Hydrogenation of toluene over β-Mo2C in the presence of thiophene

Unsupported beta-Mo2C have been synthesized by temperature programmed reaction in CH4/H-2 mixtures and characterized by XRD, XPS and BET measurements. These solid compounds have been tested for the hydrogenation of toluene at 3.0 MPa with or without thiophene in a fixed bed reactor. Their activities have been compared to those of a reference catalyst I wt.% Pt/gamma-Al2O3. beta-Mo2C hydrogenates toluene and shows a deactivation during the first stages of the reaction at 150degreesC. With 50 ppm thiophene the 1% Pt/gamma-Al2O3 deactivates rapidly and totally after exposure of six sulfur atoms on each Pt. beta-Mo2C shows a high activity at 200degreesC which reflects a good tolerance to sulfur in the first stages of the reaction but then deactivates quite linearly with time. It seems that one sulfur atom titrates one surface molybdenum atom. Characterization of the spent catalysts show that the bulk structure is retained. XPS results reveal that the surface is sulfided (as a carbosulfide and/or MoS2). This surface transformation is believed to be responsible for the deactivation of the catalysts as these phase sites are inactive for toluene hydrogenation. (C) 2002 Elsevier Science B.V. All rights reserved.