Cellulose Conversion to Glycols over a Carbon-Supported Ni–WxC Nanocatalyst: The N-Doping Effect on Catalyst Stability

Cellulose is an attractive nonedible feedstock for the production of chemicals, especially through metal catalysis. However, its hydrothermal catalytic conversion induces severe deactivation of catalysts, notably by metal leaching and structure sintering. In this work, we studied a series of nickel- and tungsten-based catalysts supported on porous carbon (C) or N-doped porous carbon (NC). These catalysts were formed from nanosized bimetallic particles of Ni and W supported on porous N-doped carbon supports. The supports were prepared by hydrothermal conversion of N-containing biopolymers, followed by pyrolysis under an inert atmosphere. The bimetallic nanoparticles were deposited by wet impregnation. The idea was to study the influence of N-doping of the support on the stability during the catalysis of the metal nanoparticles on the support. For instance, an amorphous nitrogen-doped carbon with a hierarchical porosity and a surface area up to 286 m2·g–1 was obtained from the hydrothermal pyrolysis of chitosan, and, depending on the activation atmosphere (H2 or N2), metal particles in the 15–30 nm size were obtained. Regarding the application to cellulose conversion, molar yields up to 20% in ethylene glycol and 8% in propylene glycol were obtained by a reaction at 245 °C for 1 h using a nitrogen-activated catalyst. When the catalyst was activated under hydrogen, the ethylene glycol yield was increased to 51% while the propylene glycol yield remained low. Very interestingly, the presence of N-containing moieties within the carbon supports proved an interest by increasing the catalyst stability during successive reaction cycles. The ethylene glycol yield remained stable during 3 reaction cycles for the N-doped catalyst, as compared to the nondoped one, which presented an important deactivation after 3 cycles.