Deoxygenation properties of Ru-based phosphide catalysts

Abstract

Bio-oil derived from fast pyrolysis of bio-mass is becoming a more viable option for addressing the growing demand for oil while being more environmentally friendly than fossil fuels. However, bio-oils have poor chemical stability and high acidity due to their high oxygen content. Metal phosphides such as ruthenium phosphide (Ru2P) have been investigated by the Bussell group to catalytically upgrade compounds contained in bio-oil, but further optimization is required before their commercial viability can be accessed. In current research, less expensive, more abundant metals (Co or Ni) are being used to replace some of the ruthenium, which is both expensive and rare. Cobalt-ruthenium phosphides (CoxRu2-xP, 0 ≤ x ≤ 2) and nickel-ruthenium phosphides (NixRu2xP, 0 ≤ x ≤ 2) supported on silica at a fixed P/M molar ratio (M = Co + Ru or Ni + Ru) of 0.72 were prepared from hypophosphite-based precursors and their properties for furan deoxygenation were investigated. The deoxygenation properties of the Co-Ru and Ni-Ru phosphides were compared with those of Co-Ru/SiO2 and Ni-Ru/SiO2 catalysts having the same metal composition as well as an industrial Co-Mo/Al2O3 hydrotreating catalyst. The deoxygenation activities were observed to be strongly influenced by the metal content of the catalysts with the highest activity observed for Mrich MxRu2-xP/SiO2 catalysts, suggesting a synergistic effect as their deoxygenation activities were significantly higher than either Ru2P/SiO2 or M2P/SiO2. The product selectivities of the metal phosphide (e.g. Co1.00Ru1.00P/SiO2) and metal catalysts (e.g. Co1.00Ru1.00/SiO2) differed significantly. The metal phosphides showed a much higher selectivity for C3 hydrocarbons, while the metal catalysts showed high selectivity towards methane. The observed trends in deoxygenation activity and selectivity of the metal phosphide catalysts will be discussed.