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

Abstract

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-WOx/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 WOx species to achieve an ethanol formation rate of 0.163 g·gCat.−1h−1. The addition of Au to Cu-WOx 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-WOx/SiO2 catalyst contributed to a specific CO bond cleavage, especially for EG hydrogenolysis to ethanol during the cellulose conversion.