In-situ and operando spectroscopies for the characterization of catalysts and of mechanisms of catalytic reactions

For almost as long as catalysts have been part of industrial chemical processes, there has been a parallel effort to understand how catalysis works at a molecular level. Pioneers such as Michel Boudart, to whom this Mini-Review is dedicated, realized that such a goal requires the ability to probe catalytic systems either in situ under realistic environments or in operando mode as the catalytic processes occur. Much has happened since, and a number of spectroscopies are now available for this purpose. Here we reference the most salient ones, including vibrational spectroscopies such as infrared absorption, Raman, and other non-linear optical arrangements, X-ray absorption, and NMR. We also introduce some surface-sensitive probes used for studies with model catalytic systems. For each of these techniques, we briefly discuss their advantages and disadvantages, and illustrate their use with a couple of recent examples from the literature.