Kinetic investigation of the effect of H2S in the hydrodesulfurization of FCC gasoline

The reactivity of different groups of olefins and S-compounds, as well as the inhibition effect of H2S on the reactivities of these groups were evaluated with a FCC gasoline over a CoMoS/γ-Al2O3 catalyst. The results demonstrated that the various degrees of steric hindrance around the double bond (CC) and of the thiophene molecules suppressed the hydrogenation (HYD) of olefins and hydrodesulfurization (HDS) of S-compounds, respectively. The inhibition effect of H2S caused by the easy adsorption of H2S on the catalyst sites was more severe on the HDS reactivity than that on the olefins HYD reactivity, thus leading to the decreased catalyst selectivity. The inhibition effect of H2S increased with the number of substituents to the olefin double bond and to the number of substituents to the thiophene molecules, which was inversely proportional to the adsorption constants of the olefin and thiophene molecules. Meanwhile, a modification of the HDS reaction pathway of thiophenes induced by H2S was also observed, and the HYD pathway was more depressed. The characterization by Fourier transformed infrared spectroscopy showed that the relative variations of the number of Lewis and Brønsted acid sites induced by the adsorbed H2S could explain the H2S effect.