Selective hydrogenation of oleic acid to fatty alcohols using Rh‐Sn‐B / TiO 2 catalysts: Influence of Sn content

Abstract

The influence of the catalyst Sn content on the production of fatty alcohol from oleic acid by selective hydrogenation was studied using Rh-Sn-B catalysts supported on TiO2. The crystal phase of the support was analyzed by X-ray diffraction (XRD), the reduction state of the metal phase by temperature-programmed reduction (TPR), and the electronic state of surface species by X-ray photoelectron spectroscopy (XPS). The metal activity was evaluated by the dehydrogenation of cyclohexane. It was found that the increase in Sn content leads to a proportional drop in the catalytic activity, which could be related to a metallic interaction between Rh and Sn, as shown by TPR. Oxide and metallic Sn, as well as Rh0 and Rh3+, were found by XPS on the catalyst surface. Metallic Rh was, however, found in higher concentration than oxidized Rh in all cases. The yield to fatty alcohols increased with Sn content, and its maximum value for oleyl and stearyl alcohol was 96%. Furthermore, a higher yield (88.3%) was obtained out of unsaturated fatty alcohol (oleyl alcohol), which has proved to be more valuable than saturated alcohol. This was attributed to an adequate Rh/Sn ratio, which modulates the hydrogenating activity of Rh and makes the metal function more selective for hydrogenation of the carbonyl group. The influence of the support on the catalyst performance decreases as the Sn content increases. The support has a practically negligible influence on the catalyst activity for 4–5 wt.% of Sn content.