Catalyst for carbon dioxide methanation and preparation method thereof

[0034] The specific steps of the preparation method of the catalyst for carbon dioxide methanation of the present invention are:

[0035] 1) Preparation of composite carrier by impregnation-precipitation method: the salt solution corresponding to the water-soluble metal oxide is impregnated in γ-Al by stirring at room temperature 2 O 3 On the carrier, the immersion time is 4-6 hours, that is, the salt solution corresponding to the water-soluble metal oxide can completely enter the γ-Al 2 O 3 In the carrier; then introduce the precipitant to the pH value of the solution 8-10 (Ce(OH) when the pH value is ≥8 3 Precipitation begins to form. In an alkaline environment with a pH value of 8-10, small crystal particles with better dispersibility are easy to form. If the pH value is too high, the particles will agglomerate sharply). The precipitant is added to better protect The salt solution corresponding to the water-soluble metal oxide is uniformly supported on the base carrier γ-Al 2 O 3 Surface: After the solution is uniformly precipitated, let it stand for 2-4 hours to form and grow up to a certain particle size, then filter, wash, dry, and heat to decompose to obtain a composite carrier;

[0036] Among them, γ-Al 2 O 3 The mass ratio to water-soluble metal oxide is 77-86:2-10; the precipitation agent is NH 3 ·H 2 O, Na 2 CO 3 , NaOH; drying conditions are 100-120 ℃ for 12-24 hours; heating and decomposition is calcined at 450-600 ℃ for 4-6 hours, preferably 550 ℃ for 5 hours; the concentration of precipitation agent is preferably 0.8 mol/L;

[0037] 2) Preparation of the catalyst precursor: the active component salt solution is supported on the composite carrier obtained in step 1) by an equal volume impregnation method; wherein the composite carrier: active component=84-90wt%:10-16wt%; impregnation The temperature is normal temperature, and the immersion time is 3-5 hours; preferably 4 hours;

[0038] 3) Preparation of the catalyst: After drying the catalyst precursor obtained in step 2), plasma treatment is carried out at room temperature and pressure. The plasma treatment conditions are: vacuum degree 2~200Pa, treatment time 45-120min, and drying conditions : Dry at 100-120°C for 12-24 hours to obtain the catalyst for carbon dioxide methanation of the present invention.

[0039] The present invention introduces plasma technology to replace the high-temperature roasting treatment in the existing preparation method (the carbon dioxide methanation catalyst in the prior art is usually prepared by impregnating transition metal salts on the surface of the oxide, and then roasting and reducing at high temperature. Because the high-temperature roasting process is avoided (the temperature in the plasma discharge area is very low), many adverse reactions at high temperatures are avoided, and it is not easy to agglomerate and sinter. The resulting catalyst active component has a small particle size and a better dispersion, making The stability of the catalyst has also been significantly improved. In addition, plasma technology can enhance and improve the adhesion and interaction between the metal and the carrier, increase the reduction degree of the catalyst active metal and the number of surface active centers, so that the reduction ability of the catalyst is enhanced, and the dispersion degree is also improved. In addition, the catalyst prepared by plasma technology has the characteristics of large specific surface area, fast reduction rate, and large number of active centers.

[0040] The present invention preferably adopts non-equilibrium cold plasma treatment, which is characterized by high electron temperature (10 4 -10 5 K) and relatively low gas temperature can effectively avoid the destruction of the catalyst structure and crystal form during high-temperature treatment; radio frequency plasma technology, as a kind of non-equilibrium cold plasma, can use external energy to make reactants on the molecular scale Molecule excitation, dissociation and ionization produce a large number of non-equilibrium high-energy activated species. Due to the bombardment of high-energy electrons and ions on the surface, the decomposition temperature and reduction temperature of the catalyst precursor can be reduced, and the thermal and chemical effects can effectively promote the active components of the catalyst. And the interaction between the carrier.

[0041] The selection of the degree of vacuum in the present invention is based on the treatment atmosphere having better treatment effect without the influence of air. When the degree of vacuum is higher than 200 Pa, the influence of air cannot be ignored. The treatment time should be controlled on the catalyst surface while Ni 0 When the treatment time is less than 45min, the catalyst will not be completely decomposed, and the treatment time is higher than 120min, so that the catalyst will have high catalytic activity and stability. 0 Phase formation, and plasma treatment gas electron temperature up to 10 4 K. Excessive treatment time will affect the interaction between the metal and the carrier, which is not conducive to the effective dispersion of the active metal.

[0042] Preferably, the plasma treatment conditions in the above method are: input voltage 60-120V, gas flow rate 20-45ml/min, radio frequency 13.56MHz; discharge parameters: anode current 100±10mA, grid current 50±10mA; gas is N 2 , H 2 , Air or Ar.

[0043] Further, the present invention also provides a method for using the above-mentioned catalyst for the methanation of carbon dioxide. The application conditions of the catalyst for catalyzing the methanation of carbon dioxide are as follows: the reaction pressure is normal pressure, and the volumetric space velocity of the raw material gas is 8100-15000 ml/(h·g cat ), H 2 /CO 2 The molar ratio is 2/1-4/1. The gas volumetric space velocity is: the volume of the raw material gas that the catalyst passes per unit time and unit mass under specified conditions, namely: space velocity = raw gas volume flow rate/catalyst mass. And the greater the space velocity, the shorter the residence time, the lower the reaction depth, but the processing capacity is enhanced; the smaller the space velocity, the longer the residence time, and the reaction depth increases, but the processing capacity decreases.

[0044] Preferably, the volumetric space velocity of the raw gas is 10000ml/(h·g cat ), H 2 /CO 2 The molar ratio is 4:1.

[0046] Example 1 12.7wt% NiO/6.0wt% CeO 2 -81.3wt%γ-Al 2 O 3 Catalyst preparation

[0047] A First, CeO is prepared by dipping-precipitation method 2 /γ-Al 2 O 3 Composite carrier: Weigh 1.06g Ce(NO 3 ) 3 ·6H 2 Put O in a beaker, add 20ml of deionized water and stir to dissolve it; weigh 4.65g of γ-Al 2 O 3 Place in the above solution, stir at room temperature for 60 minutes, and then slowly add the precipitation agent NH dropwise 3 ·H 2 O(0.8mol/L) to pH=9, stir for 2 hours to make the precipitation uniform and then aging (aging, that is, let stand at room temperature) for 2 hours, filter, wash, dry overnight at 120°C, and calcinate at 550°C for 5 hours CeO 2 /γ-Al 2 O 3 Composite carrier, of which CeO 2 The mass fraction of is 6.0wt%;

[0048] Preparation of B catalyst precursor: Weigh 2.83g Ni(NO 3 ) 2 (Analytical grade, commercially available) Place in a beaker, add 20ml of deionized water and stir to dissolve; Weigh 5g of CeO prepared in step A 2 /γ-Al 2 O 3 The composite carrier is placed in a magnetic crucible, and the Ni(NO 3 ) 2 The immersion liquid is added dropwise to the crucible at room temperature, and it is absorbed and immersed for 4 hours with constant stirring until all the immersion liquid is completely immersed in CeO 2 /γ-Al 2 O 3 Composite carrier

[0049] Preparation of catalyst C: After the catalyst precursor obtained in step B is evaporated to dryness in a water bath at 80°C, it is placed in a drying box and dried overnight at 110°C. The dried sample is placed in a glass desiccator for later use; at room temperature, weigh the above 1.0g of the sample is laid flat in the discharge glass tube, plasma treated under the condition of a vacuum of 100Pa, and the discharge gas N is introduced 2 (The flow rate is 30ml/min), the input voltage is adjusted to 100V, the radio frequency is 13.56MHz, and the treatment time is 60min to prepare the finished catalyst.

[0050] The mass percentage composition of each component in the catalyst is: NiO: 12.7%; γ-Al 2 O 3 : 81.3%; CeO 2 : 6.0%.

[0051] Example 2-11

[0052] Compared with Example 1, only the content of catalyst components or the types of nickel salt and water-soluble metal salt used are different, and the other processes are the same as those of Example 1, and each finished catalyst is prepared. The catalyst composition of Examples 2 to 11 and the nickel salt and water-soluble metal salt used are shown in Table 1.

[0053] Table 1 Catalyst composition table

[0054]

[0055] The catalyst obtained in Examples 1-11 was tableted and sieved to obtain catalyst particles of 60-80 mesh, and 200 mg was filled in a fixed bed reactor, and hydrogen was used for in-situ reduction. The reduction temperature was 450°C and the reaction pressure was normal pressure. The raw material gas ratio is n(H 2 ): n(CO 2 )=4∶1, gas volumetric space velocity 10000ml/h·g cat The temperature range of the investigation is 240-360℃, and the composition of the tail gas is analyzed by the TDX01 column of the GC-1690 gas chromatograph (TCD), and the data is recorded by the chromatographic workstation N2000.

[0056] The calculation formulas for the conversion rate, selectivity and yield of the reaction are as follows:

[0057] x p = F p ·A p /∑(f i ·A i )

[0058] X(CO 2 )=(F in ·X in (CO 2 )-F out ·X out (CO 2 ))/(F in ·X in (CO 2 ))×100%

[0059] X(H 2 )=(F in ·X in (H 2 )-F out ·X out (H 2 ))/(F in ·X in (H 2 ))×100%

[0060] S(CH 4 )=F out ·X out (CH 4 )/(F in ·X in (CO 2 )-F out ·X out (CO 2 ))×100%

[0061] Y(CH 4 )=X(CO 2 )·S(CH 4 )×100%

[0062] Where: x p -Percentage content of species p; f p -Correction factor for species p; F-gas flow;

[0063] A p -Peak area of ​​species p; X-conversion rate; Y-yield rate; S-selectivity

[0064] The activity test results of the catalysts obtained in Examples 1-11 (i.e. CO 2 Conversion rate X CO2 /% and CH 4 Selective S CH4 /%)As shown in table 2. In addition, we counted different CeO 2 The content corresponds to the activity of the catalyst obtained in the example, and the evaluation result (CO 2 Conversion rate) see Table 3.