JP2011031162A - Plate-shaped nickel catalyst object for steam reforming reaction of hydrocarbon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plate-shaped nickel catalyst object excellent not only in the steam reforming capacity of a hydrocarbon but also in durability, and a method for manufacturing the same. <P>SOLUTION: The plate-shaped nickel catalyst object for the steam reforming reaction of a hydrocarbon is characterized by providing a nickel catalyst layer containing a noble metal element as a dopant on the alumina layer of a plate-shaped substrate having the alumina layer on its surface through an intermediate layer. The method of manufacturing the plate-shaped nickel catalyst object for the steam reforming reaction of a hydrocarbon is characterized by adhering nickel on the alumina layer of the plate-shaped substrate having the alumina layer on its surface, subsequently baking the nickel adhered alumina layer of the plate-shaped substrate to 500°C or above to form a nickel spinel intermediate layer, next baking the intermediate layer after nickel is adhered to provide the nickel catalyst layer and finally adhering a noble metal to the nickel catalyst layer before baking the nickel catalyst layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a plate catalyst body for hydrocarbon steam reforming reaction, and in particular, a catalyst nickel layer containing a noble metal element as a dopant is provided on a plate alumina support having an alumina surface through a nickel spinel intermediate layer. The present invention relates to a plate-like nickel catalyst body for hydrocarbon steam reforming reaction.

  The steam reforming reaction of methane is expected not only as a method for producing hydrogen as a fuel for a fuel cell (Non-Patent Document 1), but also conventionally, for example, in a gas turbine using natural gas as a fuel, It is used for decomposing methane contained into hydrogen gas and carbon dioxide gas (Patent Document 1), and it is known that the nickel catalyst is good in any case.

  On the other hand, from the viewpoint of ease of heating and uniformity, in recent years, development of a plate-shaped catalyst in which a catalyst is supported on a heating element has been promoted, and a fuel reformer using the same has also been proposed (Patent Document 2). ). In the case of such a plate-shaped catalyst body or a catalyst body further processed into a honeycomb shape, for example, it is advantageous to use a plate-shaped alumite having excellent processability as a catalyst carrier. However, the conventional plate-like nickel catalyst using alumina as a carrier has a drawback that not only the catalytic ability for the steam reforming reaction is not sufficient, but also the durability is not sufficient.

The above disadvantages are remarkably improved by interposing a nickel spinel intermediate layer represented by NiAl ₂ O ₄ between the surface of the γ-alumina layer of the alumina support and the catalyst nickel layer (for example, Non-Patent Documents 2 and 3). However, it is complicated because it requires a hydrogen reduction treatment immediately before use as a catalyst, and there is still room for improvement in durability.

  Therefore, as a result of further research on a plate-like nickel catalyst that is excellent in durability and does not require a hydrogen reduction treatment before use, the present inventors have found that an aqueous nickel solution used for impregnation of nickel when forming a nickel spinel intermediate layer. The durability can be improved by adjusting the pH, and by adding a trace amount of a noble metal element as a dopant to the catalyst nickel layer, the durability is further improved and self-activation is possible. The present inventors have found that the hydrogen reduction treatment before use is not necessary, and have reached the present invention.

JP 2005-002928 A JP 2007-099596 A

"Reforming reaction of methane with supported Ni catalyst prepared by solid-phase crystallization method" The 90th Catalysis Conference, Discussion Session A Proceedings p12 H. Kameyama et.al. J. Chem. Eng. Japan 40 (2007) 1221-1228 Lif, M. Skoglundh et.al. Appl. Cat A. 274 (2004) 61-69

Accordingly, a first object of the present invention is to provide a plate-like nickel catalyst body which is excellent in steam reforming performance of hydrocarbons and also excellent in durability.
A second object of the present invention is to provide a plate-like nickel catalyst for a hydrocarbon steam reforming reaction that does not require a hydrogen reduction treatment before use.
A third object of the present invention is to provide a method for producing a plate-like nickel catalyst body that is excellent in the steam reforming performance of hydrocarbons and also excellent in durability.

The above objects of the present invention are a catalyst body in which a nickel catalyst layer is provided via an intermediate layer on the alumina layer of a plate-like substrate having an alumina layer on the surface, wherein the nickel catalyst layer is a dopant. The present invention has been achieved by a plate-like nickel catalyst body for hydrocarbon steam reforming reaction, characterized by containing a noble metal element, and a method for producing the same.
In the present invention, the intermediate layer is preferably a nickel spinel intermediate layer represented by NiAl ₂ O ₄ , and the plate-shaped substrate is preferably an anodizable metal substrate.
The alumina layer is preferably a layer formed by anodization, and the alumina layer is preferably further hydrated after anodization.
Further, when the nickel spinel intermediate layer is provided, it is necessary to fire at 500 to 750 ° C., and it is particularly preferable to fire at around 700 ° C.
Moreover, it is preferable to add nickel at the time of providing a nickel spinel intermediate | middle layer at least by the impregnation method using nickel aqueous solution, It is preferable that pH of this nickel aqueous solution is 3.7-6.7.

  The plate-like nickel catalyst body of the present invention is not only in direct contact between the catalyst nickel and the alumina support, but also contains a noble metal as a dopant in the catalyst layer. As a result of preventing nickel re-oxidation and coking due to the above, it has excellent durability and does not require a hydrogen reduction treatment before use.

FIG. 1 is a conceptual diagram for explaining the reason why a plate-like nickel catalyst body having a short life and a plate-like nickel catalyst body having a nickel spinel intermediate layer has a long life. FIG. 2 is a conceptual diagram illustrating the production process of the plate-like nickel catalyst body of the present invention. FIG. 3 is a graph showing that a plate-like nickel catalyst body having a nickel spinel intermediate layer is excellent in coking resistance. FIG. 4 is a graph demonstrating that a plate-like nickel catalyst body having a nickel spinel intermediate layer has sufficient durability for a methane steam reforming reaction using 13A city gas. FIG. 5 is a graph showing that the firing for forming the nickel spinel intermediate layer should be performed at 500 ° C. or higher. FIG. 6 is a graph showing the pH dependency of a solution when Ni supported on forming a nickel spinel intermediate layer is deposited by an impregnation method with respect to a methane steam reforming reaction. FIG. 7 is a graph demonstrating that the catalyst body of the present invention doped with a small amount of Ru as a noble metal self-activates without requiring hydrogen reduction. FIG. 8 is a diagram for explaining the self-activation mechanism of the catalyst body of the present invention when a small amount of Ru is doped as a noble metal. FIG. 9 is a graph demonstrating that the durability of the catalyst body of the present invention, which is slightly doped with Ru or Pt as a noble metal, is improved. FIG. 10 is a graph demonstrating that the catalyst body of the present invention doped with a small amount of Pt is hardly affected by repeated steam purges at high temperatures and is extremely excellent in durability. FIG. 11 is a graph demonstrating that the catalyst body of the present invention doped with a small amount of Ru has excellent coking resistance. FIG. 12 is a graph demonstrating that the catalyst body of the present invention has excellent durability even for DSS operation using 13A city gas.

  The substrate used in the catalyst body of the present invention may be any substrate on which an alumina oxide surface is formed. In particular, aluminum, an aluminum alloy, or aluminum having an anodized alumina film on the surface, iron, stainless steel, copper, etc. It is preferable to use a clad material. In addition, in the present invention, in order to increase the specific surface area of the anodized film surface, as is well known, a hydration treatment is performed by treatment with water vapor or warm water at room temperature to 80 ° C. for 5 minutes to 24 hours. Is preferred. Thereby, the surface area of the catalyst body of the present invention can be greatly increased.

  In the present invention, an intermediate layer is formed on the alumina oxide surface in order to prevent sintering of the Ni catalyst. A preferred intermediate layer is nickel spinel, which is formed by providing a moderate nickel layer on the alumina oxide surface and heating and firing. A conceptual diagram of the action and effect of this intermediate layer is as shown in FIG. 1, and Ni supported on the intermediate layer is prevented from being sintered in alumina oxide or reoxidized by water vapor. It is a layer for.

  That is, since the nickel spinel intermediate layer is strongly bonded to the alumina surface of the substrate and the catalyst nickel, desorption of nickel as a catalyst component in a high temperature atmosphere is suppressed, and nickel sintering is prevented. As a result, contact between nickel as a catalyst component and alumina is prevented, so that reoxidation of nickel by water vapor is also suppressed. Further, as described above, the nickel spinel intermediate layer suppresses the growth (so-called sintering) of the nickel particles as the catalyst component, so the particle diameter of the nickel particles remains small. For this reason, the reforming performance can be kept high, and as a result, coking is also suppressed.

Thus, if there is no nickel spinel intermediate layer, the catalyst nickel gradually sinters according to the following formulas (1) and (2) during the steam reforming reaction of methane performed at 500 to 750 ° C. The life as a catalyst body is shortened.
Ni + H ₂ O → NiO (1)
NiO + Al ₂ O ₃ → NiAl ₂ O ₄ (2)

  FIG. 2 is a process diagram showing an outline of a preferred method for producing the catalyst body of the present invention. The numbers shown in this block diagram indicate preferred conditions. Below, this invention is explained in full detail based on the Example of methane steam reforming reaction.

  The durability of the plate-like nickel catalyst body having a nickel spinel intermediate layer with respect to the methane steam reforming reaction is extremely superior to the durability of the conventional Ni alumite catalyst. This is demonstrated by FIG. 3 and FIG.

That is, methane steam reforming is performed at 700 ° C. at the following flow rate ratio on a catalyst body subjected to hydrogen reduction treatment in which pure hydrogen is flowed at a flow rate of 100 mL / min at 500 ° C. for 1 hour and further at 800 ° C. for 2 hours. As a result of the reaction, the methane conversion after 100 hours was 100% unchanged only when the nickel spinel intermediate layer was provided.
_{CH 4: H 2 O: N} 2 = 50mL / min: 150 mL / min: 100 mL / min;
GHSV [mL / (h · g)] (space velocity of mixed gas of CH ₄ and H ₂ O) = 157000

Further, regarding a catalyst body having a Ni-based reforming catalyst FCR-4 (Ni supported amount: 12% by mass) and a nickel spinel intermediate layer manufactured by Sued Chemie without an intermediate layer, the caulking properties were compared as follows. It was confirmed that the catalyst body having the spinel intermediate layer was remarkably superior in coking resistance (FIG. 3).
Experimental conditions:
The flow rate of pure hydrogen was 100 mL / min, hydrogen reduction treatment was performed at 500 ° C. for 1 hour, and then at 800 ° C. for 2 hours, and then charged with nitrogen gas and cooled at room temperature for 10 hours. Methane was flowed at room temperature at a flow rate of 60 mL / min for 1 hour, during which time it was heated to 200 ° C. at a heating rate of 10 ° C./min. Subsequently, it heated to 700 degreeC with the temperature increase rate of 10 degree-C / min, and maintained as it was for 10 hours.
The caulking property was evaluated by measuring the weight increase of the catalyst body using a thermogravimetric balance.

Further, the plate-like nickel catalyst body having a nickel spinel intermediate layer has sufficient durability for a steam reforming reaction test conducted in a DSS operation mode (daily start up and shut down) using 13A city gas. It was also confirmed that it has (FIG. 4). It is known that hydrocarbons such as propane contained in 13A city gas are more susceptible to coking than methane.
Experimental conditions:
After hydrogen reduction treatment at 800 ° C. for 0.5 hours with a pure hydrogen flow rate of 100 mL / min, nitrogen gas was not used, GHSV [mL / (h · g)] = 34000, water vapor / methane = 3 Under the conditions, a methane steam reforming reaction was performed.

  In the present invention, the method of providing a nickel layer on the alumina oxide surface can be appropriately selected from known methods, but in the present invention, not only the apparatus is simple, but also from the viewpoint of excellent mass productivity, It is preferable to employ a so-called impregnation method in which a substrate having an alumina oxide surface is immersed in a nickel-containing aqueous solution, and then pulled up and dried. After drying, a nickel spinel intermediate layer can be formed by firing, and if a nickel layer is again provided on this intermediate layer and fired, it becomes a catalyst layer, and further, a noble metal as a dopant is attached and fired. The catalyst body of the invention is produced.

That is, the nickel supported for the first time is converted into nickel spinel (NiAl ₂ O ₄ ) by high-temperature firing. In the present invention, nickel is supported on the nickel spinel intermediate layer for the second time. This second supported nickel functions as a catalyst. If there is no nickel spinel intermediate layer as in the past, the supported Ni gradually sinters under the methane steam reforming reaction at a high temperature (650 to 750 ° C) and at the same time reacts with the alumina as the carrier to react with the nickel spinel. As a result, the catalytic activity is lost. On the other hand, the catalyst body of the present invention has nickel spinel (NiAl ₂ O ₄ ) as an intermediate layer, so that the life as a catalyst body is prolonged as described above.

  The firing temperature at the time of forming the intermediate layer greatly affects the durability of the catalyst body of the present invention, and is therefore an important factor in the production method of the present invention. In the present invention, the firing temperature is preferably 500 ° C. or higher. Although an upper limit should just be below the heat durability of a board | substrate, when it is an alumite board | substrate, it is safe to restrain to about 750 degreeC. In addition, FIG. 5 is a graph which shows the calcination temperature dependence at the time of the said intermediate | middle layer formation with respect to durability of the catalyst body of this invention. From this result, it is confirmed that the firing temperature when forming the intermediate layer should be 500 ° C. or higher.

Further, the pH of the nickel-containing aqueous solution used when the intermediate layer is formed by the impregnation method also affects the durability of the catalyst body of the present invention (FIG. 6). As is clear from FIG. 6, the pH of the nickel-containing aqueous solution is preferably 3.7 or more, and particularly preferably 4.6 or more. From the viewpoint of ensuring the dissolution concentration of the nickel salt, the upper limit of the pH Is about 6.7. The conditions for the durability test are as follows.
Experimental conditions The flow rate of pure hydrogen was 100 mL / min, and hydrogen reduction treatment was performed at 500 ° C. for 1 hour and then at 800 ° C. for 2 hours. The flow rate ratio of the gas during the methane reforming reaction is CH ₄ : H ₂ O: N ₂ = 50 mL / min: 150 mL / min: 100 mL / min, and GHSV [mL / (h · g)] (CH ₄ and The space velocity of the mixed gas of H ₂ O was 157000.

Furthermore, the nickel content in the nickel spinel intermediate layer also affects the durability of the catalyst body of the present invention. Naturally, the durability is different depending on whether the intermediate layer is present or not. However, even if the amount of catalyst nickel is the same (17.9 wt%), the durability is improved if the amount of nickel in the intermediate layer is reduced. Deteriorate. The nickel adhesion amount for forming the intermediate layer needs to be 5 wt% or more, and more preferably 9 wt% or more.
The nickel deposited on the intermediate layer and the catalyst layer does not necessarily have to be deposited at once, and may be deposited in multiple steps.

To summarize the above results, the production conditions and most preferred production conditions of the catalyst body of the present invention are summarized as shown in Table 1 below.

  In the catalyst body of the present invention in which a trace amount of a noble metal element such as Ru, Pt, Rh, Ir, Co or the like is added to the nickel catalyst layer as a dopant, the hydrogen reduction treatment immediately before use, which is usually required for the generation of self-activity, is performed. Not only is it unnecessary, but the durability can be further improved (FIG. 7). The content of the noble metal element in the catalyst layer is preferably 0.01 to 0.5% by mass, and particularly preferably 0.05 to 0.1% by mass.

The reaction mechanism in which the self-activity occurs when a trace amount of a noble metal element is added as a dopant to the nickel catalyst layer is explained by an increase in the amount of hydrogen generated, as shown in FIG. That is, when the above-mentioned Ni / NiAl ₂ O ₄ / Al ₂ O ₃ / Alloy is doped with a trace amount of noble metals such as Ru and Pt, the hydrogen spillover effect at the noble metal site immediately before the reaction. It is estimated that the hydrogen reduction treatment of the nickel catalyst can be omitted.

More specifically, it is estimated as follows. When methane and water vapor are flowed at high temperature, methane starts a decomposition reaction (CH ₄ → CHx + H ₂ ) on RuOx to generate hydrogen. During this methane decomposition reaction, CHx adsorbed on RuOx reacts with free oxygen O of RuOx itself, and RuOx is reduced to Ru and simultaneously produces CO (RuOx + CHx → Ru + CO + H ₂ ) . The H ₂ and CO produced here first cause reduction of nickel oxide on the catalyst. In addition, a large amount of hydrogen is generated by the progress of the reforming reaction of methane and the shift reaction of CO and water vapor on the reduced Ru. The generated hydrogen further reduces the crusts of nickel oxide and Ru—Ni—Ox. In this way, nickel oxide is self-reduced by the hydrogen spillover effect of Ru, and a Ru—Ni alloy is formed on the surface of the Ni metal. Thus, it is presumed that the noble metal-Ni alloy plays an extremely important role in the manifestation of self-activation and self-revitalization in the catalyst doped with the noble metal.

FIG. 9 is a graph demonstrating that the durability of the catalyst body of the present invention is improved when a small amount of Ru or Pt is doped as a noble metal. In the case of this example, only in the case of a catalyst body not doped with a noble metal, the flow rate of pure hydrogen was set to 100 mL / min, and hydrogen reduction treatment was performed at 500 ° C. for 1 hour and then at 800 ° C. for 2 hours. The flow rate ratio of the gas during the methane steam reforming reaction is as follows: CH ₄ : H ₂ O: N ₂ = 50 mL / min: 150 mL / min: 100 mL / min, GHSV [mL / (h · g)] (CH ₄ And the space velocity of the mixed gas of H ₂ O was 157000 or 471000, and the reaction temperature was 700 ° C.

The effect of the noble metal doping was particularly remarkable when Pt was used as the noble metal (FIG. 10). In this example, hydrogen reduction treatment is not performed, and the flow rate ratio of the gas during the methane steam reforming reaction is CH ₄ : H ₂ O: N ₂ = 50 mL / min: 150 mL / min: 100 mL / min, and GHSV [mL / (H · g)] (space velocity of the mixed gas of CH ₄ and H ₂ O) was 157000, and the reaction temperature was 700 ° C.

  By the way, normally, when operating the reformer, it is rare to perform steam purge or fuel purge. Here, the water vapor purge is to stop the fuel gas and flow only water vapor, and the fuel purge is to stop the water vapor and flow only fuel gas. Actually, such a possibility arises in the case of an erroneous operation or an accident. These steam purge and fuel purge are said to lead to catalyst deterioration. In other words, Ni re-oxidation caused by steam purge or deterioration due to coking caused by fuel purge can provide catalyst performance at the initial activity level even if fuel and steam are reintroduced together after solving the accident. Absent. Therefore, these adverse effects must be minimized in practical use. That is, high robustness is required. Further, from the viewpoint of energy saving, it is preferable to reduce the amount of water vapor, but generally, when the ratio of water vapor / fuel (S / C) becomes small, coking tends to occur.

  Therefore, when the performance of the catalyst was evaluated under various severe conditions using the alumite catalyst body of the present invention doped with a noble metal, this catalyst body is strong not only for steam purge but also for methane purge, Operation under low S / C conditions is also possible, and it was confirmed to have high robustness (FIGS. 10 and 11).

  Furthermore, since the stationary fuel cell is operated in the DSS (Daily startup and shutdown) mode, the results of the test of the DSS operation mode using 13A city gas for the nickel alumite catalyst body of the present invention are shown in FIG. In particular, when a small amount of noble metal was doped, it was confirmed that the performance of the catalyst could be maintained at almost the initial activity level even after several hundred DSS operations.

  The catalyst body of the present invention is useful as a catalyst for a fuel cell in which startability is particularly important because the catalyst can be heated up to 800 ° C. in a few seconds when energized and heated in the start stage in order to improve startability. It is. In the case of using current heating, it is preferable to generate water vapor by keeping the temperature just before and after the catalyst from the outside. The catalyst itself can be maintained at 700 ° C. only by energization heating without external heat retention. Even in this case, it was confirmed that the catalyst was not deteriorated even after 16 hours and the reaction could be continued extremely stably.

  The catalyst body of the present invention has excellent methane steam reforming performance and durability even though it does not require a hydrogen reduction treatment before use. Useful as a medium.

Claims (11)

  A catalyst body in which a nickel catalyst layer is provided on the alumina layer of a plate-like substrate having an alumina layer on the surface via an intermediate layer, wherein the nickel catalyst layer contains a noble metal element as a dopant. A plate-like nickel catalyst body for hydrocarbon steam reforming reaction. The plate-like nickel catalyst body for hydrocarbon steam reforming reaction according to claim 1, wherein the intermediate layer is a nickel spinel intermediate layer represented by NiAl ₂ O ₄ .   The plate-like nickel catalyst body for hydrocarbon steam reforming reaction according to claim 1 or 2, wherein the plate-like substrate is a metal substrate that can be anodized.   The plate-like nickel catalyst body for hydrocarbon steam reforming reaction according to claim 3, wherein the alumina layer is a layer formed by anodic oxidation.   The plate-like nickel catalyst body for hydrocarbon steam reforming reaction according to claim 4, wherein the alumina layer is an alumina layer obtained by further hydrating after anodizing.   Nickel is deposited on the alumina layer of the plate-like substrate having an alumina layer on the surface, and then calcined at 500 ° C. or more to form a nickel spinel intermediate layer, and then catalytic nickel is deposited on the intermediate layer. After calcining and forming a catalyst layer, a trace amount of noble metal element is further deposited and calcined, and a nickel catalyst layer containing a noble metal element as a dopant is provided. Plate-like nickel for hydrocarbon steam reforming reaction A method for producing a catalyst body.   The method for producing a plate-like nickel catalyst body for a hydrocarbon steam reforming reaction according to claim 6, wherein the firing for forming the nickel spinel intermediate layer is performed at about 700 ° C.   The method for producing a plate-like nickel catalyst body for a hydrocarbon steam reforming reaction according to claim 6 or 7, wherein nickel for forming the intermediate layer and / or the catalyst layer is attached by an impregnation method.   The production of a plate-like nickel catalyst body for a hydrocarbon steam reforming reaction according to claim 8, wherein the adhesion of nickel in the intermediate layer is performed by an impregnation method using a nickel aqueous solution having a pH of 3.7 to 6.7. Method.   The method for producing a plate-like nickel catalyst body for hydrocarbon steam reforming reaction according to any one of claims 6 to 9, wherein the catalyst layer is calcined at 500 ° C or higher. The method for producing a plate-like nickel catalyst body for a hydrocarbon steam reforming reaction according to any one of claims 6 to 10, wherein the firing during the noble metal doping is performed at 500 ° C or higher.

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