(669h) Photon Induced Structural and Chemical Changes of Optically Active Perovskite Oxide Catalysts

Photon illumination of catalyst surfaces is viewed as a method of increasing reaction selectivity and rates not possible through the supply of thermal energy.¹ Reactive intermediates can poison catalyst sites, limiting activity – modulating the binding energy of these intermediates through generation of photoexcited electrons assists in reaching reaction rates beyond the volcano plot, breaking scaling relationships associated with traditional catalysts.² However in studies to date, photon induced desorption processes are limited by low photon absorption and highly specific photon energies, hindering applications for tandem photothermal reaction systems.³ Optically active mixed metal oxides, specifically titanate perovskites, through their tunable bandgap can increase photon absorption and, ultimately, provide insight into kinetic limitations associated with light induced desorption processes.

We show that incorporating catalytically active dopants into perovskite frameworks facilitates increased light absorption through altering the optical bandgap. CO chemisorbed on the surface is monitored through in situ DRIFTS, and CO coverage on dispersed on dopant cations in the perovskite lattice is lowered when the catalyst is photoirradiated. We show that the wavelength is not the determining factor for lowering the coverage, but the number of photons is, indicative of a photoexcitation mechanism into the dopant cations. This perturbs the binding energy of chemisorbed CO, lowering surface coverage. The rate of CO photodissociation is calculated under different light intensities and wavelengths to show this phenomenon. This photoexcitation arises because of the energy level of the dopant band which acts as the site for harvesting photoexcited electrons. These findings provide insights toward development of optically active catalysts for chemistries involving strongly bound intermediates, for which photons can control the surface coverage of intermediates.

References

1. Linic, S. et al., Mater. 2015, 14, 567– 576
2. Qi, J. et al., ACS Energy Lett., 2020, 5, 3518-3525
3. Wovchko, E. et al., Phys. Chem. B, 1998, 102, 10535-1-541