In situ IR, NMR, EPR, and UV/Vis Spectroscopy: Tools for New Insight into the Mechanisms of Heterogeneous Catalysis

Abstract

The development of new solid catalysts for use in industrial chemistry has hitherto been based to a large extent upon the empirical testing of a wide range of different materials. In only a few exceptional cases has success been achieved in understanding the overall, usually very complex mechanism of the chemical reaction through the elucidation of individual intermediate aspects of a heterogeneously catalyzed reaction. With the modern approach of combinatorial catalysis it is now possible to prepare and test much more rapidly a wide range of different materials within a short time and thus find suitable catalysts or optimize their chemical composition. Our understanding of the mechanisms of reactions catalyzed by these materials must be developed, however, by spectroscopic investigations on working catalysts under conditions that are as close as possible to practice (temperature, partial pressures of the reactants, space velocity). This demands the development and the application of new techniques of in situ spectroscopy. This review will show how this objective is being achieved. By the term in situ (Lat.: in the original position) is meant the investigation of the chemical reactions which are taking place as well as the changes in the working catalysts directly in the spectrometer.

Correlation between structural and electronic order–disorder effects and optical properties in ZnO nanocrystals

“…These values are similar to those previously reported in the literature, [47][48][49][50] and a review of the subject has been reported by Hunger and Weitkamp. 56 To understand, the origins of the EPR signal could be assigned to the holes trapped on oxygen atoms, in particular, oxygen vacancies at the particle surface or bulk. Based on our EPR results, we can observe V þ1 O which was discussed previously, and also showed a mixture of V 0 O and V þ2 O for these materials prepared by a microwave-assisted hydrothermal method.…”

Characterization of Biofield Energy Treated 3-Chloronitrobenzene: Physical, Thermal, and Spectroscopic Studies

“…In this method, the wavelength of light absorbed by the sample depends on the structure of the sample. With UV-Vis spectroscopy, it is possible to investigate electron transfer between orbitals or bands of atoms, ions and molecules from the ground state to the first excited state [22].…”

In situ Spectroscopy of Catalysts

“…Therefore, the only solution is to adapt spectroscopic techniques in such a way that they are able to monitor catalysts in action"; in other words, to track the physicochemical processes taking place in an active catalyst in real time and under operating conditions. This is the field of in-situ spectroscopy [10,11,[14][15][16][17][18][19][20][21][22][23][24][25]. On the ohter hand, the name operando spectroscopy is gaining popularity in the field because the term defines in a better way the experimental conditions under which spectroscopic data of a catalyst surface should be measured [24].…”