(9f) Template-Induced Structuring and Tunable Polymorphism of Three-Dimensionally Ordered Mesoporous (3DOm) Titania Materials As Novel Catalysts

The hydrothermal instability of conventional catalyst supports demands the development of next generation materials for high-selectivity catalytic conversions in the biofinery (e.g., dehydration/oxidation chemistries, isomerizations).  Specifically, in this and other applications hydrothermally stable heterogeneous catalysts bearing three-dimensionally ordered mesoporous (3DOm) and hierarchical (i.e., macro-meso-microporous) pore structures are sought in order to accommodate diffusion of bulky sugar molecules and their derivatives.  The enhanced hydrothermal stability and reducible structure of titania establishes its promise as a robust substrate for liquid phase biofuel catalysis. A sacrificial nanotemplating strategy involving the infiltration of colloidal crystals composed of size-tunable (ca. 10 nm and larger) silica nanoparticles with titania precursor solutions followed by confined hydrolysis therein enables the fabrication of three-dimensionally ordered mesoporous (3DOm) titania structures with controlled pore body size in the range of nanometers to tens of nanometers. The hard silica template enables calcination-induced improvement in titania crystallinity, with the templated pores robust to collapse upon template removal.  This approach results in 3DOm titania materials with attractive textural properties, including surface areas (ca. 289 m²/g) and pore volumes that are up to four times and more than an order of magnitude larger, respectively, then commercially available titania.  Fundamental insight into titania polymorphism (i.e., rutile, anatase, or fraction thereof) has been elucidated as it relates to its sensitivity to the degree of titania confinement imparted by the template as well as the template surface chemistry.  Specifically, increasing confinement helps to stabilize the active anatase polymorph, while tuning the degree of surface hydroxylation of the template enables fine control over fractional polymorphism, the latter having potential implications on inherent reactivity.  Functionalization of these materials with both organic (sulfonic acid groups) and inorganic (Pt) moieties has been studied for the purpose of creating multifunctional dehydration-oxidation catalysts for processing of sugars.  In the case of Pt functionalization, template transfer techniques have been explored as a means for realizing uniformly distributed, partially embedded functionality within the 3DOm structures for enhancing catalyst stability.  We will present characterization of sugar adsorption and reaction within these materials ranging from sugar isomerization, dehydration, and oxidation to photochemical decompositions.