KR20210051179A - Catalyst for steam methane reforming having an active metal concentration gradient in an spinel structured inorganic oxide support, a method for preparing the same, and a method for preparing a synthesis gas using the catalyst - Google Patents

Abstract

The present invention relates to a method for preparing a catalyst applied to a steam methane reforming (SMR) reactor for a hydrogen charging station in the form of a catalyst having excellent thermal stability and strong resistance against carbon deposition. The catalyst for SMR reaction is required to have high thermal stability as a pellet catalyst in order to maintain a high reaction temperature, and thus pellets including an inorganic oxide having excellent thermal stability and a spinel structure are selected as a support for the catalyst. The SMR reaction shows a significantly high reaction rate as compared to the diffusion rate of reactants, and thus the reaction substantially occurs on the other surfaces of the pellets, thereby making it difficult to use an active metal effectively. To solve this, the catalyst according to the present invention has a concentration gradient by supporting an active metal merely on the outer surfaces of pellets selectively. For the purpose of comparison in terms of reactivity, a catalyst having no concentration gradient is also prepared by supporting an active metal homogeneously throughout the pellets. As a result, the catalyst having a concentration gradient shows better results in terms of pellet durability and carbon deposition degree in the SMR reaction even under a severe condition, as compared to the catalyst having no concentration gradient and commercially available catalysts. Therefore, the catalyst having a concentration gradient is shown to be more suitable for the SMR reaction.

Description

A catalyst for a steam methane reforming reaction with a concentration gradient of an active metal on an inorganic oxide support having a spinel structure, a method for producing the same, and a method for producing a synthesis gas using the catalyst {CATALYST FOR STEAM METHANE REFORMING HAVING AN ACTIVE METAL CONCENTRATION GRADIENT IN AN SPINEL STRUCTURED INORGANIC OXIDE SUPPORT, A METHOD FOR PREPARING THE SAME, AND A METHOD FOR PREPARING A SYNTHESIS GAS USING THE CATALYST}

The present invention relates to a catalyst for a steam methane reforming reaction in which an active metal has a concentration gradient and supported on an inorganic oxide support having a spinel structure, a method for preparing the same, and a method for preparing a syngas using the catalyst.

Steam methane reforming (SMR) reaction is a synthetic gas that is a mixture of hydrogen (H ₂ ) and carbon monoxide (CO) by reacting water (H _{2 O) with methane (CH 4) as shown below.} Is a reaction that generates.

CH ₄ + H ₂ O → CO + 3H ₂ (SMR)

In general, in SMR reactions that produce large amounts of hydrogen, nickel (Ni), noble metals (Pt, Pd, Ag, Au, and Ru) are used as catalytic active materials, among which nickel, a transition metal, which is inexpensive, is suitable. [D. E. Ridler, M. V. Twigg, in: MV Twigg (Ed.), Catalyst Handbook, 2nd Edition, Wolfe, London, 1989, p. 225.] Meanwhile, as CO generated during the SMR reaction is adsorbed on the surface of the active metal, a Boudouard reaction in which carbon is deposited as shown in the following equation can occur.

2CO ↔ CO ₂ + C (coke)

Therefore, to prevent this carbon deposition reaction, excess water vapor is supplied and [steam (H ₂ O) to methane (CH ₄ ) ratio exceeds 3 (S/C> 3)], and basic metal oxides (BaO, MgO, etc.) are also added. do.

The commercial SMR reaction uses a pellet-type catalyst, which exhibits a very high reaction rate compared to the diffusion rate of the reactant, so that the SMR reaction occurs only on the outer surface of the pellet, and the quantified effectiveness factor is 0.03. [J. Xu, G.F. Froment, Methane steam reforming: II. Diffusional limitations and reactor simulation, AIChE Journal, 35 (1989) 97-103.] This means that the utilization of the active metal carried on the entire pellet is very small. In order to overcome this, research on a catalyst in a form having a concentration gradient by supporting the catalytic active material only on the outer surface of the pellet is being actively conducted.

The present invention relates to the development of a catalyst for SMR reaction used in a reformer for hydrogen production in a hydrogen filling station. The catalyst for SMR reaction is generally used as an active metal such as nickel and noble metal and is in the form of a pellet. These catalysts are required to have high activity, thermal stability at high temperatures, and strong resistance to carbon deposition. In addition, the SMR reaction exhibits a very high reaction rate compared to the diffusion rate of the reactant, and the SMR reaction has a disadvantage in that the reaction occurs only on the surface of the pellet, so that 100% of the catalytically active material is not utilized.

Therefore, it is intended to solve the above problems by developing a catalyst in a form having a concentration gradient by using a pellet-type support made of inorganic oxide having a spinel structure having excellent thermal stability at high temperature and selectively supporting the active metal only on the surface of the pellet.

One embodiment is an inorganic oxide support having a spinel structure; And an active metal, wherein the inorganic oxide support has a concentration gradient of the active metal.

The active metal may include one or two or more selected from the group consisting of nickel, platinum, palladium, silver, gold, and ruthenium metals.

The active metal may include one or two or more phases selected from the group consisting _{of NiAl 2} O _{4, NiO, and Ni.}

The concentration gradient of the active metal may increase in a surface direction from the center of the inorganic oxide support.

The inorganic oxide support having a spinel structure may support 10% by weight or less of active metal with respect to the total weight of the active metal in a region of 30 length% or less of the radius of the support from the center.

The inorganic oxide support having a spinel structure may support 50% by weight or more of active metal with respect to the total weight of the active metal in a region of 30 length% or less of the radius of the support from the surface.

The active metal may be included in an amount of 1 to 10% by weight based on the total weight of the catalyst for steam methane reforming.

The active metal may be included in an amount of 1 to 5% by weight based on the total weight of the steam methane reforming catalyst.

The inorganic oxide support having the spinel structure may be one or two or more selected from the group consisting _{of MgAl 2} O ₄ , NiAl ₂ O ₄ , and MgAl ₂ O ₄ -NiAl ₂ O _4.

The inorganic oxide support having the spinel structure may be one or two or more selected from the group consisting of a pellet type, a cylinder type, a tube type, and a spherical shape.

In another embodiment, a) a first immersion step of impregnating an inorganic oxide support having a spinel structure with a hydrophobic first solvent to prepare an inorganic oxide support filled with a hydrophobic first solvent; b) a second immersion step of impregnating a metal precursor solution in which a hydrophilic second solvent and an active metal precursor are mixed into the inorganic oxide support filled with the hydrophobic first solvent; And c) heat-treating the inorganic oxide support impregnated with the metal precursor solution at 873 to 1273K to prepare a catalyst.

The step a) may be impregnating the inorganic oxide support with the hydrophobic first solvent by vacuum distillation.

In the step b), the metal precursor solution may be impregnated into the inorganic oxide support by rotary stirring and distillation under reduced pressure.

The hydrophobic first solvent may have a higher viscosity than the hydrophilic second solvent.

The first hydrophobic solvent may be a polyhydric alcohol having 2 to 6 carbon atoms.

The metal precursor may be a water-soluble metal salt.

Step c) may include drying at 323 to 423K for 0.5 to 2 hours and then heat treatment at 873 to 1273K for 1 to 3 hours.

Another embodiment provides a method for producing syngas through steam reforming of methane, characterized in that in the presence of the catalyst for steam methane reforming, methane and steam are injected and reacted at a molar ratio of 1:1 to 1:3. .

The synthesis gas manufacturing method may be characterized by reacting at 973 to 1273K.

The synthesis gas manufacturing method may be characterized by reacting while injecting steam and methane at a space velocity of 6,000 to 24,000 mL/(h·g _cat).

By using an inorganic oxide having a spinel structure as a catalyst support, the catalyst has excellent thermal stability at a high reaction temperature, has durability against carbon deposition, and can prevent agglomeration of active metals.

By selectively supporting the active metal on the surface of the support, even with a small amount of active metal, it exhibits the same level of activity as the existing catalyst, and it can improve the performance at a fast space velocity of the raw material for SMR reaction, and improve carbon deposition and durability. have.

In addition, in the SMR reaction, there is no active material inside the catalyst, so that carbon deposits therein can be suppressed, and destruction of the catalyst can be prevented as carbon growth selectively occurs on the catalyst surface.

Accordingly, the catalyst having the concentration gradient of the active metal prepared in the present invention is a catalyst having superior thermal stability and strong durability against carbon deposition, and is a very suitable catalyst for the SMR reaction.

1 is a cross-sectional photograph of the catalyst prepared in Comparative Examples 3 and 2, and a cross-sectional photograph of the catalyst before reduction after calcination, and a cross-sectional photograph of the catalyst after reduction,
2A and 2B are cross-sectional photographs of the catalysts prepared in Comparative Examples 1 to 3 and Examples 1 to 3, and SEM-EDS (Scanning electron microscopy-energy dispersive X-ray spectroscopy) analysis photographs,
3 is an X-ray diffraction graph of the catalysts prepared in Comparative Examples 1 to 3 and Examples 1 to 3,
4 is a graph of the reduction temperature analysis of the catalysts prepared in Comparative Examples 1 to 3 and Examples 1 to 3 through _{H 2 -Temperature programmed reduction (TPR) analysis,}
5 is a transmission electron microscopy (TEM) analysis photograph of the catalysts prepared in Comparative Examples 1 to 3 and Examples 1 to 3,
6 is a graph showing the reaction characteristics of steam methane reforming (SMR) according to the reaction temperature in the catalysts prepared in Example 2, Comparative Example 3, and Comparative Example 5;
7 is a graph showing SMR reaction characteristics according to the space velocity of reactants in the catalysts prepared in Example 2, Comparative Example 2, Comparative Example 3, and Comparative Example 5;
8 is a graph showing SMR reaction characteristics according to harsh environments in the catalysts prepared in Example 2, Comparative Example 3, and Comparative Example 5;
9 is a photograph of catalyst particles for evaluating carbon deposition resistance after SMR reaction of the catalysts prepared in Examples 1 to 3 and Comparative Examples 1 to 5.

Advantages and features of the present invention, and a method of achieving them will become apparent with reference to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms different from each other, and only these embodiments make the disclosure of the present invention complete, and common knowledge in the technical field to which the present invention pertains. It is provided to completely inform the scope of the invention to the possessor, and the invention is only defined by the scope of the claims. With reference to the accompanying drawings below will be described in detail for the implementation of the present invention. Regardless of the drawings, the same reference numerals refer to the same elements, and "and/or" includes each and all combinations of one or more of the recited items.

Unless otherwise defined, all terms (including technical and scientific terms) used in the present specification may be used with meanings that can be commonly understood by those of ordinary skill in the art to which the present invention belongs. When a part of the specification "includes" a certain component, it means that other components may be further included rather than excluding other components unless specifically stated to the contrary. Also, the singular form includes the plural form unless specifically stated in the text.

In this specification, when a part such as a layer, film, region, or plate is said to be “on” or “on” another part, this includes not only the case where the other part is “directly above”, but also the case where there is another part in the middle. do.

Hereinafter, a catalyst for reforming steam methane according to an embodiment will be described.

The steam methane reforming catalyst includes an inorganic oxide support having a spinel structure; And an active metal, wherein the inorganic oxide support has a concentration gradient of the active metal.

The active metal has a concentration gradient from the center of the inorganic oxide support to the surface direction and, as it is supported on the inorganic oxide support, 100% of the catalytic active material is utilized in the steam methane reforming reaction showing a high reaction rate compared to the diffusion rate of the reactant. Since there is an advantage that can be achieved, it can exhibit sufficient activity even if the active metal is supported in a small amount compared to the conventional catalyst. Therefore, a catalyst having a concentration gradient has better thermal stability than a catalyst that does not have a concentration gradient, has strong durability against carbon deposition, and can be very suitable for SMR reaction.

In the catalyst for steam methane reforming according to an embodiment, the concentration gradient of the active metal may increase in a surface direction from the center of the inorganic oxide support.

For example, the inorganic oxide support having a spinel structure is 10% by weight or less, for example, 9% by weight or less, or 8.5% by weight or less with respect to the total weight of the active metal, in a region of 30 length% or less of the radius of the support from the center. It may be to support the active metal of. That is, by selectively supporting the active metal on the surface of the support, even with a small amount of active metal, it exhibits the same level of activity as the existing catalyst, and the performance can be improved at a fast space velocity of the SMR reaction raw material, and carbon deposition and durability are improved. can do.

In addition, the inorganic oxide support having a spinel structure is 50% by weight or more, for example, 55% by weight or more, 60% by weight or more, or 65% by weight, based on the total weight of the active metal, in a region of 30 length% or less of the radius of the support from the surface. % Or more of the active metal may be supported. The catalyst is preferable in terms of improving catalyst durability because it can inhibit carbon from depositing inside the catalyst during the SMR reaction by supporting a small amount of the active metal in the internal region and prevent catalyst destruction by inducing selective carbon growth on the catalyst surface. Do.

The active metal may include one or two or more selected from the group consisting of nickel, platinum, palladium, silver, gold, and ruthenium metals. As the catalyst for the SMR reaction, nickel, noble metal, etc. are generally used as catalytic active materials, and the types of active metals described above can be used without limitation. In general, SMR reactions that produce large amounts of hydrogen use nickel, which is an inexpensive transition metal. When used as a catalyst, it can be good in terms of economy. However, CO generated during the SMR reaction is particularly well adsorbed on the nickel surface, so that a large amount of carbon may be deposited on the surface of the active metal, but in the case of the present invention, since the active metal is selectively supported on the support surface or the catalyst surface as described above. Accordingly, the above carbon deposition problem can be effectively solved.

On the other hand, the active metal may be present in the at least one or two selected from the group consisting of NiAl ₂ O _4, NiO, and Ni, may be present in the well of the NiAl ₂ O _4, NiO, and Ni.

The active metal may be included in an amount of 1 to 10% by weight based on the total weight of the steam methane reforming catalyst, for example, 1% by weight or more and 9% by weight or less, or 1% by weight or more and 7% by weight or less, preferably It may be included in an amount of 1% by weight or more and 5% by weight or less, and most preferably 2% by weight or more and 4% by weight or less. Accordingly, even with a small amount of active metal, the same level of activity as the existing catalyst can be sufficiently achieved, and carbon deposition and durability of the catalyst can be improved.

The inorganic oxide support having a spinel structure may be specifically a spinel structure of MgAl ₂ O ₄ , and the support is selected from the group consisting _{of MgAl 2} O ₄ , NiAl ₂ O ₄ , and MgAl ₂ O ₄ -NiAl ₂ O ₄ It may exist in one or two or more phases. In particular, the inorganic oxide having a spinel structure in the support has excellent heat resistance, and the spinel structure acts as an oxygen carrier, so it is possible to inhibit carbon deposition by preventing oxidation of the active metal and CO adsorbed on the surface of the support during the SMR reaction. have. As a result, it is possible to provide a catalyst having strong durability and excellent thermal stability.

In general, a steam reforming catalyst is used after supporting and reducing a precursor of an active metal to form metallic particles of an active metal. At this time, when the reaction is performed at a high temperature, active metal particles tend to be aggregated. At this time, the support also serves to prevent the aggregation of the active metal. In particular, the spinel structure of MgAl ₂ O ₄ is known to more effectively inhibit the aggregation of catalytically active metals (J. Guo, et. al., Dry reforming of methane over nickel catalysts supported on magnesium aluminate spinels, Appl. Catal. A., 273 (2004) 75-82.). In addition, the inhibition of the aggregation of the active metal means that the high dispersion degree formed at the beginning of the catalyst production is maintained as the reaction proceeds, so as the active specific surface area is maintained high, the advantage of exhibiting high activity even with a small amount of active metal supported. There is this. In addition, carbon deposition on the surface of the catalytically active metal is suppressed, so that durability of the catalyst may be enhanced.

Meanwhile, the inorganic oxide support having a spinel structure may be one or two or more selected from the group consisting of a pellet type, a cylinder type, a tube type, and a spherical shape, but the present invention is not limited thereto.

Hereinafter, a method of preparing the catalyst for steam methane reforming according to another embodiment will be described.

Another embodiment of the present invention relates to a method for preparing the catalyst for steam methane reforming, wherein the method for preparing the catalyst comprises pelleting, cylindrical, tubular, and spherical catalytically active materials by using a repulsive force between a hydrophobic solvent and a hydrophilic solvent. The present invention relates to a method of selectively supporting or impregnating only pores on the surface of a catalyst support formed of one or more particles selected from the group consisting of or in a region close to the outside connected to the surface.

The manufacturing method of the steam methane reforming catalyst includes: a) a first immersion step of impregnating an inorganic oxide support having a spinel structure in a hydrophobic first solvent to prepare an inorganic oxide support filled with a hydrophobic first solvent; b) a second immersion step of impregnating a metal precursor solution in which a hydrophilic second solvent and an active metal precursor are mixed into the inorganic oxide support filled with the hydrophobic first solvent; And c) preparing a catalyst by heat-treating the inorganic oxide support impregnated with the metal precursor solution at 873 to 1273K.

First, a porous inorganic oxide having various types of spinel structures having a spherical or cylindrical shape is prepared as a catalyst support. The porous inorganic oxide support having a spinel structure used in the present invention has micropores formed on the surface and/or inside, and in the group consisting of _{MgAl 2} O ₄ , NiAl ₂ O ₄ , and MgAl ₂ O ₄ -NiAl ₂ O ₄ Any one or two or more selected may be used, and the shape is not particularly limited, but it is suitable in the case of a pellet type, a cylinder type, a tube type, or a spherical shape.

Subsequently, in the a) first immersion step, the inorganic oxide support filled with the hydrophobic first solvent is prepared by impregnating the inorganic oxide support having the spinel structure with the hydrophobic first solvent.

At this time, by using a vacuum distillation method, it is preferable to prepare the hydrophobic first solvent so that it can flow into the porous catalyst support particles having the spinel structure. Conventionally, ultrasonic treatment was performed when immersing the solvent, but in the case of immersing a large amount of solvent, a vacuum distillation method is suitable in terms of securing productivity.

The hydrophobic first solvent may be characterized in that it has a higher viscosity than the hydrophilic second solvent, and specifically, the density of the hydrophobic first solvent may be equal to or higher than the density of the hydrophilic second solvent. The hydrophobic first solvent is preferably a polyhydric alcohol having 2 to 6 carbon atoms, specifically selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexylene glycol, and derivatives and isomers thereof. It is more preferable to use any one or two or more.

When benzene, toluene, hexane, or the like is used as the hydrophobic first solvent, the interaction force between the porous catalyst support and the first solvents is relatively weak. Therefore, when a catalytically active material or a hydrophilic metal precursor solution containing a catalytically active material precursor is impregnated into the porous catalyst support, the hydrophilic metal precursor solution repels benzene, toluene, and hexane and penetrates into the pores of the porous catalyst support particles. can do. That is, solvents with weak interaction power with the porous catalyst support particles, such as benzene, toluene, and hexane, are not suitable for selective impregnation of the catalytically active material of the present invention on the surface of the porous catalyst support.

On the other hand, alcohols having 2 to 6 carbon atoms in the alkyl group (e.g., ethanol, propanol, butanol, pentanol, hexanol, etc.) and polyhydric alcohols such as ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexyl In the case of silene glycol, since the -OH group, which is a functional group of alcohols, has an appropriately strong interaction force with the pore surface of a catalyst support such as porous silica or porous alumina, the pores during the first immersion step and the first drying step described below. Can be fixed inside.

However, in the second immersion step described below, when the metal precursor solution is impregnated into the inorganic oxide support by rotating agitation and reduced pressure distillation instead of simple ultrasonic treatment, a stronger interaction force compared to monohydric alcohols is obtained. Eggplant polyhydric alcohols and at least dihydric or higher alcohols are required as the hydrophobic first solvent.

In addition, when the number of carbon atoms of the alkyl group of the polyhydric alcohol increases between 2 and 6, the viscosity and density of the first solvent increase, so that it becomes more difficult for the hydrophilic metal precursor solution to penetrate to the inner pores of the porous catalyst support particle. Accordingly, while effectively blocking access of the hydrophilic metal precursor solution to pores inside the catalyst support particles, a large amount of the metal precursor solution can be selectively supported or impregnated in the catalyst support. On the other hand, when the number of carbon atoms in the alkyl group of the polyhydric alcohol exceeds the above range, the viscosity and density of the hydrophobic first solvent may become excessively high, so that it may not be easy to remove the solvent after preparing the catalyst.

On the other hand, after sufficiently introducing the hydrophobic first solvent to the internal pores of the catalyst support particles, the first drying step using appropriate drying conditions may be performed so that the hydrophobic first solvent remains only in a specific area inside the particles. The invention is not necessarily limited thereto. When performing the first drying step, the drying temperature is preferably 50° C. lower or 50° C. higher than the boiling point of the hydrophobic first solvent, and the drying time is preferably 1 minute to 120 minutes. However, the dryness temperature and time of the first drying step vary depending on the amount of the first hydrophobic solvent remaining in the pores of the porous catalyst support particles through the first drying step, or depending on the type of the hydrophobic first solvent used. Of course, it can be adjusted accordingly. For example, by passing through the first drying step, a hydrophobic first solvent on the surface of the catalyst support and an area of 30 length% or less of the support radius from the surface of the catalyst support, preferably 50 length% or less, more preferably 70 length% The hydrophobic first solvent filled in the inner pores of the following regions may be removed. Through this drying step, the first hydrophobic solvent may remain only in the pores inside the catalyst support.

Subsequently, in step b), a metal precursor solution in which a hydrophilic second solvent and an active metal precursor are mixed is impregnated into the inorganic oxide support filled with the hydrophobic first solvent.

At this time, a specific region inside the porous catalyst support, that is, the hydrophobic first solvent filled in the inner region is characterized by having a higher viscosity and the same or higher density than the hydrophilic second solvent. Accordingly, the hydrophilic metal precursor solution is difficult to impregnate to the inner region of the porous catalyst support filled with the hydrophobic first solvent, and thus is filled only in the surface region of the catalyst support and the outer pore region near the surface.

In the step b), the metal precursor solution may be impregnated into the inorganic oxide support by rotary stirring and distillation under reduced pressure. When a large amount of metal precursor solution is selectively immersed or impregnated in the inorganic oxide support, rotational stirring and vacuum distillation may be appropriate in terms of securing productivity.

The rotary agitation may apply a known technique in the same technical area, and the present invention is not limited thereto. When the metal precursor solution is impregnated into the inorganic oxide support by rotary stirring and reduced pressure distillation, it is possible to suppress the solidification of the metal precursor solution, achieve homogenization and refinement of catalyst particles, and temperature homogenization. It is preferable because immersion or impregnation can be effectively performed.

The metal precursor solution used in step b) is characterized in that the catalytically active material or the catalytically active material precursor is dissolved in a hydrophilic second solvent, and the metal precursor is a water-soluble metal salt.

The water-soluble metal salt is preferably a water-soluble salt of a metal containing one or two or more selected from the group consisting of nickel, platinum, palladium, silver, gold and ruthenium metal, and more preferably a water-soluble salt of nickel.

As the hydrophilic second solvent, a polar solvent is preferable, and water, which is a representative polar solvent, is preferably used.

Subsequently, in step c), the inorganic oxide support impregnated with the metal precursor solution is heat-treated at 873 to 1273 K to prepare a catalyst. For example, step c) may be characterized in that after drying at 323 to 423K for 0.5 to 2 hours, heat treatment at 873 to 1273K for 1 to 3 hours.

The drying is performed by drying the porous catalyst support particles that have passed through the second immersion step to remove the hydrophobic first solvent and the hydrophilic second solvent remaining on the surface and internal pores of the porous catalyst support, and the catalytically active material or the catalytically active material The precursor of the porous catalyst support remains only in a region where the hydrophilic metal precursor solution was present on the surface of the porous catalyst support and the active metal can be selectively left only on the surface portion of the formulated catalyst support.

The heat treatment may be to prepare a catalyst by heat treatment under conditions of 973 to 1173K, preferably 1023 to 1123K, more preferably 1050 to 1100K in an air atmosphere, a heating time of 4 to 6 hours and a holding time of 1 to 3 hours.

Another embodiment of the present invention provides a method for producing a syngas through a steam reforming reaction of methane using the steam methane reforming catalyst.

The synthesis gas production method through the steam reforming reaction of methane is characterized in that in the presence of the steam methane reforming catalyst, methane and water vapor are injected at a molar ratio of 1:1 to 1:3 while reacting.

The steam methane reforming catalyst is as described above, and the methane and steam are injected in a molar ratio of 1:1 to 1:3, and preferably in a molar ratio of 1:2 to 1:3. In the case of a catalyst in which an active metal was supported without a concentration gradient in the support, the problem of catalyst collapse occurred due to carbon deposition due to the adsorption of CO on the surface of the active metal, and to solve this problem, water vapor was injected at a higher ratio compared to methane. The activity was lowered and the production of syngas was lowered. In the case of the present invention, since the active metal having a concentration gradient is selectively supported on the surface of the support, the ratio of water vapor injection to methane can be reduced to the above numerical range, which may lead to an increase in the production of syngas.

The steam reforming reaction of methane may be to react at a temperature of 973 to 1273K for 1 to 5 hours, preferably at a temperature of 973 to 1200K, or 973 to 1073K, to react for 1 to 5 hours. The steam reforming reaction of methane was analyzed to be greatly influenced by the amount of active metal supported on the catalyst as the reaction temperature increased, and the activity of the catalyst selectively supported on the surface of the inorganic oxide supporter of the present invention in the reaction temperature range It was the most effective. In addition, when the reaction temperature is excessively high, an autothermal reforming reaction, which is a combination of steam reforming and partial oxidation, occurs, which is not preferable in terms of the steam reforming reaction of methane of the present invention. Does not. On the other hand, the inorganic oxide support, in particular, _{MgAl 2 O 4, NiAl 2 O} 4, MgAl ₂ O ₄ and -NiAl steam reforming of methane by using the one or more than one support selected from the group consisting of ₂ O ₄ having a spinel structure It is preferable because it has excellent heat resistance in a high temperature range in which the reaction proceeds, thereby improving catalyst durability, and more effectively suppressing carbon deposition due to the spinel structure of the inorganic oxide support.

The steam reforming reaction of methane may be to react while injecting methane and steam at a space velocity (WHSV) of 6,000 to 24,000 mL/(h·g _cat ), preferably 12,000 to 24,000 mL/(h·g _cat ) or It may be injected at a space velocity of 6,000 to 12,000 mL/(h·g _cat ), more preferably 14,000 to 24,000 mL/(h·g _cat ) or 18,000 to 24,000 mL/(h·g _{cat ).} As the catalyst of the present invention improves high temperature stability and durability, it is possible to further improve catalytic activity at a faster space velocity compared to a conventional catalyst.

Hereinafter, preferred examples and comparative examples of the present invention will be described. However, the following examples are only preferred examples of the present invention, and the present invention is not limited to the following examples.

Example

Comparative Examples 1 to 4

After impregnating a nickel precursor (Nickel nitrate hexahydrate (Sigma aldrich, 98%) at various concentrations into _{MgAl 2} O ₄ pellets using a vacuum distillation method, drying for 1 hour at 373 K, 1073 K under air (5 hours heating, 2 maintenance) Time) to prepare a catalyst.

Comparative Examples 1 to 4 were prepared so that the nickel metal was included in 3.5% by weight, 5% by weight, 10% by weight, and 2% by weight, respectively, based on the total weight of the _{MgAl 2} O _{4 pellet and the nickel metal.}

Comparative Example 5

MgAl ₂ O ₄ pellet nickel metal is 15 wt% (Com-R, ^{manufacturer: Clariant, HyProGen ® R-70} ) A commercial catalyst supported on the used.

Examples 1 to 3

After immersing the MgAl ₂ O ₄ pellet in a hydrophobic solvent (ethylene glycol), a hydrophobic solvent was supported inside the pellet using a vacuum distillation method.

The sifted pellets were impregnated with nickel precursors (Nickel nitrate hexahydrate, Sigma aldrich, 98%) at various concentrations using a vacuum distillation method, dried at 373 K for 1 hour, and then dried at 373 K for 1 hour, followed by 1073 K in air (heating 5 hours, maintaining 2 hours). ) To prepare a catalyst.

Examples 1 to 3 were prepared so that nickel metal was contained in an amount of 2% by weight, 3.5% by weight, and 5% by weight based on the total weight of the _{MgAl 2} O _{4 pellet and the nickel metal.}

Evaluation example

Evaluation Example 1: Cross-sectional photographing of the prepared catalyst and Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analysis

The distribution of nickel concentration at each point inside the pellet of the catalyst was confirmed through cross-sectional photographing and SEM-EDS analysis of the catalysts prepared in Comparative Examples 1 to 3 and Examples 1 to 3.

The concentration at each point of the scaffold was compared through Scanning Electron Microscopy-Energy dispersive X-ray spectroscopy (SEM-EDS) analysis. Specifically, the amount of nickel supported was analyzed using the blue point as the point. As a result, graphs and cross-sectional images It is shown in Figure 2a by overlapping. The results of all the prepared catalysts are shown in Figure 2b.

Referring to FIGS. 2A and 2B, it was possible to confirm a large difference in the nickel concentration distribution for each of the catalysts of Comparative Examples 1 to 3 without a concentration gradient and the catalysts of Examples 1 to 3 having a concentration gradient. The catalyst prepared in a form without a concentration gradient showed that the distribution of nickel concentration inside the pellet was almost constant, and the catalyst prepared in a form with a concentration gradient confirmed that the concentration of nickel was high only in both outer portions of the pellet. Through this, it was confirmed that the catalyst having a concentration gradient was well prepared.

Evaluation Example 2: Analysis of Structural Characteristics of the Prepared Catalyst

(1) X-ray diffraction (XRD) analysis of the catalysts prepared in Examples 1 to 3 and Comparative Examples 1 to 3

Each prepared catalyst was sampled by grinding in a mortar. XRD pattern after firing of the catalyst prepared in the form without the concentration gradient of Comparative Examples 1 to 3 in FIG. 3 (a), and the catalyst prepared in the form with the concentration gradient of Examples 1 to 3 in FIG. 3 (b) Shown.

Referring to Figure 3, the catalyst prepared through XRD analysis was confirmed that the MgAl ₂ O ₄ , NiAl ₂ O ₄ , NiO phase is the main phase constituting the prepared catalyst, and the catalyst without a concentration gradient and the catalyst with a concentration gradient. It was confirmed that there were no structural differences in the XRD pattern.

(2)H ₂ -Analysis of the reduction temperature of the catalysts prepared in Examples 1 to 3 and Comparative Examples 1 to 3 through Temperature Programmed Reduction (TPR) analysis

Each prepared catalyst was sampled by grinding in a mortar. _{The results of H 2} -TPR analysis to determine the reduction temperature of the prepared catalyst are shown in FIG. 4.

Referring to FIG. 4, the MgAl ₂ O ₄ support itself has a very small reduction peak and a peak is located at a temperature lower than the reduction temperature of the prepared catalyst. Through this, it was confirmed that the support did not affect the reduction temperature of the prepared catalyst. Reduction peak of the prepared catalyst was formed in a more than 1000 K the temperature is equivalent to reducing the temperature of the NiAl ₂ O _4, the main structure to affect the reduction in the produced catalyst was identified as NiAl ₂ O _4. In addition, the degree of peak depended on the amount of nickel impregnated. As the amount of nickel impregnated increased, the intensity of the peak increased, and the behavior of the reduction peak of the catalyst without concentration gradient and the catalyst with concentration gradient was similar.

(3) Confirmation of nickel particle size through transmission electron microscopy (TEM) analysis

Each of the prepared catalysts was ground in a mortar, _{and reduction was performed at 1073K for 2 hours under 10 vol.% H 2} /N ₂ conditions (total flow rate = 100 mL/min) (heating 2 hours 30 minutes, holding 2 Time), TEM analysis results, and nickel particle sizes are shown in Fig. 5 and Table 1, respectively.

Nickel particle size (nm) Comparative Example 1 10~16 Comparative Example 2 10-20 Comparative Example 3 10-25 Example 1 6-10 Example 2 8-12 Example 3 8-14

Referring to the TEM results of FIG. 5 and the nickel particle size in Table 1, it was confirmed that the larger the nickel content, the larger the nickel particle size. This behavior was similar for the catalyst without concentration gradient and the catalyst with concentration gradient.

However, when reviewed in connection with FIG. 2B, when examining the nickel concentration on the surface of the support of Comparative Example 2 and Example 2, it can be seen that they are similar at 5 wt%, respectively, but in FIG. 6, Comparative Example 2 is a nickel particle compared to Example 2 It was found that the size was large and the distribution was small. That is, in the case of a catalyst without a concentration gradient, it was confirmed that agglomeration of nickel metal particles occurred after catalyst reduction. From these results, the catalyst with a concentration gradient has a high nickel content on the surface of the support despite supporting nickel in a small amount, and as the agglomeration of nickel metal particles is suppressed despite the high nickel content on the support surface, the catalytic activity is reduced. It turns out to be very good.

In conclusion, the supported amount of nickel in the commercial catalyst is relatively high, such as 10% by weight or more and 20% by weight or less, but the present invention selectively supports nickel only on the surface and effectively uses it. A minimum of 1% by weight was sufficient to proceed with the steam reforming reaction.

Evaluation Example 3: SMR reaction characteristics of the catalyst

(1) The manufactured pellet catalyst is pulverized and applied to the SMR reaction.

After the catalysts prepared in Example 2, Comparative Example 3, and Comparative Example 5 were placed in a mortar, only catalyst particles having a particle size of 100 to 212 µm were selected and used.

The catalyst was subjected to SMR reaction in a 1/4-inch fixed bed reactor. Under the condition of 10 vol.% H ₂ /N ₂ before the reaction (total flow = 100 mL/min) 1073K (heating 2 hours and 30 minutes, maintenance 2 hours) after the reduction process, steam (H ₂ O) and carbon (methane) SMR reaction was performed with a ratio of 3:1 (reaction temperature: 973 K, 1073 K, weight hourly space velocity (WHSV) = 7,200 mL·g _cat ^-1 ·h ^-1 ), and the results are shown in FIG. Indicated.

Referring to FIG. 6, Comparative Example 5 (15wt%), a commercial catalyst, had the highest nickel content than the prepared catalysts, and thus had the highest methane conversion rate at each reaction temperature, and the prepared catalyst had a nickel content at a high reaction temperature. The high methane conversion rate of Comparative Example 3 (10 wt%) was higher than that of the catalyst of Example 2 (3.5 wt%) having a relatively low nickel content. However, at lower reaction temperatures, the catalyst's methane conversion rate was similar for both catalysts. In conclusion, it was confirmed that the conversion rate of methane at high temperature was more influenced by the nickel content.

(2) Applied to the SMR reaction of the manufactured pellet catalyst

The catalysts prepared in Comparative Example 5 (commercial catalyst), Example 2, and Comparative Examples 2 and 3 were tested in the form of pellets.

SMR reaction was carried out in a 1-inch fixed bed reactor, and _{steam (H 2} O) after 1073 K (heating 2 hours and 30 minutes, maintenance 2 hours) reduction process under the condition of _{20 vol.% H 2} /N _{2 before the reaction.} The SMR reaction was performed with a ratio of carbon (methane) to 3:1 (reaction temperature: 973, 1073 K, WHSV = 6,000-24,000 mL·g _cat ^-1 ·h ^-1 ), and the results are shown in FIG. 7 Indicated.

7 is a graph showing the results after SMR reaction experiments of the pellet catalysts prepared in Comparative Example 5 (commercial catalyst), Example 2, Comparative Examples 2 and 3 at various space velocities. Referring to FIG. 7, the methane conversion rates of all catalysts decreased as the space velocity increased. In addition, the methane conversion rate of the prepared catalysts was higher than that of the commercial catalyst. Comparing only catalysts without a concentration gradient, the higher the nickel content, the higher the methane conversion rate. However, the catalyst of Example 2 (nickel metal content 3.5 wt%), which is a catalyst having a concentration gradient, has a lower nickel content than the catalyst in Comparative Example 2 (nickel metal content 5 wt%), but shows a high methane conversion rate at the total space velocity. Methane conversion rate was lower than 3 (nickel metal content 10wt%). In the above-described experimental results of the powder catalyst, considering that the nickel content is a factor affecting the methane conversion rate, it can be seen that this experiment shows a completely different aspect. However, in connection with FIG. 2B, when the catalysts in the order of the higher nickel content in both outer portions of the prepared catalyst are listed in the order of Comparative Example 3, Example 2, and Comparative Example 2. This is certainly a meaningful result by applying the theory that the SMR reaction occurs only on the outer surface of the pellet catalyst.

As a result of this experiment, it was confirmed that the SMR reaction occurred only on the outer surface of the pellet catalyst, and the nickel distribution of the catalyst having a concentration gradient had an influence on the SMR reaction even with the use of a small amount of nickel.

(3) Applied to the SMR reaction of the manufactured pellet catalyst under severe conditions

The catalysts prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were tested in the form of pellets.

The catalyst was subjected to SMR reaction in a 1-inch fixed bed reactor, and after the reduction process at 1073 K (2 hours and 30 minutes of heating, 2 hours of maintenance) under the condition of _{20 vol.% H 2} /N _{2 before the reaction, steam (H 2} O) and carbon (methane) ratio of 0.5:1 was carried out SMR reaction (reaction temperature: 973 K, WHSV = 14,000 mL·g _cat ^-1 ·h ^-1 , reaction time: 6 h). Among them, the reaction results (methane conversion rate) of Example 2 and Comparative Examples 3 and 5 are shown in FIG. 8.

In addition, in FIG. 9, after performing the SMR reaction under severe conditions, the pellet catalyst was recovered, and the change in the color or shape of the pellets was shown as a photograph.

Referring to FIG. 8, this experiment shows the results of an experiment under severe conditions with a ratio of steam and methane of 0.5:1 in order to confirm the carbon deposition resistance of the commercial catalyst and the prepared catalyst. As a result, it was confirmed that there was no significant difference in the conversion rate of methane.

However, there was a very large difference in the recovered catalyst after the reaction was over. Referring to FIG. 9, the catalysts of Comparative Example 5 and Comparative Example 3 were broken so that the shape of the catalyst was not recognizable, and Comparative Example 2 also confirmed that the outer surface of the pellet was partially broken. However, it was confirmed that the pellets were not broken in the catalysts having a concentration gradient (Examples 1 to 3) and a catalyst without a concentration gradient having a low nickel content (Comparative Example 4). Normal carbon deposition occurs on nickel particles. The higher the nickel content and the better the nickel is dispersed in the pellet, the more carbon is deposited in the nickel particles inside the pellet, and the pellet is cracked while stress is applied to the pellet. Therefore, the catalysts of Comparative Example 5 and Comparative Example 3 were crushed to such an extent that the shape cannot be recognized as shown in FIG. 9, and it was found that the catalyst of Comparative Example 2 having a relatively low nickel content was partially damaged. However, catalysts with a concentration gradient do not have a relatively internal stress compared to catalysts without a concentration gradient because nickel is concentrated only on the outer surface of the pellet, and there is less risk of pellet crushing due to carbon deposition only on the outside. Through this phenomenon, it was confirmed that the catalyst having a concentration gradient is a catalyst with strong resistance to carbon deposition and is more suitable for SMR reaction.

(4) Analysis of carbon deposition in catalyst through thermo gravimetric analysis (TGA) after SMR reaction under severe conditions

After the SMR reaction, each catalyst was ground in a mortar to analyze the amount of carbon deposition. After the SMR reaction was completed, the weight reduced by heating (TGA) by flowing air based on the weight of the recovered catalyst sample was converted to the amount of carbon deposited, and the weight reduced to the total weight of the catalyst sample was calculated as a percentage, and the following Table 2 shows Coke. It was described as the total production amount.

On the other hand, when the total amount of Coke produced is 50% by weight, it means that 50% by weight of the sample recovered after the SMR reaction is deposited carbon, and 100% by weight means that the entire sample is made of carbon.

Nickel metal content
(weight%) Total amount of coke produced
(weight%) Comparative Example 5 15 50.0 Comparative Example 3 10 39.5 Comparative Example 2 5 15.0 Comparative Example 1 3.5 11.3 Comparative Example 4 2 1.5 Example 1 2 1.1 Example 2 3.5 2.5 Example 3 5 10.0

As shown in Table 2, the greater the content of nickel, and when nickel is supported in the support without a concentration gradient, the amount of carbon deposition is greater. When the results of the shape of the pellet and the amount of carbon deposition after the SMR reaction under severe conditions are combined, nickel has a concentration gradient and has a high resistance to carbon deposition when supported, so the catalyst with the concentration gradient is the SMR reaction. It was confirmed that it is more suitable for.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, but may be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains to the technical idea of the present invention. It will be appreciated that it can be implemented in other specific forms without changing any or essential features. Therefore, it should be understood that the embodiments described above are illustrative in all respects and are not limiting.

Claims (20)

Inorganic oxide support having a spinel structure; And an active metal,
The inorganic oxide support, characterized in that having a concentration gradient of the active metal, steam methane reforming catalyst. In claim 1,
The active metal comprises one or two or more selected from the group consisting of nickel, platinum, palladium, silver, gold and ruthenium metals, steam methane reforming catalyst. In claim 1,
The active metal is NiAl ₂ O ₄ , NiO, and a catalyst for steam methane reforming comprising one or more phases selected from the group consisting of Ni. In claim 1,
The concentration gradient of the active metal is in the form of increasing in the surface direction from the center of the inorganic oxide support, steam methane reforming catalyst. In claim 1,
The inorganic oxide support having the spinel structure,
In the area of less than 30% of the length of the radius of the support from the center,
A catalyst for steam methane reforming that supports 10% by weight or less of an active metal based on the total weight of the active metal. In claim 1,
The inorganic oxide support of the spinel structure,
In the area of less than 30% of the length of the radius of the support from the surface,
A catalyst for steam methane reforming that supports 50% by weight or more of an active metal based on the total weight of the active metal. In claim 1,
The active metal is contained in an amount of 1 to 10% by weight based on the total weight of the steam methane reforming catalyst. In claim 1,
The active metal is contained in an amount of 1 to 5% by weight based on the total weight of the steam methane reforming catalyst. In claim 1,
The inorganic oxide support having the spinel structure is one or two or more selected from the group consisting _{of MgAl 2} O ₄ , NiAl ₂ O ₄ , and MgAl ₂ O ₄ -NiAl ₂ O _{4, a catalyst for steam methane reforming.} In claim 1,
The inorganic oxide support having a spinel structure is one or two or more selected from the group consisting of a pellet type, a cylinder type, a tube type, and a spherical shape, a catalyst for steam methane reforming. a) a first immersion step of impregnating an inorganic oxide support having a spinel structure with a hydrophobic first solvent to prepare an inorganic oxide support filled with the hydrophobic first solvent;
b) a second immersion step of impregnating a metal precursor solution in which a hydrophilic second solvent and an active metal precursor are mixed into the inorganic oxide support filled with the hydrophobic first solvent; And
c) preparing a catalyst by heat-treating the inorganic oxide support impregnated with the metal precursor solution at 873 to 1273K. In clause 11,
In the step a), the hydrophobic first solvent is impregnated into the inorganic oxide support by vacuum distillation. In clause 11,
In the step b), the metal precursor solution is impregnated into the inorganic oxide support by rotary stirring and distillation under reduced pressure. In clause 11,
The first hydrophobic solvent has a viscosity higher than that of the second hydrophilic solvent. In clause 11,
The first hydrophobic solvent is a method for producing a catalyst for steam methane reforming, characterized in that a polyhydric alcohol having 2 to 6 carbon atoms. In clause 11,
The metal precursor is a water-soluble metal salt, a method for producing a catalyst for steam methane reforming. In clause 11,
The step c) is a method for producing a catalyst for steam methane reforming comprising drying at 323 to 423 K for 0.5 to 2 hours and then heat treatment at 873 to 1273 K for 1 to 3 hours. Synthetic gas production through steam reforming reaction of methane, characterized in that in the presence of the catalyst for steam methane reforming of any one of claims 1 to 10, injecting methane and steam at a molar ratio of 1:1 to 1:3. Way. In paragraph 18,
The reaction is a method for producing syngas through steam reforming of methane, characterized in that the reaction is carried out at 973 to 1273K. In paragraph 18,
Synthetic gas production method through a steam reforming reaction of methane, characterized in that the reaction while injecting the steam and methane at a space velocity of 6,000 to 24,000 mL/(h·g _cat).

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