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Unravelling the secrets of Cu-based catalysts for C-H activation

Periodic Reporting for period 2 - CUBE (Unravelling the secrets of Cu-based catalysts for C-H activation)

Reporting period: 2021-11-01 to 2023-04-30

Catalysis is key to sustainable production of commodity products, and to life itself. While industrial catalysts are generally robust and provide high turn-over rates, they are less selective than their enzymatic analogues, which are, on the other hand, quite fragile. The successful combination of the advantages of each catalysis field would have tremendous societal impact. Among prime target reactions, selective C-H activation has been vigorously pursued for more than 70 years in all areas of catalysis – homogeneous, heterogeneous and biological – yet with scarce cross-fertilization. CUBE will bridge this gap, by synergistically disclosing the secrets of Cu-containing biological and synthetic catalysts and by translating the acquired knowledge into rationally designed new synthetic and biological catalysts with unprecedented activity, selectivity and turn-over numbers.
In the first reporting period, the CUBE team has synthesized and characterized Cu-Nx complexes that strongly resemble active sites in enzymes, and built complexes into a metal organic framework lattice, to more precisely mimic the first and second shell of the Cu site [1].
New spectroscopic methods have been developed. In particular, a combination of XAS and VtC XES was applied to a series of copper model complexes spanning formal oxidation states from Cu(I) to Cu(III). By combining these experimental data with computations, it was shown that the spectroscopic oxidation states may be robustly assessed and that experimental evidence for the controversial Cu(III) oxidation state assignment could be supported [5]. The method is currently applied to CUBE-relevant samples. In the area of Cu-zeolites, a relevant achievement was the development of a new approach to quantify the amount of Cu(I) with a standard volumetric apparatus bypassing the use of a facilities such as XAS measurement [6]. Catalytic studies are on-going.

Furthermore, the team has developed novel tools for looking deeper into LPMO catalysis, such as stopped-flow methods combined with spectroscopic methods for detection of intermediates under turnover conditions. A large collection of natural and engineered LPMO variants has been produced, where mutations in the first and second coordination sphere have been shown to modulate enzyme performance in a manner that can be linked to the reactivity and stability of the catalytic copper site. The unraveling of structure-function correlations is underway, utilizing a combination of (transient) kinetics, spectroscopic and computational approaches, which should help reveal how nature uniquely tunes the reactivity of LPMO active sites. These studies will provide vital input for the next generation of engineered biological, molecular and heterogeneous catalysts.
The systematic evolution of enzymes and enzyme-mimicking complexes and materials carried out during the first two years, as well as the parallel development of new spectroscopic tools, already constitute an excellent position for enabling the fundamental insight and achievements aimed for in this project, well beyond state-of-the-art.
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