Supported noble metal nanoparticles (including nanoclusters) are widely used in many industrial catalytic processes. While the finely dispersed nanostructures are highly active, they are usually thermodynamically unstable and tend to aggregate or sinter at elevated temperatures. This scenario is particularly true for supported nanogold catalysts because the gold nanostructures are easily sintered at high temperatures, under reaction conditions, or even during storage at ambient temperature. Here, we demonstrate that isolated Au single atoms dispersed on iron oxide nanocrystallites (Au 1 /FeO x ) are much more sinteringresistant than Au nanostructures, and exhibit extremely high reaction stability for CO oxidation in a wide temperature range. Theoretical studies revealed that the positively charged and surface-anchored Au 1 atoms with high valent states formed significant covalent metal-support interactions (CMSIs), thus providing the ultra-stability and remarkable catalytic performance. This work may provide insights and a new avenue for fabricating supported Au catalysts with ultra-high stability.

Au/CeO(2) catalysts are highly active for low-temperature CO oxidation and water-gas shift reaction, but they deactivate rapidly because of sintering of gold nanoparticles, linked to the collapse or restructuring of the gold-ceria interfacial perimeters. To date, a detailed atomic-level insight into the restructuring of the active gold-ceria interfaces is still lacking. Here, we report that gold particles of 2-4 nm size, strongly anchored onto rod-shaped CeO(2), are not only highly active but also distinctively stable under realistic reaction conditions. Environmental transmission electron microscopy analyses identified that the gold nanoparticles, in response to alternating oxidizing and reducing atmospheres, changed their shapes but did not sinter at temperatures up to 573 K. This finding offers a new strategy to stabilize gold nanoparticles on ceria by engineering the gold-ceria interfacial structure, which could be extended to other oxide-supported metal nanocatalysts.

Electron microscopy and its associated techniques have contributed significantly to the characterization of heterogeneous catalysts, especially supported metal catalysts, and can provide nano‐ or atomic‐scale information on the structure, morphology, composition, and electronic state of the area of interest. With the recent advancement in aberration corrections to achieve an image resolution below 0.1 nm and the rapid development of in situ techniques, advanced electron microscopy is poised to probe fundamental questions of heterogeneous catalysis and catalysts. Understanding the nature of metal–support interactions becomes critical if we want to achieve the goal of designing and fabricating nanoarchitectured catalysts with desired performances. To reliably probe the fundamental mechanisms of charge transfer, which is the core of catalysis, between individual nanoscale components and under a realistic gas environment and temperature is still a formidable challenge. This Review discusses the recent contribution of advanced electron microscopy to the study of metal–support interactions, as well as the challenges and opportunities of applying aberration‐corrected electron microscopy techniques to the investigation of atomic‐scale structures of complex heterogeneous catalysts.

A catalytic site typically consists of one or more atoms of a catalyst surface that arrange into a configuration offering a specific electronic structure for adsorbing or dissociating reactant molecules. The catalytic activity of adjacent bimetallic sites of metallic nanoparticles has been studied previously. An isolated bimetallic site supported on a non-metallic surface could exhibit a distinctly different catalytic performance owing to the cationic state of the singly dispersed bimetallic site and the minimized choices of binding configurations of a reactant molecule compared with continuously packed bimetallic sites. Here we report that isolated Rh 1 Co 3 bimetallic sites exhibit a distinctly different catalytic performance in reduction of nitric oxide with carbon monoxide at low temperature, resulting from strong adsorption of two nitric oxide molecules and a nitrous oxide intermediate on Rh 1 Co 3 sites and following a low-barrier pathway dissociation to dinitrogen and an oxygen atom. This observation suggests a method to develop catalysts with high selectivity.