Size dependence over Cu-based catalysts for semi-hydrogenation of symmetric-structured molecules

Identification the size dependence behavior of copper active species are crucial for achieving semi-hydrogenation of carbon–oxygen bonds in the symmetric-structured molecules. Semi-hydrogenation of dimethyl oxalate (DMO) was used as typical for investigation, providing a promising pathway for the production of methyl glycolate (MG), an important feedstock for high value-added materials. Here, by employing a theoretical study, we elucidated the structure-sensitivity and emphasized the vital role of electronic and geometric structure in the reaction mechanism over Cu_n/CeO₂ catalysts. The Cu₄ cluster with a “ridge-like” structure and dual sites (Cu⁰-Cu^δ+) exhibited the best performance for semi-hydrogenation of DMO to MG, agreed with the experimental results. Electronic structure of small Cu clusters influences MG selectivity by affecting the strength of donor–acceptor interactions between empty d orbitals of Cu and the π orbitals of CO group. In contrast, steric hindrance induces a downward-directed configuration of acyl species on larger Cu clusters, reducing the Pauli repulsion in the transition state of MG dissociation, and promoting undesired further hydrogenation of MG. Our findings provided a rational guideline for designing catalysts with optimal particle size and morphology in the semi-hydrogenation of symmetric-structured molecules.