Targeted Synthesis and Characterization of Novel Nanostructured Titanosilicates for Epoxidation and Hydrogen Storage

The Barnes’ research group has developed a general synthetic methodology for creating nanostructured silicate with targeted single sites. This methodology provides researchers with the ability to control the dispersion of surface functionality and metal centers, the number of linkages from metal center to the support, the surface area and the porosity of the support. This dissertation describes work aimed at synthesizing and characterizing nanostructured titanosilicates for hydrogen storage applications and as heterogeneous catalysts. Furthermore, none of the materials prepared in our investigations exhibited significant hydrogen bind beyond physisorption

Isolated surface titanium species were synthesized by reacting a nanostructured silicate support with titanium tetrachloride. These isolated titanium(IV) sites serve as a well-defined starting point for a “complex” reduction, resulting in reduced titanium centers that may be capable of Kubas’ binding of hydrogen. These sites were exposed to a variety of reductants: lithium aluminum hydride, sodium borohydride, cobaltocene, hydrogen, and UV radiation with hydrogen. The majority of the work with these systems focused on characterizing the titanium species after reduction to understand their composition. Due to the amorphous nature and instability of the reduced titanium species, we were unable to develop a clear understand of their composition.

Nanostructured heterogeneous catalysts with isolated titanium(IV) centers were synthesized by reacting a limiting amount of metal chloride with octatrimethyltin spherosilicate, followed by dimethyldichlorosilane. Three catalyst ensembles were synthesized: 2-, 3-, and 4-connected titanium. The catalytic activity of each catalyst was examined in the epoxidation of cyclohexene with cumene hydroperoxide. Under identical conditions, high activities were observed in a sequence 2-connected > 3- connected > 4-connected titanium catalysts. Furthermore, these single site catalysts were compared to two commercially used catalysts (Grafted Titanium Mobil Composition of Matter-41 and Titanium Silicalite -1) and found to be superior in both activity and selectivity. A structure-function relationship was therefore developed through targeted synthesis of novel single sites titanosilicates.