A systematic study of the synthesis of transition metal phosphides and their activity for hydrodeoxygenation of phenol

Abstract Five different unsupported transition metal phosphides were synthesized and tested for hydrodeoxygenation of phenol in gas phase at 300 °C and atmospheric pressure. The metal phosphide phases were synthesized in two steps: synthesis of phosphates and temperature programmed reduction. In situ X-ray diffraction and temperature programmed reduction revealed the formation of the phosphide phases: Ni2P, MoP, CoP/CoP2, FeP and WP. The in situ diffractograms showed that the metal phosphate precursor is decomposed during reduction, producing metal oxide (Molybdenum) or pyrophosphate (Nickel, Iron) phases, without the formation of a metallic phase. All catalysts showed high selectivity to direct deoxygenation products, indicating that the phosphide phases promoted the direct cleavage of C O bond. However, product distribution varied significantly depending on the metal phosphide phase. Ni2P catalyst exhibited the highest selectivity to benzene, whereas CoP, FeP and WP showed a significant formation of cyclohexene. FeP also produced cyclohexane, while a large amount of C5 – C6 hydrocarbons was formed over MoP. Product distribution was correlated to the type of crystal structure of transition metal phosphides.