Impact of hydrophobic organohybrid silicas on the stability of Ni₂P catalyst phase in the hydrodeoxygenation of biophenols

Hydrodeoxygenation (HDO) of lignocellulose-derived pyrolysis oils offers an option to produce fuel substitutes. However, catalyst deactivation and stability constitute a significant issue. Herein, the dependence of stability and activity of Ni₂P/SiO₂ HDO catalysts on the support surface polarity is addressed in detail. The support surface polarity was adjusted by copolymerizing tetraethyl orthosilicate (TEOS) with different types and amounts of organosilanes by a sol-gel process in the presence of nickel nitrate and citric acid. After thermal treatment under an inert atmosphere, Ni/SiO₂ precursors were formed. They were converted into Ni₂P/SiO₂ catalysts by using NaH₂PO₂ as a PH₃ source. The catalyst surface polarity was characterized by inverse gas chromatography measurements of the free energy of methanol adsorption, and specific and dispersive surface energies derived from polar and nonpolar probe molecule adsorption. The correlation between catalyst performance and support surface polarity indicates that, to prevent deactivation of the catalyst by water under reaction conditions, the affinity of the support towards polar substances must be decreased below a threshold value.