Evaluation of transition metal phosphides supported on ordered mesoporous materials as catalysts for phenol hydrodeoxygenation†
A series of transition metal phosphides (Ni2P, Co2P and MoP) have been synthesized by temperature programmed reduction of the corresponding metal phosphate precursors loaded over mesostructured Al-SBA-15, mesoporous γ-Al2O3 (m-Al2O3) and ordered mesoporous carbon (CMK-3). Both the dispersion and metal phosphide phases attained are strongly influenced by the support features, such as their acidic and textural properties. XRD, TEM and H2 chemisorption results revealed that the MoP phase was probably formed but it underwent a fast re-oxidation in air. On the other hand, metal phosphide formation was hindered over m-Al2O3 as only metallic Ni and Co were detected. All the materials prepared have been evaluated as catalysts in hydrodeoxygenation (HDO) using phenol as a bio-oil model compound. The highest phenol conversions were attained with the catalysts based on the acidic supports (Al-SBA-15 and m-Al2O3). Nevertheless, Co2P/Al-SBA-15, Ni2P/m-Al2O3 and Co2P/m-Al2O3 yielded cyclohexanol as the main product denoting very low HDO efficiency. In contrast, Ni2P/Al-SBA-15 showed remarkable catalytic properties, being the only catalyst that provided almost full phenol conversion and extremely high HDO efficiency, with cyclohexane selectivity higher than 90%. This may be due to a synergetic effect between the high electron deficiency, generated by the Niα+ (0 < α < 1) species owing to an electron transfer from Ni to P and the different acidic sites present in the catalyst.