Regulation of oxygen vacancy concentration over ZnCr oxide in bifunctional catalyst for the direct conversion of syngas to light olefins

Metal oxides play a crucial role in catalytic activity of bifunctional catalyst for directly converting syngas into light olefins. A series of ZnCr oxides were synthesized with varying concentrations of precipitant and different atmospheres of precipitate treatment via co-precipitation method. The characterization results indicate that suitable concentration of precipitant and hydrogen calcination contribute to the generation of more oxygen vacancies that can promote the chemical adsorption of CO. Density function theory calculations confirmed that the adsorption energy of CO could be decreased with increasing concentration of oxygen vacancies, and that the formation energy of oxygen vacancies was lower under the hydrogen atmosphere as compared to the oxygen atmosphere. The catalytic activity demonstrated that more oxygen vacancies promoted the chemisorption and conversion of CO. The ZnCr oxide obtained through hydrogen calcination exhibited the highest concentration of oxygen vacancy and achieved a C-2(=)-C-4(=) selectivity of 86 % and a CO conversion of 43 % at 4 MPa and 5400 mL g(-1)h(-1) combined with SAPO-34 zeolite. These findings suggest that increasing oxygen vacancy concentration on the surface of metal oxides is an effective approach for designing high-performance catalysts for directly converting syngas into light olefins.