NiMo nitride supported on γ-Al2O3 for hydrodeoxygenation of oleic acid: Novel characterization and activity study

Abstract

Oxide and nitride phases of NiMo supported on Al2O3 were employed for hydrodeoxygenation (HDO) of oleic acid. Synthesized catalysts were characterized using Raman Spectroscopy, X-ray absorption near edge structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS). Raman spectroscopy was employed to understand the active-site distribution in NiMo catalysts and elucidate the relation between distribution of active species and catalytic activity. Catalyst evaluation studies showed that NiMo supported on γ-Al2O3 has higher conversion (80%) in comparison to NiMo supported on SBA-15 and HMS during the HDO of oleic acid. Raman maps were obtained for the oxide phase of catalyst and it indicates that the Mo supported on Al2O3 is present as polyanions ([Mo7O24]6− or [Mo8O26]4−). XANES and EXAFS analyses were carried out to understand the oxidation state and co-ordination environment of the catalyst. Occurrence of Mo-Ni and Mo-Mo interactions were proved by the Mo K-edge EXAFS spectra and the bond lengths were determined. The presence of the promoter metal (Nickel) aids in the hydrogenation of oleic acid to stearic acid and direct hydrodeoxygenation, decarboxylation and decarboxylation reactions were observed. The occurrence of polymeric molybdates as confirmed by the Raman spectroscopy leads to the decrease in the availability of active metals for the selective removal of water without breaking the carbon bond leading to the formation of C18H38.