Spatiotemporal operando UV-vis spectroscopy: Development and mechanistic alternation of CO oxidation on Pt/Al2O3 on the reactor scale

Operando methodologies are widely used in heterogenous catalysis to understand unique state of catalyst materials emerging under specific reaction conditions and to establish catalyst structure-activity relationships. Recent studies highlight the importance of combining multiple operando techniques (multimodal approach) to gain complementary information as well as looking into chemical and material gradients and spatial variations on the reactor scale. In this work, we developed an operando UV-vis diffuse reflectance spectroscopy (DRS) setup compatible with a common fixed-bed tubular reactor. The design is based on optical calculations, validation experiments and signals considerations. A spatial resolution of 1 mm along the axial direction of the reactor was successfully demonstrated and combined with a time resolution of seconds with good signal to noise. CO oxidation over Pt/Al2O3 was performed as a proof of principle experiment demonstrating the capabilities of the new setup. The information gained by the space-resolved operando UV-vis DRS was combined with other spaceresolved operando studies such as diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), gas sampling and temperature profiling. The study shows that the nature of active sites (Pt redox state) and thus the reaction mechanism alter with reaction temperature and also in space. Spatiotemporal UV-vis DRS is also demonstrated, showing the capability for transient studies with space-resolution.