Design and control of Lewis acid sites in Sn-substituted microporous architectures. Issue 15 (31st March 2016) - Mohammed, Khaled M. H.
Abstract : Modulation of tetrahedral Sn(iv ) active sites in framework architectures influences the generation of Lewis and Brønsted acid sites in heterogeneous catalysts. Abstract : Monometallic and bimetallic tin-containing framework architectures have been prepared by hydrothermal methods. Structural and spectroscopic techniques were used to probe the nature of the solid-acid sites, at the molecular level, using a combination of XRD, DR UV-Vis, solid state MAS NMR ( 119 Sn, 27 Al and 31 P) and XAFS. The nature and strength of the solid-acid sites were experimentally probed by FT-IR spectroscopy using CD3 CN as a probe molecule. To elucidate further the local-structure, the structural characteristics of the Sn sites were probed using DFT calculations, with a view to rationalising the experimental findings. These detailed structural and spectroscopic studies revealed the presence of multiple Sn environments, with the monometallic SnAlPO-5 catalyst displaying a greater number of tetrahedral Sn(iv ) active centres. These framework Sn(iv ) centres generated strong Lewis acid sites, when compared with their bimetallic Co–Sn analogue, thereby affording attractive possibilities for modulating catalytic reactivity.