Catalytic amounts of phosphines, such as P ⁿ Bu₃ and PCy₃, have a positive effect on the activity of cobalt phosphide nano-urchins for the semi-hydrogenation of phenylacetylene at 100 °C under H₂ (7 bars).

Abstract

Transition metal phosphides are promising, selective, and air-stable nanocatalysts for hydrogenation reactions. However, they often require fairly high temperatures and H₂ pressures to provide quantitative conversions. This work reports the positive effect of phosphine additives on the activity of cobalt phosphide nano-urchins for the semi-hydrogenation of phenylacetylene. While the nanocatalyst's activity was low under mild conditions (7 bar of H₂, 100 °C), the addition of a catalytic amount of phosphine remarkably increased the conversion, e. g., from 13 % to 98 % in the case of P ⁿ Bu₃. The heterogeneous nature of the catalyst was confirmed by negative supernatant activity tests. The catalyst integrity was carefully verified by post-mortem analyses (TEM, XPS, and liquid ³¹P NMR). A stereo-electronic map was proposed to rationalize the activity enhancement provided over a selection of nine phosphines: the strongest effect was observed for low to moderately hindered phosphines, associated with strong electron donor abilities. A threshold in phosphine stoichiometry was revealed for the enhancement of activity to occur, which was related to the ratio of phosphine to surface cobalt atoms.