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 in 5−15 nm via a two-step procedure: preparation of supported Ni particles from layered double hydroxide precursors, followed by a further reaction with 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 show 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.

Influence of Synthesis Conditions on the Structure of Nickel Nanoparticles and their Reactivity in Selective Asymmetric Hydrogenation

“…However, the spectra of these samples (Figure a) do not show significant edge‐shift as reported for phosphides but rather a systematic increase of the peak P2 intensity and correspondingly a decrease of the P1 resonance. P2 is significantly pronounced in the Ni/SiO 2 _5x0.75y spectrum, resembling NiO XANES spectra reported in the literature . Based on this, we propose that the samples are composed of a mixed Ni oxide and metallic phases, whereby spectral variations amongst the samples account for changes in composition of the two phases.…”

“…Furthermore, we note that previous literature on Ni phosphides has indicated that the radial distribution function presents pronounced changes with the content of P and that the FT EXAFS of the Ni/SiO 2 _5x3y sample is similar to the spectrum reported for a Ni 12 P 5 phase with a calculated oxidation state of 0.43 . Therefore, it could also be possible that the Ni/SiO 2 _5x3y sample might contain a small amount of P as an amorphous phase, as we would have expected considering that the OAm:TOP ratio used in its synthesis was similar to the one used in the preparation of the unsupported Ni _2.5x1.5y sample.…”

“…With respect to the Ni foil, Ni/SiO 2 _5x1.5y and Ni/SiO 2 _5x3y clearly show a less intense pre‐edge region P1 and a more intense P2 peak. The position of the K‐edge (defined as the position of maximum first derivative) was previously found for Ni phosphides between NiO and Ni standards, indicating that the formal oxidation state for phosphides ranges between 0 and 2, where the higher the amount of P, the higher the energy position of the edge . However, the spectra of these samples (Figure a) do not show significant edge‐shift as reported for phosphides but rather a systematic increase of the peak P2 intensity and correspondingly a decrease of the P1 resonance.…”

Electrons and Hydroxyl Radicals Synergistically Boost the Catalytic Hydrogen Evolution from Ammonia Borane over Single Nickel Phosphides under Visible Light Irradiation

“…The lattice fringes with spacing of 0.221, 0.193 and 0.180 nm corresponded to the (111) plane of Ni 2 P, (240) plane of Ni 12 P 5 and (222) plane of Ni 3 P. The XPS investigations showed that the Ni 2p 3/2 edges in the three nickel phosphides were deconvolved into three peaks (Figure ). The peaks at 853.0, 852.7 and 852.4 eV were assigned to the positive charge Ni δ+ for Ni 2 P, Ni 12 P 5 and Ni 3 P, respectively . The value of δ was δ(Ni 2 P)>δ(Ni 12 P 5 )>δ(Ni 3 P).…”

Ensemble Design in Nickel Phosphide Catalysts for Alkyne Semi‐Hydrogenation

“…2000 times cheaper than palladium) [20,21] and of the abundance and hydrogen splitting ability of this metal, nickel phosphides have also attracted interest for alkyne semihydrogenation, although only a few contributions have evaluated their activity. In this respect, Corma and coworkers [22] assessed colloidal nickel phosphides in the semi-hydrogenation of functionalized alkynes, while bulk Ni x P y phases were prepared by thermal treatment of hydrotalcite-like compounds containing Ni and tested in phenylacetylene hydrogenation by Chen et al [23] These two contributions showed that the well-known unselective behavior of bare nickel [9,10] can be modulated by treatment with phosphorus. Similar findings have been recently extrapolated by Anderson et al [24] to nanostructured palladium phosphide catalysts for gas-phase applications.…”