Common intermediate species from reducing and activation of CoMo-based catalyst revealed via multivariate augmented system applied to time-resolved in situ XAS data

Abstract

Time-resolved spectroscopy has reached great importance in studies of chemical transformations, particularly in heterogeneous catalysis, where in situ or operando conditions are suitable to correlate precursor transformation and/or genesis of active sites with catalytic efficiency. In this work we present advantages of using chemometric analysis to resolve multi-step chemical reactions in time-resolved XAS experiment. We followed complementary experiments (temperature programmed reduction and activation) of a Ti-supported CoMo HDS catalyst to unravel details in the evolution of the different species appearing during each process. A multivariate analysis uncovered that (i) at Mo K-edge, activation of oxidic precursor is a 3-step mechanism with one reduced-like and one oxysulfide species as intermediates and (ii) TPR is a 2-step process with in which the reduced intermediate is a common species between the two processes. This approach was fundamental to properly number the steps during the TPR and to correctly assign the first intermediate of the activation as a non-sulfide species. Further, when applied to low loading catalyst, remarkably structural differences on the kinetics was found, but a similar active phase was reach at the end. Thereby, using augmented analyses we demonstrated that a careful planning of the experiments is essential to resolve fine details in the kinetics of the reaction.