Preparation, characterization and catalytic activity of monodisperse colloidal metal borides

Abstract

A new method, proposed for the preparation of colloidal (d= 20–70 Å) monodisperse particles of Ni₂B, Co₂B and Ni–Co–B, has been examined from the mechanistic point of view. The metal boride catalysts are prepared by reduction with NaBH₄ of Ni^II and Co^II ions solubilized in the inner water cores of reversed micelles composed of cetyltrimethylammonium bromide-hexan-1-ol-water. The curve of particle size as a function of either Ni^II or Co^II concentration shows a clear-cut minimum. This behaviour can be explained, provided a critical number of metal ions is assumed for the initial nuclei formation. The catalytic properties of the metal boride particles have been tested for the room temperature liquid phase hydrogenation of croton-aldehyde. On Ni₂B particles the CC double bond is preferentially hydrogenated, while on Co₂B particles a non-negligible hydrogenation of the CO group also occurs.