Highly-active nickel phosphide hydrotreating catalysts prepared in situ using nickel hypophosphite precursors

• Unsupported and supported Ni(H2PO2)2 reacts to form Ni2P at 468–561 K.
• Ni(H2PO2)2 precursors can be reduced in situ to give highly-active Ni2P catalysts.
• Ni2P/SiO2 and Ni2P/Al2O3 had higher turnover frequencies than Ni–Mo/Al2O3.
• The surfaces of hypophosphite-derived Ni2P catalysts are highly enriched in P.

An in situ method for the preparation of nickel phosphide (Ni2P) on silica, alumina, and amorphous silica-alumina (ASA) supports is described. The synthesis avoids the use of nickel and phosphorus salts by employing the reaction between nickel hydroxide (Ni(OH)2) and hypophosphorus acid (H3PO2), allowing the impregnation of nickel hypophosphite (Ni(H2PO2)2) onto the oxide supports in the absence of salt by-products. Temperature-programmed reduction (TPR) in flowing hydrogen at 573–773 K yields phase pure Ni2P on the supports with small average particle sizes (3–4 nm) as measured using transmission electron microscopy. The conversion of Ni(H2PO2)2 to Ni2P and related reactions were probed using TPR with on-line mass spectral analysis of the gas effluent. Unsupported Ni(H2PO2)2 reacts in flowing hydrogen to produce PH3 and H2O at 468 and 482 K, respectively; the reaction is shifted to increasingly higher temperatures for Ni(H2PO2)2 supported on SiO2, Al2O3 and ASA. The hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) properties of the Ni2P catalysts were probed using a mixed feed containing carbazole and benzothiophene. While Ni2P/SiO2 catalysts prepared by the different methods exhibited similar HDN and HDS activities, the in situ prepared Ni2P/Al2O3 and Ni2P/ASA catalysts were substantially more active than their ex situ counterparts prepared from hypophosphite- and phosphate-based precursors.

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