A real support effect on the hydrodeoxygenation of methyl oleate by sulfided NiMo catalysts

摘要

The effect of the support on the catalytic performance of sulfided NiMo in the hydrodeoxygenation of methyl oleate as a model compound for triglyceride upgrading to green diesel was investigated. NiMo sulfides were prepared by impregnation and sulfidation on activated carbon, silica,gamma-alumina and amorphous silica-alumina (ASA). High sulfidation degrees were obtained in all cases. Despite the use of a chelating agent to minimize metal-support interactions, the support had a significant influence on the morphology of the active phase (MoS2 dispersion and stacking). All catalysts convert methyl oleate to C17 and C18 olefins and paraffins. Initially, NiMo/Al2O3 and NiMo/ASA displayed the highest overall HDO activity, but these catalysts deactivated slowly during the week on stream. Finally, they exhibited similar activity as NiMo/SiO2. NiMo/C and NiMo/SiO2 did not deactivate. The NiMo/C catalyst was appreciably more active than the others after prolonged reaction. The high initial and then deactivating performance of NiMo/Al2O3 and NiMo/ASA is due to the Lewis acidity of surface Al species active in methyl oleate hydrolysis. It has earlier been demonstrated that deposition of heavy products on the alumina surface deactivates these sites. SiO2 lacks such sites, resulting in lower catalytic performance. The NiMo/C support is more active in methyl oleate hydrolysis. This can be either due to intrinsically higher activity of the metal sulfide on carbon or to acidic surface groups. Besides, the reaction data show that the C18 hydrocarbons selectivity for NiMo/SiO2 and NiMo/C was substantially higher than for the other two catalysts. Clearly, the support has a significant influence on the performance of NiMo sulfide in methyl oleate HDO. The use of activated carbon as the support presents high and stable HDO activity of methyl oleate with good C18 hydrocarbons selectivity.