A joint experimental-theoretical study on trimethylphosphine adsorption on the Lewis acidic sites present in TS-1 zeolite

P-31 MAS NMR desorption experiments and density functional calculations were combined to study the interactions between TS-1 zeolite and probe molecules. Two types of Lewis acidic sites at -34.2 and -32.0 ppm in the P-31 MAS NMR spectra were identified, which correspond to the Ti(OSiO3)(4) and (OSiO3)(3)Ti(OH) species with the Ti atoms at the T12 sites. Trimethylphosphine (TMP) was chemisorbed on the Lewis acidic sites with the adsorption energies calculated to be - 6.2 and - 19.6 kJ mol(-1), respectively. On all the other T sites, TMP was physisorbed with slightly positive adsorption energies, in the range 0.82-5.92 kJ mol(-1). The two types of Lewis acidic sites are responsible for the catalytic reaction of TMP oxidation, with their catalytic activities explained by structural and Mulliken charge analyses. It was also found that further hydrolysis of Si-O-Ti links to form (SiO)(2)Ti(OH)(2) or (SiO)Ti(OH)(3) species were not observed in TS-1 zeolite. (C) 2007 Elsevier B.V. All rights reserved