Plasma Synthesis of Ni2P from Mixtures of NiCl2 and Hypophosphites

A series of mixtures of NiCl 2 , hypophosphites (NaH 2 PO 2 and NH 4 H 2 PO 2 ), and additives were used as precursors (denoted as x additive: y hypophosphite: z NiCl 2 , where x, y , and z represents the molar ratios of the compounds) for the synthesis of Ni 2 P both in N 2 and H 2 plasma. The catalytic performances of the obtained catalysts were evaluated by the hydrodenitrogenation (HDN) of quinoline (Q) and decahydroquinoline (DHQ). Ni 2 P was stoichiometrically synthesized by the treatment of 1.0NH 4 H 2 PO 2 :2.0NiCl 2 with N 2 plasma at a low total power input of 8 W (40 V × 0.2 A). In H 2 plasma, the precursor was over-reduced to a mixture of Ni and Ni 2 P, with Ni 2 P as the minor phase. The over-reduction can be inhibited by the addition of proper amount of alkali-metal chloride (NaCl or KCl) or P 2 O 5 . CaCl 2 facilitated the reduction of nickel salts to Ni. KCl was the best among the additives investigated. Both the surface and bulk over-reduction of 1.0NH 4 H 2 PO 2 :2.0NiCl 2 was inhibited by KCl, while P 2 O 5 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 P 2 O 5 .