Preparation Of MGaZrO_x (M=Zn,Ce)/SAPO-34 Bifunctional Catalyst And Its Catalytic CO₂ Hydrogenation To Light Olefin

CO₂ hydrogenation to light olefins is an effective way to utilize CO₂ resources.Currently,metal oxide-molecular sieve（OX-ZEO）bifunctional catalysts have received much attention because of their high light olefins selectivity.Among them,the recently reported GaZrO_x/SAPO-34 shows excellent catalytic performance due to its abundant surface oxygen vacancies,but there is still much room for exploration of this catalytic system in improving CO₂ conversion and reducing CO selectivity.In addition,the introduction of additives in bimetallic oxides is considered an effective strategy to enhance the catalytic performance.Therefore,in this thesis,GaZrO_x/SAPO-34 was used as the center of research,and two additives,Zn with excellent hydrogen dissociation ability and Ce with strong CO₂ adsorption ability,were introduced into GaZrO_x for modification,and the physical and chemical properties of MGaZrO_x ternary metal oxides and and their catalytic performance of composite SAPO-34 for CO₂hydrogenation to light olefins.The combination of multiple characterization tools to reveal the conformational relationship and reaction mechanism of bifunctional catalysts is expected to provide a new research idea to enhance the yield of CO₂ hydrogenation to light olefins.The ternary metal oxides of ZnGaZrO_x were prepared by the co-precipitation method to investigate the effects of the doping amount of Zn additives and the calcination temperature of the metal oxides on the adsorption activation capacity of ZnGaZrOx for H₂ and CO₂.Both the appropriate amount of Zn and calcination temperature significantly improved the H₂ and CO₂ adsorption activation capacity of the catalyst.3.5%ZnGaZrO_x calcination temperature was 650℃,and the catalyst showed excellent catalytic performance and high-temperature inhibition of inverse water gas.Further optimization of 3.5%ZnGaZrO_x and SAPO-34 two-phase composite ratio and mode,process conditions（temperature,space velocity,pressure）.The results showed that with a mass ratio of 3.5%ZnGaZrO_x:SPAO-34 at 2:1,the compound was physically mixed,and the reaction conditions were 390℃,3 Mpa,3600 m L·g_cat^-1·h^-1,the CO₂ conversion was 26.6%,CO selectivity was only 46.1%,C₂⁼-C₄⁼selectivity was82.1%,and C₂⁼-C₄⁼yield was as high as 11.8%.And the catalyst can maintain good stability within 100 h,where light olefins yield is the highest yield reported in the literature so far.The DRIFTS study demonstrated that the doping of suitable Zn could increase the rate and concentration of HCOO*and CH₃O*intermediates,promote the production of methanol,and inhibit the occurrence of the side reaction RWGS reaction.The ternary metal oxides of CeGaZrO_x were prepared by co-precipitation method to investigate the adsorption and activation capacity of CO₂ for x%CeGaZrO_x with different Ce additives doping and the effect of calcination temperature of SAPO-34molecular sieve on the catalytic performance.The doping of an appropriate amount of Ce induced abundant oxygen vacancies,which effectively promoted the activation of CO₂.Increasing the calcination temperature of SAPO-34,the specific surface area decreased,the grain size increased slightly,and the strong acidity increased,resulting in excessive hydrogenation and lower selectivity of light olefins.the catalyst showed excellent catalytic performance at the calcination temperature of 450℃for the Ce doping of 4%and SAPO-34.Further optimization of 4%CeGaZrO_x and SAPO-34 two-phase composite ratio and mode,process conditions（temperature,space velocity,pressure）.The results showed that the CO₂ conversion was 9.5%,CO selectivity was34.7%,C₂⁼-C₄⁼selectivity was 87.4%,and the yield reached 5.4%at 4%CeGaZrO_x:SPAO-34 mass ratio of 2:1,the compounding method was physical mixing,and the reaction conditions were 350℃,2 Mpa,and 3600 m L·g_cat^-1·h^-1.And the catalyst can maintain good stability within 100 h.The DRIFTS study demonstrated that the doping of appropriate Ce could accelerate the production rate of CO₂ to HCOO*and CH₃O*and promote the production of methanol.