Direct Conversion of Syngas into Light Olefins over Zirconium-Doped Indium(III) Oxide and SAPO-34 Bifunctional Catalysts: Design of Oxide Component and Construction of Reaction Network

The direct synthesis of light olefins from syngas over a bifunctional catalyst containing an oxide and zeolite has been proven to be a promising strategy. Nevertheless, an unclear reaction network hinders any further enhancement in catalytic performance, such as increasing the conversion of CO. We herein report a novel bifunctional catalyst composed of a InZr binary oxide and SAPO-34 zeolite displaying superior CO conversion (27.7 %) with selectivity to light olefins (73.6 %) at 400 °C, 2.0 MPa. We demonstrate that the Zr-doped body-centered cubic In₂O₃ phase, exhibiting higher stability than pure In₂O₃ under a reducing atmosphere, is the active oxide component for the initial activation of CO. A complete reaction network is proposed by DFT calculations and model reactions, revealing that CO activation over Zr-In₂O₃ follows a quasi-CO₂ hydrogenation pathway and methanol is the key intermediate to be transformed into light olefins in zeolites. Moreover, inhibiting excessive hydrogenation is an effective strategy to achieve higher performance.