Kinetics of thiophene reactive adsorption on Ni/SiO2 and Ni/ZnO

Kinetics of thiophene reactive adsorption on Ni/SiO2 and Ni/ZnO was studied by thermal gravimetric analysis at 280-360 degrees C under 5-40 mbar of thiophene in H-2. In the case of Ni/SiO2 the interaction proceeds in two steps: a rapid surface reaction is followed by a slower bulk transformation into Ni3S2. Maximum Ni conversion depends on reaction conditions and observed conversion profiles can be described by an exponential equation corresponding to a reaction of first order relatively to both sulfidable Ni amount and thiophene. The interaction between Ni/ZnO and thiophene proceeds in a rather different manner. A rapid increase of weight, similar to the first stage observed on Ni/SiO2, is not followed by bulk Ni sulfidation, but instead by a nucleation-controlled ZnO surface transformation. After formation of the surface ZnS layer, a complete particles sulfidation occurs with kinetics being strongly dependent on the reaction conditions possibly due to comparable rates of different reaction steps. (c) 2007 Elsevier B.V. All rights reserved.