Oxygen Vacancy-Rich Amorphous ZnCr Oxides Combined with Zeolites for Highly Active and Stable Conversion of Syngas into Light Olefins

Abstract

The remarkable selectivity of light olefins makes bifunctional catalysis a highly promising technique for directly producing light olefins from syngas. Amorphous ZnCr oxides were synthesized by low-temperature calcination in a H 2 atmosphere and combined with SAPO-34 zeolites to convert syngas to light olefins. The characterizations revealed that the amorphous ZnCr oxides exhibited a noteworthy capability to adsorb and activate more CO molecules due to a larger specific surface area and more oxygen vacancies compared to the crystalline ZnCr oxides. More active intermediate species would exist on the surface of the amorphous ZnCr oxides and within the pores of the SAPO-34 zeolite. Simultaneously, amorphous ZnCr oxides exhibited greater stability compared to crystalline ZnCr oxides because structural reconstruction would occur on crystalline ZnCr oxides, leading to the appearance and agglomeration of ZnO particles during harsh reaction conditions. Consequently, the bifunctional catalyst composed of amorphous ZnCr oxides and SAPO-34 zeolites demonstrated superior catalytic activity and stability in syngas conversion. After reaction for 50 h, the bifunctional catalyst maintained a CO conversion of 49.8% and a C 2 = −C 4 = selectivity of 80.2%, achieving a space−time yield of 16.2 mmol•g −1 •h −1 . The findings suggest that controlling the structure of metal oxide is an efficient method for developing catalysts with high catalytic activity and stability in syngas conversion.