Realizing and Recognizing Syngas-to-Olefins Reaction via a Dual-Bed Catalyst

Abstract

Nowadays, a considerable progress in the syngas-to-olefins (STO) reaction has been made by physically mixed oxide-zeolite catalysts; however, contradictions concerning the reaction mechanism still exist. Although complete separation of the mixed catalysts should help to understand the STO reaction, it can result in lower CO conversion and selectivity of light olefins. Here, we report a stable and selective dual-bed STO catalyst ZnAlOx/SAPO-34, which contains a SAPO-34 molecular sieve packed below ZnAlOx oxide. C2–4 olefins in hydrocarbons can reach 77.0% with only 33.1% CO2 selectivity at 663 K. No significant deactivation is observed during a 100 h test. ZnAlOx itself can be used as a catalyst for the syngas-to-dimethyl ether (STD) reaction. Because the dual-bed catalyst presents similar reaction results and “hydrocarbon pool” intermediates to the mixed one, the STO reaction over a mixed catalyst can be understood as the combination of STD and MTO reactions regardless of catalytic behaviors and mechanisms.