Transition Metal Phosphides (Ni, Co, Mo, W) for Hydrodeoxygenation of Biorefinery Products (a Review)

Abstract

The active use of transition metal phosphides in catalysis commenced at the beginning of the 2000s primarily in hydrodesulfurization and hydrodenitrogenation reactions. Owing to an increased interest in biomass-based feedstocks the intensive use of phosphides in hydrodeoxygenation reactions started in the first part of the 2010s. In earlier reviews devoted to phosphides, which were published before the 2010s, no information pertaining to hydrodeoxygenation is available. This review addresses monometallic phosphides of such transition metals as nickel, cobalt, molybdenum, and tungsten and covers their structure, synthesis, and properties. Transition metal phosphides are promising catalysts for hydroprocesses. They possess both metal active sites and acid sites, and, therefore, demonstrate activity not only in hydrogenation but in a number of acid-catalyzed processes. The review concerns the hydrodeoxygenation reactions of higher fatty acids and their esters; vegetable oils; and bio-oil and its model compounds. The hydrotreatment of vegetable oils and their derivatives over phosphides makes it possible to obtain hydrocarbons, which can be used as diesel fuel components or as a pure fuel. Using the hydrodeoxygenation of bio-oil model compounds catalyzed by phosphides partially or fully deoxygenated products may be obtained; however, the hydrotreatment of bio-oil itself did not provided positive results so far and calls for further research.