Effect of the hydrogen and hydrogen sulfide partial pressures in the hydrodesulfurisation of thiophene and hydrogenation of cyclohexene on rhodium-tungsten catalysts

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WS 2, alumina-supported rhodium sulfide, and mechanical mixtures of both were studied in the simultaneous hydrodesulfurisation (HDS) of thiophene and hydrogenation (HYD) of cyclohexene under hydrogen pressures of 2.2 and 1.1 MPa and with H 2S partial pressure varying from 0.0 to 15 kPa. Rhodium sulfide has a promotional effect on WS 2 both for HDS and HYD, as long as the H 2S pressure remains low. At a H 2S pressure in excess of about 3 kPa the activity of both the mechanical mixture and the pure rhodium sulfide decrease drastically. The control of the activity of WS 2 by spillover of hydrogen from rhodium sulfide seems to explain the promotional effect. The accompanying loss of the promotional effect could be explained by an inhibition of the production of spillover hydrogen by H 2S.