INFLUENCE OF WATER IN THE DEACTIVATION OF A SULFIDED NIMO GAMMA-AL2O3CATALYST DURING HYDRODEOXYGENATION

Water and oxygenated compounds are generally viewed as highly detrimen tal to the stability of sulfided hydrotreating catalysts. In this pape r, a sulfided NiMo/gamma-Al2O3 catalyst was treated in a batch reactor under typical hydrotreating conditions with or without water vapor. C hanges of the HDO activity, composition, and texture of the various ca talyst samples were further evaluated. Catalyst samples used in the HD O of organic oxygenated compounds were also characterized by XPS for m odifications of the chemical surface composition. Water caused a decre ase of the catalytic activity to one-third the activity of the fresh c atalyst but did not change the hydrogenation-hydrogenolysis selectivit y. Water was also the cause of a small loss of the specific surface ar ea conjugated to some crystallization of the gamma-alumina support in a hydrated boehmite phase. On the other hand, the metal content, the d ispersion, and the sulfidation state were not specifically affected by water. The deactivation would rather be related to the appearance of oxidized nickel species. The observations can be interpreted as result ing from the formation of an inactive nickel sulfate layer covering th e active sulfide phases or from the formation of nickel aluminate. Oth erwise, the oxidation of the molybdenum sulfide phase by water or oxyg enated compounds in reaction conditions is very limited. (C) 1994 Acad emic Press. Inc.