NiFe Catalysts Supported on Nb$_2$O$_5$ for Enhanced Hydrodeoxygenation: A Study on Performance and Selectivity

Biomass-derived bio-oils, particularly those obtained from fast pyrolysis, offer a renewable alternative to fossil fuels. However, their high oxygen content and low stability limit their direct use as transportation fuels. Catalytic hydrodeoxygenation (HDO) represents a promising strategy to increase the quality of bio-oil by removing oxygen from organic compounds. This study investigated the catalytic performance of monometallic and bimetallic Ni-Fe catalysts supported on Nb2O5 and SiO2 for the hydrodeoxygenation (HDO) of guaiacol, a model compound representative of bio-oil derived from lignin. The catalysts were synthesized, characterized, and tested under identical conditions to evaluate the effects of metal composition, support properties, and reaction temperature on activity and selectivity. Compared with their monometallic counterparts, bimetallic Ni-Fe catalysts demonstrated superior performance, with the 5Ni1Fe/Nb2O5 catalyst achieving the highest guaiacol conversion (59%) and enhanced selectivity toward cyclohexanol (34%) and cyclohexane (10%) at 300 degrees C. The synergistic interaction between Ni and Fe facilitated hydrogenation and hydrogenolysis pathways, whereas the acidic and oxophilic properties of Nb2O5 promoted direct deoxygenation (DDO) by enhancing C-O bond cleavage. ... mehrIn contrast, SiO2-supported catalysts exhibited greater Ni dispersion but were more selective toward partially deoxygenated intermediates, such as cyclohexanone and catechol. Among the different temperatures investigated, the HDO at 300 degrees C maximized fully deoxygenated products, whereas lower and higher temperatures favored partial deoxygenation and hydrogenolysis pathways, respectively.