Yujie Zhao,Jianhua Li,Shuo Liu,Tianyu Han,Yuanyuan Wang,Shetian Liu
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.
13-Ni/ZrO2, 13-Ni3P/ZrO2, 13-Ni/SiO2, and 13-Ni3P/SiO2 catalysts were used in the hydrogenation of diethyl oxalate (DEO) to ethyl glycolate (Egly) to investigate the modulating effect of phosphorus. XRD, TEM and FT-IR results show that phosphorus act as a divider of Ni metallic particle and shows a segregation effect. The presence of P transformed the linkage of surface metals from the original -Ni-Ni-Ni-Ni- to the P-Ni-P-Ni-P state, and FT-IR shows that the former adsorbed CO in a combination of linear and bridging adsorption mode, whereas the latter predominantly in CO linear adsorption. Bridging adsorption is via dual sites and makes the preliminary hydrogenation products less likely to detach from the catalyst surface thus facilitating deep hydrogenation, while linear adsorption facilitates partial hydrogenation by a rapid detachment of intermediate product like Egly. The various loading Ni3P/SiO2 catalysts show incomplete phosphorylation with increasing nickel loading, giving rise to a state of coexistence of Ni and Ni3P crystalline phases. This may lead to a coexistence of surface -Ni-Ni-Ni-Ni- and P-Ni-P-Ni-P and the corresponding assort of adsorption, e.g. bridging/linear ones, making deep hydrogenation occur partially besides stepwise hydrogenation.
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