Investigating Reaction Mechanisms for Furfural Hydrodeoxygenation on Ni and the Effect of Boron Doping on the Activity and Selectivity of the Catalyst

Fast pyrolysis is a promising route for the production of fuels and high value chemicals from non-fossil fuel resources like biomass. However, the design of active and inexpensive catalysts that can selectively convert furfural, an important component in pyrolysis derived bio-oil, to target chemicals remains a challenge. In this context, Ni-based catalysts are potential candidates for the vapor phase activation of furfural in the presence of H-2. In this paper, mechanisms and energetics (kinetics and thermodynamics) of the catalytic conversion of furfural to furans, furfuryl alcohol, and C-4 products in the presence of H-2 on Ni(111) are established, and the experimentally observed change in the selectivity with temperature is explained, using first-principles density functional theory. Hydrogen adsorbs stronger than furfural on the Ni surface. At low operating temperatures, hydrogen adsorption is spontaneous, leading to high hydrogen surface coverages that favor furfural hydrogenation and decarbonylation over ring-opening, to form furfuryl alcohol and furans. At higher temperatures, hydrogen adsorption is not thermodynamically favorable, leading to a relatively clean Ni surface on which furfural ring-opening and decarbonylation are favored, leading to C- (4) products and furans. We reveal that the incorporation of subsurface boron in Ni leads to a corrugated catalyst surface (NiB) on which furfural adsorbs stronger than hydrogen. The free energy barriers for the formation of furans and C-4 products are also considerably lower in the presence of boron, suggesting an enhanced catalytic activity of NiB. Thus, we propose that the boron-doped Ni catalyst is a potential candidate for selectively converting furfural to furan and C-4 products at lower operating temperatures, relative to Ni.