Hydrodeoxygenation of guaiacol over Ni₂P/SiO₂–reaction mechanism and catalyst deactivation

The catalytic hydrodeoxygenation of guaiacol, a phenolic model compound of biomass lignin pyrolysis products, has been investigated under atmospheric pressure in H₂ utilizing a Ni₂P/SiO₂ catalyst. Reaction networks are proposed based on the product distribution as a function of contact time and the temperature programmed surface reaction of adsorbed guaiacol and anisole. Guaiacol is mainly converted to benzene through demethoxylation and dehydroxylation via phenol and anisole as intermediates. Demethylation of guaiacol is a side-reaction, which produces small amounts of catechol. Spent catalyst samples were characterized by means of XRD, XPS, TEM, and temperature programmed oxidation to gain understanding the observed slight deactivation. Coke deposition, sintering, and the altering properties of Ni and P species on catalyst surface all contribute to deactivation, while there is no indication of surface oxidation after reaction. The increase of Ni^δ+ or Ni⁰ on the Ni₂P surface and the decrease of Brønsted acid sites (i.e. P–OH) are considered to be the major reasons of product distribution changes.