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 CO 2 conversion by assigning CO 2 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/ZrO 2 with different ZrO 2 crystalline phases modulated by Li doping has been used as an oxide catalyst to combine with SAPO-34 as a bifunctional composite catalyst for CO 2 hydrogenation to light olefins . With the transformation of the support ZrO 2 crystalline phase from tetragonal phase to mixed crystalline phase in the catalyst, the CO 2 conversion and yield of target product light olefins were significantly improved. The best-performing ZnO/5Li-ZrO 2 catalyst exhibited a CO 2 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 °C, 3 MPa, and 6000 mL/g/h. The characterization results by XRD , Raman, HRTEM , XPS and CO 2 -TPD confirmed that the highly enhanced catalytic performance was attributed to the strong interaction between the mixed crystal phase 5Li-ZrO 2 and ZnO, which generated a large number of oxygen vacancies for CO 2 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 CO 2 to light olefins conversion.