Abstract:

In the hydrogenation of CO₂ to low-carbon olefins（C₂⁼-C₄⁼），the calcination temperature of the bifunctional catalyst has significant effects on its catalytic performance.Based on this，ZnGaZrO _x oxides were prepared by co-precipitation method and SAPO-34 molecular sieves were prepared by hydrothermal method，and then both of them were milled to produce ZnGaZrO _x /SAPO-34 bifunctional catalysts，and the effects of calcination temperature on the physicochemical properties and catalytic performance of ZnGaZrO _x and SAPO-34 were investigated.It was found by XRD，XPS，H₂/CO₂/NH₃-TPD，SEM，N₂ adsorption-desorption and in situ DRIFTS characterization that during the preparation of ZnGaZrO _x，when the calcination temperature was 650 ℃，ZnGaZrO _x had the strongest activation ability of H₂ and CO₂ adsorption，and it could effectively increase the rate and concentration of the generation of HCOO* and CH₃O* to promote the methanol product generation.During the preparation of SAPO-34，when the calcination temperature was 450 ℃，the molecular sieve had the largest specific surface area，the smallest grain size，and the weakest acidity of the strong acid site，which could effectively avoid the secondary hydrogenation of low-carbon olefins，thus obtaining higher selectivity of low-carbon olefins.The ZnGaZrO _x /SAPO-34 bifunctional catalysts synthesized under the optimal conditions showed a CO₂ conversion of 28.3%，a CO selectivity of only 44.6%，a C₂⁼-C₄⁼ selectivity of 84.4%，a C₂⁼-C₄⁼ yield of as high as 13.2% at a reaction temperature of 390 ℃，a pressure of 3 MPa，and an airspeed of 3 600 mL/（g∙h）.And the catalytic performance did not decay significantly within 100 h of reaction.This work provided a new research idea for the modification of bifunctional catalysts.

Key words: CO₂ hydrogenation, light olefins, calcination temperature, oxygen vacancy, acidity