Achievements and challenges in deciphering heterogeneous catalytic reaction mechanisms using operando infrared spectroscopies.

In situ / operando infrared spectroscopy is commonly used to investigate heterogeneous catalytic reactions. Adsorbates, such as carbonyl and formates, present under reaction conditions can be monitored and quantitative infrared techniques enable discriminating between main reaction intermediates and spectator species. It should yet be stressed that some of the sites occupied by species subsequently reacting should be more considered as "storage" sites rather than active sites. Care should thus be taken in the interpretation of the kinetic and spectral data. These aspects are discussed in this article, using examples from catalytic CO oxidation and CO and CO2 hydrogenation.