Synthesis and Characterization of Discrete Nickel Phosphide Nanoparticles: Effect of Surface Ligation Chemistry on Catalytic Hydrodesulfurization of Thiophene

Abstract Discrete, unsupported nanoparticles of Ni 2 P have been prepared by using a solution‐phase method with bis(1,5‐cyclooctadiene)nickel(0) [Ni(COD) 2 ] as the nickel source and trioctylphosphine (TOP) as the phosphorus source in the presence of the coordinating solvent trioctylphosphine oxide (TOPO). Ni 2 P nanoparticles prepared at 345 °C have an average crystallite size of 10.2 ± 0.7 nm and are capped with TOP and/or TOPO coordinating agents. The surface of the Ni 2 P nanoparticles can be modified by washing with CHCl 3 or by exchanging TOP/TOPO groups with mercaptoundecanoic acid (MUA). The surface areas of these nanoparticles are on the order of 30–70 m 2 g –1 . As‐prepared and MUA‐capped nanoparticles undergo a phase transformation at 370 °C under reducing conditions, but CHCl 3 ‐washed Ni 2 P nanoparticles retain the Ni 2 P structure. CHCl 3 ‐washed and MUA‐capped nanoparticles exhibit higher HDS catalytic activity than as‐prepared nanoparticles or unsupported Ni 2 P prepared by temperature‐programmed reduction of a phosphate precursor. The surface modifications have a clear effect on the catalytic activity as well as the thermal stability of Ni 2 P nanoparticles under reducing conditions.