Bioinspired and Sustainable Catalysis for Chlorite Conversion and Dioxygen Reduction

Purdue University, West Lafayette IN

Investigators

Abstract

In this project funded by the Chemical Catalysis Program of the Chemistry Division, Professor Mahdi Abu-Omar of Purdue University is developing catalysts to make important chemicals via greener processes. Catalysts are reagents that accelerate and direct reactions toward desirable products without themselves being consumed. A popular example is the catalytic converter in automobiles, which reduces certain gaseous emissions such as carbon monoxide and renders vehicles significantly less polluting. Often catalysts are based on precious elements that are rare and expensive such as platinum and rhodium. In contrast, biological catalysts or enzymes, often use abundant and inexpensive elements such as iron and copper to carry out important physiological reactions. Professor Abu-Omar is drawing inspiration from biology to develop and study catalysts based on manganese and iron, earth-abundant elements, for chemical reactions that are important for energy and the environment: making hydrogen peroxide directly from air, decomposing an environmental contaminant made up of chlorine and oxygen atoms into harmless table salt and oxygen, and also converting this contaminant into a disinfectant on-demand in water and at room temperature. Professor Abu-Omar is developing high-valent oxo complexes of first row transition metals, specifically manganese and iron, supported by corrole, prophyrin, and pyridyl or amidato macrocylic ligands. Some of these complexes are being used to study the kinetics and mechanism of proton coupled electron transfer (PCET) in manganese(V)-oxo corrole to establish a catalytic system for the selective two-electron reduction of dioxygen to hydrogen peroxide. Generation of hydrogen peroxide directly from air would provide greener methods for making this important industrial chemical and contribute to strategies for renewable energy conversion and storage. Others of these complexes are being used to study the reaction chemistry of the oxyanion, chlorite. Professor Abu-Omar is developing catalysts for the selective dismutation of chlorite to dioxygen and innocuous chloride by incorporating a hydrogen bonding pocket in the second-coordination sphere. Picket fence porphyrin ligand designs are being guided by computational investigations into the mechanism of catalytic chlorite decomposition and the structural and functional features of the active pocket. Iron non-heme catalysts are being studied for the production of chlorine dioxide on-demand from chlorite under ambient temperature and noncorrosive conditions. Chlorine dioxide is used in pulp bleaching as well as in disinfection and water purification. Other broader impacts of the research include outreach activities for a group of high school students and high and middle school teachers to introduce them to sustainable catalysis science.