Study of the sulfidation process of CrO3–Al2O3 hydrodesulfurization catalysts by a 35S-labeled H2S pulse tracer method Original Research Article

Sulfidation of CrO3–Al2O3 catalysts (11.1, 16.6 and 22.2 wt.% CrO3) synthesized by incipient wetness impregnation method was monitored by a 35S radioisotope ([35S]H2S) pulse tracer in situ method. This original method permitted us a better understanding of these relatively poorly documented catalytic systems. Experiences confirmed that, in a first step, for temperatures inferior to 400 °C, CrSx species are progressively formed. Then, in a second step for a temperature near 400 °C, formation of Cr2S3 entities is achieved, leading to their decomposition into CrS. This showed that the catalytic phase morphology depends drastically on the sulfidation temperature. Moreover, it was found that the increase in DBT activity with the Cr content previously observed was due to a modification of the nature of the active phase and not to an increase in its quantity. Indeed, whilst the sulfur quantity that accumulated on the catalysts containing 11.1 and 22.2 wt.% CrO3 was almost the same, the DBT HDS activity of the latter was ∼50% higher.