Beware of beam damage under reaction conditions: X-ray induced photochemical reduction of supported VOx catalysts during in situ XAS experiments. Issue 36 (7th September 2022)

• Record Type: Journal Article
• Authors: Zabilska, Anna; Clark, Adam H.; Ferri, Davide; Nachtegaal, Maarten; Kröcher, Oliver; Safonova, Olga V.
• Is Part Of: Physical chemistry chemical physics. Volume 24:Issue 36(2022)
• Page Start: 21916
• Page End: 21926
• Publication Date: 2022-09-07
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d2cp02721f
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : X-ray photoreduction of V 5+ in supported vanadia catalysts was detected by XAS during in situ experiments at a synchrotron beamline. Practical strategies helping to recognize and mitigate such problems are suggested. Abstract : In situ X-ray absorption spectroscopy (XAS) is a powerful technique for the investigation of heterogeneous catalysts and electrocatalysts. The obtained XAS spectra are usually interpreted from the point of view of the investigated chemical processes, thereby sometimes omitting the fact that intense X-ray irradiation may induce additional transformations in metal speciation and, thus, in the corresponding XAS spectra. In this work, we report on X-ray induced photochemical reduction of vanadium in supported vanadia (VO x ) catalysts under reaction conditions, detected at a synchrotron beamline. While this process was not observed in an inert atmosphere and in the presence of water vapor, it occurred at room temperature in the presence of a reducing agent (ethanol or hydrogen) alone or mixed with oxygen. Temperature programmed experiments have shown that X-ray induced reduction of VO x species appeared very clear at 30–100 °C but was not detected at higher temperatures, where the thermocatalytic ethanol oxidative hydrogenation (ODH) takes place. Similar to other studies on X-ray induced effects, we suggest approaches, which can help to mitigate vanadium photoreduction, including defocusing of the X-ray beam and attenuation of the X-ray beam intensity by filters. To recognize beam damage under in situ / operando conditions, we suggest performing X-ray beam switching (on and off) tests at different beam intensities under in situ conditions.