Engineering crystal phases of oxides in tandem catalysts for high-efficiency production of light olefins from CO2 hydrogenation

Advances in design concept of oxide-zeolite (OX-ZEO) bifunctional tandem catalysts have demonstrated its potential for highly enhanced selectivity and yield in CO2 conversion by assigning CO2 activation and C-C coupling to specific oxide and zeolite, respectively. However, the crystalline structural effects of oxides have not been thoroughly investigated. Here, ZnO/ZrO2 with different ZrO2 crystalline phases modulated by Li doping has been used as an oxide catalyst to combine with SAPO-34 as a bifunctional composite catalyst for CO2 hydrogenation to light olefins. With the transformation of the support ZrO2 crystalline phase from tetragonal phase to mixed crystalline phase in the catalyst, the CO2 conversion and yield of target product light olefins were significantly improved. The best-performing ZnO/5Li-ZrO2 catalyst exhibited a CO2 conversion of 28.56%, light olefins selectivity of 82.00% with a yield of 8.77% along with good stability under the reaction conditions of 380 degrees C, 3 MPa, and 6000 mL/g/h. The characterization results by XRD, Raman, HRTEM, XPS and CO2-TPD confirmed that the highly enhanced catalytic performance was attributed to the strong interaction between the mixed crystal phase 5Li-ZrO2 and ZnO, which generated a large number of oxygen vacancies for CO2 activation. The results indicate that controlling the crystal phase of the oxide support is of prime importance in designing more active and selective oxide-zeolite bifunctional catalysts for high-efficiency CO2 to light olefins conversion.

Automated summary

The design of bifunctional tandem catalysts combining oxide and zeolite has shown great potential in enhancing the selectivity and yield of CO2 conversion. However, the effect of crystalline structural of oxides has not been well studied. In this study, ZnO/ZrO2 catalysts with different crystalline phases modulated by Li doping were used to convert CO2 to light olefins. The transformation of ZrO2 crystalline phase in the catalyst significantly improved the CO2 conversion and yield of light olefins. The best-performing catalyst exhibited a high CO2 conversion and selectivity for light olefins, and good stability under reaction conditions. The enhanced catalytic performance was attributed to the interaction between the mixed crystal phase of Li-ZrO2 and ZnO, which provided oxygen vacancies for CO2 activation. The results highlight the importance of controlling the crystal phase of the oxide support in designing efficient CO2 conversion catalysts.