Disentangling the Catalytic Mechanisms of C60-Buffered Cu/SiO2 Catalyst for DMO-to-EG Conversion

Both ethylene glycol and methyl glycolate, which can be synthesized by hydrogenating dimethyl oxalate, are important chemical feedstocks, and understanding the mechanistic details underlying those hydrogenation reactions is of pivotal importance for the design of high-performance catalysts. In this work, we employ carefully constructed model cluster catalysts, including Cu4, C60Cu, C60Cu3, and C60Cu4, to mimic the widely utilized Cu/SiO2 catalyst and the recently discovered C60-buffered Cu/SiO2 catalyst based on joint efforts from mass spectrometry, photoelectron spectroscopy, density functional theory calculations, and molecular dynamics simulations. We explored the catalytic mechanisms of the hydrogenation of dimethyl oxalate catalyzed by our model cluster catalysts and uncovered the possibility to tune the product selectively by changing the copper cluster size. Our results reveal important geometric and electronic effects of C60 in promoting the catalytic reactions by reversibly accepting and donating, i.e., serving as an electron buffer, electrons to the adsorbed copper, resulting in the alternating formation of Cu0 and Cuδ+ sites in different steps of the hydrogenation reactions. These oxidation state changes are crucial for the hydrogenation and stabilization of the reaction intermediates.