Role of nanosized sheet-like SAPO-34 in bifunctional catalyst for syngas-to-olefins reaction

Direct conversion of syngas to light olefins via oxide-zeolite strategy attracted extensive attention recently. Nanosized sheet-like SAPO-34, denoted as SAPO-34(NS), was synthesized and utilized as the zeotype in the bifunctional catalyst to enhance the activity of syngas-to-olefins (STO) reaction. SEM and Ar physisorption demonstrated that SAPO-34(NS) exhibited abundant outer cages and facilitated the diffusion of reactant and products. GC-MS revealed that the carbonaceous species in ZnCrOx + SAPO-34(NS) was lighter because of the enhancement of diffusion, thus ZnCrOx + SAPO-34(NS) was more active during STO reaction than the bifunctional catalyst containing micron-sized cubic SAPO-34. The evolution of carbonaceous species in the bifunctional catalyst proved that maintaining tetramethyl-benzenes as the majority of carbonaceous species was benefit to enhance CO conversion in STO reaction over bifunctional catalyst. 18.49% CO conversion and 88.18% light olefins selectivity (free of CO2) were achieved over ZnCrOx + SAPO-34(0.061NS) at 653 K, 1.0 MPa, GHSV = 6000 ml.g(-1).h(-1). The catalytic performance was stable after 6000 min of reaction.