Ni and Fe mixed phosphides catalysts for O-removal of a bio-oil model molecule from lignocellulosic biomass

Silica-supported catalysts based on mono and bimetallic nickel and iron phosphides with different Ni:Fe molar ratios (1:0,3:1,2:1 and 0:1) were synthesised and tested in the hydrodeoxygenation (HDO) reaction of phenol, a model molecule present in bio-oil derived from pyrolysis of biomass. Tests were performed in a fixed bed reactor under hydrogen pressure (1.5 and 3 MPa) for different contact times. Freshly reduced catalysts were characterised by physisorption of N-2 at 196 degrees C, CO chemisorption, X-ray diffraction, transmission electronic microscopy, temperature-programmed desorption of ammonia and hydrogen, and X-ray photoelectron spectroscopy. Characterization results revealed that the presence of Ni increased their ability to activate hydrogen and the number of active sites, while the presence of Fe favored the spillover process. By increasing the amount of Ni, the surface became enriched with P, and this was associated with the presence of surface P-OH groups that provided Bronsted acid sites to activate O-containing compounds as well as surface hydrogen species that minimised deactivation by coke deposition. Ni-containing phases presented higher HDO capabilities than FeP ones, but generated some O-containing intermediates. In contrast, the FeP catalyst transformed all phenol molecules into O-free compounds (cyclohexane and mainly cyclohexene). (C) 2017 Elsevier B.V. All rights reserved.