Effect of different weight loadings of MoO x /SBA-15 on the oxidative dehydrogenation of n-octane

Abstract

This study examines the effect of different weight loadings of molybdenum as molybdenum oxide, supported on SBA-15 for the oxidative dehydrogenation of n-octane. The loadings of molybdenum on SBA-15 were performed by wet impregnation method the resultant catalysts were characterised by ICP-OES, BET physisorption studies, PXRD, Raman spectroscopy, TEM and SEM. Raman spectroscopy showed the presence of monomeric MoOx species at 4 wt%, monomeric and polymeric species at 7 wt%, polymeric and crystalline MoO3 species at 10 wt% and only crystalline Mo oxide at 18 wt%. SBA-15 as the catalyst is active but mainly selective to cracked products (33 %) and COx (32 %), whereas the loaded catalysts produced octenes and C8 aromatics. At similar conversion, the highest selectivity to octenes was observed with the 4 wt% catalyst which decreased with an increase in the molybdenum loadings. The highest selectivity to aromatics was observed with the 7 wt% catalyst. When the 10 wt% catalyst was tested over the temperature range of 350–550 °C, the conversion increased and selectivity towards aromatics was promoted. The extent of non-selective oxidation increased with an increase in the oxygen content in the feed while a variable GHSV study revealed that the octenes, cracked products and CO2 are the primary products of the reaction.National Research Foundation (South Africa