Catalytic performances of Ni3P for hydrodeoxygenation of phenol in aqueous phase using methanol as hydrogen donor

Developing efficient and stable catalysts for the aqueous-phase hydrodeoxygenation (HDO) of phenolic compounds using sustainable hydrogen sources remains a significant challenge. This work investigates unsupported nickel phosphide (Ni 3 P) as a bifunctional catalyst for the in-situ HDO of phenol with methanol as a hydrogen donor. The Ni 3 P catalyst, prepared via a simple temperature-programmed reduction method, demonstrated excellent performance under optimized conditions (230 °C, 12 h), achieving phenol conversion > 94% and cyclohexane selectivity of 72.4%. This significantly outperformed a monometallic Ni catalyst (15.8% conversion), highlighting the beneficial electronic modification induced by phosphorus. Mechanistic studies revealed a complex reaction network where methanol reforming supplies active hydrogen, and the Ni₃P surface facilitates sequential hydrogenation-dehydration-hydrogenation steps. However, the catalyst exhibited severe deactivation upon recycling, attributed to poor hydrothermal stability of Ni 3 P. Comprehensive characterization (XRD, XPS, TEM) of spent catalysts identified the root causes of deactivation as surface oxidation to nickel oxyhydroxide (NiOOH) and phosphate species, phosphorus leaching, and a dissolution-recrystallization process leading to particle agglomeration and morphological restructuring. This study not only establishes unsupported Ni 3 P as a highly active catalyst for transfer HDO but also critically addresses its stability limitations, providing essential insights for the design of robust phosphide catalysts for sustainable aqueous-phase upgrading processes.