CO2 hydrogenation to light olefins on ZnO–ZrO2/SAPO-34 tandem catalysts: optimizing the Zn/Zr ratio†

Abstract

The hydrogenation of CO₂ to light olefins is a promising method for CO₂ resource utilization. Tandem catalysts composed of metal oxides and zeolites have been widely studied for the hydrogenation of CO₂ to light olefins, but there are bottlenecks in terms of CO₂ conversion and light olefin yield. ZnO–ZrO₂ catalysts are extensively employed in CO₂ hydrogenation because of their excellent stability at high temperatures, but there is still a “see-saw” problem between the CO₂ conversion and light olefin selectivity. In addition, the synergetic effect between Zn and Zr sites on the reaction process remains unclear. In this work, a series of ZnO–ZrO₂ catalytic materials with various Zn : Zr ratios were synthesized via co-precipitation, and the interaction between Zn and Zr could be regulated by altering the Zn : Zr ratio. XRD and TEM results confirmed the successful synthesis of ZnO–ZrO₂ composite oxides and the existence of a certain interaction between Zn and Zr. CO₂-TPD, H₂-TPR and XPS results indicated that the interaction between Zn and Zr could improve the hydrogenation capacity of the catalyst and also induce the generation of abundant oxygen vacancies to effectively promote the adsorption and activation of CO₂. Catalytic performance results showed that ZnO–ZrO₂(1 : 4)/SAPO-34 exhibits the best CO₂ to light olefin conversion activity with a CO₂ conversion rate of 26.4% and a C⁼₂–C⁼₄ selectivity of 72.6%. This work provides a feasible strategy for rational design and optimization of CO₂ hydrogenation catalysts.