Etherification of biomass-derived furanyl alcohols with aliphatic alcohols over silica-supported nickel phosphide catalysts: Effect of surplus P species on the acidity

Abstract

The acidity of nickel phosphide (Ni2P) catalysts plays a crucial role in producing a desired hydrodeoxygenation molecule from biomass-derived substrates; yet, it has never been explored in acid-catalyzed reactions. Herein, we demonstrated the activity of silica-supported Ni2P catalyst prepared with the nominal P/Ni ratio of 2 (Ni2P/SiO2-2P) in the etherification of furanyl alcohols (particularly, 5-(hydroxymethyl)furfural) with aliphatic alcohols including ethanol. By comparing the characteristics of Ni/SiO2, PxOy/SiO2, and Ni2P/SiO2-xP (x = 0.5 and 1), Ni2P/SiO2-2P was revealed to contain the Brønsted and Lewis acid sites of which both contributed to the etherification reaction. Notably, the Brønsted acidity was associated with the surplus P species added to produce the Ni2P phase. Consequently, supported Ni2P catalysts can work in acid-catalyzed reactions if an adequate ratio of Brønsted to Lewis acid sites is provided by the amount of the surplus P species determined by adjusting the P/Ni ratio.