The influence of Montmorillonite K10 as a support in the nickel catalyzed hydrogenation of octanal

Abstract

Ni supported on Montmorillonite was tested for the hydrogenation of octanal to octanol. Different loadings of Ni were tested including 10, 15 and 20 wt% across a temperature range from 110 to 180 °C. For the lower loading of Ni, that is 10 wt %, selectivity toward the alcohol was reduced due to the formation of C24 acetal and octyl ether. This poor selectivity to octanol was ascribed to acidic sites present on the clay support. At higher Ni loadings, octanal was more easily hydrogenated to octanol with high selectivity due to the increased surface area of the metal. Subsequently, the rates of side reactions, to form aldol products, acetals and ether were suppressed. The increase in metal surface area as a function of loading was confirmed by chemisorption studies. TEM analysis showed larger particles being formed at the higher loading; however, the average particle size was similar for all the catalysts synthesized which was deduced from the N₂ chemisorption experiments. The highest yield of octanol was obtained over the 20 wt% loaded catalyst which was only slightly higher than that achieved over the 15 wt% catalyst. The effect of the support was assessed by comparing a 10 wt% Ni catalyst loaded on alumina. The alumina supported catalyst showed a higher selectivity to the alcohol at all the temperatures studied and this difference was ascribed to a higher dispersion of NiO on the alumina support compared to the clay support, as well as the difference in acidity of the two supports.