270 resultados para SUPPORTED COBALT CATALYSTS
Resumo:
Two series of sulfided Ni or Co promoted Mo/alumina catalysts, having different Ni or Co loadings, were characterized by their activities for the transformation of cyclopentanone into cyclopentanethiol (flow reactor, 220 degrees C, atmospheric pressure) and for the hydrodesulfurization of dibenzothiophene (flow reactor, 340 degrees C, 3 MPa hydrogen pressure). The addition of the promoter increased significantly the activity of the Mo/alumina catalyst for both reactions, up to a maximum obtained with the catalysts having a (promoter)/(promoter+Mo) molar ratio equal to 0.3-0.4. This increase in activity was due in part to an increase in the hydrogenating properties of the Mo/alumina catalyst. However, an additional modification of the catalyst (basic and nucleophilic properties) must be considered to account for the spectacular effect of the promoter on the rate of the dibenzothiophene direct desulfurization reaction. (C) 1999 Elsevier Science B.V. All rights reserved.
Resumo:
The states of surface Co and Mo sites on nitrided CoMo supported on Al2O3 were studied by adsorption of CO and NO as IR probe molecules. Three IR bands at 2200, 2060 and 2025 cm(-1) were detected for adsorbed CO. These bands can be respectively attributed to the surface NCO species as a result of CO adsorbed on surface N sites, and linearly adsorbed CO on surface Co and Mo sites in low valence states. The addition of cobalt to the Mo nitride diminishes the band at 2200 cm(-1). This may be due to either the change of the surface structure of the supported nitride, or the formation of a new phase, CoxMoyNz, as suggested in the literature Kim et al., Catal. Lett., 1997, 43, 91 and Logan et al., Catal. Lett., 1998, 56, 165. Comparison of CO and NO adsorption on Mo2N/Al2O3 and CoMoNx/Al2O3 indicates that the presence of cobalt can promote the reduction and nitridation of Mo.
