One-pot hydrogenolysis of cellulose to bioethanol over Pd-Cu-WO_x/SiO₂ catalysts

The chemo-catalytic production of ethanol from nonedible lignocellulosic biomass is essential for mitigating energy shortage. In this work, we developed a multifunctional Pd-Cu-WO_x/SiO₂ catalyst for the one-pot aqueous-phase conversion of cornstalk-derived cellulose to ethanol with a yield of 42.5C% at 300 °C and 4 MPa H₂. Kinetic studies demonstrated that the transformation of cellulose to ethanol followed a number of consecutive steps namely, cellulose hydrolysis to glucose with H⁺ in hot water (k₁), glucose conversion to glycolaldehyde over W species (k₂), glycolaldehyde hydrogenation to ethylene glycerol (EG) over Pd (k₃), and EG hydrogenolysis to ethanol over Cu (k₄, rate-determining step). The individual rates were well balanced on Pd, Cu, and WO_x species to achieve an ethanol formation rate of 0.163 g·g_Cat.⁻¹h⁻¹. The addition of Au to Cu-WO_x species led to a relatively low k₃ and thus the formation of a substantial amount of humins, while the Ru introduction catalyzed the over-hydrogenolysis of ethanol to methane and ethane with a high rate, thereby lowering the selectivity to ethanol. The characterization results showed that both the electronic properties of Cu⁺ species and the Cu⁺/Cu⁰ ratio on the Pd-Cu-WO_x/SiO₂ catalyst contributed to a specific C–O bond cleavage, especially for EG hydrogenolysis to ethanol during the cellulose conversion.