Insights into effects of ZrO2 crystal phase on syngas-to-olefin conversion over ZnO/ZrO2 and SAPO-34 composite catalysts

The utilization of metal oxide-zeolite catalysts in the syngas-to-olefin reaction is a promising strategy for producing C2–C4 olefins from non-petroleum resources. However, the effect of the crystal phase of metal oxides on the catalytic activity of these oxides is still ambiguous. Herein, typical metal oxides (ZnO/ZrO2) with different crystal phases (monoclinic (m-ZrO2) and tetragonal (t-ZrO2)) were employed for syngas conversion. The (ZnO/m-ZrO2+SAPO-34) composite catalyst exhibited 80.5% selectivity for C2–C4 olefins at a CO conversion of 27.9%, where the results are superior to those (CO conversion of 16.4% and C2–C4 olefin selectivity of 76.1%) obtained over (ZnO/t-ZrO2+SAPO-34). The distinct differences are ascribed to the larger number of hydroxyl groups, Lewis acid sites, and oxygen defects in ZnO/m-ZrO2 compared to ZnO/t-ZrO2. These features result in the formation of more formate and methoxy intermediate species on the ZnO/m-ZrO2 oxides during syngas conversion, followed by the formation of more light olefins over SAPO-34. The present findings provide useful information for the design of highly efficient ZrO2-based catalysts for syngas conversion.