SusChEM: Deep Photochemical Reduction of Carbon Dioxide to Methanol

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The NSF Chemical Catalysis Program supports the efforts of Professors Frederick M. MacDonnell and Norma S. Tacconi of the University of Texas at Arlington to develop a class of molecular photocatalysts designed to drive the reduction of carbon dioxide all the way to methanol. Energy derived from fossil fuels, while central to today's economy, is not a sustainable solution to global energy needs and has potentially severe environmental consequences upon continued use. Liquid transportation fuels derived from fossil fuels are difficult to replace, however solar technologies that efficiently convert carbon dioxide (a greenhouse gas) to liquid fuels (such as methanol), could directly address this problem. This research team is using well-established ruthenium polypyridyl complexes as chromophores because of their stability, tunability, and favorable photophysical properties. These molecules are coupled with pyridine-based catalysts to obtain a deep 6-electron reduction of the carbon dioxide to methanol. Notably, despite all the advances with carbon dioxide electro- and photo-reduction with homogeneous transition metal catalysts, reduction has been limited to the two-electron reduction products (carbon monoxide or formic acid) with deeper reduction to methanol or methane conspicuously absent. The well understood ruthenium chromophore is being used to provide proof-of-concept results that establish the reaction mechanism before chromophores based on organics dyes or more earth-abundant elements are utilized. Photocatalytic activity is being studied in both aqueous (as a function of pH) and non-aqueous environments, in the presence and absence of metallic surfaces, and with various electrolytes and neutral modifiers to promote the desired reaction. Photocatalyst function is screened and interrogated using custom designed photoreactors and their catalytic efficiency is optimized by determining quantum yield and catalytic turnover as a function of reaction conditions. The technical implications of this research may help develop a carbon-neutral fuel cycle and produce a liquid fuel that requires minimal infrastructure changes to adopt. This research falls under the "SusChEM" program as it utilizes non-petroleum based resources (i.e., carbon dioxide) to produce a liquid fuel (methanol). The investigators are actively involved in K-12 education through a number of outreach programs, most notably through the development and implementation of an externally-funded "Chemistry Magic Show" run through the Science Ambassadors program in the College of Science. Over 43,400 students have seen the "Chemistry Magic Show" since its inception in 2008.