Unveiling the Anti-Trap Effect for Bridging Intermediates on ZnAlOx/AlPO-18 Bifunctional Catalysts to Boost Syngas to Olefin Conversion

The migration of bridging intermediates (methanol) from oxides to zeolites is crucial in the direct conversion of syngas to light olefins via the tandem process. As the initiation step of this migration, the adsorption and desorption effect of methanol on oxide components remains elusive. Herein, we systematically compared the catalytic performances of the syngas conversion on a series of ZnAlOx oxides with different Zn/Al ratios and the corresponding bi-component catalysts integrated with the AlPO-18 zeolite component. The structures and surface acidity of ZnAlOx oxides were characterized by XANES, STEM, and py-IR, and the adsorption behavior of methanol on ZnAlOx oxides was characterized by in situ infrared spectroscopy. It is confirmed that the ZnAl₂O₄ spinel surface is the intrinsic active site for CO activation while the strong Lewis acid sites of the oxide surface adsorb methanol strongly, serving as “traps” to inhibit methanol desorption. The additional Zn-containing phase in ZnAlOx oxides with the Zn/Al ratio higher than the stoichiometry of spinel ZnAl₂O₄ is identified as the ZnO component to cover the strong acid sites of the oxide surface and thus enhance the desorption of methanol, benefiting toward the higher catalytic performance of the syngas conversion. A high CO conversion of 41.6% with a C2–C4 olefin selectivity of 79.3% is achieved when the Zn/Al ratio of oxide is 1, and the C2–C4 olefin space time yield reaches 147.0 g kg_cat^–1 h^–1. The anti-trap effect for bridging intermediates on oxide components is thus proposed in bifunctional catalysis, which serves as an effective strategy to exploit and design more efficient multifunctional catalytic systems.