Ultrathin ZSM-5 Zeolite Supporting Platinum Nanoparticles Enabling Enhanced Catalytic Performance in Hydrodeoxygenation of Vanillin

Abstract

The catalytic selectivity of heterogeneous reaction can be effectively regulated by the design of the thickness of zeolite in zeolite-supported noble metal catalysts. Herein, taking the industrially important hydrogenolysis of the biomass-derived compound vanillin as an example, ZSM-5 zeolite with a thinner b-axis (75 nm) loaded with platinum particles (denoted as Pt/ut-ZSM-5) exhibited 99% conversion and 97% selectivity toward the target product 2-methoxy-4-methylphenol. In contrast, the ZSM-5-supported platinum catalyst with a longer b-axis (175 nm) showed only 63.4% conversion and 50% selectivity, respectively. Molecular dynamics simulations reveal that the translocation times for intermediate vanillyl alcohol through thinner ZSM-5 is longer than vanillin, and the diffusion of 2-methoxy-4-methylphenol in thinner ZSM-5 is faster than that of vanillin. The dynamics of vanillin, vanillyl alcohol and 2-methoxy-4-methylphenol exhibit discontinuous behavior, accompanied by intermittent kinetic restrictions arising from free energy barriers within the straight tunnel of ZSM-5. The translocation times of vanillin and vanillyl alcohol through the thicker ZSM-5 zeolite are typically longer than those through the thinner one; the movement of vanillyl alcohol is still slower than vanillin in thicker zeolite. The slower release of intermediate vanillyl alcohol in both thinner and thicker ZSM-5 demonstrates the possible rate-limiting step in the reaction-diffusion process.