Highly Dispersed Ni Based Catalyst For The Low Temperature Performance Of CO₂ Methanation Reaction

Global warming caused by the greenhouse effect is getting worse.In order to reduce carbon emissions and realize the resource utilization of CO₂,CO₂ methanation has become a research hotspot.At present,there are two problems to be solved in the reaction,including improving the low-temperature performance and thermal stability of the Ni-based catalyst.Numerous studies have shown that increasing the dispersion of the active components and alkaline of the catalytic system can effectively increase the CO₂ conversion.In addition,the doping of structure additive is advantageous for improving the sintering resistance of the catalyst.In order to improve the low-temperature performance of the catalyst,the structure of the catalyst was optimized from three aspects:support characteristics,dispersion and particle size of the active metal Ni,and doping of basic additives.Small-sized Ni nanoparticles with low-loading and high dispersion supported on single-crystal m-ZrO₂with large specific surface area is prepared.The catalyst exhibits excellent catalytic performance in the CO₂ methanation reaction.the CO₂ conversion of 6 wt.%Ni-MgO_1/4/ZrO₂ catalyst is as high as 90%,and the CH₄ selectivity is nearly 100%at250°C,0.1 MPa,WHSV=15,000 m L·g^-1·h^-1.Combined with CO₂-TPD,XRD,TEM characterization tests and TOF calculation,it is found that the surface of single-crystal m-ZrO₂ with large specific surface area has a large number of CO₂ adsorption and activation sites,which is the key role to increase the adsorption capacity of CO₂ and improve the low-temperature performance of the catalyst.;Ni nanoparticles are highly dispersed on the surface of the support,the dispersion is as high as 45.2%;the TOF value is related to the size effect of the metal Ni.When the average particle size of the Ni nanoparticles is 2.3 nm,the corresponding TOF value is as high as 1.22×10^-2 s^-1 at200°C;the doping of a small amount of basic additive MgO does not change the metal dispersion and TOF value of the catalyst,and has little effect on the CO₂ conversion.Therefore,it is not necessary to add extra alkaline to the Ni/ZrO₂ catalytic system.In order to improve the thermal stability of Ni-based catalysts,the effect of MgO as a structural additive on the thermal stability of Ni/ZrO₂ catalyst system was investigated.The results show that Mg O is spread on the surface of ZrO₂ support,and the interaction between metal Ni nanoparticles and Mg O modified ZrO₂ support is regulated by the interaction between Ni-Mg,which effectively improves the resistance to sintering of Ni-based catalyst.The NiMg_1/4 catalyst was continuously operated for 110 h at high temperature and high space velocity of 60,000 m L·g^-1·h^-1,and remained stable without obvious signs of deactivation.Combined with TEM,XPS,H₂-uptakes and TG analysis,it is known that the catalyst deactivation is mainly attributed to the sintering agglomeration of Ni nanoparticles in the Ni/ZrO₂ catalytic system,rather than carbon deposition.