Keynote
Electrocatalytic Oxidation of Hydrocarbons and Photo/Electrocatalytic Reduction of CO₂

As recently stated in an editorial (Acc. Chem. Res. 2017, 50, 445) “The conversion and storage of solar energy in a sustainable fashion with minimal adverse impact on the planet” and “perfect catalysts” are among the top three holy grails in chemistry. Based on our ability to transform sunlight to electricity using photovoltaic technology, it would, therefore, seem appropriate as will be shown in this talk to develop electro/photocatalytic reactions and processes. Four examples will be given that demonstrate new such types of transformations all involving the use of polyoxometalates as catalysts or electron relays.

• The selective cathodic electrocatalytic oxidation in water of light alkanes and alkenes with O₂ catalyzed by an iron-tungsten polyoxometalate porous capsule, {Fe^III₃₀ W^VI₇₂}. For example, the unique selective oxidation of ethane to acetic acid and ozone type cleavage of ethylene to formaldehyde and formic acid.

• The anodic formation of formyloxy radicals catalyzed by {Co^IVW₁₂} to activate C‑H bonds of benzene and other substrates to yield the corresponding formate esters. Since the latter are easily hydrolyzed, the sum transformation, for example for benzene, is PhH + H₂O → PhOH + H₂.

• A cascade of transformations involving a new photoelectrochemical pathway wherein phosphotungstic acid, H₃PW₁₂O₄₀, is used to transfer electrons from the polyoxometalate to a specifically designed rhenium bipyridine-based catalyst that is active for selective reduction of CO₂ to CO. In this way is CO₂ is selectively reduced at low potential using low intensity visible light (60 W tungsten lamp or red LED).

• The coupling of a hydrocarbon dehydrogenation reaction to a CO₂ to CO reduction reaction where a carbon nitride semiconductor is used as a support and photosensitizer. A polyoxometalate acts as a catalyst for the photo dehydrogenation of a hydrocarbon, and then relays the electron and protons to a CO₂ reduction catalyst.