Controlled Phase-Transition Synthesis of Transition Metal Phosphide Nickel and Analysis of Its Hydrodechlorination Performance for Trichloroethylene

Transition metal phosphides (TMPs) are promising non-precious metal catalysts with Pt-like catalytic performance for hydrodechlorination (HDC). Herein, a series of nickel phosphide catalysts (x-Ni x P y ) with tunable crystal phases were fabricated via a one-pot hydrothermal route by adjusting ammonia dosage, realizing controlled phase transition from pure Ni 2 P, Ni 2 P/Ni 12 P 5 dual-phase intermediates to pure Ni 12 P 5 . XRD, BET, SEM, HRTEM, SAED and XPS characterizations confirm ammonia acts as an effective crystal regulator to redistribute surface energy and modulate crystal plane exposure, while barely altering the pore structure and specific surface area of catalysts. Fixed-bed tests on trichloroethylene (TCE) HDC show catalytic activity rises first then declines within 400–600 °C, with the optimal reaction temperature at 450 °C. Dual-phase Ni 2 P/Ni 12 P 5 catalysts outperform single-phase Ni 2 P and Ni 12 P 5 samples, among which 1.8-Ni x P y achieves the highest molar-basis C–Cl bond cleavage efficiency of 53.84 %. The superior activity originates from abundant bulk and surface defects generated during crystal reconstruction as well as the synergistic electronic effect of two phases, which creates high-quality interfacial active sites and improves the intrinsic activity of each catalytic center rather than simply increasing the number of surface sites. This work reveals the structure-activity relationship between crystal phase evolution and TCE HDC performance, offering a facile strategy for designing high-efficiency nonnoble metal hydrodechlorination catalysts.