Influence of the Preparation Conditions of Oxidic NiMo/Al2O3 Catalysts on the Sulfidation Ability: A Quick-XAS and Raman Spectroscopic Study

• Published in: Journal of physical chemistry. C Vol. 119; no. 42; pp. 23928 - 23942
• Main Authors: Rochet, Amélie, Baubet, Bertrand, Moizan, Virginie, Devers, Elodie, Hugon, Antoine, Pichon, Christophe, Payen, Edmond, Briois, Valérie
• Format: Journal Article
• Language: English
• Published: American Chemical Society 22-10-2015
• DOI: 10.1021/acs.jpcc.5b06219
• EISSN: 1932-7455
• ISSN: 1932-7447

The structure of oxidic precursors of supported NiMo hydrodesulfurization catalysts has been investigated in-depth by the combination of laser Raman spectroscopy and X-ray absorption spectroscopy measured at the Mo and Ni K edges at the different stages of the preparation. The oxidic catalysts were prepared by incipient wetness impregnation of δ-alumina with a solution obtained by dissolving MoO3 in H2O2 and subsequently adding Ni­(NO3)2·6H2O in this as-prepared solution (8 wt % MoO3; 2 wt % NiO). The formation of the 6-molybdoaluminate Anderson-type heteropolyanion (AlMo6O24H6)3– and of a mixture of oxo–hydroxo nickel species and bulk and/or surface NiAl-layered double hydroxide dispersed at the surface of the support has been identified after drying. Upon further thermal treatment at 723 K under dried air, calcined dehydrated catalyst is constituted of highly distorted isolated or partially condensed tetrahedral Mo units with terminal mono-oxo groups and of bulk and/or surface NiAl2O4-type and NiO-type species. After further exposure of the calcined catalyst to air moisture, a partial recovery of the Anderson-type molybdenum heteropolyanion and NiAl-layered double hydroxide species is evidenced by X-ray absorption spectroscopy. The nature and dispersion of active species formed after sulfidation under H2S/H2 of the different oxidic catalysts (dried-NiMo, dehydrated-calcined NiMo, and calcined-NiMo samples) are finally discussed in light of the structure of the parent oxidic precursors.