Support effects in HDS catalysts: DFT analysis of thiolysis and hydrolysis energies of metal-support linkages

We have carried out a theoretical investigation of the active phase-support interaction for HDS catalysts using density functional theory to calculate the thiolysis and hydrolysis reaction energies for the metalsupport linkages. These metal-support linkages are represented by simplified cluster modells with -SH or -OH terminations to represent the sulfide (active) and oxide (support) phases, respectively. fhe calculated rank order of the supports representing Type-I (strong interaction) tendency (SiO2 < carbon < Al2O3 < TiO2 < ZrO2 < Y2O3) is in agreement with the experimentally observed behavior. Based on the calculated energetics the temperature-induced Type-II nature of the MoS2-Al2O3 interaction is predicted by a higher equilibrium constant of the thiolysis reaction at higher temperature. Thus, the thiolysis energy provides a qualitative scale of the Type-I/Type-II nature of the support and is, therefore, a useful descriptor of catalytic behavior. (c) 2008 Elsevier Inc. All nights reserved.