Promoting effect of hierarchical zeolite on Ag catalysts for the gas-phase selective hydrogenation of α-methylacrolein

In the field of heterogeneous catalysis, the selective hydrogenation of α,β-unsaturated aldehyde to α,β-unsaturated alcohol is a prominent focus in the synthesis of fine chemicals. Herein, we present a straightforward protocol for constructing hierarchical zeolite supported catalysts for the gas-phase selective hydrogenation of α-methylacrolein to methallyl alcohol. Compared to the original microporous zeolite, the incorporation of mesoporous channels within the hierarchical zeolite gives rise to ample space to embed Ag nanoparticles, thereby delivering a positive effect on enhancing accessibility to metal active sites and leading to increased reactivity. Moreover, unlike the typical transition metals (Pt, Ni, Cu and Co), the unique surface properties of metal Ag inherently plays a crucial role in the formation of a desirable adsorption configuration. The resulting vertical orientation (on-top η1-σ(O) mode) causes the carbonyl group to interact with the Ag active sites via the terminal oxygen atom, while the C=C bond tilts away from the metal surface. Specifically, the selectivity to the targeting methallyl alcohol reaches ~75% over the hierarchical ZSM-5 and Silicalite-1 supported Ag catalysts under optimal reaction conditions. This discovery highlights the significance of pore architecture and adsorption configuration on the catalytic performance, and aims to deepen understanding for the rational design of heterogeneous catalysts in the gas-phase selective hydrogenation of α,β-unsaturated aldehydes.