Insights into the Mn-doping effects on the catalytic performance of ZnCrAlOy/SAPO-34 bifunctional catalyst for the direct conversion of syngas to light olefins

Abstract

Direct conversion of syngas to light olefins (C2=-C4=) over oxide-zeolite bifunctional catalyst provides a new strategy for light olefins production. Herein, we report a series of bifunctional catalysts composed of SAPO-34 zeolite and Mn-doped ZnCrAlOy oxide with the Mn/Cr ratio ranging from 0 to 0.3 for directing conversion of syngas to light olefins. We achieved a C2=-C4= selectivity of 78.60% (free of CO2) in all hydrocarbon products with a CO conversion of 23.53% and STY of 0.19 g/h·gcat. No obvious deactivation was observed after 220 h reaction. The impact of Mn doping on the physicochemical properties of ZnCrAlOy spinel oxides was explored by various in-situ and ex-situ characterizations. It was found that the Mn doping could decrease the particle size of ZnCrAlOy spinel, which leads to the formation of more oxygen vacancies on the surface of catalyst. The oxygen vacancies (Odef/Olatt) were increased from 0.34 to 0.41 when the Mn content ranges from 0 to 0.2. The abundant oxygen vacancies are beneficial to protect more light olefins and intermediate from hydrogenation. These findings are significant for the further development of high-efficiency bifunctional catalysts for the conversion of syngas to hydrocarbons.