Heterogeneities of individual catalyst particles in space and time as monitored by spectroscopy

Recent years have witnessed the introduction of spatiotemporal spectroscopy for the characterization of catalysts at work at previously unattainable resolution and sensitivity. They have revealed that heterogeneous catalysts are more heterogeneous than often expected. Dynamic changes in the nature of active sites, such as their distribution and accessibility, occur both between and within particles. Scientists now have micro- and nanospectroscopic methods at hand to improve the understanding of catalyst heterogeneities and exploit them in catalyst design. Here we review the latest developments within this lively field. The trends include detection of single particles or molecules, super-resolution imaging, the transition from two- to three-dimensional imaging, selective staining, integration of spectroscopy with electron microscopy or scanning probe methods, and measuring under realistic reaction conditions. Such experimental approaches change the hitherto somewhat static picture of heterogeneous catalysis into one that acknowledges that catalysts behave almost like living objects--explaining why many characterization methods from the life sciences are being incorporated into catalysis research.