KR102298272B1 - 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 an SMR reactor for a hydrogen charging station into a catalyst having excellent thermal stability and strong resistance to carbon deposition. Since the catalyst for SMR reaction requires the pellet catalyst to have high thermal stability in order to maintain a high reaction temperature, pellets made of inorganic oxide having excellent thermal stability and having a spinel structure were selected as the catalyst support. The SMR reaction exhibits a very high reaction rate compared to the diffusion rate of the reactant, so that most of the reaction occurs on the surface of the pellet, making it difficult to effectively use the active metal. In order to solve this problem, in the present invention, a catalyst having a concentration gradient in which the active metal is selectively supported only on the outer surface of the pellet was prepared. For reactivity comparison, a catalyst without a concentration gradient in which the active metal is evenly supported throughout the pellet was also prepared. As a result, the catalyst with the concentration gradient showed that the durability of the pellets and the degree of carbon deposition in the SMR reaction under severe conditions were superior to the catalyst without the concentration gradient and the commercial catalyst. It was confirmed that the catalyst with a concentration gradient is more suitable for the SMR reaction.

Description

Catalyst for steam methane reforming reaction having a concentration gradient of active metal on an inorganic oxide support having a spinel structure, a preparation method thereof, and a synthesis gas production method using the catalyst 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 steam methane reforming reaction supported with a concentration gradient of an active metal on an inorganic oxide support having a spinel structure, a method for preparing the same, and a method for producing synthesis gas using the catalyst.

Steam methane reforming (SMR) reaction is a mixture of hydrogen (H ₂ ) and carbon monoxide (CO) by reacting water (H _{2 O) with methane (CH 4 ) as shown in the following formula Synthetic gas (synthetic gas)} is a reaction that produces

CH ₄ + H ₂ O → CO + 3H ₂ (SMR)

In general, in the SMR reaction that produces a large amount of hydrogen, nickel (Ni), noble metals (Pt, Pd, Ag, Au, and Ru), etc. are used as catalytically active materials, and among them, nickel, a low-cost transition metal, is suitable. [D. E. Ridler, M. V. Twigg, in: MV Twigg (Ed.), Catalyst Handbook, 2nd Edition, Wolfe, London, 1989, p. 225.] On the other hand, CO generated during the SMR reaction is adsorbed on the surface of the active metal, so that the Boudouard reaction in which carbon is deposited can occur as shown in the following equation.

2CO ↔ CO ₂ + C (coke)

Therefore, in order to prevent this carbon deposition reaction, an excess of steam 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.

Commercial SMR reaction uses a catalyst in the form of pellets, and since it shows a very high reaction rate compared to the diffusion rate of the reactants, the SMR reaction occurs only on the 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 supported on the entire pellet is very low. In order to overcome this problem, studies on a type of catalyst having a concentration gradient by supporting the catalytically active material only on the outer surface of the pellets are 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. Catalysts for SMR reaction are generally used as active metals such as nickel and noble metals, and are in the form of pellets. These catalysts require 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 reactants, so that the SMR reaction occurs only on the surface of the pellet, so that 100% of the catalyst active material cannot be utilized.

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

One embodiment is an inorganic oxide support having a spinel structure; and an active metal, wherein the inorganic oxide support provides a catalyst for steam methane reforming, characterized in that it 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 metal.

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 be increased in the surface direction from the center of the inorganic oxide support.

The inorganic oxide support having the spinel structure may support 10 wt% or less of active metal based on the total weight of active metal in a region of 30 length% or less of the radius of the support from the center.

The inorganic oxide support having the spinel structure may support 50 wt% or more of the active metal 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.

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 catalyst for steam methane reforming.

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 cylindrical type, a tubular type, and a spherical type.

Another embodiment includes a) a first immersion step of impregnating the inorganic oxide support having a spinel structure with a hydrophobic first solvent to prepare an inorganic oxide support filled with the first hydrophobic 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 1273 K to prepare a catalyst.

Step a) may be to impregnate the inorganic oxide support with the hydrophobic first solvent by vacuum distillation.

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

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

The hydrophobic first 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-treating 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 in a molar ratio of 1:1 to 1:3 and reacted. .

The synthesis gas production method may be characterized in that the reaction at 973 to 1273K.

The synthesis gas production method may be characterized by reacting while injecting water vapor 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 aggregation of active metals.

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

In addition, since there is no active material inside the catalyst in the SMR reaction, it is possible to suppress the deposition of carbon inside and to prevent the destruction of the catalyst as carbon growth occurs selectively on the catalyst surface.

Therefore, the catalyst having a concentration gradient of active metal prepared in the present invention is excellent in thermal stability than a catalyst without a concentration gradient, and is a catalyst having strong durability against carbon deposition, and is a very suitable catalyst for SMR reaction.

1 is a cross-sectional photograph of the catalyst before reduction after calcination of the catalysts prepared in Comparative Examples 3 and 2, and a cross-sectional photograph of the catalyst after reduction;
2a and 2b are cross-sectional photographs and SEM-EDS (Scanning electron microscopy-energy dispersive X-ray spectroscopy) analysis photographs of the catalysts prepared in Comparative Examples 1 to 3 and Examples 1 to 3;
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 showing 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 SMR (steam methane reforming) reaction characteristics according to the reaction temperature in the catalysts prepared in Example 2, Comparative Example 3 and Comparative Example 5;
7 is a graph showing the SMR reaction characteristics according to the space velocity of the 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 the carbon deposition resistance after the 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 methods of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in a variety of different forms, and only these embodiments allow the disclosure of the present invention to be complete, and common knowledge in the technical field to which the present invention belongs It is provided to fully inform the possessor of the scope of the invention, and the present invention is only defined by the scope of the claims. Detailed contents for carrying out the present invention will be described in detail with reference to the accompanying drawings below. Regardless of the drawings, like reference numbers refer to like elements, and "and/or" includes each and every combination of one or more of the recited items.

Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used with meanings commonly understood by those of ordinary skill in the art to which the present invention belongs. In the entire specification, when a part "includes" a certain component, this means that other components may be further included, rather than excluding other components, unless otherwise stated. The singular also includes the plural, unless the phrase specifically states otherwise.

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

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

The catalyst for steam methane reforming 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 catalytically active material is utilized in the steam methane reforming reaction, which shows a high reaction rate compared to the diffusion rate of the reactant. Since there is an advantage that can be achieved, it is possible to exhibit sufficient activity even if the active metal is supported in a small amount compared to the conventional catalyst. Therefore, a catalyst with a concentration gradient has better thermal stability than a catalyst without 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 one embodiment, the concentration gradient of the active metal may be in the form of increasing from the center of the inorganic oxide support to the surface direction.

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

In addition, the inorganic oxide support of the spinel structure, in a region of 30% by length or less of the radius of the support from the surface, 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. % or more of the active metal may be supported. The catalyst suppresses the deposition of carbon inside the catalyst during the SMR reaction by supporting an active metal in a small content in the inner region and can prevent catalyst destruction by inducing selective carbon growth on the catalyst surface, which is preferable in terms of improving catalyst durability do.

The active metal may include one or two or more selected from the group consisting of nickel, platinum, palladium, silver, gold and ruthenium metal. As a catalyst for SMR reaction, nickel, noble metal, etc. are generally used as catalytically active materials, and the above-described active metal types can be used without limitation. When used as a catalyst, it may be good in terms of economy. However, the CO generated during the SMR reaction is particularly well adsorbed on the nickel surface, so that a large amount of carbon can be deposited on the surface of the active metal. Accordingly, the above-mentioned 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 wt% based on the total weight of the catalyst for steam methane reforming, for example, 1 wt% or more and 9 wt% or less, or 1 wt% or more and 7 wt% or less, preferably 1 wt% or more and 5 wt% or less, and most preferably, 2 wt% or more and 4 wt% or less may be included. Accordingly, even with a small amount of active metal, the same level of activity as that of the existing catalyst can be sufficiently produced, and the carbon deposition degree and durability of the catalyst can be improved.

The inorganic oxide support having the spinel structure may specifically be MgAl ₂ O ₄ having a spinel structure, and the support may be MgAl ₂ O ₄ , NiAl ₂ O ₄ , and MgAl ₂ O ₄ -NiAl ₂ O ₄ Selected from the group consisting of 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 since the spinel structure acts as an oxygen carrier, oxidation of active metal and CO adsorbed on the surface of the support during SMR reaction can be prevented, thereby suppressing carbon deposition. have. As a result, it is possible to provide a catalyst having strong durability and excellent thermal stability.

In general, the steam reforming catalyst is used after the active metal precursor is supported and reduced to form active metal particles in a metallic state. At this time, when the reaction is carried out at a high temperature, the active metal particles tend to agglomerate. In this case, the support also serves to prevent aggregation of the active metal. In particular, MgAl ₂ O ₄ having a spinel structure 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, since the inhibition of active metal aggregation means that the high dispersion degree formed at the beginning of catalyst preparation is maintained as the reaction proceeds, the active specific surface area is maintained high, so that high activity can be exhibited even with a small amount of active metal supported. There is this. In addition, carbon deposition on the surface of the catalytically active metal may be suppressed, thereby enhancing the durability of the catalyst.

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

Hereinafter, a method for 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 uses the repulsive force between a hydrophobic solvent and a hydrophilic solvent to form a catalytically active material in pellets, cylinders, tubes and spheres. It relates to a method of selectively supporting or impregnating the surface of a catalyst support formed of one or more particles selected from the group consisting of or only pores in a region close to the outside connected to the surface.

The method for preparing the catalyst for steam methane reforming includes: a) a first immersion step of impregnating an inorganic oxide support having a spinel structure in a first hydrophobic solvent to prepare an inorganic oxide support filled with the first hydrophobic 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, porous inorganic oxides having various types of spinel structures having a spherical or cylindrical shape are prepared as catalyst supports. The porous inorganic oxide support having a spinel structure used in the present invention has micropores formed on the surface and/or inside, MgAl ₂ O ₄ , NiAl ₂ O ₄ , and MgAl ₂ O ₄ -NiAl ₂ O _{4 From} the group consisting of Any one or two or more selected may be used, and the shape is not particularly limited, but it is appropriate in the case of a pellet type, a cylinder type, a tubular type, or a spherical type.

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

In this case, it is preferable to prepare the hydrophobic first solvent to be introduced into the porous catalyst support particles having the spinel structure by using the reduced pressure distillation method. Conventionally, ultrasonic treatment was performed during solvent immersion, but when a large amount of solvent is immersed, vacuum distillation is appropriate 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 the same as or higher than that 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 solvent is relatively weak. Therefore, when the porous catalyst support is impregnated with a hydrophilic metal precursor solution including a catalytically active material or a precursor of a catalytically active material, the hydrophilic metal precursor solution penetrates to the internal pores of the porous catalyst support particles while pushing out benzene, toluene, and hexane. can do. That is, solvents having a weak interaction force with the porous catalyst support particles, such as benzene, toluene, and hexane, are not suitable for selectively impregnating the surface of the porous catalyst support with the catalytically active material of the present invention.

On the other hand, alcohols having between 2 and 6 carbon atoms in the alkyl group (eg, ethanol, propanol, butanol, pentanol, hexanol, etc.) and polyhydric alcohols such as ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, and hexyl alcohol In the case of silene glycol, etc., 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, pores during the first immersion step and the first drying step described below. It can be fixed inside.

However, in the second immersion step described below, in the case where the metal precursor solution is impregnated into the inorganic oxide support by rotational stirring and vacuum distillation rather than simple sonication, a stronger interaction force compared to monohydric alcohols Polyhydric alcohols, at least dihydric or higher alcohols, are required as the first hydrophobic 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, making it more difficult for the hydrophilic metal precursor solution to penetrate to the internal pores of the porous catalyst support particles, and thus Accordingly, it is possible to effectively block the access of the hydrophilic metal precursor solution to the internal pores of the catalyst support particles, and at the same time, it is possible to selectively support or impregnate a large amount of the metal precursor solution 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 first hydrophobic solvent may be excessively increased, so that it may not be easy to remove the solvent after the catalyst is prepared.

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

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

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

In step b), the metal precursor solution may be impregnated into the inorganic oxide support by rotary stirring and vacuum distillation. When a large amount of a 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 stirring can be applied to a known technique in the same technical field, the present invention is not limited thereto. When the metal precursor solution is impregnated into the inorganic oxide support by rotary stirring and vacuum distillation, solidification of the metal precursor solution can be suppressed, and homogenization and refinement of catalyst particles, temperature homogenization, etc. can be achieved. 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 a precursor of the catalytically active material 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 including 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.

The hydrophilic second solvent is preferably a polar solvent, and water, which is a representative polar solvent, is preferably used.

Then, 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 for 0.5 to 2 hours at 323 to 423K, heat treatment at 873 to 1273K for 1 to 3 hours.

In the drying, when the hydrophobic first solvent and the hydrophilic second solvent remaining on the surface and internal pores of the porous catalyst support are removed by drying the porous catalyst support particles that have undergone the second immersion step, the catalytically active material or the catalytically active material Since the precursor of the porous catalyst remains only on the surface of the porous catalyst support and the region where the hydrophilic metal precursor solution near the surface was present, it is possible to selectively leave the active metal only on the surface of the formulated catalyst support.

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

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

The synthesis gas production method through the steam reforming reaction of methane is characterized in that the reaction is performed while injecting methane and steam in a molar ratio of 1:1 to 1:3 in the presence of the catalyst for steam methane reforming.

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

The steam reforming reaction of methane may be a reaction for 1 to 5 hours at a temperature of 973 to 1273K, preferably, a reaction for 1 to 5 hours at a temperature of 973 to 1200K, or 973 to 1073K. It was analyzed that the steam reforming reaction of methane is greatly affected by the amount of active metal supported on the catalyst as the reaction temperature increases, and the activity of the catalyst selectively supported on the surface of the inorganic oxide support of the present invention in the reaction temperature range is was the most effective. In addition, if the reaction temperature is excessively high, an autothermal reforming reaction, which is a combination of steam reforming and partial oxidation reaction, occurs, which is not preferable in terms of the steam reforming reaction of methane of the present invention. On the other hand, if the reaction temperature is too low, sufficient reforming reaction does not proceed. does not Meanwhile, steam reforming of methane by using an inorganic oxide support having a spinel structure, in particular, one or more supports selected from the group consisting of _{MgAl 2} O ₄ , NiAl ₂ O ₄ , and MgAl ₂ O ₄ -NiAl ₂ O _{4 .} It is preferable because it is excellent in heat resistance in the high temperature range in which the reaction proceeds, and thus catalyst durability can be improved, and carbon deposition can be more effectively suppressed by 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 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 ) may be injected at a space velocity. The catalyst of the present invention can further improve the catalytic activity at a faster space velocity compared to the conventional catalyst as the high temperature stability and durability are improved.

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 thereto.

Example

Comparative Examples 1 to 4

_{After impregnating MgAl 2} O ₄ pellets with various concentrations of nickel precursor (Nickel nitrate hexahydrate (Sigma aldrich, 98%) using reduced pressure distillation method), after drying at 373 K for 1 hour, 1073 K under air (temperature increase 5 hours, maintenance 2) time) to prepare a catalyst.

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

Comparative Example 5

A commercial catalyst (Com-R, manufacturer: Clariant, HyProGen ^® R-70) in which 15 wt% of nickel metal was supported on MgAl ₂ O _{4 pellets was used.}

Examples 1 to 3

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

The sieved pellets were impregnated with various concentrations of nickel precursor (Nickel nitrate hexahydrate, Sigma aldrich, 98%) using a reduced pressure distillation method, dried at 373 K for 1 hour, and then dried at 1073 K under air (temperature increase 5 hours, maintenance 2 hours). ) to prepare a catalyst.

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

evaluation example

Evaluation Example 1: Cross-sectional photography 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 imaging 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 support was compared through Scanning Electron Microscopy-Energy dispersive X-ray spectroscopy (SEM-EDS) analysis. Specifically, the amount of nickel loaded was analyzed using the blue dot as a point. It is shown in FIG. 2A by overlapping. The results of all the prepared catalysts are shown in FIG. 2B.

Referring to FIGS. 2A and 2B , it was confirmed that there was a large difference in the nickel concentration distribution between the catalysts of Comparative Examples 1 to 3 without the concentration gradient and the catalysts of Examples 1 to 3 with the concentration gradient. The catalyst prepared in the form without a concentration gradient showed that the nickel concentration distribution inside the pellet was almost constant. Through this, it was confirmed that the catalyst having a concentration gradient was well prepared.

Evaluation Example 2: Structural Characteristics Analysis 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 ground in a mortar and sampled. XRD pattern after calcination of the catalyst prepared in the form without the concentration gradient of Comparative Examples 1 to 3 in (a) of FIG. 3, and the catalyst prepared in the form having the concentration gradient of Examples 1 to 3 in FIG. was shown.

Referring to FIG. 3 , it was confirmed that the catalyst prepared through XRD analysis was _{the main phase constituting the catalyst in which MgAl 2} O ₄ , NiAl ₂ O ₄ , and NiO phases were prepared. 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 ground in a mortar and sampled. _{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 the peak depends on the amount of nickel impregnated. As the amount of nickel impregnated increases, the intensity of the peak increases, and the behavior of the reduction peaks of the catalyst without a concentration gradient and the catalyst with a concentration gradient are similar.

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

After each of the prepared catalysts were ground in a mortar _{, reduction was carried out at 1073K under 10 vol.% H 2} /N ₂ conditions (total flow = 100 mL/min) for 2 hours (temperature increase of 2 hours and 30 minutes, maintenance 2) time), TEM analysis results and nickel particle size are shown in FIG. 5 and Table 1 below, 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 result of FIG. 5 and the nickel particle size of Table 1, it was confirmed that the nickel particle size increased as the nickel content increased. The behavior was similar for the catalyst without the concentration gradient and the catalyst with the concentration gradient.

However, when examining in conjunction with FIG. 2b, it can be seen that the nickel concentration on the surface of the support of Comparative Example 2 and Example 2 is similar to 5 wt%, respectively, but in FIG. 6, Comparative Example 2 is a particle of nickel 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 with a small content, and as the aggregation of nickel metal particles is suppressed despite the high nickel content on the surface of the support, the catalytic activity is reduced found to be very good.

In conclusion, the commercial catalyst has a relatively high nickel loading of 10 wt% or more and 20 wt% or less, but since the present invention selectively supports nickel only on the surface and effectively uses it, the nickel loading amount is most preferably 3.5 wt%, and the maximum is 5 wt%. Weight % 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) Pulverize the prepared pellet catalyst and apply it to SMR reaction

After the catalysts prepared in Example 2, Comparative Example 3 and Comparative Example 5 were put 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. Before the reaction, under the condition of 10 vol.% H ₂ /N ₂ (total flow = 100 mL/min), 1073K (temperature rise 2 hours 30 minutes, maintenance 2 hours) reduction process followed by 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 , the commercial catalyst Comparative Example 5 (15wt%) had a higher nickel content than the prepared catalysts, so the methane conversion rate was the highest 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 Example 2 (3.5 wt%) catalyst having a relatively low nickel content. However, the methane conversion rates of the catalysts at low reaction temperatures were similar for both catalysts. In conclusion, it was confirmed that the methane conversion rate at high temperature was more affected by the nickel content.

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

The catalysts prepared in Comparative Example 5 (commercial catalyst), Example 2, 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 1073 K (temperature rise 2 hours 30 minutes, maintenance 2 hours) under the condition of _{20 vol.% H 2} /N _{2 before the reaction was reduced to steam (H 2} O) The SMR reaction was carried out with a ratio of carbon and carbon (methane) of 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. indicated.

7 is a graph showing the results of SMR reaction experiments using 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 catalysts. Comparing only catalysts without concentration gradient, the higher the nickel content, the higher the methane conversion rate. However, the catalyst of Example 2 (nickel metal content 3.5wt%), which is a catalyst with a concentration gradient, had a lower nickel content than the catalyst of Comparative Example 2 (nickel metal content 5wt%), but showed a high methane conversion rate at the overall space velocity, Comparative Example The methane conversion rate was lower than 3 (nickel metal content 10wt%). From the experimental results of the above-described powder catalyst, it was found that the present experiment showed a completely different aspect considering that the nickel content was a factor affecting the methane conversion rate. However, in connection with FIG. 2b, if the catalysts are listed in the order of increasing the nickel content in both outer parts of the prepared catalyst, Comparative Example 3, Example 2, and Comparative Example 2 are in the order. It is clear that this is a meaningful result if the theory that the SMR reaction occurs only on the surface of the pellet catalyst is applied.

As a result of this experiment, it was confirmed that the SMR reaction occurs only on the surface of the pellet catalyst, and that the nickel distribution of the catalyst with a concentration gradient has an influence on the SMR reaction even when a small amount of nickel is used.

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

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 before the reaction, _{under the condition of 20 vol.% H 2} /N ₂ , the reduction process was performed at 1073 K (temperature rise 2 hours 30 minutes, maintenance 2 hours), and then steam (H ₂ O) and carbon (methane) ratio of 0.5:1, the SMR reaction was carried out (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, Comparative Examples 3 and 5 are shown in FIG. 8 .

In addition, the pellet catalyst was recovered after the SMR reaction was performed under severe conditions in FIG.

Referring to FIG. 8, this experiment shows the results of experiments under harsh 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 completed. Referring to FIG. 9 , the catalysts of Comparative Example 5 and Comparative Example 3 were broken to such an extent that the shape could not be recognized, and it was confirmed that the outer surface of the pellets in Comparative Example 2 was also partially broken. However, it was confirmed that the pellets were not broken in the catalyst having a concentration gradient (Examples 1 to 3) and the catalyst without a concentration gradient having a low nickel content (Comparative Example 4). Normal carbon deposition takes place on nickel particles. The higher the nickel content and the better the nickel is dispersed in the pellet, the more carbon deposition occurs in the nickel particles inside the pellet, and the pellet breaks while applying stress to the pellet. Therefore, the catalysts of Comparative Examples 5 and 3 were crushed to the extent that the shape could not be recognized as shown in FIG. 9, and it was found that only the outer surface of the catalyst of Comparative Example 2 having a relatively low nickel content was partially damaged. However, catalysts with a concentration gradient have nickel concentrated only on the surface of the pellets, so there is relatively no internal stress compared to catalysts without a concentration gradient, and carbon is deposited only on the outside, so there is less risk of crushing the pellets. Through this phenomenon, it was confirmed that the catalyst with a concentration gradient is a catalyst with strong resistance to carbon deposition and is more suitable for SMR reaction.

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

After the SMR reaction, the catalyst was grinded in a mortar, respectively, and the amount of carbon deposition was analyzed. Based on the weight of the recovered catalyst sample after the SMR reaction, the weight reduced by heating (TGA) while flowing air was converted into carbon deposition. It was described as the total production amount.

On the other hand, when the total amount of coke is 50% by weight, 50% by weight of the sample recovered after the SMR reaction is carbon deposited, 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 nickel content, and the greater the carbon deposition amount when nickel was supported in the support without a concentration gradient. Combining the results of the pellet shape and the carbon deposition amount after the SMR reaction under severe conditions, the resistance to carbon deposition is great when nickel is supported with a concentration gradient. was found to be 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 a variety of different forms, and those of ordinary skill in the art to which the present invention pertains will appreciate the technical spirit of the present invention. However, it will be understood that the invention may be embodied in other specific forms without changing essential features. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (20)

an inorganic oxide support having a spinel structure; and an active metal;
The active metal is one or two or more selected from the group consisting of nickel, platinum, palladium, silver, gold and ruthenium metal,
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 ,}
The inorganic oxide support is a catalyst for steam methane reforming, characterized in that it has a concentration gradient of the active metal. delete In claim 1,
The active metal is NiAl ₂ O ₄ , NiO, and a catalyst for steam methane reforming comprising one or two 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 from the center of the inorganic oxide support to the surface direction, the catalyst for steam methane reforming. In claim 1,
The inorganic oxide support having the spinel structure,
In an area of 30% length or less of the radius of the support from the center,
A catalyst for steam methane reforming that supports 10 wt% or less of active metal based on the total weight of active metal. In claim 1,
The inorganic oxide support of the spinel structure,
In an area of up to 30 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 catalyst for steam methane reforming, the catalyst for steam methane reforming. In claim 1,
The active metal is contained in an amount of 1 to 5% by weight based on the total weight of the catalyst for steam methane reforming, the catalyst for steam methane reforming. delete In claim 1,
The inorganic oxide support having the spinel structure is one or two or more selected from the group consisting of a pellet type, a cylinder type, a tubular type and a spherical shape, the catalyst for steam methane reforming. a) a first immersion step of impregnating the inorganic oxide support having a spinel structure with a hydrophobic first solvent to prepare an inorganic oxide support filled with the first hydrophobic 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;
The inorganic oxide support having the spinel structure is one 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 method for producing a catalyst for steam methane reforming, wherein the active metal precursor is a water-soluble salt of a metal containing one or more selected from the group consisting of nickel, platinum, palladium, silver, gold and ruthenium metal. In claim 11,
In step a), the method for producing a catalyst for steam methane reforming, characterized in that the inorganic oxide support is impregnated with the hydrophobic first solvent by vacuum distillation. In claim 11,
Step b) is a method for preparing a catalyst for steam methane reforming, characterized in that the metal precursor solution is impregnated into the inorganic oxide support by rotary stirring and vacuum distillation. In claim 11,
The hydrophobic first solvent is a method for producing a catalyst for steam methane reforming, characterized in that it has a higher viscosity than the hydrophilic second solvent. In claim 11,
The hydrophobic first solvent is a method for producing a catalyst for steam methane reforming, characterized in that the polyhydric alcohol having 2 to 6 carbon atoms. delete In claim 11,
Step c) is a method for preparing a catalyst for steam methane reforming, comprising drying at 323 to 423K for 0.5 to 2 hours, and then heat-treating at 873 to 1273K for 1 to 3 hours. In the presence of the catalyst for steam methane reforming of any one of claims 1, 3 to 8 and 10, methane and steam are injected in a molar ratio of 1:1 to 1:3 and reacted while being reacted. A method for producing syngas through steam reforming. In claim 18,
The reaction is a synthesis gas production method through the steam reforming reaction of methane, characterized in that the reaction at 973 to 1273K. In claim 18,
Syngas production method through steam reforming of methane, characterized in that the reaction is performed while injecting the steam and methane at a space velocity of 6,000 to 24,000 mL/(h g _{cat ).}

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