Intermediate Species Revealed During Sulfidation Of Bimetallic Hydrotreating Catalyst: A Multivariate Analysis Of Combined Time-Resolved Spectroscopies

For the first time, the sulfidation process of a bimetallic time-resolved laser Raman spectroscopy (LRS) and X-ray absorption NiMo catalyst supported on alumina has been followed by combining spectroscopy (XAS) quasi simultaneously at both Ni and Mo K edges. Multivariate data analysis reveals that the thermal activation upon 15% H2S/H-2 atmosphere of a dehydrated-calcined NiMo(VI) catalyst involves (i) a 5-stepped mechanism with oxysulfided or fully sulfided Mo intermediate species and (ii) a direct transformation of oxidic nickel species into NiSx and NiMoS ones. Complementary information extracted from LRS and Quick-XAS data permitted to identify at the early stage of the sulfidation the trimeric Mo(V/VI) oxysulfide species [Mo-3(mu O-2)(4)(mu S-2)mu(2){S-2}(O-t)(2)(S-t)(3)] grafted to the support surface, which is quickly transformed into the Mo(IV) intermediate species [Mo-3(mu S-3)(mu S-2)(2)mu(2){S-2}(O-t)(2){S-2}(t)]. Above 190 degrees C, the Mo(IV) second intermediate is transformed into Mo(IV)S-3, itself transformed into the final Mo(IV)S-2 at T > 220 degrees C. Thanks to the unambiguous comparison of sulfidation kinetics for both metals the incorporation of promoter into the extended sulfidic molybdenum-based phase has been unprecedentedly related to the formation of the MoS3 intermediate species.