Tuning product selectivity in dimethyl oxalate hydrogenation via Ga-promoted Cu/SiO2 catalysts: the interplay between Cu+/Cu0 sites and surface acidity

The development of efficient catalysts for the selective hydrogenation of dimethyl oxalate (DMO) to high-value oxygenates is of great industrial importance. This study presents a systematic investigation into the promotional effect of gallium (Ga) on Cu/SiO 2 catalysts for tailoring product selectivity in DMO hydrogenation. A series of Ga x Cu 30 /SiO 2 catalysts with varying Ga loadings (x = 0.5, 1, 3 wt%) were synthesized via the ammonia evaporation method. With a moderate Ga doping of 0.5 wt%, the Ga 0.5 Cu 30 /SiO 2 catalyst achieved an exceptional ethylene glycol (EG) yield of 74 %, which is three times higher than its Ga-free counterpart (23 %). Further increases in Ga loading to 1 and 3 wt% redirected the reaction pathway, steering the selectivity towards ethanol (ET, 81 %) and 2-methoxyethanol (MT, 54 %), respectively. Characterization by N 2 O titration, XRD, XPS, in situ FT-IR and H 2 -TPR revealed that Ga incorporation fine-tunes the synergy between metallic Cu 0 (for H 2 dissociation) and Cu + sites (for C=O bond polarization). Concurrently, the generated surface acid sites facilitate subsequent dehydration and hydrogenolysis steps. Consequently, the catalytic performance is directly correlated with the evolution of Cu valence states and surface acidity. This work provides a rational strategy for designing multifunctional catalysts for the selective synthesis of target chemicals from DMO.