Combining operando techniques in one spectroscopic-reaction cell:: New opportunities for elucidating the active site and related reaction mechanism in catalysis

Operando spectroscopic techniques are suitable for studying homogeneous and heterogeneous catalysts in real-time under working conditions at, e.g. elevated pressures and temperatures in the gas and liquid phase. These techniques are nowadays frequently used to obtain mechanistic insight into the active site and the related reaction mechanism. Over the past several years, new instrumental developments combining two or three operando spectroscopic techniques in one spectroscopic-reaction cell have emerged, giving ample opportunities for reaching a more detailed understanding of many relevant catalytic systems. In this paper, an overview of the different operando set-ups currently available for obtaining combined spectroscopic and catalytic information on catalytic systems is presented. The crucial advantage of such multiple couplings is the fact that in principle spectroscopic and catalytic data are obtained from the same catalyst system for which identical reaction conditions are guaranteed. Besides delivering complementary spectroscopic information on the catalyst system, it will be shown that there are additional advantages in combining spectroscopic techniques in one reaction set-up. This point will be illustrated with three examples. The first example focuses on the development of real-time quantitative operando Raman spectroscopy of supported metal oxide catalysts, making use of operando UV-vis spectroscopy. The second example deals with the problems of synchrotron radiation effects when measuring operando EXAFS spectra of homogeneous copper catalysts. The third example discusses the reduction process of supported metal oxide catalysts and the possible heating problems associated with the use of operando Raman spectroscopy. (c) 2005 Elsevier B.V. All rights reserved.