Metal Phosphides Derived from Hydrotalcite Precursors toward the Selective Hydrogenation of Phenylacetylene

Abstract

We report a new synthetic strategy for the fabrication of several supported nickel phosphides (Ni 12 P 5, Ni 2 P, and NiP 2 ) with particle size ranging from 5 to 15 nm via a two-step procedure: preparation of supported Ni particles from layered double hydroxide precursors, followed by a further reaction with a certain amount of red phosphorus. The selective hydrogenation of phenylacetylene over these metal phosphides was evaluated, and the as-prepared Ni 2 P/Al 2 O 3 catalyst shows a much higher selectivity to styrene (up to 88.2%) than Ni 12 P 5 /Al 2 O 3 (48.0%), NiP 2 /Al 2 O 3 (65.9%), and Ni/Al 2 O 3 (0.7%) catalysts. EXAFS and in situ IR measurements reveal that the incorporation of P increases the bond length of Ni–Ni, which imposes a key influence on the adsorption state of alkene intermediates: as the Ni–Ni bond length extends to 0.264 nm, the alkene intermediate undergoes di-π(C═C) adsorption, facilitating its desorption and the resulting enhanced selectivity. Moreover, electron transfer occurs from Ni to P, as confirmed by EXAFS, XPS, and in situ CO-IR experiment, in which the positively charged Ni reduces the desorption energy of alkene and thus improves the reaction selectivity.