C. M. Kowalchuk, J. Corrigan, Yining Huang
Jun 6, 2005
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Microporous and Mesoporous Materials
Abstract
Abstract We have examined the adsorption of the phosphine stabilized cluster Cu 6 (TePh) 6 (PPh 2 Et) 5 as well as the free ligands ethyldiphenylphosphine (EDPP) and ethyldiphenylphosphine oxide (EDPPO) in several MCM-41 types of mesoporous materials by 31 P solid-state NMR spectroscopy. The results indicate that upon loading into siliceous MCM-41 (Si-MCM-41), the phosphine shell of the copper cluster dissociates from the metal core. After dissociation, some EDPP molecules exist as physisorbed species and a significant amount of phosphine is oxidized to the corresponding phosphine oxide, occluded in the channels of Si-MCM-41. The reaction seems to be catalyzed by the Cu(I) species since direct loading of EDPP under the same conditions does not yield any phosphine oxide in the framework of Si-MCM-41. The 31 P NMR spectra of EDPP and EDPPO adsorbed in Si-MCM-41 suggest that neither Bronsted nor Lewis acid sites exist on the channel surface of Si-MCM-41. The adsorption of EDPP and EDPPO in the acidic form of aluminium-containing MCM-41 (Al-MCM-41), however, does indicate the interactions between the guest species and three Bronsted acid sites with different strengths. No Lewis acid site was observed in Al-MCM-41.