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

Abstract Sulfidation of CrO 3 –Al 2 O 3 catalysts (11.1, 16.6 and 22.2 wt.% CrO 3 ) synthesized by incipient wetness impregnation method was monitored by a 35 S radioisotope ([ 35 S ]H 2 S) 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, CrS x species are progressively formed. Then, in a second step for a temperature near 400 °C, formation of Cr 2 S 3 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.% CrO 3 was almost the same, the DBT HDS activity of the latter was ∼50% higher.