Determination of Specific Electrocatalytic Sites in the Oxidation of Small Molecules on Crystalline Metal Surfaces

The identification of active sites in electrocatalytic reactions is part of the elucidation of mechanisms of catalyzed reactions on solid surfaces. However, this is not an easy task, even for apparently simple reactions, as we sometimes think the oxidation of adsorbed CO is. For surfaces consisting of non-equivalent sites, the recognition of specific active sites must consider the influence that facets, as is the steps/defect on the surface of the catalyst, cause in its neighbors; one has to consider the electrochemical environment under which the “active sites” lie on the surface, meaning that defects/steps on the surface do not partake in chemistry by themselves. In this paper, we outline the recent efforts in understanding the close relationships between site-specific and the overall rate and/or selectivity of electrocatalytic reactions. We analyze hydrogen adsorption/desorption, and electro-oxidation of CO, methanol, and ammonia. The classical topic of asymmetric electrocatalysis on kinked surfaces is also addressed for glucose electro-oxidation. The article takes into account selected existing data combined with our original works.M.J.S.F. is grateful to PNPD/CAPES (Brazil). J.M.F. thanks the MCINN (FEDER, Spain) project-CTQ-2016-76221-P

Control of coordinatively unsaturated Zr sites in ZrO2 for efficient C–H bond activation

Identifying active sites and designing rationally heterogeneous catalysts are not inherently straightforward due to their complexity. Here, the authors reveal the nature of active sites for efficient C–H bond activation in C1-C4 alkanes over bare ZrO2 and provide fundamentals for controlling their concentration

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