Deactivation of MoS2/Al2O3 in thiophene hydrodesulfurization:: An infrared spectroscopic analysis by adsorbed CO

Fourier transform infrared spectroscopy on adsorbed carbon monoxide was used to study the deactivation and rejuvenation of a MoS2/gamma -Al2O3 catalyst during hydrodesulfurization (HDS) of thiophene. The study covered several sample pretreatment steps, each resembling a stage in the catalyst life. The number of active sites on the sulfided sample was correlated to the intensity of CO-stretch absorption bands in the infrared spectrum. It was concluded that with increasing HDS time on stream the intensity of bands correlated to CO adsorbed on edge and corner sites decreases, while simultaneously those in the carbon-carbon stretch region (1800-1200 cm(-1)) increase in intensity. Rejuvenation of a spent catalyst under H2S/H-2 at 673 K revealed an increase in the number of gas-phase exposed edge and corner sites of the MoS2 slabs, while concurrently the intensities of bands correlated to carbon-carbon stretch vibrations decreased. Thus, it was concluded that catalyst deactivation was caused by preferential coke deposition on the active sites, which can be removed under H2S/H-2. No differences were found in the coking behavior of edge and corner sites. (C) 2000 Academic Press.