From Co to Co@Co₂P and CoP nanorods: synthesis and performances in selective hydrogenation of phenylacetylene

Transition metal phosphides are emerging catalysts for reactions traditionally catalyzed by noble metals. Cobalt phosphide nanostructures are currently intensively studied as electrocatalysts, but their catalytic properties in thermocatalytic reactions are much less explored. Here we report the topochemical reaction of ferromagnetic metallic cobalt nanorods with tris(trimethylsilyl) phosphine (PTMS) at 165 °C, which leads to the conservation of the nanorod shape while transforming them to Co@Co₂P core@shell nanorods. The Co₂P shell thickness can be controlled through the PTMS/Co ratio. Modulation of the core-shell structure allows tuning the magnetic properties of the resulting nano-objects. Increasing both the temperature and PTMS/Co ratio results in the complete transformation of Co into well-crystallized CoP nanorods. The catalytic performances Co@Co₂P and CoP nanorods in the selective hydrogenation of phenylacetylene have been evaluated. It is shown that increasing the P/Co ratio in the nanorods allows increasing both the activity and the selectivity to styrene. Comparison with cobalt phosphide nanoparticles reported in the literature for the selective hydrogenation of phenylacetylene shows the superior performance of the Co@Co₂P and CoP nanorods prepared in this work.