A08: Capturing the Dynamic of the Interface-Localized Frustrated Phase Transition of a Working Catalyst

Dr. Sharif Najafishirtari • Dr. Philipp Schienbein

In FP2, project A08 developed operando techniques based on diffuse reflectance infrared Fourier transform (DRIFT) and Raman spectroscopy to investigate surface intermediates of 2-propanol oxidation. Methodology and data analysis protocols were successfully developed to apply modulation-excitation spectroscopy (MES) in the gas-phase reaction mixture with an excess number of solvent molecules to bridge the gap between the gas- and liquid-phase reactions. Our methods proved to be insightful in deciphering the complex phenomena occurring on the surface, including its interaction with solvent and reactants forming transient or deactivating intermediates, and the surface-localized transformations of the catalyst, which may reveal the dynamics of the frustrated phase transitions to the active phase at the surface. Understanding such dynamics remains one of the central challenges in catalysis. While experimental methods provide access to observables with high temporal resolution, they cannot directly resolve the atomistic dynamics that govern interfacial reactivity.

For FP3, we extended the scope to include quantitative vibrational spectroscopy from atomistic simulations. In concert with experiments, theory can deliver an atomistic picture of how individual atoms and molecules interact with the catalyst surface, while the experiment observes the macroscopic ensemble average of numerous processes happening simultaneously at the interface due to much longer time and length scales. In A08, we propose a joint experimental–theoretical approach that bridges these scales. The connection is provided by vibrational spectroscopy: operando Raman and DRIFTS measurements that can deliver spectroscopic fingerprints of the evolving surface phases, while machine-learning–accelerated molecular dynamics enables us to quantitatively calculate corresponding spectra and assign them to atomistic motifs. By combining experiment and simulation, we will construct an atomistic “movie” of the dynamic phase evolution at the catalyst–reactants interface; an outcome that neither experiment nor theory can achieve alone. Beyond resolving the elusive surface-localized solvated and poorly ordered active phase, this approach also allows us to address the frustrated phase transition at the interface, a central theme of the consortium, by directly measuring and simulating surface phonon modes as markers of this transition.

Figure: Phase-resolved spectra at 100 °C (a,c) and 200 °C (b,d) on LFO & LFCO at fundamental demodulation index.