Application of time-resolved in-situ X-ray absorption spectroscopy in solid-state chemistry

Abstract

Time-resolved X-ray absorption spectroscopy (TR-XAS) possesses excellent capabilities to reveal quantitative phase composition and average valence together with the evolution of the local structure of a system under dynamic reaction conditions. The work discussed here focused on time-resolved in situ XAS investigations aiming, first, at understanding structural evolution under dynamic conditions and, second, at revealing properties of the system studied not available from investigations under stationary conditions. Hence, not only was the local structure of a material studied under reaction conditions, but also were characteristic properties of the reaction elucidated, such as reaction intermediates or the kinetics of the reaction. The solid-gas reactions presented here clearly demonstrate the potential of TR-XAS investigations to extend the suitability of XAS for in situ studies in solid-state chemistry to investigations under dynamic conditions.

“Inverting” X-ray Absorption Spectra of Catalysts by Machine Learning in Search for Activity Descriptors

“…For example, it was used to identify reaction intermediates from the time-dependent Cu K-edge XANES spectra for Ce 0.8 Cu 0.2 O 2 catalyst reduction in hydrogen , and to study changes in oxidation state of copper in bimetallic CuPd catalyst on zeolite support . PCA was used for speciation of molybdenum oxides (which are active catalysts for oxidation of propene) under reaction conditions, study of Mn-promoted Fe-based Fischer–Tropsch catalysts, and study of the oxidation state of Fe in complex Fe–Mo–Bi catalysts for propylene ammoxidation . In addition to time-dependent studies, PCA is actively used for the interpretation of spatially resolved data of catalysts collected with focused X-ray beam or in full-field mode with 2D detectors. , For example, in ref , the distributions of oxidized and reduced species in illuminated by UV radiation CuNi photocatalyst were obtained by PCA analysis of XANES data collected with a microfocused beam, confirming the presence of Cu 2+ species only in the illuminated zone of the material (Figure ).…”

In‐situPowder X‐ray Diffraction in Heterogeneous Catalysis

“…Identifi cation of the intermediate phases and determination of their timeresolved mixing fractions is carried out by fi tting the abstract principal components obtained by PCA to various standard compounds, also known as the target transform procedure in PCA. It was successfully applied to a number of TR-XAS data in catalytic systems and resulted in the determination of the following phases: Ni + NiO for the H 2 reduction of NiO [58] ; CuO + Cu 2 O + Cu for the CO [11] and H 2 [59] reduction of CuO, the same three standards for the H 2 reduction of CuO/ZnO [60] ; and MoO 3 + Mo 18 O 52 + MoO 2 for MoO 3 reduction in propene and MoO 2 oxidation in oxygen [61] . We will show how such analysis can be conducted using two different examples, for the one-step and the two-step reactions.…”

Effects of Anion Substitution in (Mo,V)5O14 on Catalytic Performance in Selective Propene Oxidation to Acrolein

“…In situ XAS experiments were performed in transmission mode in af low reactor at atmospheric pressure with 5% propene in helium (~30 mL min À1 ). [18] TPR experiments were performed in at emperature range from 298 to 763 K. The gas-phase composition at the cell outlet was continuously monitored by using am ass spectrometer (Omnistar,P feifer). Data analysis was performed by using the software package WinXAS v3.2.…”