Inhibiting effect of hydrogen sulfide on toluene hydrogenation over a molybdenum disulfide/alumina catalyst

Abstract

The influence of hydrogen sulfide partial pressure on the activity of a model MoS[sub 2]/[gamma]-Al[sub 2]O[sub 3] catalyst for toluene hydrogenation has been investigated over a wide range of hydrogen sulfide partial pressure, from 0 to 0.3 MPa, under a total pressure of 6 MPa, reaction temperature between 320 and 410 C, and liquid hourly space velocity between 0.5 and 7.5 h[sup [minus]1]. A moderate inhibiting effect of H[sub 2]S on the hydrogenation activity is found for H[sub 2]S partial pressure up to 60,000 Pa with an order of reaction relative to H[sub 2]S comprised between 0 and [minus]1/2. For H[sub 2]S partial pressure higher than 60,000 Pa, no apparent inhibiting effect of H[sub 2]S on the hydrogenation activity is detected. The results have been best interpreted in term of a kinetic model whereby the reaction occurs on a surface containing two sites, one unsaturated Mo ion and one stable sulfur host of the proton generated by the heterolytic dissociative adsorption of hydrogen and hydrogen sulfide.