Promoting effect of hierarchical zeolites 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 aldehydes to α,β-unsaturated alcohols 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 with the original microporous zeolite, the incorporation of mesoporous channels into 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, the unique surface properties of metal Ag, unlike those of typical transition metals (Pt, Ni, Cu and Co), 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 Ag active sites via the terminal oxygen atom, while the CC bond tilts away from the metal surface. Specifically, the selectivity towards the target methallyl alcohol reaches ∼75% over 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 catalytic performance and aims to deepen the understanding of the rational design of heterogeneous catalysts for the gas-phase selective hydrogenation of α,β-unsaturated aldehydes.