Bas M. Vogelaar

Deactivation of Mo/Al2O3 and NiMo/Al2O3 catalysts during hydrodesulfurization of thiophene

Abstract A Mo/Al 2 O 3 and a NiMo/Al 2 O 3 catalyst were subjected to the gas-phase hydrodesulfurization (HDS) of thiophene. The mechanism of catalyst deactivation was investigated. Sintering or modification of the active phase and blocking of the active sites or the pore structure by coke deposition were considered as possible causes. The freshly sulfided and the spent catalysts were characterized by quasi in situ TEM, IR spectroscopy on adsorbed CO, total carbon analysis, N 2 chemisorption and Hg porosimetry. For the NiMo/Al 2 O 3 catalyst the main cause for deactivation is loss of sulfur during the reaction. This process is fully reversible by H 2 S/H 2 treatment. In contrast coke deposition on the active sites is a major cause for deactivation of the Mo/Al 2 O 3 catalyst.

67 Activity and deactivation of HDS catalysts: Studying the active phase using CO as a probe molecule

Publisher Summary This chapter investigates the initial deactivation of several hydrodesulfurization (HDS) catalysts using infrared spectroscopy using CO as a probe molecule (IR-CO). The chapter discusses the IR spectra of CO adsorbed on a freshly sulfided Mo/A12O3 catalyst at increasing CO pressure. Three prominent bands can be distinguished—the one at 2153 cm-1, which adsorbs CO weakly, is attributed to the hydroxyl groups on the alumina surface. Two other bands with a high CO adsorption strength, at 2105 and 2064 cm-1, are attributed to coordinatively unsaturated Mo2+ sites located at the edges and comers of the MoS2 slabs, respectively. The chapter reveals the IR spectra of 10 mbar CO adsorbed on the conventional NiMo/Al2O3 catalyst after being exposed to thiophene for different reaction times. Again, the interaction of CO with the support is evidenced by a band at 2153 cm-1. The thiophene treated catalysts show a broad band at 2080 cm-1, which is attributed to promote active sites responsible for the enhanced HDS activity.