Elucidating the Role of Cu in Ni-Based Catalyst at Nanoscale in Aqueous-Phase Reforming of Ethylene Glycol

Hydrogen is a clean energy source with high mass-based energy density, necessitating the exploration of sustainable production methods, such as aqueous-phase reforming (APR) of biomass-derived feedstocks. In the APR reaction, the Ni-based catalysts have shown promising activity; however, the hydrogenation side reactions prevail throughout the whole reaction gradient, consuming the produced hydrogen. In this study, the Cu-modified Ni catalysts were synthesized and evaluated in APR of ethylene glycol (EG), aiming at the development of a selective Ni-based APR catalyst and elucidation of the role of Cu at the nanoscale. Incorporating an appropriate amount of Cu on Ni enhanced the hydrogen selectivity from 40% for 0Cu/Ni to 71% for 30Cu/Ni with maintained hydrogen production rate, while the activity diminished when the Cu content exceeded the optimal. Kinetic analyses and complementary characterization techniques demonstrated that Cu incorporation into the Ni matrix resulted in the formation of Cu–Ni alloy at the nanoscale and hybridization of the electronic orbital at the metal surface, decreasing the electron density of Ni to change its affinity to the specific functional groups. Consequently, the adsorption configuration of ethylene glycol was switched from the oxygen site on Ni to the carbon site on Cu-modified Ni, which may lead to the distinct barrier for both C–C bond cleavage and the hydrogenation of the formed intermediates. The methanation was inhibited by Cu incorporation with promoted hydrogen selectivity and maintained hydrogen productivity. This study may contribute to the future catalyst design for selective hydrogen production in APR reactions.