(560hi) Understanding Molecular Structural Changes in Sulfated Mixed Metal Oxides

Sulfated metal oxides, a class of solid acid catalysts, have received considerable attention over the past three decades for their promise in replacing reactions traditionally catalyzed by homogenous acids. These homogenous acids present a number of problems ranging from the difficulty of separation to corrosivity that do not exist for heterogenous acid such as sulfated metal oxides, which provide equal or greater activity while benefitting from generally mild reaction conditions and relatively facile methods of separation from reaction solutions1,2. The strength and availability of both Lewis and Brønsted acid sites on the surfaces of sulfated metal oxides provides the opportunity to catalyze a range of reactions including isomerization, alkylation, acylation, and oxidative dehydrogenation reactions. However, much work towards characterization and elucidation of the pertinent structure-reactivity relationships is still required.

This work seeks to characterize the behavior of sulfate species on the surface of mixed metal oxides containing tin and zirconium at varying molar ratios. It is hypothesized that these materials could optimize the selectivity and yield of a given reaction by effecting the distribution of catalytically active sites in order to avoid undesirable side products. In-situ Raman spectroscopy is coupled with ATR-FTIR, XRD, and BET analysis in order to probe the effects of support composition and environment on the predominant sulfate chelation structure. Our findings suggest that a tridentate configuration of the dispersed sulfate species is preferred at dehydrated conditions for the entire range of catalysts, while a large number of different hydrated species are present for the various catalysts tested.

References:

[1] Tanabe, K.; Hölderich, W.F. App. Cat. A. 181 (1999) 399-434.

[2] Corma, A. Chem. Rev. 95 (1995) 559-614.”