[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.