Hydrogenation of dimethyl oxalate to ethylene glycol on Cu/SiO2 catalysts prepared by a deposition-decomposition method: Optimization of the operating conditions and pre-reduction procedure

Cu/SiO2 catalysts prepared by a deposition-decomposition (DD) method using ammonium hydroxide are currently among the most promising catalysts for oxalates hydrogenation to ethylene glycol (EG). Here, a Cu/SiO2 catalyst prepared by the DD method was pre-reduced at a) 200–350 °C in 100% H2, and 2) 200 °C in a 50% H2/N2 mixture. Then, it was tested at 200 °C, and 25 barg, while EG yields were optimized, with H2-GHSV and H2/DMO ratios in the ranges 1000–4000 h−1 and 30–200 mol/mol. The calcined catalyst presents an XRD amorphous Cu phyllosilicate phase. After pre-reduction in pure H2 at 200–250 °C (Tred), the Cu metallic surface area increased from 6 to 12 m2/gcat and slightly decreased at 350 °C. Simultaneously, the silanol's band, measured by DRIFT experiments, increased with Tred. The highest ethylene glycol yield (91%) was achieved after pre-reduction at 200 °C in pure hydrogen, working with an H2-GHSV and H2/DMO of 1050 h−1 and 68 mol/mol, respectively. The catalyst was stable for more than 36 h after a 20 h induction period. Catalyst characterization results as a function of Tred confirm that mixed-valence copper nanoparticles favor the EG selective formation, while side reactions leading to ethanol and 1,2-butanediol are related to exposed acidic and basic sites due to decreased Cu/support interactions.