Plasma Synthesis of Ni 2 P from Mixtures of NiCl 2 and Hypophosphites

A series of mixtures of NiCl2, hypophosphites (NaH2PO2 and NH4H2PO2), and additives were used as precursors (denoted as x additive:y hypophosphite:z NiCl2, where x, y, and z represents the molar ratios of the compounds) for the synthesis of Ni2P both in N2 and H2 plasma. The catalytic performances of the obtained catalysts were evaluated by the hydrodenitrogenation (HDN) of quinoline (Q) and decahydroquinoline (DHQ). Ni2P was stoichiometrically synthesized by the treatment of 1.0NH4H2PO2:2.0NiCl2 with N2 plasma at a low total power input of 8 W (40 V × 0.2 A). In H2 plasma, the precursor was over-reduced to a mixture of Ni and Ni2P, with Ni2P as the minor phase. The over-reduction can be inhibited by the addition of proper amount of alkali-metal chloride (NaCl or KCl) or P2O5. CaCl2 facilitated the reduction of nickel salts to Ni. KCl was the best among the additives investigated. Both the surface and bulk over-reduction of 1.0NH4H2PO2:2.0NiCl2 was inhibited by KCl, while P2O5 mainly inhibited the bulk over-reduction. The addition of KCl strongly suppressed the hydrogenation of Q to DHQ, but facilitated the HDN of DHQ. On the other hand, not only the hydrogenation of Q but also the dehydrogenation of DHQ was substantially inhibited by P2O5.