Adsorption of thiophene on transition metal atoms (Co, Ni and Mo) modified Al20O30 clusters: DFT approaches

Transition metal atoms (Co, Ni and Mo) modified alumina are of interest in hydrodesulfurization catalysis. In this study, full geometry optimization, bonding characters, electronic structures and vibrational analysis for thiophene adsorption on MAl20O30 (M = Co, Ni and Mo) clusters are carried out by density functional theory method. The impurity of transition metal atoms promotes the activity of catalyst by an elongation of the SC bond in all thiophene adsorption modes. The bonding characteristics analysis, based on the values of charge transfer and molecular orbital pictures for different adsorption modes, indicates that π-backdonation exists for η2 and η5 bonding modes. In addition, compared with the vibrational frequencies of free thiophene, the ν(CC)sym bands for η5 bonding mode are shifted to lower wavenumbers, which is consistent with experimental results.