Analysing and understanding the active site by IR spectroscopy.

IR spectroscopy is a technique particularly adapted for understanding the mechanism of catalytic reactions, being able to probe the surface mechanisms at the molecular level. In this critical review the main advances in the field are presented, both under the aspects of the in situ and operando approaches. A broad view of the most authoritative literature of the domain is given, based largely on the experience built up at the LCS laboratory in the last decades. After having presented the general methodology to observe a potential active site directly or by probe molecule adsorption, several examples illustrate the qualitative and quantitative analysis of the physical-chemical properties of the surface entities. The last part of the review is dedicated to the discrimination of the role of the active site and its links with the catalytic steps; the hot problem of the reaction intermediates and their visibility via spectroscopic techniques is critically addressed (138 references).