Templated Growth of Three-Dimensionally Ordered Mesoporous (3DOm) Zirconia Materials as Tunable Catalysts for Biomass Conversion

Biomass offers a renewable carbon source that could be utilized as a raw material in the chemicals industry. A potential route for the conversion of biomass feedstock’s into industrial chemicals is through the catalytic conversion of biomass sugars (glucose) to furan based compounds through an aqueous reforming process. However, to accommodate the transport of these bulky sugars within the catalytic framework, a new breed of hydrothermally stable catalysts is required with either: a three dimensionally ordered mesoporous (3DOm) or a hierarchical micromesoporous pore topology. Zirconia offers a candidate catalytic material due to its hydrothermal stability and surface properties. Additionally, recent synthetic techniques offer the ability to produce monodispersed silica particles, which form a pore size-tunable colloidal crystal template when dried. [1] This work examines the use of solgel based zirconia precursors to prepare 3DOm zirconia through a hard templating technique. Dynamic light scattering was used to select a zirconia precursor solution (zirconyl chloride octahydrate) for the infiltration of the pre-formed mesoporous silica templates. The solutions were successfully templated, resulting in monoclinic and tetragonal 3DOm zirconia upon removal of the silica template. Crystallinity was characterized with X-Ray diffraction and Raman spectroscopy; while, nitrogen adsorption provided insight into pore size tunability and resistance to collapse. Transmission electron microscopy was used to assess structural integrity and development at various stages during calcination. Results suggest that the zirconia polymorphism is tunable by controlling the degree of template-induced confinement during nucleation, crystallization, and higher-temperature processing of the zirconia materials. Specifically, apparent stabilization of the tetragonal phase of zirconia (i.e., resistance of tetragonal-to-monoclinic transformation) is achievable on the basis of confinement rather than through doping or the incorporation of additives.