Space- and Time-Resolved Investigation of the Gas Phase and the Active Surface/Bulk

Background: Catalyst performance is governed by multiple interdependent length scales. At the microscopic level, the atomic surface structure or the arrangement of molecular units defines the intrinsic physical and chemical properties, and thus the catalytic activity. At the meso- and macroscale, the structural design of the catalyst influences heat and mass transfer processes, which are crucial for efficient operation. At the reactor scale, overall reaction rates depend on the flow regime (laminar or turbulent) and the specific catalyst configuration, both of which strongly affect transport phenomena. Mass transport occurs not only within catalyst pores but also in the surrounding fluid phases, while the local temperature field results from a complex interplay of conduction in solid and gas phases, convection, radiation, and the heat released by chemical reactions. These coupled processes highlight the complexity of transport phenomena spanning from the molecular to the reactor scale, but they also offer opportunities for optimizing catalyst and reactor design as well as operating conditions.

In practice, reactor performance evolves over time due to changing operating conditions and catalyst aging. Monitoring is commonly performed using sensors that measure gas-phase compositions at reactor inlets and outlets. Recently, there has been increasing interest in spatially resolved diagnostic techniques capable of probing conditions directly inside reactors. Despite these advances, catalyst design, structural evolution under operating conditions, transport phenomena, and numerical modeling are still often addressed separately. A holistic approach that integrates these aspects is essential for developing next-generation catalytic systems.

Project: This project (C4) is part of the CRC 1441 (TrackAct), which aims to track catalytically active sites across spatial and temporal dimensions at the reactor scale, with a particular focus on bridging the existing complexity gap. To investigate structure-activity relationships, the project combines two complementary operando characterization techniques: planar laser-induced fluorescence (PLIF) and X-ray absorption spectroscopy (XAS). This unique approach enables, for the first time, the direct correlation of structural information on catalytically active species obtained by XAS with spatially resolved concentration fields measured by PLIF inside a catalytic channel reactor.

The experimental work is supported by other non-invasive methods, such as DRIFTS and surface Raman, as well as time- and space-resolved numerical simulations of reactive flow and catalytic conversion. Together, these non-invasive experimental methods and simulations provide deeper insights into realistic catalytic systems and enable the derivation of detailed two-dimensional structure–activity relationships. Such an integrated understanding is essential for advancing multiscale modeling and for optimizing catalyst activation and regeneration strategies. Ultimately, the project establishes a framework for tracking catalyst structure in direct relation to local reaction conditions and catalytic performance.

Contact: Thomas Häber, Olaf Deutschmann

Collaboration:

• Prof. Dr. J.-D. Grunwaldt (KIT)

Selected publications:

T. Häber, S. Wan, S. Struzek, C. Cárdenas, A. Zimina, F. Maurer, P. Lott, R. Suntz, J.-D. Grunwaldt, O. Deutschmann, Novel advanced channel reactor for spatio-temporal activity and catalyst state correlations applied for the reduction of NO by CO over Pt/Al₂O₃, Appl. Catal., A 712 (2026) 120748. https://doi.org/10.1016/j.apcata.2025.120748.

T. Häber, S. Struzek, L. Caulfield, S. Wan, F. Maurer, P. Lott, A. Nefedov, C. Wöll, J.-D. Grunwaldt, O. Deutschmann, Time-resolved dynamics during the initial decline in catalytic activity of the CO + NO reaction over platinum – elucidating the role of NCO, Emiss. Control Sci. Technol. 12 (2026) 16. https://doi.org/10.1007/s40825-026-00297-8.

S. Wan, K. Keller, P. Lott, A.B. Shirsath, S. Tischer, T. Häber, R. Suntz, O. Deutschmann, Experimental and numerical investigation of NO oxidation on Pt/Al₂O₃- and NOx storage on Pt/BaO/Al₂O₃-catalysts, Catal. Sci. Technol. 12 (2022) 4456–4470. https://doi.org/10.1039/D2CY00572G.

S. Wan, T. Häber, P. Lott, R. Suntz, O. Deutschmann, Experimental investigation of NO reduction by H₂ on Pd using planar laser-induced fluorescence, Appl. Energ. Comb. Sci. (2023) 100229. https://doi.org/10.1016/j.jaecs.2023.100229.

K. Keller, S. Wan, M. Borchers, P. Lott, R. Suntz, O. Deutschmann, Treating NOx emission of hydrogen fueled combustion engines by NOx storage and reduction catalysts: A transient kinetic study including PLIF measurements, Proc. Comb. Inst. 39 (2023) 4247–4256. https://doi.org/10.1016/j.proci.2022.07.027.