by Dr. Nirman Chakraborty, Technical University of Darmstadt, Germany

Abstract:

Efficient detection of environmental pollutants and their conversion into renewable energy sources holds key to mitigating problems of global energy crisis and climate change. [1] Heterogeneous catalysis plays a significant role in both processes, with surface-analyte interactions deciding the fate of a certain molecular conversion. While conventional spectroscopic techniques primarily reveal the initial and final molecular states of a certain analyte (say CO or NO 2 ), operando spectroscopy, by virtue of its real-time spectroscopic monitoring of surfaces alongside performance evaluation provides information on complex reaction intermediates deciding the course of a certain reaction. [2] This also involves identifying the crucial rate determining step (RDS) of a catalytic process, which resolves surface selectivity. [3] In this talk, I shall introduce a modified “perturbative” version of operando spectroscopy of surfaces, where helicity-resolved circularly polarized Raman spectroscopy is employed to understand real-time surface-analyte hybridization (spin-spin coupling) in NO 2 -OH interactions on Au@CuO gas sensors. [4] Under a Stark tuning rate of 2.5 cm -1 per kV/cm, a 14→25% change in intensity of polarized emission has been identified as hybridization of degeneracy-broken π* 2px and π* 2py orbitals in NO 2 with p orbitals of surface hydroxyl species, during NO 2 →N 2 O conversion. Combined with operando UV-Vis studies, the roles of surface and sub-surface defects were simultaneously probed. Distributions of surface oxygen vacancies and -OH orientation were identified as crucial factors in controlling the overall reaction mechanism. [4] The methodology developed has been successfully implemented to explain NO 2 reduction reaction processes on Sb single atom-MnPS 3 (few layered) based hybrid materials, where the significant intermediary NOOH was generated by modulating p - p (Sb - O) orbital hybridization towards successful NH 3 formation. [5] Above understanding opens a new dimension in field of surface structure-catalytic property correlation, aiming towards advanced catalyst design.

References

[1] Zhou, C., Beydokhti, M.T., Rammal, F. et al. Nat Catal 2025, 8, 270–281.

[2] Elger, A.-K.; Baranyai, J.; Hofmann, K.; Hess, C. ACS Sens. 2019, 4 (6), 1497– 1501.

[3] Pestman, R.; Chen, W.; Hensen, E. ACS Catal. 2019, 9, 5, 4189–4195.

[4] Chakraborty, N.; Nandy, S.; Bhattacharjee, S.; Pfeiffer, M.; Adabifiroozjaei, E.; Molina-

Luna, L.; Hess, C. J. Am. Chem. Soc. 2025 (under revision)

[5] Chakraborty, N.; Bhattacharjee, S.; Ghosh, A.; Lifshitz, E.; Mondal, S. J. Mater. Chem. A 2025, 13,    16491–16507.