Temporal analysis of products-Raman (TAP-Raman): An integrated setup for operando spectroscopy and transient kinetic...

The Temporal Analysis of Products (TAP) technique offers (sub-)millisecond time resolution and (sub-)nanomole titration resolution for probing chemical reaction kinetics over the catalyst surface and quantifying surface site distributions. However, it lacks direct structural insight. Conversely, operando Raman spectroscopy identifies molecular-level catalyst structures but lacks time-resolved kinetic information. These limitations hinder the quantitative determination of site-specific chemical rates and mechanistic understanding of structure-activity relationships. Here, we present the development of a TAP-Raman setup that integrates a custom-designed TAP setup with operando Raman spectroscopy, enabling the simultaneous acquisition of structural and transient kinetic data for an understanding of their relationship during chemical reactions. The setup achieves sub-nanomole-level titration resolution, allowing the catalyst surface to be perturbed with well-defined and ultra-small pulses of probes. Such sub-millisecond transient kinetic measurements are necessary to capture the dynamics of surface catalysis, and this pulsed operation bridges the temporal gap between these rapid events of chemical reactions and the slow Raman spectra acquisition. The capabilities of this integrated setup are demonstrated through two case studies: (i) oxidation of a pre-reduced ceria-based catalyst by O2, revealing redox-driven lattice dynamics, and (ii) oxidation of carbon deposits from the propane dehydrogenation reaction on a ZrO2 catalyst, elucidating the reactivities of ZrO2 catalyst for carbon oxidation and oxidation pathways. The results from both cases demonstrate the successful application of the TAP-Raman approach for directly coupling time-resolved reactivity with structural evolution under operando conditions. This setup offers a broadly applicable tool for quantitative, time-resolved structure-activity correlations, providing unprecedented mechanistic insight into dynamic catalytic processes.