CN108654628A - Ni-Ce-Zr composite oxide/gamma-alumina catalyst and preparation method thereof - Google Patents

Abstract

The invention provides a Ni-Ce-Zr composite oxide/gamma-alumina catalyst and a preparation method thereof. The preparation method of the Ni-Ce-Zr composite oxide/gamma-alumina catalyst provided by the invention comprises the following steps: providing a mixed aqueous solution of nickel salt, cerium salt, zirconium salt and citric acid; mixing the mixed aqueous solution with gamma-alumina and heating to obtain gel; the specific surface area of the gamma-alumina is 250-550 m²A pore volume of 0.2 to 0.4 cm/g³Per g, the aperture is 2-5 nm; and drying the gel and then roasting to obtain the Ni-Ce-Zr composite oxide/gamma-alumina catalyst. Experimental results show that when the catalyst prepared by the preparation method is used for methanation catalysis of carbon dioxide, the conversion rate of the carbon dioxide reaches 92%, and the conversion selectivity of the methane reaches 100%.

Description

A kind of Ni-Ce-Zr composite oxide/γ-alumina catalyst and preparation method thereof

technical field

The invention relates to the technical field of catalyst preparation, in particular to a Ni-Ce-Zr composite oxide/γ-alumina catalyst and a preparation method thereof.

Background technique

The increase of carbon dioxide content in the atmosphere intensifies the "greenhouse effect", which has a serious impact on the earth's ecosystem, social development, human health and quality of life. With the enhancement of human's awareness of environmental protection, the absorption and treatment of carbon dioxide has attracted widespread attention from the whole society. How to eliminate and utilize carbon dioxide has become a problem of relations among countries all over the world. In recent years, the main research direction is the capture, separation, storage and recycling of carbon dioxide, and the synthesis of methane from carbon dioxide has become one of the research hotspots.

The methanation of carbon dioxide is an exothermic reaction. Due to the limitation of kinetics, a suitable catalyst is needed to make the reaction occur rapidly at low temperature and low pressure, and it has good selectivity. The carbon dioxide methanation catalyst is generally group VIII of the periodic table of elements Metals such as iron, cobalt, palladium, nickel and ruthenium, etc. Among them, the supported nickel-based catalyst has high catalytic activity, good selectivity, easy control of reaction conditions, low production cost, and relatively low price, and has always been a favored key research object.

When the methanation reaction temperature was 250℃, the order of catalytic activity of supported Ni-based catalysts was Ni/MgO<Ni/Al ₂ O ₃ <Ni/SiO ₂ <Ni/TiO ₂ <Ni/ZrO ₂ . γ-Al ₂ O ₃ has the advantages of large specific surface area and low price, and is the most widely used catalyst carrier in industry. Both Al ³⁺ and O ^2- ions on the surface of γ-Al ₂ O ₃ have strong residual bonding ability, and can interact with O ^2- and Ni ²⁺ in NiO to form a strong surface ionic bond, which is beneficial to The uniform dispersion of NiO on the surface of γ-Al ₂ O ₃ produces very fine Ni grains after firing and reduction. In addition, the stabilizing effect of Al ₂ O ₃ can also prevent the aggregation and growth of Ni grains during calcination and reduction. However, too strong interaction between NiO and Al ₂ O ₃ will cause difficulty in catalyst reduction, and ultimately lead to low catalytic activity, and the preparation methods in the prior art often lead to Al ₂ O ₃ and NiO will form nickel-aluminum spikes that are difficult to reduce. The spar species (NiAl ₂ O ₄ ), while the nickel-aluminum spinel species are difficult to reduce, thus reducing the catalyst activity.

Contents of the invention

The object of the present invention is to provide a Ni-Ce-Zr composite oxide/γ-alumina catalyst and a preparation method thereof. The Ni-Ce-Zr composite oxide/γ-alumina catalyst prepared by the preparation method provided by the invention has good catalytic activity.

The invention provides a kind of preparation method of Ni-Ce-Zr composite oxide/γ-alumina catalyst, comprising the following steps:

(1) providing a mixed aqueous solution of nickel salt, cerium salt, zirconium salt and citric acid; heating the mixed aqueous solution with gamma-alumina to obtain a gel;

The specific surface area of the γ-alumina is 250-550m ² /g, the pore volume is 0.2-0.4cm ³ /g, and the pore diameter is 2-5nm;

(2) Drying and calcining the gel obtained in the step (1) in sequence to obtain a Ni-Ce-Zr composite oxide/γ-alumina catalyst.

Preferably, the sum of the amounts of nickel, cerium and zirconium in the mixed aqueous solution is 1 to 2 times the amount of citric acid.

Preferably, the mass of nickel element in the mixed aqueous solution is 5-50% of the mass of γ-alumina.

Preferably, the total mass of cerium element and zirconium element in the mixed aqueous solution is 10-30% of the mass of γ-alumina.

Preferably, the heating temperature in the step (1) is 70-90°C.

Preferably, the drying temperature in the step (2) is 90-110° C., and the drying time is 10-14 hours.

Preferably, the calcination temperature in the step (2) is 450-550° C., and the calcination time is 8-12 hours.

The present invention also provides the Ni-Ce-Zr composite oxide/γ-alumina catalyst prepared by the preparation method described in the above technical scheme, comprising a γ-alumina matrix and Ni-Ce-alumina dispersed on the surface of the γ-alumina Zr composite oxide, the specific surface area of the γ-alumina matrix is 250-550m ² /g, the pore volume is 0.2-0.4cm ³ /g, and the pore diameter is 2-5nm.

Preferably, the mass of the nickel element is 5-50% of the mass of γ-alumina.

Preferably, the total mass of the cerium element and zirconium element is 10-30% of the mass of γ-alumina.

The invention provides a method for preparing a Ni-Ce-Zr composite oxide/γ-alumina catalyst, comprising the following steps: providing a mixed aqueous solution of nickel salt, cerium salt, zirconium salt and citric acid; mixing the mixed aqueous solution with γ-alumina is mixed and heated to obtain a gel; the specific surface area of the γ-alumina is 250-550m ² /g, the pore volume is 0.2-0.4cm ³ /g, and the pore diameter is 2-5nm; The glue is dried and calcined to obtain a Ni-Ce-Zr composite oxide/γ-alumina catalyst. The invention uses gamma-alumina with a suitable pore structure as a carrier to improve the activity and stability of the catalyst, and uses citric acid as an additive for impregnation and loading, so that the precursors of nickel, cerium and zirconium are uniformly loaded on the surface of gamma-alumina , to avoid the clogging of the pores in the carrier, and after drying and roasting, the Ni-Ce-Zr composite oxide supported by γ-alumina is obtained. The oxides of zirconium and cerium change the interaction between NiO and the carrier, and inhibit the nickel-aluminum oxide. The formation of spinel species (NiAl ₂ O ₄ ) improves the reduction performance of NiO, and the catalyst obtained after reduction has good catalytic activity. The experimental results show that when the catalyst prepared by the preparation method provided by the invention is used for the methanation catalysis of carbon dioxide, the conversion rate of carbon dioxide reaches 92%, which is close to the theoretical equilibrium value (95%), and the catalyzed CO can be completely converted into _CH by continuing to raise the temperature. ₄ , so the methane conversion selectivity reaches 100%.

Description of drawings

Fig. 1 is the XRD figure of the catalyst prepared by embodiment 1 and comparative examples 2～4;

Fig. 2 is the low magnification SEM figure of the catalyst prepared in embodiment 1;

Fig. 3 is the high power SEM figure of the catalyst prepared in embodiment 1;

Fig. 4 is the catalyst catalyst prepared in the embodiment 1 and comparative example 1～5 catalyzed _CO Methanation reaction _CO conversion test result;

Fig. 5 is that the catalyst prepared in embodiment 1 and comparative example 1～ ₅ catalyzes CO The reaction _CH of methanation Selectivity test result;

Fig. 6 shows the BET characterization results of γ-Al ₂ O ₃ and catalyst prepared in Examples 1-3 and Comparative Example 1.

Detailed ways

The invention provides a kind of preparation method of Ni-Ce-Zr composite oxide/γ-alumina catalyst, comprising the following steps:

(1) providing a mixed aqueous solution of nickel salt, cerium salt, zirconium salt and citric acid; heating the mixed aqueous solution with gamma-alumina to obtain a gel;

The specific surface area of the γ-alumina is 250-550m ² /g, the pore volume is 0.2-0.4cm ³ /g, and the pore diameter is 2-5nm;

(2) Drying and calcining the gel obtained in the step (1) in sequence to obtain a Ni-Ce-Zr composite oxide/γ-alumina catalyst.

The invention provides a mixed aqueous solution of nickel salt, cerium salt, zirconium salt and citric acid. In the present invention, the sum of the amounts of nickel, cerium and zirconium in the mixed aqueous solution is preferably 1 to 2 times the amount of citric acid. In the present invention, the citric acid is used as an additive to adjust the pH value of the reaction system, so that the precursors of nickel, cerium and zirconium are evenly distributed on the surface of the carrier, and the blockage of the pores in the carrier is avoided.

The type and source of the nickel salt, cerium salt and zirconium salt are not particularly limited in the present invention, and the commercially available products of nickel salt, cerium salt and zirconium salt well known to those skilled in the art can be used. In an embodiment of the present invention, the nickel salt is preferably Ni(NO ₃ ) ₂ ·6H ₂ O, the cerium salt is preferably Ce(NO ₃ ) ₃ ·6H ₂ O, and the zirconium salt is preferably Zr( NO ₃ ) ₄ ·5H ₂ O.

In the present invention, there is no special limitation on the preparation operation of the mixed aqueous solution, and the technical solution for preparing the mixed solution well known to those skilled in the art can be adopted. In the present invention, nickel salt, cerium salt, zirconium salt and citric acid are preferably mixed with water to obtain a mixed aqueous solution. In the present invention, the mixing of the nickel salt, cerium salt, zirconium salt and citric acid with water is preferably carried out under stirring conditions; the stirring is preferably magnetic stirring; the stirring speed is preferably 200 to 500r/min, More preferably, it is 300-400 r/min; in the present invention, there is no special limitation on the stirring time, as long as each component can be dissolved.

After obtaining the mixed aqueous solution of nickel salt, cerium salt, zirconium salt and citric acid, the present invention mixes the mixed aqueous solution with γ-alumina and heats to obtain a gel. In the present invention, the mass of nickel element in the mixed aqueous solution is preferably 5-50% of the mass of γ-alumina, more preferably 10-40%, and most preferably 20-30%. In the present invention, the total mass of cerium and zirconium in the mixed aqueous solution is preferably 10-30% of the mass of γ-alumina, more preferably 15-25%, and most preferably 20%. In the present invention, the mass ratio of the nickel element, cerium element, zirconium element and γ-alumina in the above range can further increase the specific surface area of the catalyst, thereby improving the catalytic activity: when the Ce content is too high, the specific surface area and The pore volume is small, and it is high when the Zr content increases, indicating that the Ni-Ce composite oxide is easier to combine with γ-MA than the Ni-Zr composite oxide; when the Ce/Zr ratio is fixed at an appropriate value, the Ni content When increasing, the specific surface area and pore volume of the catalyst gradually decreased, indicating that Ni particles gradually covered the γ-MA pore structure with the increase of Ni content.

In the present invention, there is no special limitation on the ratio of the cerium element and the zirconium element, and any ratio can be adopted. In an embodiment of the present invention, the amount of the cerium element is preferably 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 times the sum of the amounts of the cerium element and the zirconium element.

In the present invention, the specific surface area of the γ-alumina is 250-550m ² /g, preferably 300-450m ² /g, more preferably 350-400m ² /g; the pore volume of the γ-alumina 0.2-0.4 cm ³ /g, preferably 0.3 cm ³ /g; the pore diameter of the γ-alumina is 2-5 nm, preferably 3-4 nm.

In the present invention, the preparation of the γ-alumina preferably includes the following steps:

(a) adding a pH regulator dropwise to the aluminum salt solution, and the hydrolysis reaction obtains a white gel; the pH regulator is ammonium carbonate solution or ammonia;

(b) aging, drying and roasting the white gel obtained in the step (a) in sequence to obtain γ-alumina.

In the present invention, the pH regulator is preferably added dropwise to the aluminum salt solution, and a white gel is obtained through hydrolysis reaction. In the present invention, the concentration of the aluminum salt solution is preferably 0.4-0.6 mol/L. The type and source of the aluminum salt are not particularly limited in the present invention, and commercially available products of water-soluble aluminum salt well known to those skilled in the art can be used. In an embodiment of the present invention, the aluminum salt is preferably Al(NO ₃ ) ₃ ·9H ₂ O, aluminum sulfate or aluminum silicate.

In the present invention, there is no special limitation on the preparation operation of the aluminum salt solution, and the technical solution for preparing the solution well known to those skilled in the art can be adopted. In the present invention, the aluminum salt is preferably mixed with water and then heated to obtain an aluminum salt solution. In the present invention, the temperature of the aluminum salt solution is preferably 65-75°C, more preferably 70°C. In the present invention, the temperature of the aluminum salt solution can further promote the hydrolysis reaction of the aluminum salt, which is beneficial to obtain mesoporous γ-alumina.

In the present invention, the heated product is preferably stirred after heating to obtain an aluminum salt solution. In the present invention, the stirring is preferably electromagnetic stirring; the stirring speed is preferably 5-20r/min, more preferably 10-15r/min; the stirring time is preferably 8-15min, more preferably 10 ~12min. In the present invention, the aluminum salt solution is stirred before the dropping to make the mixing more uniform.

In the present invention, the pH regulator is preferably ammonium carbonate solution or ammonia water. In the present invention, there is no special limitation on the concentration of the pH regulator, and the concentration well known to those skilled in the art can be used. In the present invention, the concentration of the pH regulator is preferably 2-10 mol/L, more preferably 4-8 mol/L. In the present invention, the pH regulator adjusts the pH value of the reaction system to 8-9.

In the present invention, the dropping rate is preferably 0.8-1.5 mL/min, more preferably 1-1.2 mL/min. In the present invention, the dropping is preferably carried out under continuous stirring; the stirring is preferably electromagnetic stirring; the stirring rate is preferably 5-20 r/min, more preferably 10-15 r/min.

In the present invention, the temperature of the hydrolysis reaction is preferably 65-75°C, more preferably 70°C. In the present invention, the hydrolysis reaction starts with the dropwise addition of the pH regulator and ends with the white gel. In the present invention, during the hydrolysis reaction, the aluminum salt is hydrolyzed to obtain aluminum carbonate.

After the white gel is obtained, in the present invention, the white gel is preferably aged, dried and calcined in stages to obtain γ-alumina. In the present invention, the aging temperature is preferably 25-35°C, more preferably 30°C; the aging time is preferably 11-13h, more preferably 12h. In the present invention, the aging makes the hydrolysis reaction more complete and ensures the stability of the product structure.

In the present invention, the drying temperature is preferably 90-110° C., more preferably 100° C.; the drying time is preferably 11-13 hours, more preferably 12 hours.

In the present invention, the staged calcination preferably includes low-temperature calcination and high-temperature calcination. In the present invention, the temperature of the low-temperature calcination is preferably 150-250° C., more preferably 200° C.; the time of the low-temperature calcination is preferably 8-12 hours, more preferably 10 hours. In the present invention, the low-temperature roasting can remove the ammonium salt obtained by the hydrolysis reaction.

After the low-temperature calcination is completed, in the present invention, the temperature of the low-temperature calcination product is preferably raised to the temperature for high-temperature calcination. In the present invention, there is no special limitation on the heating rate to the high-temperature calcination temperature, and the heating rate well-known to those skilled in the art can be used, preferably 1-5° C./min.

In the present invention, the temperature of the high-temperature calcination is preferably 450-550° C., more preferably 480-520° C.; the time of the high-temperature calcination is preferably 8-12 hours, more preferably 10 hours. In the present invention, aluminum carbonate is decomposed during the high-temperature calcination process to obtain mesoporous γ-alumina.

The gamma-alumina prepared by the preparation method provided by the invention has a high specific surface area, a large pore volume and a narrow pore size distribution, so that the loading capacity of Ni can reach a large value without blocking the pores, and is uniformly dispersed in the catalyst bulk phase, thereby The catalyst exhibits good CO ₂ catalytic activity, CH ₄ selectivity and long-term reaction stability.

In the present invention, there is no special limitation on the operation of mixing the mixed aqueous solution and γ-alumina, and the technical scheme of mixing materials well known to those skilled in the art can be adopted. In the present invention, the mixing of the mixed aqueous solution and γ-alumina is preferably carried out under stirring conditions; the stirring is preferably magnetic stirring; the stirring speed is preferably 200-500r/min, more preferably 300-400r /min; the stirring time is preferably 1 to 2 hours.

After the mixing of the mixed aqueous solution and γ-alumina is completed, the present invention heats the mixed product to obtain a gel. In the present invention, the heating temperature is preferably 70-90° C., more preferably 75-85° C.; the heating time is preferably 2-6 hours, more preferably 3-4 hours. In the present invention, during the heating process, the mixed aqueous solution is impregnated into γ-alumina.

After the gel is obtained, in the present invention, the gel is dried and then calcined to obtain a Ni-Ce-Zr composite oxide/γ-alumina catalyst. In the present invention, the drying temperature is preferably 90-110° C., more preferably 100° C.; the drying time is preferably 10-14 hours, more preferably 12 hours. In the present invention, the calcination temperature is preferably 450-550°C, more preferably 500°C; the calcination time is preferably 8-12h, more preferably 10h. In the present invention, during the calcination process, nickel salt, cerium salt, and zirconium salt are oxidized and decomposed at high temperature to obtain respective oxides.

The preparation method provided by the invention uses gamma-alumina with a suitable pore structure as a carrier to improve the activity and stability of the catalyst, and uses citric acid as an impregnated and loaded additive to uniformly load the precursors of nickel, cerium and zirconium on gamma - Alumina surface, avoiding the clogging of the pores in the carrier, and obtaining γ-alumina-supported Ni-Ce-Zr composite oxide after drying and roasting, the oxides of zirconium and cerium change the interaction between NiO and the carrier, The formation of nickel-aluminum spinel species (NiAl ₂ O ₄ ) is suppressed, the reduction performance of NiO is improved, and the catalyst obtained by reduction has good catalytic activity.

The present invention also provides the Ni-Ce-Zr composite oxide/γ-alumina catalyst prepared by the preparation method described in the above technical scheme, comprising a γ-alumina matrix and Ni-Ce-alumina dispersed on the surface of the γ-alumina Zr composite oxide, the specific surface area of the γ-alumina matrix is 250-550m ² /g, the pore volume is 0.2-0.4cm ³ /g, and the pore diameter is 2-5nm.

The Ni-Ce-Zr composite oxide/γ-alumina catalyst provided by the present invention includes a γ-alumina substrate, and the specific surface area of the γ-alumina substrate is 250-550m ² /g, preferably 300-450m ² /g g, more preferably 350-400m ² /g; the pore volume of the γ-alumina matrix is 0.2-0.4cm ³ /g, preferably 0.3cm ³ /g; the pore diameter of the γ-alumina matrix is 2 ~5nm, preferably 3~4nm. In the present invention, the special pore structure of the γ-alumina matrix can improve the activity and stability of the _{Al2O3 -} supported Ni-based catalyst.

The Ni-Ce-Zr composite oxide/γ-alumina catalyst provided by the invention includes Ni-Ce-Zr composite oxide dispersed on the surface of the γ-alumina. In the present invention, the mass of the nickel element is preferably 5-50% of the mass of γ-alumina, more preferably 10-40%, and most preferably 20-30%. In the present invention, the total mass of the cerium element and the zirconium element is preferably 10-30% of the mass of γ-alumina, more preferably 15-25%, and most preferably 20%.

In the present invention, the Ni-Ce-Zr composite oxide preferably includes NiO, CeO ₂ , ZrO ₂ and Cex Zr _{1-x O 2} , and the value range of x is preferably (0.1, 1). In the present invention, the particle diameters of NiO, CeO ₂ , ZrO ₂ and Cex Zr _{1-x O 2} are independently preferably 3-4 nm.

In the present invention, the Ni-Ce-Zr composite oxide/γ-alumina catalyst is preferably subjected to a reduction reaction before use, so that NiO is reduced to generate metal Ni active species. The present invention has no special limitation on the conditions of the reduction reaction, and the technical scheme of catalyst reduction well known to those skilled in the art can be used. In the present invention, the temperature of the reduction reaction is preferably 200-300° C., more preferably 250° C.; the time of the reduction reaction is preferably 2-3 hours.

In the present invention, the ZrO ₂ improves the thermal stability of the catalyst, and the CeO ₂ changes the interaction between the active component Ni and the carrier γ-alumina, inhibits the formation of NiAl ₂ O ₄ spinel, and improves the NiO In the reduction process, more NiO _is reduced _to generate metal Ni active species, which provides more active sites for _{CO 2} catalytic methanation reaction and improves catalytic activity. The joint effect of the active components can also improve the dispersion of the active components in the catalyst, increase the number of active centers, and improve the catalytic efficiency.

In order to further illustrate the present invention, the preparation method of the Ni-Ce-Zr composite oxide/γ-alumina catalyst provided by the present invention is described in detail below in conjunction with the examples, but they cannot be interpreted as limiting the protection scope of the present invention.

Example 1:

a). Preparation of mesoporous γ-Al ₂ O ₃

The preparation of mesoporous γ-Al ₂ O ₃ adopts the one-pot method of partial hydrolysis of (NH ₄ ) ₂ CO ₃ in Al(NO ₃ ) ₃ aqueous solution without template and without addition of organic solution. The preparation process is as follows: 0.1mol Al( NO ₃ ) ₃ ·9H ₂ O was dissolved in a beaker filled with 50 mL of deionized water, placed in a water bath at 70°C for 10 minutes under electromagnetic stirring, and then the (NH ₄ ) ₂ CO ₃ solution was gradually dripped in with a peristaltic pump, 500r /min Stir continuously until the whole system forms a white gel state and does not stir;

Cover the beaker with plastic wrap, age at 30°C for 12h, transfer the aged gel into a watch glass and dry at 100°C for 12h, then bake the sample in a muffle furnace at 200°C for 10h, and then place the sample at 1 ℃·min ^-1 heating up to 500℃ and roasting for 10h;

The prepared γ-Al ₂ O ₃ has high specific surface area (348m ² /g), large pore volume (0.3cm ³ /g) and narrow pore size distribution (3.4nm).

b). Preparation of Ni-Ce-Zr-γ-Al ₂ O ₃ series catalysts by impregnation method

The catalyst was prepared by citric acid (Citric Acid, CA) impregnation method, based on γ-Al ₂ O ₃ mass as 100%, Ni content 15%, Ce _0.7 Zr _0.3 (Ce, Zr molar ratio 7:3) content 10%, The specific preparation method is as follows:

Dissolve Ni(NO ₃ ) ₂ ·6H ₂ O, Ce(NO ₃ ) ₃ ·6H ₂ O, Zr(NO ₃ ) ₄ ·5H ₂ O and citric acid (CA) in a 10ml In the crucible of deionized water, the crucible is placed in a constant temperature magnetic stirring water bath, and the γ-Al ₂ O ₃ is poured into the above solution at one time under continuous stirring at room temperature. After continuous stirring for 2 hours, the temperature is raised to 80°C and dried until the system Form a gel state, then dry at 100°C for 12h, and finally heat up at room temperature at 1°C/min to 500°C for 10h to obtain a catalyst.

In this embodiment, the molar ratio n of citric acid to (Ni ²⁺ +Ce ⁴⁺ +Zr ⁴⁺ ) is 1.

Comparative example 1:

The preparation method of Example 1 is adopted, except that citric acid is not added.

Comparative example 2:

The preparation method of Example 1 was adopted, except that citric acid was replaced by equimolar hydrochloric acid.

Comparative example 3:

Adopt the preparation method of Example 1, the difference is that citric acid is replaced by equimolar amount of urea.

Comparative example 4:

The preparation method of Example 1 was adopted, except that citric acid was replaced by equimolar ammonium citrate.

Comparative example 5:

The Ni-Ce-Zr-γ-MA catalyst is prepared by the ammonium carbonate co-precipitation method, that is, the ammonium carbonate partial hydrolysis method, commonly known as one-step method, wherein the Ni content is 15%, and the Ce/Zr is fixed at the same time as 7:3 and its total content is 10%. The specific preparation method refers to the preparation of mesoporous γ-Al ₂ O ₃ , but the corresponding proportion of Ni(NO ₃ ) ₂ 6H ₂ O, Ce(NO ₃ ) is added to the precursor Al(NO ₃ ) ₃ 9H ₂ O 3.6H ₂ O and Zr(NO ₃ ) _{4 .5H 2 O.}

The XRD patterns of the catalysts prepared in Example 1 and Comparative Examples 2-4 are shown in Figure 1, wherein a is citric acid, b is urea, c is ammonium citrate, and d is hydrochloric acid. It can be seen from Figure 1 that the Ni-Ce-Zr-γ-MA sample prepared by the citric acid impregnation method has three main diffraction peaks, namely 2θ=37.0°, 45.0°, and 66.0°, and these three peaks are The diffraction peaks of γ-Al ₂ O ₃ ; the diffraction peaks of the NiO phase (2θ=37.2°, 43.3° and 62.9°) overlap with it and are difficult to distinguish, while the diffraction peaks of CeO ₂ and ZrO ₂ and the cerium-zirconium solid solution formed by them are negligible , can hardly be seen, indicating that Ni-Ce-Zr composite oxide is well dispersed on γ-Al ₂ O ₃ , forming a uniform dispersed phase with smaller particles.

The low-magnification and high-magnification SEM images of the catalyst prepared in Example 1 are shown in Figure 2 and Figure 3, respectively. It can be seen from Figures 1 to 3 that the catalyst prepared in Example 1 includes various types of massive and granular aggregates, and these larger massive substrates are Al ₂ O ₃ , Ni-Ce-Zr composite oxidation The particles were uniformly dispersed on the surface of the block, and SEM showed that the catalyst was formed by the aggregation of nanoparticles to form a worm-like porous structure.

The reaction results of the catalysts prepared in Example 1 and Comparative Examples 1 to 5 after reduction to catalyze _CO2 methanation are shown in Figure 4 and Figure 5, respectively, where Figure 4 shows the test results of the _CO2 conversion rate, and Figure 5 shows the CH ₄ Selective test results. The activity of Ni-Ce-Zr-γ-MA catalysts prepared by different preparation routes was evaluated by _{CO 2} methanation reaction. It can be seen from Fig. 4 and Fig. From the view of CH ₄ selectivity, the catalyst prepared by citric acid (CA) impregnation method had the best catalytic activity.

Example 2:

The preparation method of Example 1 was adopted, except that the molar ratio n of citric acid to (Ni ²⁺ +Ce ⁴⁺ +Zr ⁴⁺ ) was 0.5.

Embodiment 3:

The preparation method of Example 1 is adopted, except that the molar ratio n of citric acid to (Ni ²⁺ +Ce ⁴⁺ +Zr ⁴⁺ ) is 2.

The BET characterization results of γ-Al ₂ O ₃ and the catalyst prepared in Examples 1-3 and Comparative Example 1 are shown in Figure 6(a) and (b), respectively, where Figure 6(a) is the nitrogen adsorption-desorption isotherm Curve, Figure 6(b) is the pore size distribution diagram. From Figure 6(a) and (b), it can be seen that with the addition of Ni-Ce-Zr composite oxide, the isotherm curve of the catalyst is basically consistent with that of the γ-Al ₂ O ₃ support. When n=0, the corresponding catalyst is prepared without adding citric acid, and its specific surface area and pore volume are the smallest, which are 172m ² /g and 0.16cm ³ /g, respectively, compared with γ-MA’s 348m ² /g and 0.30 cm ³ /g is much smaller. Simply using H ₂ O to dissolve the Ni-Ce-Zr precursor compound and impregnate it into γ-MA, the impregnated components are likely to block the pores of the carrier and accumulate on the outer surface and pores of the carrier, reducing the overall specific surface area and pore volume of the catalyst.

Table 1 shows the BET characterization results of the catalysts prepared in Example 1 and Comparative Examples 1-5. As can be seen from Table 1, when adding other substances such as HCl, urea or ammonium citrate, the specific surface area and pore volume of the catalyst are all low; the specific surface area and pore volume of the catalyst prepared by the one-step method and adding citric acid are all close to γ-MA, about 300m ² /g and 0.27cm ³ /g, indicating that these two preparation methods can make the Ni-Ce-Zr precursor compound evenly dispersed in the support structure, and will not accumulate into large particles to block the pores and cover the carrier surface.

The BET characterization results of the catalysts of Table 1 Comparative Examples 1 to 5

It can be seen from the above comparative examples and examples that the catalyst prepared by the preparation method provided by the present invention has good catalytic activity and selectivity.

The above descriptions are only preferred embodiments of the present invention, and do not limit the present invention in any form. It should be pointed out that those skilled in the art can make some improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims (10)

1. a preparation method of Ni-Ce-Zr composite oxide/γ-alumina catalyst, comprising the following steps: (1) providing a mixed aqueous solution of nickel salt, cerium salt, zirconium salt and citric acid; heating the mixed aqueous solution with gamma-alumina to obtain a gel; The specific surface area of the γ-alumina is 250-550m ² /g, the pore volume is 0.2-0.4cm ³ /g, and the pore diameter is 2-5nm; (2) Drying and calcining the gel obtained in the step (1) in sequence to obtain a Ni-Ce-Zr composite oxide/γ-alumina catalyst. 2. The preparation method according to claim 1, characterized in that the sum of the amounts of nickel, cerium and zirconium in the mixed aqueous solution is 1 to 2 times the amount of citric acid. 3. The preparation method according to claim 1, characterized in that the mass of the nickel element in the mixed aqueous solution is 5-50% of the mass of gamma-alumina. 4. The preparation method according to claim 1, characterized in that the total mass of cerium and zirconium elements in the mixed aqueous solution is 10-30% of the mass of γ-alumina. 5. The preparation method according to claim 1, characterized in that, the heating temperature in the step (1) is 70-90°C. 6. The preparation method according to claim 1, characterized in that, the drying temperature in the step (2) is 90-110° C., and the drying time is 10-14 hours. 7. The preparation method according to claim 1 or 6, characterized in that, in the step (2), the roasting temperature is 450-550° C., and the roasting time is 8-12 hours. 8. The Ni-Ce-Zr composite oxide/γ-alumina catalyst prepared by the preparation method described in any one of claims 1 to 7 comprises a γ-alumina substrate and Ni- In the Ce-Zr composite oxide, the specific surface area of the γ-alumina matrix is 250-550m ² /g, the pore volume is 0.2-0.4cm ³ /g, and the pore diameter is 2-5nm. 9. The Ni-Ce-Zr composite oxide/γ-alumina catalyst according to claim 8, characterized in that the mass of the nickel element is 5-50% of the mass of the γ-alumina. 10. The Ni-Ce-Zr composite oxide/γ-alumina catalyst according to claim 8 or 9, characterized in that the total mass of the cerium element and zirconium element is 10 to 30% of the γ-alumina quality %.