Up-conversion of carbon dioxide into value-added products is an essential component in the quest for the renewable synthesis of carbon-based fuels. To date, known catalytic systems for this reaction generally suffer from high energy input, poor product selectivity, and short lifetimes. Reticular chemistry of covalent organic frameworks (COFs) has attracted a lot of attention because their large surface areas, the rational design and the organic backbone of the structure hold great promise for the use of this class of materials in heterogeneous catalysis. We report a series of oriented thin films of COFs that effectively reduce CO<sub>2</sub> to CO at low overpotential (550mV) with high selectivity (87%) at high current densities (80mA/mg) which is a significant improvememnt over the previously reported microcrystalline powder sample. These catalysts are stable for more than 12 hours without any loss in reactivity. The modular synthesis of the structure allows for controlled functionalization of the framework with functional groups of varying inductive effects, without changing the underlying topology of the COF (Fig. 1). Due to the good electronic communication throughout the COF framework, a facile strategy for electronic tuning of the catalytically active cobalt sites in the framework was accomplished. The systematic modification of the electronic structure of the active sites can be monitored by X-ray absorption data on the cobalt L=edge and directly translates into substantial differences in reactivity. This work constitutes the first example of frontier-orbital engineering for the rational catalyst optimization of covalent organic frameworks and exemplifies a powerful example for the notion of covalent chemistry beyond the molecule.

Catalyst optimization of covalent organic frameworks by frontier orbital engineering

253rd National Meeting (2017)

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