Combining in situ characterization methods in one set-up: looking with more eyes into the intricate chemistry of the synthesis and working of heterogeneous catalysts

Abstract

Several in situ techniques are known which allow investigations of catalysts and catalytic reactions under real reaction conditions using different spectroscopic and X-ray methods. In recent years, specific set-ups have been established which combine two or more in situ methods in order to get a more detailed understanding of catalytic systems. This tutorial review will give a summary of currently available set-ups equipped with multiple techniques for in situ catalyst characterization, catalyst preparation, and reaction monitoring. Besides experimental and technical aspects of method coupling including X-ray techniques, spectroscopic methods (Raman, UV-vis, FTIR), and magnetic resonance spectroscopies (NMR, EPR), essential results will be presented to demonstrate the added value of multitechnique in situ approaches. A special section is focussed on selected examples of use which show new developments and application fields.

Future Challenges in Heterogeneous Catalysis: Understanding Catalysts under Dynamic Reaction Conditions

“…With the help of specially designed reaction cells enabling spectroscopic characterization of the catalyst under industrially relevant conditions and simultaneous monitoring of the catalytic performance, detailed structure‐function relationships can be derived 20, 21, 22, 60. Here, also information obtained from the combination of multiple spectroscopic methods within the same cell are of high importance 61, 62, 63. Such structure–function relationships are the basis for understanding the complex chemical processes and finally also for establishing a knowledge‐based design of catalysts and reactors.…”

Trends and advances in Operando methodology

“…Newton has pioneered the combination of diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) and X-ray absorption spectroscopy (XAS), the former providing information about chemical bonds of surface species and the latter providing geometrical and electronic structures of active metals [23]. The advent of low-noise, high-resolution 2D detectors has enabled X-ray diffraction (XRD) to be combined with other techniques like XAS using the same capillary reactor cell [21,22,24,25]. Another combination gaining popularity recently using X-ray is XAS/X-ray emission spectroscopy (XES), which can yield a detailed picture of electronic states (unoccupied and occupied orbitals).…”

“…Therefore, combined use of complementary techniques is desired to gain holistic views on catalytic processes ( Figure 2a) [21]. Powerful combination to gain molecular, electronic and structural information is vibrational (IR/Raman) spectroscopy combined with X-ray spectroscopy/diffraction [22].…”

Active Site Elucidation in Heterogeneous Catalysis via In Situ X-Ray Spectroscopies

“…2D imaging has also been utilized to study the spatiotemporal evolution of reacting wavefronts of oxidized and reduced metal species within a Pt-Rh/Al 2 O 3 catalyst, which respectively promote the total or partial oxidation of methane at 2838C. [78,79] In situ XAS can be readily coupled with other analytical techniques, [80][81][82][83] such as diffraction, diffuse-reflectance infrared spectroscopy (DRIFTS), Raman, [84] or mass spectrometry (MS), to provide additional real-time insight into heterogeneous catalysts. The powerful combination of three spectroscopic techniques to probe the active site in heterogeneous catalysis under operando conditions was first demonstrated via energydispersive XAS/UV-Vis/Raman measurements of silica-and alumina-supported molybdenum oxide catalysts for propane dehydrogenation, enabling discrimination of two deactivation pathways via coking or MoO 3 clustering, and tentative assignemt of Mo 4þ as the active site.…”