The Birth of Nickel Phosphide Catalysts: Monitoring Phosphorus Insertion into Nickel

Abstract

Tri‐n‐octylphosphine (TOP) is used widely as a phosphorating agent to yield metal phosphide nanocatalysts, which are receiving intense attention because of their high performance in both electrochemical and hydrotreatment catalytic processes, such as the hydrogen evolution reaction and the hydrodesulfurization reaction. We used in situ ambient‐pressure X‐ray photoelectron spectroscopy to investigate the formation of nickel phosphide on the surface of a nickel foil at temperatures close to those employed to form nickel phosphide nanoparticles in the colloidal route. We showed that the onset of phosphorus insertion into nickel occurs at as low as 150 °C, which is much lower than that reported previously (>210 °C). Moreover, the formation of sp2 carbon was observed on the surface as the consequence of TOP alkyl chain decomposition. These findings provide new insights into the surface chemistry of metal phosphide nanoparticles, which are increasingly employed in several fields of catalysis. Our results demonstrate that even below 150 °C, significant phosphorus and carbon incorporation can occur during metal nanoparticle syntheses if TOP is employed as the stabilizing agent.

Designing Nanoparticles and Nanoalloys with Controlled Surface and Reactivity

“…Differential thermal analysis highlighted that nickel is reduced at 212 °C in an endothermic process . The reaction temperature of 220 °C, found empirically, is in fact the optimal one that allows the quantitative reduction of Ni(II) while minimizing the inclusion of carbon (as carbide) and phosphorus (as phosphide), in the forming nanoparticles. Yet, at this temperature the reduction is swift (completed in the first minutes), resulting in a burst of nucleation and favoring a narrow size dispersion.…”

“…These decomposition pathways are not quantitative but allowed obtaining Ni 3 C 1− x nanoparticles covering the whole range of x from 0 to 1, and forming several phases of metal phosphide nanoparticles, such as Cu 3 P, Co 2 P and CoP, Ni 12 P 5 and Ni 2 P . Carbon and phosphorus insertion are obtained in similar temperature range (150–300 °C) and reaction medium . It is therefore difficult to assert that syntheses using TOP produce carbon‐free phosphides, especially in the case of nickel, into which carbon is highly soluble.…”

“…Because of the difficulties inherent to working with TOP, a phosphorus source that is also a source of carbon, other precursors were explored, such as white phosphorus P 4 . This molecule is highly reactive, at the proper oxidation state (0) to react with a metal(0) precursor, and soluble in the reaction medium.…”

Silber‐ und Bronze‐Medaillen des CNRS 2018

“…Carenco sucht nach neuen Wegen zur gezielten Synthese von Nanopartikeln mit bestimmten Zusammensetzungen und Oberflächenzuständen, deren Reaktivität und katalytische Anwendungen sie untersucht. Sie diskutierte die Kohlenmonoxid‐induzierte dynamische Nanostrukturierung von Metalloberflächen in einem Kurzaufsatz in Chemistry—A European Journal , und sie berichtete in ChemCatChem über Nickelphosphid‐Katalysatoren …”

Describing inorganic nanoparticles in the context of surface reactivity and catalysis

“…For instance, tri-noctylphosphine (TOP) decomposes at much lower temperature (150 °C) onto a nickel nanoparticle surface than as a free species. 57 As a consequence of ligand decomposition, phosphorus contamination was observed in several cases with consequences on the activity and selectivity of the nanoparticles in heterogeneous catalysis.…”