Optimization of Porous Metal Oxides and Metal-Organic Frameworks for High Temperature Catalysis

Abstract

The structural integrity of porous materials is critical to their application as heterogeneous catalysts. For high temperature catalysis, sintering and decomposition are common routes to structural destabilization and ultimately to irreversible deactivation of porous catalysts. This thesis describes the optimization of two types of porous catalysts, namely, porous metal oxides and metal-organic frameworks, for application in solar thermochemical fuel production and high temperature natural gas conversion. Thermochemical cycles can use the heat generated from solar thermal power to split H2O and CO2 into H2 and CO, both of which are valuable fuel and chemical feedstocks. These cycles can be catalyzed by metal oxides. In the first part of this thesis, wood-templating is demonstrated as an approach to generate a macroporous oxide structure that balances high thermal stability and accessible porosity for enhanced thermochemical cycling kinetics. The other part of this thesis describes the development of a silica nanocasting method for the thermal stabilization of metal-organic framework (MOF)-based catalytic metal sites. Nanocasting incorporates a thermally stable silica layer in the MOF pores, which serves as a scaffold for the metal active sites in the MOF after the organic linkers are removed at high temperatures. The work described here shows the applicability of the nanocasting method to MOFs with different pore sizes and compositions, and demonstrates that the method is capable of producing MOF-derived materials that retain their catalytic properties after exposure to high temperatures.