For centuries, the world has relied on catalysts to facilitate chemical transformations. With the growing need for a more circular carbon economy, radiative energy (a.k.a. light) has emerged as a promising alternative energy source which may replace petroleum-intensive chemical processes. This work presents strategies in heterogenous catalysis for the direct conversion of methane to methanol, a value-added fuel, through selective C-H oxidation chemistry, using light. Methanol synthesis suffers from low selectivity due to overoxidation caused by the higher activity of methanol compared to methane. Combining the optical properties of plasmonic nanoparticles, materials that exhibit collective oscillations of free electrons after interaction with light, with small concentrations of catalytically active late transition metals, allowed for the design of optically tunable photocatalysts with engineered active sites. This emerging class of photoactive materials are known as dilute plasmonic alloys. This approach offers a balance between the bulk characteristics of the plasmonic metals, where surface reactivity is often low, and the active sites comprised of late transition metals; altering the ratio of these two components allows tailored reaction pathways in methanol synthesis. Pt in Cu was targeted since it has been demonstrated to reduce C-H activation barriers in methane oxidation. Upon plasmon decay, subsequently generated hot carriers are funneled into the solute active sites, from which they can scatter into product antibonding orbitals for increased desorption rates. Leveraging the interplay between C-H bond activation and methanol desorption under optical illumination allows to control product selectivity and catalyst stability in ways not typically attainable with traditional thermocatalytic methods. This work presents current advances in direct methanol synthesis using dilute plasmonic alloy photocatalysts and develops a more unified picture at the interface between nanophotonics and heterogeneous catalysis.

Dilute plasmonic alloys for direct methane to methanol photocatalysis

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