Synthesis and Characterization of Novel Single-Site Titanosilicates with Targeted Connectivites and Geometries as Selective Oxidation Catalysts

The primary focus of this research was to synthesize and characterize two families of titanosilicate catalysts, first generation and second generation, that were single site, atomically dispersed with targeted connectivities to the silicate matrices but had different geometries about the active sites. First generation catalysts have tetrahedral active sites, while second generation catalysts have altered geometries for a more accessible active site, but maintain the same targeted connectivities.

A building block methodology is employed to prepare single site, isolated, atomically dispersed titanium active sites within a silicate matrix. The synthetic approach uses a molecular precursor, i.e., building block and the method of sequential additions to construct the support matrix around the active site. This methodology can be used to target titanium connectivities (2, 3, or 4 linkages) to the matrix, namely 2-connected (2C-), 3-connected (3C-Ti) and 4-connected (4C-Ti)

Several characterization techniques are used to compare and contrast first and second generation catalysts; NMR, gravimetric analysis (determine connectivity), FTIR, XAS (XANES/EXAFS), DRUV, and catalytic activity are used to characterize the final catalysts. Based on spectroscopic characterization, two families of catalysts with different geometries were successfully synthesized.

Catalytic studies showed two distinct relationships could be made: 1) The activities of these catalysts correlate with the connectivity of the titanium site as long as leaching does not occur. 4C-Ti catalysts were less active than 3C-Ti catalysts. The 2C-Ti catalysts leached from the support matrix and therefore cannot be considered true heterogeneous catalysts. 2) Second generation catalysts were more active than first generation catalysts due to the more open geometry of the active site.