CAREER: Photocatalytic Transfer Hydrogenation of CO2 Using Transition Metal Cluster Arrays

University Of Oregon Eugene, Eugene OR

Investigators

Abstract

With support from the Chemical Catalysis Program in the Division of Chemistry, Christopher H. Hendon of the University of Oregon is studying photocatalytic carbon dioxide (CO2) reduction mediated by transition metal clusters. Carbon dioxide reduction is an important chemical reaction because it can reduce atmospheric CO2 levels, while also forming valuable products like formic acid and formaldehyde. CO2 conversion is a difficult chemical transformation because the desired products (e.g. formic acid and formaldehyde) are formed in competition with one another, differing in the number of protons and electrons required to form them. To overcome this problem, Dr. Hendon will use computational modeling to study photocatalytic reduction of CO2 with inorganic clusters, which will provide precise numbers of protons and electrons for the reaction. The research will examine how these metal clusters can be used to starve hydrogenation reactions of reactants (H•) to select for target products, and demonstrate that the ligands that support the metal clusters allow for energetic tuning of the metal sites. If successful, this work has the potential to guide experimentalists to achieve more selective conditions for CO2 reduction to the desired product. Moreover, this computational work may prove useful in other problematic hydrogenations, plagued by selectivity issues, including the regioselective reduction of alkenes and alkynes. This work will synergize with Dr. Hendon’s existing program in electrocatalysis of beverage extracts, a successful program that teaches fundamental chemistry and physics through the lens of coffee. This award will support the development of a formal curriculum for non-traditional students, that will be made open-source and community-maintained. While the the all-important CO2 reduction reaction can be promoted through conventional hydrogenation with H2, selectivity can be achieved by using other H-sources. One promising route involves transfer hydrogenation, whereby hydrogen commutes from one species to another. This proposal seeks to demonstrate that selective CO2 transfer hydrogenation (reduction) can be achieved using atomically precise inorganic clusters in metal-organic frameworks (MOFs). In this award, Dr. Hendon will use computational chemistry to examine a family of heterogeneous polynuclear transition metal catalysts and will study the general mechanism in which hydrogen is extracted from donors (e.g. alcohols, water, etc.) and transferred to acceptors (e.g. CO2). The reaction mechanism likely depends on differences in pKa of the donor/catalyst/acceptor, as well as their redox potentials. From these studies, the Hendon group will search for target MOF clusters with improved chemical selectivity with tunable numbers of available hydrogen atoms through cluster modulation. Together, these studies aspire to yield a general design principle for selection of donor, acceptor, and MOF-based catalysts, based on electron energy alignments. Through collaboration with experimentalists the work aims to generate a family of CO2 reduction photocatalysts that source their H• from abundant donors. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.