Heterogeneous catalysts supported on semiconducting oxide materials play a decisive role in governing catalytic performance in reactions such as CO₂ hydrogenation and ammonia oxidation [1,2]. It is widely recognized that oxygen vacancies (Vo) are key active sites, either facilitating reactant activation or enabling oxygen release in Mars-van Krevelen type mechanisms. By using contactless operando conductivity measurements and operando electron paramagnetic resonance (EPR) spectroscopy, we are able to monitor oxygen vacancies in real time under reaction conditions. Operando EPR provides direct insight into the presence of isolated Vo as well as exchange-coupled vacancy-bound polarons during catalysis [3], whereas contactless conductivity measurements reveal relative changes in electronic transport that can be correlated with vacancy dynamics and reaction kinetics [4]. From a catalysis perspective, the simultaneous application of these complementary techniques is highly desirable. However, this approach poses intrinsic challenges: highly conductive samples are typically unsuitable for EPR measurements, while poorly conductive materials do not exhibit measurable changes in conductivity.

In this contribution, I will present our approach to contactless operando conductivity measurements [4], emphasizing the potential of this emerging technique for a broad catalysis audience. I will further discuss selected catalytic model systems that exhibit strong performance in either contactless operando condutivity or operando EPR measurements, thereby demonstrating the complementary strengths of both methods. Building on these examples, I will illustrate how such operando techniques provide valuable insights into heterogeneous catalysis. Finally, I will address the challenge of combining contactless operando condcutivity with operando EPR measurements, outlining the inherent limitations, potential strategies to overcome them, and their broader significance for advancing mechanistic understanding in the field.

[1] Chiang, Y.T., Ritopecki, M., Willi P.O., et.al. Nat. Nanotechnol. 2026, 21, 588-597.

[2] Beshara, G.M., Heinrich, T. Pitzer, A. et. al., ACS Catal. 2026, 16, 6509-6524.

[3] Pinheiro Araújo, T., Mondelli, C., Agrachev, M. et. al., Nat. Commun. 2022, 13, 5610.

[4] Agrachev, A., Beshara, G.M., Raue, K. et. al. ChemRxiv, 2026.