative examples, but the present disclosure is not limited to the following examples. In addition, each physical property of complex oxide and mixed oxide was measured with the following method.

<Specific surface area>
Using a fully automatic specific surface area measuring device, the BET single point method using N ₂ adsorption at liquid nitrogen temperature (−196 ° C.) was used.

<Dispersibility of each metal atom of particle>
Using a field emission scanning transmission microscope (FE-STEM, “HD-2000” manufactured by Hitachi, Ltd.), the dispersibility of the metal atoms of the composite oxide particles before supporting rhodium was observed by the following method. .

That is, in the FE-STEM, one non-overlapping particle in the composite oxide powder is irradiated with an electron beam with a diameter of 0.5 nm at an acceleration voltage of 200 kV, and characteristic X-rays generated from a sample are irradiated with the FE-STEM. The composite oxide particles were subjected to elemental analysis in a minute region having a cross-sectional diameter of 0.5 nm. The detection was performed by an EDX detector (“VAGE EDX system” manufactured by NCRAN). This elemental analysis was performed on five minute regions. Note that “a microscopic region having a cross-sectional diameter of 0.5 nm” means a region in the composite oxide through which an electron beam with a diameter of 0.5 nm irradiated to the composite oxide particle is transmitted.

Example 1
0.2 mol (75.1 g) of aluminum nitrate nonahydrate was added to 2000 ml of ion-exchanged water, and dissolved by stirring for 5 minutes with a propeller stirrer. The solution was stirred by adding the concentration of CeO ₂ in terms of 28% by weight of the aqueous cerium nitrate solution 265 g (corresponding to 0.43 mol in terms of CeO ₂₎ 5 minutes. Next, an aqueous solution in which 0.068 mol (18.1 g) of zirconyl nitrate dihydrate was dissolved in 30 g of ion-exchanged water was added to the mixed aqueous solution, followed by stirring for 5 minutes. To the obtained mixed aqueous solution, 177 g of 25 mass% ammonia water was added and stirred for 10 minutes to obtain an aqueous solution containing a precipitate. The aqueous solution was heat-treated at 120 ° C. for 2 hours under a pressure of 2 atm to age the precipitate.

The aqueous solution containing the aged precipitate is heated to 400 ° C. at a rate of 100 ° C./hour, further calcined at 400 ° C. for 5 hours, and then calcined at 600 ° C. for 5 hours to ceria-zirconia-alumina composite oxidation A product powder was prepared. The obtained composite oxide powder was composed of about 80% by mass of CeO ₂ , about 9% by mass of ZrO ₂ and about 11% by mass of Al ₂ O ₃ , and the specific surface area was 100 m ² / g. It was.

The obtained composite oxide particles were subjected to elemental analysis in a minute region having a cross-sectional diameter of 0.5 nm according to the method described above. The result is shown in FIG. In FIG. 1, “●” represents a preparation ratio, and “◯” represents a composition ratio obtained by elemental analysis by the above method (hereinafter, the same applies to other examples). As is clear from this result, the obtained composite oxide powder has Ce, Zr, and Al contents in each minute region subjected to elemental analysis, and their charging ratios (Ce = 61%, Zr = 10%, Al = 29%) ± 10% (within the dotted line in FIG. 1). That is, the composite oxide powder contains a metal element having a substantially charged ratio in any minute region having a cross-sectional diameter of 0.5 nm, and ceria, zirconia, and alumina are dispersed in nm scale in the particles. It was confirmed that

Next, 240 g of the obtained ceria-zirconia-alumina composite oxide powder, 267 g of ceria sol binder (solid content concentration: 10% by mass) and a predetermined amount of ion-exchanged water were mixed, and this mixture was mixed with a wet attritor with a predetermined particle size. To obtain a slurry. The slurry was applied to a cordierite honeycomb monolith substrate (400 cells / square inch) having a diameter of 23 mm × length of 25 mm and a volume of 10.4 ml at a rate of 240 g per liter of the substrate, and then 500 ° C. For 3 hours.

Next, a base material provided with the composite oxide powder is impregnated with a predetermined amount of rhodium nitrate solution in which rhodium is dissolved, and after supporting rhodium by a selective adsorption method, the base material is baked at 500 ° C. for 3 hours in the atmosphere. A monolith sample containing rhodium and a composite oxide was prepared by supporting 4.8 g of rhodium per liter.

Next, the monolith sample containing rhodium and the composite oxide was allowed to absorb a predetermined concentration and amount of an aqueous solution of sodium acetate trihydrate, dried at 110 ° C. for 16 hours, and then calcined at 500 ° C. for 3 hours. Thus, the monolith catalyst of Example 1 was obtained. The amount of sodium supported per liter of monolith substrate was 0.024 mol / L.

(Example 2)
A monolith catalyst of Example 2 was obtained in the same manner as in Example 1 except that an aqueous solution of potassium acetate having a predetermined concentration and a predetermined amount was used instead of the aqueous solution of sodium acetate trihydrate. The amount of potassium supported per liter of monolith substrate was 0.024 mol / L.

In addition, elemental analysis was performed on the obtained composite oxide particles in the same manner as in Example 1. As a result, the obtained composite oxide powder had Ce, Zr, and Al contents in each of the minute regions subjected to elemental analysis, and the charge ratios thereof (Ce = 61%, Zr = 10%, Al = 29%) ± about 10% (within the range of the dotted line in FIG. 1), and the composite oxide powder has almost the same charge ratio in any of the minute regions having a cross-sectional diameter of 0.5 nm. It contained a metal element, and it was confirmed that ceria, zirconia, and alumina were dispersed in nm scale in the particles.

Example 3
A monolith catalyst of Example 3 was obtained in the same manner as in Example 1 except that an aqueous solution of cesium acetate having a predetermined concentration and a predetermined amount was used instead of the aqueous solution of sodium acetate trihydrate. The amount of cesium supported per liter of monolith substrate was 0.024 mol / L. The obtained composite oxide particles were subjected to elemental analysis in the same manner as in Example 1. As a result, it was confirmed that the obtained composite oxide powder was obtained by dispersing ceria, zirconia, and alumina on the nm scale.

Example 4
A monolith catalyst of Example 4 was obtained in the same manner as in Example 1 except that an aqueous solution of magnesium acetate tetrahydrate having a predetermined concentration and a predetermined amount was used instead of the aqueous solution of sodium acetate trihydrate. The amount of magnesium supported per liter of monolith substrate was 0.024 mol / L. The obtained composite oxide particles were subjected to elemental analysis in the same manner as in Example 1. As a result, it was confirmed that the obtained composite oxide powder was obtained by dispersing ceria, zirconia, and alumina on the nm scale.

(Example 5)
A monolith catalyst of Example 5 was obtained in the same manner as in Example 1 except that an aqueous solution of strontium acetate having a predetermined concentration and a predetermined amount was used instead of the aqueous solution of sodium acetate trihydrate. The amount of strontium supported per liter of monolith substrate was 0.024 mol / L. The obtained composite oxide particles were subjected to elemental analysis in the same manner as in Example 1. As a result, it was confirmed that the obtained composite oxide powder was obtained by dispersing ceria, zirconia, and alumina on the nm scale.

(Example 6)
A monolith catalyst of Example 6 was obtained in the same manner as in Example 1 except that an aqueous solution of barium acetate having a predetermined concentration and a predetermined amount was used instead of the aqueous solution of sodium acetate trihydrate. The amount of barium supported per liter of monolith substrate was 0.024 mol / L. The obtained composite oxide particles were subjected to elemental analysis in the same manner as in Example 1. As a result, it was confirmed that the obtained composite oxide powder was obtained by dispersing ceria, zirconia, and alumina on the nm scale.

(Example 7)
A monolith catalyst of Example 7 was obtained in the same manner as in Example 1 except that an aqueous solution of lanthanum (III) nitrate hexahydrate having a predetermined concentration and a predetermined amount was used instead of the aqueous solution of sodium acetate trihydrate. . The amount of lanthanum supported per liter of monolith substrate was 0.024 mol / L. The obtained composite oxide particles were subjected to elemental analysis in the same manner as in Example 1. As a result, it was confirmed that the obtained composite oxide powder was obtained by dispersing ceria, zirconia, and alumina on the nm scale.

(Example 8)
A monolith catalyst of Example 8 was obtained in the same manner as in Example 1 except that an aqueous solution of neodymium (III) nitrate hexahydrate having a predetermined concentration and a predetermined amount was used instead of the aqueous solution of sodium acetate trihydrate. . The supported amount of neodymium per liter of monolith substrate was 0.024 mol / L. The obtained composite oxide particles were subjected to elemental analysis in the same manner as in Example 1. As a result, it was confirmed that the obtained composite oxide powder was obtained by dispersing ceria, zirconia, and alumina on the nm scale.

Example 9
A monolith catalyst of Example 9 was obtained in the same manner as in Example 1 except that an aqueous solution of potassium acetate having a predetermined concentration and a predetermined amount was used instead of the aqueous solution of sodium acetate trihydrate. The amount of potassium supported per liter of monolith substrate was 0.048 mol / L. The obtained composite oxide particles were subjected to elemental analysis in the same manner as in Example 1. As a result, it was confirmed that the obtained composite oxide powder was obtained by dispersing ceria, zirconia, and alumina on the nm scale.

(Example 10)
0.2 mol (75.1 g) of aluminum nitrate nonahydrate was added to 2000 ml of ion-exchanged water, and dissolved by stirring for 5 minutes with a propeller stirrer. The solution was stirred by adding the concentration of CeO ₂ in terms of 28% by weight of cerium nitrate aqueous solution 304g (corresponding to 0.5 mol CeO ₂ conversion) 5 minutes. To the obtained mixed aqueous solution, 177 g of 25 mass% ammonia water was added and stirred for 10 minutes to obtain an aqueous solution containing a precipitate. The aqueous solution was heat-treated at 120 ° C. for 2 hours under a pressure of 2 atm to age the precipitate.

The aged aqueous solution containing the precipitate is heated to 400 ° C. at a rate of 100 ° C./hour, further calcined at 400 ° C. for 5 hours, and then calcined at 600 ° C. for 5 hours to obtain ceria-alumina composite oxide powder. Was prepared. The obtained composite oxide powder was composed of about 89% by mass of CeO ₂ and about 11% by mass of Al ₂ O ₃ , and the specific surface area was 90 m ² / g.

The obtained composite oxide particles were subjected to elemental analysis in a minute region having a cross-sectional diameter of 0.5 nm according to the method described above. The result is shown in FIG. In FIG. 1, “●” represents a preparation ratio, and “◯” represents a composition ratio obtained by elemental analysis by the above method (hereinafter, the same applies to other examples). As is clear from this result, the obtained composite oxide powder has a Ce and Al content ratio in each of the microscopic regions subjected to elemental analysis, and the charge ratios thereof (Ce = 71%, Al = 29%). ) Within a range of about ± 10% (within the dotted line in FIG. 1). That is, the composite oxide powder contains a metal element having a substantially charged ratio in any minute region having a cross-sectional diameter of 0.5 nm, and ceria and alumina are dispersed in nm scale in the particles. It was confirmed that there was.

Next, 240 g of the obtained ceria-alumina composite oxide powder, 267 g of ceria sol binder (solid content concentration 10% by mass) and a predetermined amount of ion-exchanged water are mixed, and this mixture is pulverized to a predetermined particle size with a wet attritor. Thus, a slurry was obtained. This slurry was applied to a cordierite honeycomb monolith substrate (400 cells / square inch) having a diameter of 23 mm × a length of 25 mm and a volume of 10.4 ml at a rate of 240 g of the composite oxide per 1 L of the substrate, and then at 500 ° C. Baked for 3 hours.

Next, the obtained monolith sample containing rhodium and composite oxide was allowed to absorb an aqueous solution of potassium acetate having a predetermined concentration and a predetermined amount, dried at 110 ° C. for 16 hours, and then calcined at 500 ° C. for 3 hours. 1 monolith catalyst was obtained. The amount of potassium supported per liter of monolith substrate was 0.024 mol / L.

(Comparative Example 1)
A monolith catalyst of Comparative Example 1 was obtained in the same manner as in Example 1 except that the aqueous solution of sodium acetate trihydrate was not absorbed.

(Comparative Example 2)
A monolith catalyst of Comparative Example 2 was obtained in the same manner as in Example 10 except that the aqueous solution of potassium acetate was not absorbed.

(Comparative Example 3)
Comparative Example as in Comparative Example 1 except that ceria-zirconia composite oxide powder (manufactured by Anan Kasei Co., Ltd., specific surface area 120 m ² / g) powder was used instead of the ceria-zirconia-alumina composite oxide powder. 3 monolith catalysts were obtained.

(Comparative Example 4)
Γ-alumina (manufactured by Showa Denko KK, specific surface area 150 m ² / g) powder was used instead of the ceria-zirconia-alumina composite oxide powder, and the coating amount of γ-alumina was 120 g / L. The monolith catalyst of Comparative Example 3 was obtained in the same manner as Comparative Example 1.

(Comparative Example 5)
A ceria-zirconia composite oxide (manufactured by Anan Kasei, specific surface area 120 m ² / g) powder and γ-alumina (manufactured by Showa Denko Co., Ltd., specific surface area 150 m ² / g) powder are rotated at a mass ratio of 89:11. Place in blender and mix thoroughly. The content of CeO ₂ , ZrO ₂ and Al ₂ O ₃ in the obtained composite oxide powder is the same as the content of CeO ₂ , ZrO ₂ and Al ₂ O _{3 in} the entire composite oxide powder obtained in Example 1. The specific surface area was 120 m ² / g. The particle diameter of the ceria-zirconia solid solution of the ceria-zirconia composite oxide used here was about 15 nm, and the particle diameter of γ-alumina was about 10 nm or less. Therefore, it is clear that even if these oxide powders are physically mixed as described above, they are not dispersed on the nm scale.

Next, 267 g of ceria sol (solid content concentration 10 mass%, U-15 manufactured by Taki Chemical Co., Ltd.) and a predetermined amount of ion-exchanged water are added to 240 g of the powder mixture of the obtained ceria-zirconia composite oxide powder and γ-alumina powder. The mixture was mixed and mixed with a wet attritor for 20 minutes to obtain a slurry. This slurry was applied to a cordierite honeycomb monolith substrate (400 cells / square inch) having a diameter of 23 mm × length of 25 mm and a volume of 10.4 ml at a rate of 240 g per liter of the substrate, and then fired at 500 ° C. for 3 hours. .

Next, after impregnating a predetermined amount of a rhodium nitrate aqueous solution in which rhodium is dissolved into a base material provided with a powder mixture of this ceria-zirconia composite oxide powder and γ-alumina and supporting rhodium by a selective adsorption method, The monolith catalyst of Comparative Example 5 which was calcined at 500 ° C. for 3 hours, loaded with 4.8 g of rhodium per liter of base material, and loaded with rhodium on the support of the mixed powder of ceria-zirconia composite oxide powder and γ-alumina. Got.

(Comparative Example 6)
Instead of the ceria-zirconia-alumina composite oxide powder, a ceria-zirconia composite oxide (Anan Kasei Co., Ltd., specific surface area 120 m ² / g) powder is used, and a predetermined amount is used instead of the aqueous solution of sodium acetate trihydrate. A monolith catalyst of Comparative Example 6 was obtained in the same manner as in Example 1 except that an aqueous solution of potassium acetate having a concentration and a predetermined amount was used. The amount of potassium supported per liter of monolith substrate was 0.024 mol / L.

(Comparative Example 7)
In place of the ceria-zirconia-alumina composite oxide powder, γ-alumina (manufactured by Showa Denko KK, specific surface area 150 m ² / g) powder was used, the coating amount of γ-alumina was 120 g / L, and sodium acetate trihydrate A monolith catalyst of Comparative Example 7 was obtained in the same manner as in Example 1 except that an aqueous solution of potassium acetate having a predetermined concentration and a predetermined amount was used instead of the aqueous solution of the Japanese product. The amount of potassium supported per liter of monolith substrate was 0.024 mol / L.

(Comparative Example 8)
Instead of the ceria-zirconia-alumina composite oxide powder, the powder mixture of ceria-zirconia composite oxide powder and γ-alumina obtained in Comparative Example 5 was used, and a predetermined concentration was used instead of the aqueous solution of sodium acetate trihydrate. A monolith catalyst of Comparative Example 8 was obtained in the same manner as in Example 1 except that a predetermined amount of an aqueous solution of potassium acetate was used. The amount of potassium supported per liter of monolith substrate was 0.024 mol / L.

[Ethanol steam reforming reaction activity test and durability test]
A steam reforming reaction activity test and a durability test were performed on the monolith catalyst samples obtained in Examples 1 to 10 and the comparative monolith catalyst samples obtained in Comparative Examples 1 to 8.

The specifications of the monolith catalyst samples of Examples 1 to 10 and Comparative Examples 1 to 8 are shown in FIG.

<Heat-resistant treatment>
The monolith catalyst samples obtained in Examples 1 to 10 and the comparative monolith catalyst samples obtained in Comparative Examples 1 to 8 were filled in stainless steel reaction tubes each having an inner diameter of 30.5 mm, and the reaction tubes were passed through a fixed bed. Attached to the reactor. Next, a steam reforming reaction gas (S / C = 0.25) is supplied at 600 ° C. for 80 minutes, and after coking is generated, baking is performed in the atmosphere at 700 ° C. for 30 minutes to oxidize and remove the coke. went.

<Steam reforming reaction activity test>
Next, an equimolar mixed aqueous solution of ethanol and water (S / C = 0.5) in a CO ₂ (14%) / Ar gas flow of 4.5 L / min was added to the monolith catalyst sample in the following manner. The gas mixture added and vaporized at 2 mL / min was supplied to the monolith catalyst while heating to 490 ° C. at the center temperature of the monolith. The H ₂ , CH ₄ , CO, and CO ₂ concentrations in the exit gas at that time were measured by gas chromatography. This ethanol steam reforming reaction is continued for 2.5 hours, the time when the maximum H ₂ production concentration is shown in the initial stage is “initial activity”, and 2.5 hours after the start of the reaction is “post-endurance activity”, Each H ₂ production concentration was used as an activity index. FIG. 2 shows a graph showing the catalyst activity at the initial stage in the steam reforming reaction of ethanol for the monolith catalysts obtained in Examples 1 to 10 and Comparative Examples 1 to 8. FIG. 3 is a graph showing the catalytic activity after endurance in the steam reforming reaction of ethanol for the monolith catalysts obtained in Examples 1 to 10 and Comparative Examples 1 to 8.

As is clear from the comparison between the results of Examples 1 to 10 and the results of Comparative Examples 1 to 8 shown in FIG. 2 and FIG. 3, the monolith catalysts of Examples 1 to 10 are in the initial stage and after the endurance. Also, it was confirmed that a high activity rate was exhibited, and it was confirmed that a sufficiently excellent activity was exhibited.

Further, the rate of decrease in activity by the durability test in the steam reforming reaction of ethanol for the monolith catalysts obtained in Examples 1 to 10 and Comparative Examples 1 to 8 (1-endurance H ₂ production concentration / initial H ₂ production concentration) × 100 (%)) is shown in FIG.

As is clear from the comparison between the results of Examples 1 to 10 and the results of Comparative Examples 1 to 8 shown in FIG. 4, the monolithic catalysts of Examples 1 to 10 have a small activity decrease rate due to the durability test. It was confirmed. From these results, a platinum group metal element is supported on a carrier made of a composite oxide in which ceria, zirconia and alumina are dispersed in nm scale, and a composite oxide in which ceria and alumina are dispersed in nm scale. Furthermore, it was confirmed that the catalyst to which one or more metal elements of alkali metal, alkaline earth metal, and rare earth element were added had sufficiently excellent durability performance.

<Carbon deposition amount measurement test>
Next, for the monolith catalysts obtained in Examples 1 to 7, 9 and Comparative Example 1, the amount of carbon deposited on the catalyst after the durability test was measured. The amount of carbon deposition was calculated from the amount of CO ₂ produced when O ₂ (10%) / N ₂ gas was supplied. The obtained results are shown in FIG.

As is clear from the comparison between the results of Examples 1 to 7 and 9 shown in FIG. 5 and the results of Comparative Example 1, the monolith catalysts of Examples 1 to 7 and 9 have any carbon deposition amount on the catalyst. It was confirmed that there were few. From these results, it is considered that the post-endurance activity of the catalyst according to the example was higher than that of the comparative example because carbon deposition was suppressed.

<Acid characteristic evaluation test of carrier>
Next, for the carrier of the monolith catalyst obtained in Examples 1 to 7, 9 and Comparative Example 1, the acid property was evaluated by the acid point amount (NH ₃ desorption amount) by ammonia temperature programmed desorption (NH ₃ -TPD) method. ). NH ₃ -TPD is supplied with NH ₃ (500 ppm) / N ₂ gas at 100 ° C. for 20 minutes, purged with N ₂ gas at 100 ° C. for 50 minutes, and then at 600 ° C. at 20 ° C./minute while supplying N ₂ gas. It was calculated from the amount of NH ₃ desorbed when the temperature was raised to ° C. The obtained result is shown in FIG.

As apparent from the comparison between the results of Examples 1 to 7 and 9 shown in FIG. 6 and the results of Comparative Example 1, the amount of acid sites per specific surface area on the support of the monolith catalysts of Examples 1 to 7 and 9 Was confirmed to be small enough. From this result, it is considered that the amount of carbon deposition in the catalyst of the example was small because the amount of acid sites on the support was small.

Based on the above results, a platinum group metal element is supported on a composite oxide in which ceria, zirconia and alumina are dispersed in nm scale, and a composite oxide in which ceria and alumina are dispersed in nm scale. Furthermore, the catalyst added with one or more metal elements of alkali metal, alkaline earth metal, and rare earth element has an acid point amount on the support of less than 0.42 μmol / m ^2, so that the ethanol steam reforming reaction is sufficiently small. It was confirmed that the decrease in activity due to coking was less likely to occur.

As described above, according to the present disclosure, hydrogen can be generated by efficiently reforming an oxygen-containing hydrocarbon such as ethanol with steam without causing coking.

Therefore, since the steam reforming catalyst of the present disclosure has high catalytic activity in the steam reforming reaction of oxygen-containing hydrocarbons and is excellent in coking resistance, oxygen-containing hydrocarbons such as ethanol are used as fuels in internal combustion engines such as automobiles. When used, it is useful as a catalyst for reforming this with steam to produce hydrogen or carbon monoxide.

Claims

A steam reforming catalyst for reforming oxygen-containing hydrocarbons with steam,
A carrier containing a composite oxide in which both ceria and alumina are dispersed on a nanometer scale;
At least one first metal element selected from the group consisting of platinum group metals supported on the carrier;
At least one second metal element selected from the group consisting of alkali metals, alkaline earth metals and rare earth elements supported on the carrier;
A steam reforming catalyst.
The steam reforming catalyst according to claim 1, wherein the composite oxide further contains zirconia, and ceria, alumina, and zirconia are dispersed in nm scale.
The steam reforming catalyst according to claim 1 or 2, wherein the first metal element supported on the carrier is rhodium.
The second metal element supported on the carrier is at least one selected from the group consisting of sodium, potassium, cesium, magnesium, strontium, barium, lanthanum, and neodymium. The steam reforming catalyst according to 1.
A method for steam reforming of an oxygen-containing hydrocarbon, comprising bringing the oxygen-containing hydrocarbon into contact with the steam reforming catalyst according to any one of claims 1 to 4 in the presence of steam.
The steam reforming method according to claim 5, wherein the oxygen-containing hydrocarbon is ethanol.
A steam reforming reaction apparatus comprising the steam reforming catalyst according to any one of claims 1 to 4.