Nanostructured Metal Oxide Catalysts via Building Block Syntheses

Abstract

Executive Summary:A broadly applicable methodology has been developed to prepare new single site catalysts on silica supports. This methodology requires of three critical components: a rigid building block that will be the main structural and compositional component of the support matrix; a family of linking reagents that will be used to insert active metals into the matrix as well as cross link building blocks into a three dimensional matrix; and a clean coupling reaction that will connect building blocks and linking agents together in a controlled fashion. The final piece of conceptual strategy at the center of this methodology involves dosing the building block with known amounts of linking agents so that the targeted connectivity of a linking center to surrounding building blocks is obtained. Achieving targeted connectivities around catalytically active metals in these building block matrices is a critical element of the strategy by which single site catalysts are obtained. This methodology has been demonstrated with a model system involving only silicon and then with two metal-containing systems (titanium and vanadium). The effect that connectivity has on the reactivity of atomically dispersed titanium sites in silica building block matrices has been investigated in the selective oxidation of phenols to benezoquinones. 2-connected titanium sites are found to be five times as active (i.e. initial turnover frequencies) than 4-connected titanium sites (i.e. framework titanium sites). Accomplishments: Proposed:In the work supported by the BES program of the DOE we proposed to develop a methodology to prepare nanostructured complex oxide catalysts. There were three specific objectives to this research program:1. To develop a general, broadly applicable synthetic methodology to prepare single site catalysts in a targeted fashion. 2. To obtain high densities of these sites on the support materials while maintaining strict site isolation. 3. To accomplish (1) and (2) on a porous, high surface area support with a distributed pore system composed of macro, meso and micropores to obtain high numbers of sites on a per unit mass or volume basis for the material. 4. To study the activity of these new nanostructured materials as catalysts in selective oxidation reactions.3 Actual:1. During an early phase of this research project objectives (1) and (2) were demonstrated and described for a model system (containing no active catalysis centers) in a publication that is given at the end of this technical report.[1] 2. This study was followed up by more detailed investigations involving titanium and vanadyl centers in silica building block matrices. The results of this work were recently reported in several publications given at the end of this technical report.[2-4] 3. More recently we have completed two additional studies focusing on how the porosity of these matrices changes with the synthetic stoichiometry used in their synthesis and the activity of single site titanosilicate catalysts in the selective oxidation of phenols...