Identification of catalytic active sites is pivotal in the design of highly effective heterogeneous metal catalysts, especially for structure-sensitive reactions. Downsizing the dimension of the metal species on the catalyst increases the dispersion, which is maximized when the metal exists as single atoms, namely, single-atom catalysts (SACs). SACs have been reported to be efficient for various catalytic reactions. We show here that the Pt SACs, although with the highest metal atom utilization efficiency, are totally inactive in the cyclohexane (C 6 H 12 ) dehydrogenation reaction, an important reaction that could enable efficient hydrogen transportation. Instead, catalysts enriched with fully exposed few-atom Pt ensembles, with a Pt−Pt coordination number of around 2, achieve the optimal catalytic performance. The superior performance of a fully exposed few-atom ensemble catalyst is attributed to its high d-band center, multiple neighboring metal sites, and weak binding of the product.

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Due to the unstable nature of isolated transition metals under real reaction condition, a systematic understanding on how much influence the isolated structure of the active site and the cofed chemicals have on fine tuning the selectivity toward specific reaction pathways is still lacking. Here, we show a combination of kinetic, thermodynamic, and in situ spectroscopy measurements to probe the rWGS and methanation of carbon dioxide on a CeO2-dispersed isolated Ru catalyst (Ru-SnO x /CeO2, structure confirmed by HAADF-STEM) derived from the [Ru@Sn9]6– Zintl cluster decoration. Kinetic measurements, in combination with isotopie-labeling reactions, prove that rWGS and methanation occur through the kinetically relevant C–O bond rupture of surface carboxyl (HOCO*) and surface formate (HCOO*) respectively. A site-selective reaction model has been established on the basis of the response of rWGS and methanation to water pressure. Probably, the rWGS was carried out at the interface between the transition-metal nanoparticles and the support and could be influenced greatly by water, while the methanation was carried out at a site far away from the interface and has a weak dependence on water. This system can be easily extended to some other hydrogenation reactions, thus attracting attention to building isolated structures with Zintl clusters.

Ethanol transformation with high product selectivity is a great challenge, especially for high weight molecules. Here, we show a combination study of kinetic, thermodynamic, and in situ spectroscopy measurements to probe the selective upgrading of ethanol over lamellar Ce(OH)SO 4 •xH 2 O catalysts, with 60− 70% Ce 3+ preserved during the catalysis. High methyl phenols (MPs) selectivity at ∼80% within condensation products was achieved at ∼50% condensation yield (3.0 kPa C 2 H 5 OH, 15 kPa H 2 , Ar balanced, 693 K, 1 atm, gas hourly space velocity (GHSV) ∼5.4 min −1 ), with acetaldehyde, acetone, 4-heptanone, and 2pentanone as the key reaction intermediates. Kinetic measurements with the assistance of isotope labeling proved that MPs generated from the kinetically relevant step (KRS) of C−C bond coupling of enolate nucleophilically attacks surface C 2 H 4 O following a Langmuir−Hinshelwood model. Low ethanol and water pressures and high acetaldehyde and hydrogen pressures were proved to be favored for MPs generation rather than dehydration, in which hydrogen could reduce the amount of lattice oxygen and facilitate the preparation of MPs while water and ethanol both compete with acetaldehyde for active sites during catalysis. On the basis of in situ X-ray diffraction (XRD), quasi-in situ X-ray photoelectron spectroscopy (XPS), and Raman characterizations, the Ce(OH)SO 4 crystal structure was proved to be maintained along with ethanol activation, and the Ce 3+ −OH Lewis acid−base pair was proved to be the active species for the selective C−C bond coupling. The KRS assumption was also supported by the apparent activation energy assessment within the reaction network on dehydration, dehydrogenation, aldol condensation, and cyclization and a series of negligible kinetic isotope effects (KIEs). This system can be easily extended to some other systems related to C−C bond coupling and is attracting attention on converting oxygenate platform molecules over lanthanide species.

Together photo‐ and thermal energy promote catalytic reactions in a synergetic way. However, how light cooperates with thermal energy is still unclear. Here, C−H bond rupture within HCOOH* was determined to be the rate‐determining step, with adsorbed CO* as the most abundant surface intermediate under both thermal and photothermal reaction conditions, as confirmed by kinetic isotopic effects and in‐situ FTIR characterizations. Clear evidence of kinetically relevant consistency was found under both thermal and photothermal HCOOH decomposition reactions over a Pd/LaCrO3/C3N4 composite. More information can be found in the Research Article by H. Zhang et al. (DOI: 10.1002/chem.202104623).