Interference-resistant Raman spectrometer with application-adapted data analysis for in situ/operando diagnostics in chemical reactors and reactive flows

• Subject Area: Chemical and Thermal Process Engineering
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 514177753

This project focuses on a Raman spectrometer for the interference-resistant quantification of chemical species in reactive flows. The overall goal is to enable future basic science-oriented research in various configurations of flow reactors: microjet mixer, CO2 electrolysis flow cell, and high-temperature catalytic channel. So far, this poses yet unmet challenges since the reactive flows in these reactors can be liquid or gaseous, steady or transient, and laminar or turbulent, often at high temperatures. Especially near catalytic walls, they are governed by high spatial gradients and fluid-surface interaction. Due to the reaction and mixing processes, the highly varying time and length scales need to be resolved diagnostically. To develop an improved understanding of these reactive flows, non-intrusive, in situ/ in operando diagnostics of the chemical species in the fluid and at the catalytic surfaces are required. Only spontaneous Raman spectroscopy fulfills the requirement of simultaneous, quantitative diagnostics of all relevant species. However, due to the very weak Raman cross-sections, its application and the analysis of the measured data is challenging, especially in the gas phase, at high temperatures and on or in close proximity to catalytic walls. Superposition of Raman scattering by apparatus- and reaction-related interferences or background signals often complicate or even impede diagnostics. Reactive flows are therefore only accessible to Raman spectroscopy to a limited extent. Three components of a modular system are intended to overcome these limitations: (1) optically accessible flow reactors, (2) interference-resistant Raman spectrometers, and (3) application-adapted data analysis. The coupling of novel instrumental approaches for interference and perturbation reduction with measurement-tailored flow reactors, that have fluid-dynamically and thermally well-defined initial and boundary conditions, enables basic science-oriented research. The heart of the project is a modular two-arm Raman spectrometer for instrumental interference reduction, which for the first time takes advantage of the simultaneous acquisition of multiple signal components of Raman scattering on one detector. The beam paths are first separated in the built-up spectrometer and then recoupled again to one detector to realize the interference suppression by polarization separation. An additional extension for interference reduction is the wavelength-shifted excitation by coupling a second laser. For in-situ diagnostics of catalytic surfaces nanoparticle sensors are specially adapted to utilize surface-enhanced Raman scattering. Chemometrics and statistical data evaluation methods are used to quantify the species measured as raw data using the Raman spectrometer. A method toolbox is developed for optimal evaluation and analysis adapted to the application.

• DFG Programme: Major Instrumentation Initiatives
• Major Instrumentation: 1D-SERDS-Raman Spektrometer ; Laser für Ramanmikroskop ; Zwei-Arm-Raman-Spektrometer
• Instrumentation Group: 1840 Raman-Spektrometer ; 5700 Festkörper-Laser
• Applicant Institution: Hochschule Darmstadt
• Leader: Professor Dr.-Ing. Dirk Geyer
• Co-Investigators: Professor Dr. Sebastian Döhler; Professorin Dr. Christina Graf; Dr.-Ing. Sandra Hartl; Professor Dr. Frank Schael; Professor Dr. Andreas Weinmann