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

International audienceFor the first time, the sulfidation process of a bimetallic NiMo catalyst supported on alumina has been followed by combining time-resolved laser Raman spectroscopy (LRS) and X-ray absorption spectroscopy (XAS) quasi simultaneously at both Ni and Mo K edges. Multivariate data analysis reveals that the thermal activation upon 15% H2S/H2 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 [Mo3(μ2O)4(μ2S)μ2{S2}(Ot)2(St)3] grafted to the support surface, which is quickly transformed into the Mo(IV) intermediate species [Mo3(μ3S)(μ2S)2μ2{S2}(Ot)2{S2}t]. Above 190 °C, the Mo(IV) second intermediate is transformed into Mo(IV)S3, itself transformed into the final Mo(IV)S2 at T > 220 °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