Book Description

Due to the continued use of fossil resources as both energy sources and as sources of carbon feedstocks since the industrial revolution, human society is facing an unprecedented climate crisis. Catalysis presents a long- or short-term solution to this problem by enabling new fields of renewable energy and chemical production in the long term while improving existing process technologies for near terms efficiency gains. Some of the most effective known catalysts are enzymes. They operate with a high degree of activity and selectivity due to their precisely engineered active catalytic sites. For my research project, I was inspired by enzyme catalysts to produce a class of materials that mimic some of the effects of enzyme catalysts yet can withstand more harsh conditions than even the most robust biological systems. To attempt to import some key aspects from enzymes to heterogeneous catalysts, I present a set of composite materials to use in a broad range of applications. These materials are produced from microporous porous organic frameworks (POFs) and inorganic colloidally synthesized nanoparticles in a hierarchical synthesis with POF core, inorganic nanoparticle layer finally encapsulated by an additional POF layer. This class of materials can mimic enzymes in the wide chemical tunability of both organic POF with new polymers reported and inorganic nanoparticles benefitting from many published colloidal nanoparticle syntheses. I characterize the materials with microscopy, spectroscopy, and probe molecule catalytic methods to demonstrate the materials and to show that Pd based hybrid materials are effective at size selective reactions, providing a mechanism of implementing selectivity. To probe the biomimetic aspect of these composite materials, I continue the characterization of the materials set with additional tools. With electron tomography and XPS based depth profiling study, I further demonstrate that metallic particles are encapsulated in the hybrid surfaces and that no exposed metal surfaces contribute to catalytic activity. In an in-depth study of the probe reaction of catalytic CO oxidation, I determine the effect of the hybrid POF structure on Pd activity. With the structures already demonstrated, this study provides indication that two aspects of enzymatic catalysis are present, namely control over transition state energetics and species-dependent transport rates based on analysis of catalytic data. Finally, I present a highly active and selective alcohol dehydration catalyst discovered during development of the POF-metal hybrid catalyst system. DMSO is the main solvent used in the formation of POF and during catalyst testing, it was observed that mixtures of POF and unreactive metal oxides were active and selective for alcohol dehydration. A spectroscopic and catalytic study documents nearly two order of magnitude increase in rate. This catalyst has applications in the biomass to fuels and chemicals space where removal of oxygen from oxygenated hydrocarbons are important transformations from waste to fuels. In summary, this presentation focuses on the development of new biologically inspired materials and assesses their potential as enzyme mimics. Importing chemical diversity around a confined metal site within an organic framework has led to success in controlling transition state energetics as well as species transport in probe reactions and presents a framework for future research and development.