Design of Active Sites for Photocatalytic Nitrogen Oxidation Based on Knowledge from Classical Catalysis

Merlin Gutgesell^a, Marcus Klahn^b, Abdelkarim Zaim^c, Julian Klein^d, Junhao Huang^a, Gerd Bacher^d, Jonathan Bloh^c, Jennifer Strunk^a^,^b

^aDepartment of Chemistry, Technical University of Munich, 85748 Garching, Germany

^bLeibniz-Institute for Catalysis at the University of Rostock, Albert-Einstein-Str. 29a, Rostock, 18059, Rostock, Germany

^cDECHEMA Research Institute, Theodor-Heuss-Allee, Frankfurt am Main, Germany

^dWerkstoffe der Elektrotechnik and CENIDE, University Duisburg-Essen

Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS Spring 2025 Conference (MATSUSSpring25)

Interlinking heterogeneous catalysts, mechanisms, and reactor concepts for dinitrogen reduction - #Nitroconversion

Sevilla, Spain, 2025 March 3rd - 7th

Organizers: Roland Marschall, Jennifer Strunk and Dirk Ziegenbalg

Oral, Jennifer Strunk, presentation 297
DOI: https://doi.org/10.29363/nanoge.matsusspring.2025.297
Publication date: 16th December 2024

Two principal pathways exist for the photocatalytic valorization of nitrogen. The reductive route targets the formation of ammonia and the replacement of the energy-intensive Haber-Bosch process. As an alternative, nitrogen can be oxidized to nitrous oxide and nitrate, as precursors to nitric acid. Since the traditional synthesis of nitric acid via the Ostwald process is based on ammonia as feedstock, photocatalytic nitric acid formation “out of thin air” is clearly also a more sustainable solution. It has already been demonstrated that titania is able to oxidize molecular nitrogen, but the yields of nitrate were low [1]. Since titania is known to allow much higher quantum efficiencies in other challenging photosynthetic reactions [2], we attempted to improve the catalytic functionality of titania for nitrogen and oxygen activation.

In previous works we have shown for the cases of methanol and isopropanol oxidation that well-known active sites from classical catalysis are capable to carry out the same reaction light induced [3,4]. Based on this concept, we modified TiO₂ with well-known nitrogen activation catalysts, based on Fe and Mo, or sites for oxygen activation, based on V and W. As a third category, based on the fundamental rule that catalysts always facilitate both forward and reverse reaction, active sites from DeNOx catalysis, based on Pd, were added to TiO₂. Using an extensive set of synthesis methods, such as grafting organometallic precursors or impregnation procedures, the size range of the active sites was varied, studying both single sites and nanoparticles.

Photocatalytic activity studies revealed that Pd, in particular, can improve significantly the formation of nitrogen oxides on TiO₂. Ongoing studies using in situ vibrational spectroscopy attempt to clarify the influence of the deposited active sites on the formation of reactive intermediates on the photocatalyst surface, to eventually understand the reaction pathway and to identify persistent kinetic barriers.

References:

[1] Pashkova, A.; Burek, B.O.; Bloh, J.Z. Sustainable nitrate production out of thin air: The photocatalytic oxidation of molecular nitrogen. Catal. Sci. Technol. 2022, 12, 2755-2760.

[2] Dilla, M.; Moustakas, N.G.; Becerikli, A.E.; Peppel, T.; Springer, A.; Schlögl, R.; Strunk, J.; Ristig, S. Judging the feasibility of TiO2 as photocatalyst for chemical energy conversion by quantitative reactivity determinants. Phys. Chem. Chem. Phys. 2019, 21 13144-13150.

[3] Kortewille, B.; Wachs, I.E.; Cibura, N.; Pfingsten, O.; Bacher, G.; Muhler, M.; Strunk, J. Proof of equivalent catalytic functionality upon photon-induced and thermal activation of supported isolated vanadia species in methanol oxidation, ChemCatChem 2018, 10, 2360-2364.

[4] Siemer, N.; Lüken, A.; Zalibera, M.; Frenzel, J.; Muñoz-Santiburcio, D.; Savitsky, A.; Lubitz, W.; Muhler, M.; Marx, D.; Strunk, J. Atomic scale explanation of O2 activation at the Au-TiO2 interface. J. Am. Chem. Soc. 2018, 140, 18082-18092

Acknowledgements:

Financial support by the DFG Priority Programme SPP 2370 "Interlinking Catalysts, Mechanisms and Reactor Concepts for the Conversion of Dinitrogen by Electrocatalytic, Photocatalytic and Photoelectrocatalytic Methods (“Nitroconversion”)” is gratefully acknowledged.

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