Composite oxide, preparation method and application thereof, carbon dioxide methanation catalyst and carbon dioxide methanation method

Abstract

The present invention relates to the field of carbon dioxide methanation, and discloses a composite oxide, a preparation method and an application thereof, a carbon dioxide methanation catalyst, and a carbon dioxide methanation method, the composite oxide contains magnesium oxide, calcium oxide, zirconium oxide, aluminum oxide, and a crystal phase structure represented by a chemical general formula MgxCayZr (1-x-y) Al2O4, 0 < x < 1, and 0 < y < 1. The composite oxide can provide better mechanical strength for a further prepared catalyst, the grain size of the loaded active component Ni is small, and better carbon dioxide conversion rate and methane selectivity are achieved in carbon dioxide methanation.

Description

Technical Field

[0001] The present invention relates to the field of carbon dioxide methanation, and in particular to a composite oxide and a preparation method and application thereof, as well as a carbon dioxide methanation catalyst and a carbon dioxide methanation method. Background Art

[0002] Carbon dioxide is one of the most abundant carbon sources on Earth. With the increasing depletion of fossil energy, how to recycle carbon dioxide and improve the environment has become a hot topic of research.

[0003] The strategic and practical significance of CO2 methanation technology is relatively large. Theory shows that CO2 methanation reaction is an important way to utilize CO2 resources, which can fully reduce CO2 emissions; at the same time, using solar water electrolysis to produce hydrogen technology to solve the problem of the source of hydrogen required for methanation can achieve efficient storage of renewable energy and improve the efficiency of CO2 methanation.

[0004] At present, the research on carbon dioxide methanation catalyst carriers mainly focuses on CeO 2 、Al 2 O 3 、TiO 2 、SiO 2 、ZrO 2 As the carrier, the main preparation methods include low-temperature plasma sintering, co-precipitation, sol-gel, etc. On this basis, combining with different active components can obtain carbon dioxide methanation catalysts with significantly different activity and stability.

[0005] CN1048194C discloses a catalyst for carbon dioxide hydrogenation reaction, which uses natural sepiolite as a carrier. After loading the active substance, the carbon dioxide conversion rate reaches over 95% and the selectivity reaches over 99%. However, the source of natural sepiolite is narrow, the cost is high, and the industrial application value is limited.

[0006] CN103551153A discloses a copper-based catalyst for carbon dioxide methanation and a preparation method thereof, wherein the preparation method of the carrier involved mainly comprises the following steps: precipitating salt solutions of various metal elements of the catalyst and alkaline solutions in stages, then slurrying and filtering with hot desalted water, drying and dehydrating the catalyst filter cake, and calcining and molding the catalyst precursor after drying.

[0007] Plasma-enhanced preparation of CO 2"Nickel-based catalyst for methanation" (Guo Fang, Chu Wei, Acta Chimica Sinica, 2007, 28(5), 429-434) discloses the use of plasma technology to prepare a carrier. The high-energy electrons and ions in the plasma bombard the catalyst surface, promoting the decomposition of the catalyst precursor, lowering its reduction temperature and refining the grains. However, the scale of plasma technology is limited, the energy consumption is high, and it is difficult to achieve industrial production.

[0008] Therefore, there is a need to provide methanation catalysts with high activity and high thermal stability. Summary of the invention

[0009] The purpose of the present invention is to overcome the problems of poor activity and thermal stability of existing methanation catalysts, and to provide a composite oxide and a preparation method and application thereof, as well as a method for methanation of carbon dioxide.

[0010] In order to achieve the above object, the present invention provides a composite oxide in the first aspect, wherein the composite oxide contains magnesium oxide, calcium oxide, zirconium oxide and aluminum oxide, and a chemical formula of Mg x Ca y Zr (1-x-y) Al 2 O 4 The crystal phase structure shown, wherein 0<x<1, 0<y<1.

[0011] The second aspect of the present invention provides a method for preparing a composite oxide, wherein the preparation method comprises: wet ball milling, drying and molding an aluminum source, a calcium source, a magnesium source and a zirconium source in sequence to obtain the composite oxide.

[0012] The third aspect of the present invention provides a use of the composite oxide of the first aspect or the composite oxide prepared by the preparation method described in the second aspect in a carbon dioxide methanation reaction.

[0013] The fourth aspect of the present invention provides a carbon dioxide methanation catalyst, wherein the catalyst comprises a carrier and an active component, wherein the carrier is the composite oxide of the present invention or the composite oxide prepared by the preparation method of the present invention; and the active component is Ni.

[0014] A fifth aspect of the present invention provides a method for methanation of carbon dioxide, wherein the method comprises: in the presence of a catalyst, subjecting carbon dioxide to a methanation reaction with hydrogen to obtain methane; wherein the catalyst is the carbon dioxide methanation catalyst of the present invention.

[0015] Through the above technical scheme, the composite oxide provided by the present invention can provide better mechanical strength for the further prepared catalyst, and the radial strength of the prepared carbon dioxide methanation catalyst is greater than 315N / cm, has good crush resistance, and can meet the high strength requirements of hydrothermal synthesis of methanation reaction. Through the preparation method of the present invention, the composite oxide has a porosity of 30-35%, has a spinel structure, and the crystal phase purity of the composite oxide is high, and the content of the crystal phase structure is greater than 97wt%; the grain size of the loaded active component Ni is 5-8nm. DETAILED DESCRIPTION

[0016] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0017] The first aspect of the present invention provides a composite oxide, wherein the composite oxide contains magnesium oxide, calcium oxide, zirconium oxide and aluminum oxide, and a chemical formula of Mg x Ca y Zr (1-x-y) Al 2 O 4 The crystal phase structure shown, wherein 0<x<1, 0<y<1.

[0018] The composite oxide of the present invention includes a crystalline part which is a composite crystal as shown in the above chemical formula, and a small amount of individual oxides.

[0019] In some embodiments of the present invention, preferably, the crystalline phase structure is a spinel structure, which can be obtained through XRD analysis.

[0020] In some embodiments of the present invention, preferably, based on the total amount of the composite oxide, in the composite oxide, the crystal phase content of the crystal phase structure (i.e., the content of the crystal phase structure) is greater than 97wt%, the content of magnesium oxide is 0.2-0.8wt%, the content of aluminum oxide is 0.3-0.9wt%, the content of calcium oxide is 0.2-1wt%, and the content of zirconium oxide is 0.2-0.6wt%; which can help provide better catalytic activity.

[0021] In some embodiments of the present invention, preferably, the composite oxide has a porosity of 30-35% and a water absorption of 28-32%.

[0022] The composite oxide having the above characteristics can provide better carrier performance, and when further used in a carbon dioxide methanation catalyst, can provide better mechanical strength and make the grain size of the loaded active component Ni smaller.

[0023] In some embodiments of the present invention, preferably, the crystalline structure has a chemical formula of at least one of the following: Mg 0.3 Ca 0.3 Zr 0.4 Al 2 O 4 Mg 0.4 Ca 0.3 Zr 0.3 Al 2 O 4 Mg 0.1 Ca 0.5 Zr 0.4 Al 2 O 4 Mg 0.5 Ca 0.25 Zr 0.25 Al 2 O 4 Mg 0.35 Ca 0.35 Zr 0.3 Al 2 O 4 Mg 0.7 Ca 0.15 Zr 0.15 Al 2 O 4 Mg 0.2 Ca 0.4 Zr 0.4 Al 2 O 4 Mg 0.2 Ca 0.6 Zr 0.2 Al 2 O 4 Mg 0.2 Ca 0.2 Zr 0.6 Al 2 O 4 .

[0024] The second aspect of the present invention provides a method for preparing a composite oxide, wherein the preparation method comprises: wet ball milling, drying and molding an aluminum source, a calcium source, a magnesium source and a zirconium source in sequence to obtain the composite oxide.

[0025] In some embodiments of the present invention, preferably, the feeding relationship of the aluminum source, calcium source, magnesium source and zirconium source satisfies that the molar ratio of Al provided by the aluminum source to (the sum of Ca+Mg+Zr provided by the calcium source, magnesium source and zirconium source) is 1:0.5, and the obtained composite oxide can contain the chemical formula Mg x Ca y Zr (1-x-y) Al 2 O 4 The crystal phase structure shown, wherein 0<x<1, 0<y<1. Preferably, the crystal phase structure has a chemical formula of at least one of the following: Mg 0.3 Ca 0.3 Zr 0.4 Al 2 O 4 Mg 0.4 Ca 0.3 Zr 0.3 Al 2 O 4 Mg 0.1 Ca 0.5 Zr 0.4 Al 2 O 4 Mg 0.5 Ca 0.25 Zr 0.25 Al 2 O 4 Mg 0.35 Ca 0.35 Zr 0.3 Al 2 O 4 Mg 0.7 Ca 0.15 Zr 0.15 Al 2 O 4 Mg 0.2 Ca 0.4 Zr 0.4 Al 2 O 4 Mg 0.2 Ca 0.6 Zr 0.2 Al 2 O 4 Mg 0.2 Ca 0.2 Zr 0.6 Al 2 O 4 .

[0026] In some embodiments of the present invention, preferably, the calcium source is selected from calcium nitrate and / or calcium acetate; the magnesium source is selected from magnesium nitrate and / or magnesium acetate; the zirconium source is selected from zirconium nitrate and / or zirconium acetate; and the aluminum source is selected from pseudo-boehmite.

[0027] In some embodiments of the present invention, preferably, the wet ball milling process comprises: co-precipitating the aqueous solution containing the aluminum source, calcium source, magnesium source and zirconium source with a precipitant and washing the filter cake to neutrality to obtain a co-precipitate; ball milling the mixture of the co-precipitate and water to a medium particle size D of the particles contained. 50 Less than 0.5 μm. The particles may include precipitate particles after neutralization. During ball milling, the weight ratio of grinding balls: coprecipitate: water can obtain the above-mentioned medium particle size, for example, preferably 1:1:1. The wet ball milling can provide a technical effect that the content of the crystalline phase structure in the composite oxide obtained after die casting is greater than 97wt%.

[0028] In some embodiments of the present invention, preferably, the precipitant is selected from Na 2 CO 3 、NaHCO 3 , K 2 CO 3 and KHCO 3 At least one of .

[0029] In some embodiments of the present invention, preferably, the drying temperature is 100-140° C. and the drying time is 8-10 h. After the drying, the obtained solid material can be crushed and then sieved through 80 mesh.

[0030] In some embodiments of the present invention, the molding can be a method for preparing particles in the preparation of catalyst carriers. Preferably, the molding is die-casting molding, wherein the molding temperature is 600-700°C, the molding pressure is 4-5MPa, and the molding holding time is 3-4min. The molding process may include filling the dried powder into a mold, heating and pressurizing the powder by electric heating, the pressurization rate is 0.2MPa / s to the required molding pressure, and then holding the pressure, and demolding after the end to obtain a molded composite oxide, which can be used as a catalyst carrier and has a shape given by the mold, such as a columnar particle with a diameter of about 4mm and a height of 4mm.

[0031] The third aspect of the present invention provides a use of the composite oxide of the first aspect or the composite oxide prepared by the preparation method described in the second aspect in a carbon dioxide methanation reaction.

[0032] The fourth aspect of the present invention provides a carbon dioxide methanation catalyst, wherein the catalyst comprises a carrier and an active component, wherein the carrier is the composite oxide of the present invention or the composite oxide prepared by the preparation method of the present invention; and the active component is Ni.

[0033] In some embodiments of the present invention, preferably, based on the total amount of the catalyst, the content of the carrier in the catalyst is 82-85wt%, and the content of the active component is 15-18wt%.

[0034] In some embodiments of the present invention, preferably, the radial strength of the catalyst is greater than 315 N / cm. The catalyst is shaped by the carrier, i.e., the shape obtained by the aforementioned die casting. The radial strength can be the crushing strength along the diameter direction of the catalyst (columnar as described above).

[0035] In some embodiments of the present invention, preferably, the crystal size of the catalyst is 5-8nm. The aforementioned composite oxide provided by the method of the present invention as a carrier can provide better mechanical strength for the obtained catalyst; and it is also beneficial to the dispersion of the active component, and the crystal size of the active component can be 5-8nm. In the preparation of the catalyst, the active component is loaded on the carrier by introducing the precursor of the active component onto the carrier, and then drying, calcining, and finally reducing. The active component can be introduced by equal volume impregnation, and finally the active component content is 15-18wt%. The reduction conditions may include: a nitrogen-hydrogen mixed gas with a hydrogen content of 5vol% as the reducing gas, and the volume space velocity of the mixed gas is 1000h -1 , the reduction temperature is 400°C, the system pressure is 0.1MPa, and the reduction time is 6 hours. At this time, in the catalyst obtained after reduction, since the composite oxide provided by the present invention is used as a carrier and has the aforementioned composition and structure, the grain size of the active component can be 5-8nm.

[0036] A fifth aspect of the present invention provides a method for methanation of carbon dioxide, wherein the method comprises: in the presence of a catalyst, subjecting carbon dioxide to a methanation reaction with hydrogen to obtain methane; wherein the catalyst is the carbon dioxide methanation catalyst of the present invention.

[0037] In some embodiments of the present invention, preferably, the conditions of the methanation reaction include: system pressure of 2.5-3MPa, bed inlet temperature of 280-320°C, volume space velocity of 6000-1000h -1 , the hydrogen-carbon molar ratio is 3-4:1. Among them, the volume space velocity is the total volume space velocity of carbon dioxide and hydrogen. The hydrogen-carbon molar ratio is the molar ratio of hydrogen to carbon dioxide.

[0038] The present invention will be described in detail below through examples. In the following examples, the crystalline content is measured by the XRD method; the porosity is measured by the porosity detector method;

[0039] The water absorption is calculated by the following formula:

[0040]

[0041] The aluminum source, calcium source, magnesium source and zirconium source are all commercially available.

[0042] The chemical composition of the obtained carrier is obtained based on the feed calculation and XRD spectrum analysis.

[0043] Example 1

[0044] Al(NO 3 ) 3 9H 2 O 375g, Mg(NO 3 ) 2 6H 2 O 76.8g, Ca(NO 3 ) 2 ·4H 2 O 70.4g, Zr(NO 3 ) 4 ·5H 2 Add 169g of O to 500mL of deionized water and stir at 60°C until completely dissolved. 2 CO 3 and 500 mL of deionized water, stirring at 60 °C until completely dissolved;

[0045] The two solutions and the precipitant were connected in parallel at a flow rate of 2 mL / s, accompanied by stirring. After the co-flow precipitation reaction was completed, stirring was continued for 30 min. After the reaction was complete, aging was performed for 5.5 h, and the filter cake was repeatedly washed with deionized water until the pH of the filtrate was 7.0 to obtain a co-precipitate filter cake.

[0046] The grinding balls, coprecipitate and water were mixed in a mass ratio of 1:1:1 and placed in a high-energy ball mill for 5 h. The median particle size D 50 The ball milled mixture was subjected to solid-liquid separation, and the obtained solid was dried at 120°C for 5h; the obtained dry product was crushed and then filled into a mold (diameter 20mm, height 30mm, embedded 2×2mm, pore diameter 5mm) for die casting, the molding temperature was 600°C, the molding pressure was 4.0MPa, the heat and pressure were maintained for 3min, cooled, demolded, and the chemical composition was Mg 0.3 Ca 0.3 Zr 0.4 Al 2 O 4 carrier.

[0047] Example 2

[0048] Al(NO 3 ) 3 9H 2 O 375g, Mg(NO 3 )2 6H 2 O 102.4g, Ca(NO 3 ) 2 ·4H 2 O 70.8g, Zr(NO 3 ) 4 ·5H 2 Add 126.9 g of O to 500 mL of deionized water and stir at 60 °C until completely dissolved. 2 CO 3 and 500 mL of deionized water, stirring at 60 °C until completely dissolved;

[0049] The two solutions and the precipitant were connected in parallel at a flow rate of 2 ml / s, accompanied by stirring. After the co-flow precipitation reaction was completed, stirring was continued for 30 minutes. After the reaction was complete, aging was performed for 5 hours, and the filter cake was repeatedly washed with deionized water until the pH of the filtrate was 7.0 to obtain a co-precipitate filter cake.

[0050] The grinding balls, coprecipitate and water were mixed in a mass ratio of 1:1:1 and placed in a high-energy ball mill for 5 h. The median particle size D 50 The ball milled mixture was subjected to solid-liquid separation, and the obtained solid was dried at 120°C for 5h; the dried product obtained by crushing was filled into a mold (diameter 20mm, height 30mm, embedded 2×2mm, pore diameter 5mm) for die casting, the molding temperature was 650°C, the molding pressure was 4.5MPa, the heat and pressure were maintained for 3min, cooled, demolded, and the chemical composition was Mg 0.4 Ca 0.3 Zr 0.3 Al 2 O 4 carrier.

[0051] Example 3

[0052] Al(NO 3 ) 3 9H 2 O 375g, Mg(NO 3 ) 2 6H 2 O 12.8g, Ca(NO 3 ) 2 ·4H 2 O 118g, Zr(NO 3 ) 4 ·5H 2 O 169g add deionized water 500mL, stir at 60℃ until completely dissolved; weigh 168g NaHCO 3 and 500 mL of deionized water, stirring at 60 °C until completely dissolved;

[0053] The two solutions and the precipitant were connected in parallel at a flow rate of 2 mL / s, accompanied by stirring. After the co-flow precipitation reaction was completed, stirring was continued for 30 min. After the reaction was complete, aging was performed for 5 h, and the filter cake was repeatedly washed with deionized water until the pH of the filtrate was 7.0 to obtain a co-precipitate filter cake.

[0054] The grinding balls, coprecipitate and water were mixed in a mass ratio of 1:1:1 and placed in a high-energy ball mill for 5 h. The median particle size D 50 The ball milled mixture was subjected to solid-liquid separation, and the obtained solid was dried at 120°C for 5h; the dried product obtained by crushing was filled into a mold (diameter 20mm, height 30mm, embedded 2×2mm, pore diameter 5mm) for die casting, the molding temperature was 650°C, the molding pressure was 4.5MPa, the heat and pressure were maintained for 4min, cooled, demolded, and the chemical composition was Mg 0.1 Ca 0.5 Zr 0.4 Al 2 O 4 carrier.

[0055] Example 4

[0056] Al(NO 3 ) 3 9H 2 O 375g, Mg(NO 3 ) 2 6H 2 O 128g, Ca(NO 3 ) 2 4H2O 59g, Zr(NO 3 ) 4 ·5H 2 Add 105.7g of O to 500mL of deionized water and stir at 60℃ until completely dissolved. 2 CO 3 and 500 mL of deionized water, stirring at 60 °C until completely dissolved;

[0057] The two solutions and the precipitant were connected in parallel at a flow rate of 2 mL / s, accompanied by stirring. After the co-flow precipitation reaction was completed, stirring was continued for 30 min. After the reaction was complete, aging was performed for 5 h, and the filter cake was repeatedly washed with deionized water until the pH of the filtrate was 7.0 to obtain a co-precipitate filter cake.

[0058] The grinding balls, coprecipitate and water were mixed in a mass ratio of 1:1:1 and placed in a high-energy ball mill for 5 h. The median particle size D 50The ball milled mixture was subjected to solid-liquid separation, and the obtained solid was dried at 120°C for 5h; the dried product obtained by crushing was filled into a mold (diameter 20mm, height 30mm, embedded 2×2mm, pore diameter 5mm) for die casting, the molding temperature was 700°C, the molding pressure was 5MPa, the heat and pressure were maintained for 4min, cooled, demolded, and the chemical composition was Mg 0.5 Ca 0.25 Zr 0.25 Al 2 O 4 carrier.

[0059] Example 5

[0060] Al(NO 3 ) 3 9H 2 O 375g, Mg(NO 3 ) 2 6H 2 O 89.6g, Ca(NO 3 ) 2 ·4H 2 O 82.6g, Zr(NO 3 ) 4 ·5H 2 O 126.9g, add deionized water 500mL, stir at 60℃ until completely dissolved; weigh 210g Na 2 CO 3 and 500 mL of deionized water, stirring at 60 °C until completely dissolved;

[0061] The two solutions and the precipitant were connected in parallel at a flow rate of 2 mL / s, accompanied by stirring. After the co-flow precipitation reaction was completed, stirring was continued for 30 min. After the reaction was complete, aging was performed for 5.5 h, and the filter cake was repeatedly washed with deionized water until the pH of the filtrate was 7.0 to obtain a co-precipitate filter cake.

[0062] The grinding balls, coprecipitate and water were mixed in a mass ratio of 1:1:1 and placed in a high-energy ball mill for 5 h. The median particle size D 50 The ball milled mixture was subjected to solid-liquid separation, and the obtained solid was dried at 120°C for 5h; the dried product obtained by crushing was filled into a mold (diameter 20mm, height 30mm, embedded 2×2mm, pore diameter 5mm) for die casting, the molding temperature was 700°C, the molding pressure was 5MPa, the heat and pressure were maintained for 3.5min, cooled, demolded, and the chemical composition was Mg 0.35 Ca 0.35 Zr 0.3 Al 2 O 4 carrier.

[0063] Example 6

[0064] Al(NO 3 ) 3 9H 2 O 375g, Mg(NO 3 ) 2 6H 2 O 179.2g, Ca(NO 3 ) 2 ·4H 2 O 35.4g, Zr(NO 3 ) 4 ·5H 2 O 63.4g, add 500mL of deionized water, stir at 60℃ until completely dissolved; weigh 225g of KHCO 3 and 500 mL of deionized water, stirring at 60 °C until completely dissolved;

[0065] The two solutions and the precipitant were connected in parallel at a flow rate of 2 mL / s, accompanied by stirring. After the co-flow precipitation reaction was completed, stirring was continued for 30 min. After the reaction was complete, aging was performed for 6 h, and the filter cake was repeatedly washed with deionized water until the pH of the filtrate was 7.0 to obtain a co-precipitate filter cake.

[0066] The grinding balls, coprecipitate and water were mixed in a mass ratio of 1:1:1 and placed in a high-energy ball mill for 5 h. The median particle size D 50 The ball milled mixture was subjected to solid-liquid separation, and the obtained solid was dried at 120°C for 5h; the dried product obtained by crushing was filled into a mold (diameter 20mm, height 30mm, embedded 2×2mm, pore diameter 5mm) for die casting, the molding temperature was 650°C, the molding pressure was 4.5MPa, the heat and pressure were maintained for 3min, cooled, demolded, and the chemical composition was Mg 0.7 Ca 0.15 Zr 0.15 Al 2 O 4 carrier.

[0067] Example 7

[0068] Al(NO 3 ) 3 9H 2 O 375g, Mg(NO 3 ) 2 6H 2 O 51.2g, Ca(NO 3 ) 2 ·4H 2 O 94.4g, Zr(NO 3 )4 ·5H 2 O 169.2g, add deionized water 500mL, stir at 60℃ until completely dissolved; weigh 320g K 2 CO 3 and 500 mL of ionized water, stirring at 60°C until completely dissolved;

[0069] The two solutions and the precipitant were connected in parallel at a flow rate of 2 mL / s, accompanied by stirring. After the co-flow precipitation reaction was completed, stirring was continued for 30 min. After the reaction was complete, aging was performed for 5.5 h, and the filter cake was repeatedly washed with deionized water until the pH of the filtrate was 7.0 to obtain a co-precipitate filter cake.

[0070] The grinding balls, coprecipitate and water were mixed in a mass ratio of 1:1:1 and placed in a high-energy ball mill for 5 h. The median particle size D 50 The ball milled mixture was subjected to solid-liquid separation, and the obtained solid was dried at 120°C for 6h; the dried product obtained by crushing was filled into a mold (diameter 20mm, height 30mm, embedded 2×2mm, pore diameter 5mm) for die casting, the molding temperature was 700°C, the molding pressure was 5MPa, the heat and pressure were maintained for 4min, cooled, demolded, and the chemical composition was Mg 0.2 Ca 0.4 Zr 0.4 Al 2 O 4 carrier.

[0071] Example 8

[0072] Al(NO 3 ) 3 9H 2 O 375g, Mg(NO 3 ) 2 6H 2 O 51.2g, Ca(NO 3 ) 2 ·4H 2 O 141.6g, Zr(NO 3 ) 4 ·5H 2 O 84.6g, add 500mL of deionized water, stir at 60℃ until completely dissolved; weigh 243g of Na 2 CO 3 and 500 mL of deionized water, stirring at 60 °C until completely dissolved;

[0073] The two solutions and the precipitant were connected in parallel at a flow rate of 2 mL / s, accompanied by stirring. After the co-flow precipitation reaction was completed, stirring was continued for 30 min. After the reaction was complete, aging was performed for 5 h, and the filter cake was repeatedly washed with deionized water until the pH of the filtrate was 7.0 to obtain a co-precipitate filter cake.

[0074] The grinding balls, coprecipitate and water were mixed in a mass ratio of 1:1:1 and placed in a high-energy ball mill for 5 h. The median particle size D 50 The ball milled mixture was subjected to solid-liquid separation, and the obtained solid was dried at 120°C for 5h; the dried product obtained by crushing was filled into a mold (diameter 20mm, height 30mm, embedded 2×2mm, pore diameter 5mm) for die casting, the molding temperature was 700°C, the molding pressure was 5MPa, the heat and pressure were maintained for 4min, cooled, demolded, and the chemical composition was Mg 0.2 Ca 0.6 Zr 0.2 Al 2 O 4 carrier.

[0075] Example 9

[0076] Al(NO 3 ) 3 9H 2 O 375g, Mg(NO 3 ) 2 6H 2 O 51.2g, Ca(NO 3 ) 2 ·4H 2 O 47.2g, Zr(NO 3 ) 4 ·5H 2 O 253.8g, add 500mL of deionized water, stir at 60℃ until completely dissolved; weigh 269g of NaHCO 3 and 500 mL of deionized water, stirring at 60 °C until completely dissolved;

[0077] The two solutions and the precipitant were connected in parallel at a flow rate of 2 mL / s, accompanied by stirring. After the co-flow precipitation reaction was completed, stirring was continued for 30 min. After the reaction was complete, aging was performed for 5.5 h, and the filter cake was repeatedly washed with deionized water until the pH of the filtrate was 7.0 to obtain a co-precipitate filter cake.

[0078] The grinding balls, coprecipitate and water were mixed in a mass ratio of 1:1:1 and placed in a high-energy ball mill for 5 h. The median particle size D 50The ball milled mixture was subjected to solid-liquid separation, and the obtained solid was dried at 120°C for 6h; the dried product obtained by crushing was filled into a mold (diameter 20mm, height 30mm, embedded 2×2mm, pore diameter 5mm) for die casting, the molding temperature was 680°C, the molding pressure was 5MPa, the heat and pressure were maintained for 3min, cooled, demolded, and the chemical composition was Mg 0.2 Ca 0.2 Zr 0.6 Al 2 O 4 carrier.

[0079] The composition, content, porosity and water absorption of the carriers obtained in Examples 1-9 are shown in Table 1.

[0080] Table 1

[0081]

[0082] Note: * refers to the content of crystal phase structure, magnesium oxide, aluminum oxide, calcium oxide and zirconium oxide in the composite oxide.

[0083] Preparation of carbon dioxide methanation catalyst

[0084] Weigh nickel nitrate nonahydrate and prepare a nickel nitrate solution with a concentration of 40wt%; soak the composite oxides in Examples 1-9 as carriers in the nickel nitrate solution for 5-6 hours by an equal volume impregnation method, wash and dry, and soak them again in a nickel nitrate solution of the same concentration, wash and dry. After two immersion and drying, the obtained product is calcined in a muffle furnace at 450°C, and then reduced to obtain the corresponding carbon dioxide methanation catalyst A1-A9. The reduction conditions include: a nitrogen-hydrogen mixed gas with a hydrogen content of 5vol% as the reducing gas, and a volume space velocity of the mixed gas of 1000h / s. -1 , the reduction temperature is 400℃, the system pressure is 0.1MPa, and the reduction time is 6 hours.

[0085] The catalyst was subjected to strength testing, and the crushing strength of the catalyst along the diameter direction was measured; the grain size of the active component obtained after reduction in the catalyst was determined by a chemical analysis method, and the results are shown in Table 2.

[0086] Table 2

[0087] serial number Ni content, wt% Strength (N / cm) Crystal size of active component, nm A1 15.0 321 5.2 A2 16.3 326 8.0 A3 18.0 318 6.7 A4 15.6 322 7.0 A5 15.9 328 5.2 A6 17.6 316 6.4 A7 16.2 319 7.8 A8 17.1 325 5.9 A9 16.8 323 7.2

[0088] Methanation of carbon dioxide

[0089] Catalyst A1 was loaded into a fixed bed reactor with a volume of 100 mL to carry out the carbon dioxide methanation reaction. The process conditions included: system pressure of 3.0 MPa, (CO 2 +H 2) has a volume space velocity of 8000 h -1 , the inlet temperature is 300℃, and the hydrogen-carbon ratio is 4: 1. After the reaction, the conversion rate of carbon dioxide is 98.07%, and the selectivity of methane in the product is greater than 99.9%.

[0090] It can be seen from the results of the above embodiments and Tables 1-2 that the composite oxide provided by the present invention has the above composition and structure, and can provide the further obtained catalyst with better strength and grain size of the active component, thereby achieving the effect of improving the methanation reaction of carbon dioxide and meeting the high strength requirements of hydrothermal synthesis of the methanation reaction.

[0091] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A composite oxide, characterized in that The composite oxide contains magnesium oxide, calcium oxide, zirconium oxide and aluminum oxide, and the chemical formula is Mg x Ca y Zr (1-x-y) The crystal phase structure shown in Al2O4, wherein 0<x<1, 0<y<1.

2. The composite oxide according to claim 1, wherein The crystal phase structure is a spinel structure; Preferably, based on the total amount of the composite oxide, in the composite oxide, the crystalline phase content of the crystalline phase structure is greater than 97wt%, the content of magnesium oxide is 0.2-0.8wt%, the content of aluminum oxide is 0.3-0.9wt%, the content of calcium oxide is 0.2-1wt%, and the content of zirconium oxide is 0.2-0.6wt%; Preferably, the composite oxide has a porosity of 30-35% and a water absorption of 28-32%.

3. The composite oxide according to claim 1 or 2, wherein The crystalline structure has a chemical formula of at least one of the following: Mg 0.3 Ca 0.3 Zr 0.4 Al2O4、Mg 0.4 Ca 0.3 Zr 0.3 Al2O4、Mg 0.1 Ca 0.5 Zr 0.4 Al2O4、Mg 0.5 Ca 0.25 Zr 0.25 Al2O4、Mg 0.35 Ca 0.35 Zr 0.3 Al2O4、Mg 0.7 Ca 0.15 Zr 0.15 Al2O4、Mg 0.2 Ca 0.4 Zr 0.4 Al2O4、Mg 0.2 Ca 0.6 Zr 0.2 Al2O4、Mg 0.2 Ca 0.2 Zr 0.6 Al2O4.

4. A method for preparing a composite oxide, characterized in that: The preparation method comprises: wet ball milling, drying and molding an aluminum source, a calcium source, a magnesium source and a zirconium source in sequence to obtain the composite oxide.

5. The preparation method according to claim 4, wherein The calcium source is selected from calcium nitrate and / or calcium acetate; the magnesium source is selected from magnesium nitrate and / or magnesium acetate; the zirconium source is selected from zirconium nitrate and / or zirconium acetate; and the aluminum source is selected from pseudo-boehmite.

6. The preparation method according to claim 4 or 5, wherein: The wet ball milling process comprises: co-precipitating the aqueous solution containing the aluminum source, calcium source, magnesium source and zirconium source with a precipitant and washing the filter cake to neutrality to obtain a co-precipitate; ball milling the mixture of the co-precipitate and water to a medium particle size D of the particles contained. 50 Less than 0.5 μm; Preferably, the precipitant is selected from at least one of Na2CO3, NaHCO3, K2CO3 and KHCO3.

7. The preparation method according to any one of claims 4 to 6, wherein: The drying temperature is 100-140°C and the drying time is 8-10h; Preferably, the molding is die-casting molding, wherein the molding temperature is 600-700° C., the molding pressure is 4-5 MPa, and the molding holding time is 3-4 min.

8. Use of the composite oxide according to any one of claims 1 to 3 or the composite oxide prepared by the preparation method according to any one of claims 4 to 7 in carbon dioxide methanation reaction.

9. A carbon dioxide methanation catalyst, characterized in that: The catalyst comprises a carrier and an active component, wherein the carrier is a composite oxide according to any one of claims 1 to 3 or a composite oxide prepared by the preparation method according to any one of claims 4 to 7; the active component is Ni; Preferably, based on the total amount of the catalyst, the content of the carrier in the catalyst is 82-85wt%, and the content of the active component is 15-18wt%; Preferably, the radial strength of the catalyst is greater than 315 N / cm, and the grain size of the active component in the catalyst is 5-8 nm.

10. A method for methanation of carbon dioxide, characterized in that: The method comprises: in the presence of a catalyst, subjecting carbon dioxide to a methanogenic reaction with hydrogen to obtain methane; Wherein, the catalyst is the carbon dioxide methanation catalyst according to claim 9; Preferably, the conditions for the methanation reaction include: system pressure of 2.5-3 MPa, bed inlet temperature of 280-320°C, volume space velocity of 6000-1000 h -1 , the hydrogen-carbon molar ratio is 3-4:1.

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