Combined Solid-State NMR and Theoretical Calculation Studies of Brønsted Acid Properties in Anhydrous 12-Molybdophosphoric Acid
Ningdong Feng†, Anmin Zheng*†, Shing-Jong Huang‡, Hailu Zhang§, Ningya Yu‡, Chih-Yi Yang‡, Shang-Bin Liu*‡, and Feng Deng*†
J. Phys. Chem. C, 2010, 114 (36), pp 15464–15472
Publication Date (Web): August 20, 2010
Copyright © 2010 American Chemical Society
Abstract: The strength and distribution of Brønsted acidic protons in anhydrous phosphomolybdic acid (H3PMo12O40, HPMo) have been studied by solid-state magic-angle-spinning (MAS) NMR, using trimethylphosphine oxide (TMPO) as the probe molecule in conjunction with density functional theory (DFT) calculations. Brønsted acid sties with strengths exceeding the threshold of superacidity (Zheng, A. et al. J. Phys. Chem. B 2008, 112, 4496) were observed for HPMo. In addition, the locations and adsorption structures of Brønsted protons on various oxygen sites in HPMo were also identified. The preferred location of the acidic proton was found to follow the trend: corner-sharing (Ob) > edge-sharing (Oc) terminal (Od) sites. Moreover, a tendency of hybridization among Brønsted protons residing at Ob and Oc sites of HPMo was inferred by experimental as well as theoretical 31P chemical shifts of the adsorbed TMPO.