Stereo-selective hydrogenation of 3-hexyne over low-loaded palladium catalysts supported on mesostructured materials

This paper studies the effect of mesostructured materials in the stereo-selective hydrogenation of 3-hexyne at 298 K and 40 psig pressure of H2 over Pd-supported catalysts at different substrate:palladium (S:Pd) molar ratios. The catalysts were prepared by impregnation using a toluene solution of Pd(acac)2 to obtain a metal content close to 1 wt.% over SBA-15 with one-dimensional hexagonal structure, MCM-48 silica with cubic structure and three-dimensional pore system and MSU-γ alumina with a lathlike particle morphology. All the supports were characterised by nitrogen adsorption–desorption isotherms at 77 K, TEM, XRD and H2 chemisorption and TEM measurements. The reactions were found to be zero order with respect to 3-hexyne concentration. The starting 3-hexyne produces primarily cis-3-hexene, which subsequently is either hydrogenated to hexane or isomerized to trans-3-hexene and 2-hexenes that are found in very small amounts depending on the nature of the support used. Palladium catalysts supported on SBA-15 was the most active and selective catalyst.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (10 K)Download as PowerPoint slideResearch highlights▶ Preparation, characterisation and screening of palladium based catalysts. ▶ Mesostructured materials were used as support of palladium catalysts. ▶ 1% Pd/SBA-15 showed high activity and stereo-selectivity for semi-hydrogenation of 3-hexyne. ▶ The starting 3-hexyne produces primarily cis-3-hexene, which subsequently is either hydrogenated to hexane or isomerized to trans-3-hexene and 2-hexenes that are found in very small amounts depending on the nature of the support used.