Insights into Cr/SiO2 catalysts during dehydrogenation of propane: an operando XAS investigation. Issue 8 (6th April 2017) - Botavina, M.
Abstract : In situ and operando XAS spectroscopic methods were applied to monitor the variations in the oxidation state and in the local structure of the chromium sites in a 2.0Cr/SiO2-DHS catalyst during propane dehydrogenation under non-oxidative and different oxidative conditions. Abstract : In situ and operando XAS spectroscopic methods were applied to monitor the variations in the oxidation state and in the local structure of the chromium sites in a 2.0Cr/SiO2-DHS catalyst during propane dehydrogenation under non-oxidative and different oxidative conditions. The spectroscopic data have been compared to the catalytic performances. Although the majority of the specialized literature ascribes the propane dehydrogenation activity mainly to Cr III species and only a few works report the presence of small amounts of Cr II species, our data unequivocally demonstrate the co-presence of both Cr III and Cr II species during the propane dehydrogenation reaction. The relative amount of the two chromium phases has been estimated by analyzing both the XANES and EXAFS spectra with a two-phase fitting approach. It was found that the Cr III -phase prevails when oxygen is present in the reaction mixture and when the reaction is performed at low flow or under static conditions. The amount of the Cr III -phase correlates well with the propane conversion. In contrast, the selectivity to propene correlates with the amount of the Cr II -phase, at least when propane dehydrogenation is performed under oxidative conditions. Although other phenomena surely contribute to the overall catalytic performances of Cr/SiO2 catalysts, our results indicate that the relative proportion of the Cr II and Cr III phases plays a role in influencing the selectivity of the propane oxidative dehydrogenation reaction.