Sequential hydrogenation enhanced by bidirectional hydrogen spillover over cascade catalyst

Abstract

Formulating a synergetic strategy to govern the catalytic function of dual metal sites is paramount to achieving precise control of cascade reactions. Herein, we construct a dual-site cascade catalyst with Pt and Ru species localized in the micropores and mesopores of zeolite, respectively. This architecture enables the spatial separation of Pt and Ru sites in nanoscale proximity. Compared to mono/bi-metallic catalysts, this cascade catalyst enables a 4.4–9.5 times enhancement in activity during the sequential hydrogenation of nitroaromatics to cyclohexylamine. Particularly, bidirectional hydrogen spillover assists hydrogenation between Pt and Ru sites is confirmed, where active hydrogen migrates from the less catalytic activity metal to the adjacent metal sites during the first/second step in the cascade reaction. Characterization studies and density functional theory calculations suggest that bidirectional hydrogen spillover enhances the coverage of active hydrogen at the active sites for each hydrogenation step, thereby reducing the energy barrier of the rate-controlling step. This intriguing phenomenon reveals the mechanism of accelerated hydrogenation and presents an opportunity for devising immensely efficient cascade catalysts.