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

•ZnCrOx spinel is prepared and mixed with SAPO-34 for syngas conversion.•Concentration of precipitant influences oxygen vacancy concentration.•Hydrogen calcination contributes to generate more oxygen vacancies.•More oxygen vacancies promote the chemisorption and conversion of CO.•A CO conversion of 43 % and a C2=-C4= selectivity of 86 % are achieved.