Abstract
Heterogeneous single-atom catalyst (SAC) opens a unique entry to establishing structure–performance relationship at the molecular level similar to that in homogeneous catalysis. The challenge lies in manipulating the coordination chemistry of single atoms without changing single-atom dispersion. Here, we develop an efficient synthetic method for SACs by using ethanediamine to chelate Pt cations and then removing the ethanediamine by a rapid thermal treatment (RTT) in inert atmosphere. The coordination chemistry of Pt single atoms on a Fe2O3 support is finely tuned by merely adjusting the RTT temperature. With the decrease in Pt-O coordination number, the oxidation state of Pt decreases, and consequently the hydrogenation activity increases to a record level without loss of chemoselectivity. The tunability of the local coordination chemistry, oxidation states of the metal, and the catalytic performance of single atoms reveals the unique role of SACs as a bridge between heterogeneous and homogeneous catalysis.
Highlights
Heterogeneous single-atom catalyst (SAC) opens a unique entry to establishing structure–performance relationship at the molecular level similar to that in homogeneous catalysis
In case that the local coordination environment of heterogeneously anchored single atoms is viewed as a rigid ligand embedded in the catalyst surface, the catalytic performance of SACs should be tailored by regulating this environment, just like what has been done in organometallic catalysts
The iron oxide-supported Pt SACs are usually prepared with a coprecipitation (CP) method followed by a reduction activation procedure[13,23] (Fig. 1a); the CP method suffers from the imbedding of a portion of Pt single atoms inside the iron oxide, decreasing the accessibility of active Pt species, while the reduction activation procedure tends to cause the aggregation of single atoms, for which the Pt metal loading must be kept pretty low (~0.1 wt%) to ensure the single-atom dispersion
Summary
Heterogeneous single-atom catalyst (SAC) opens a unique entry to establishing structure–performance relationship at the molecular level similar to that in homogeneous catalysis. The tunability of the local coordination chemistry, oxidation states of the metal, and the catalytic performance of single atoms reveals the unique role of SACs as a bridge between heterogeneous and homogeneous catalysis. In case that the local coordination environment of heterogeneously anchored single atoms is viewed as a rigid ligand embedded in the catalyst surface, the catalytic performance of SACs should be tailored by regulating this environment, just like what has been done in organometallic catalysts Along this way some long-standing issues in heterogeneous catalysis, such as the role of oxidation state variation at the active site, support effects on the reactivity of metal species, and the nature of the interfacial sites, can hopefully be resolved with fundamental understanding at the atomic level. Medium-spin five coordinated Fe-N5 was several times more active than the other Fe-Nx species in the selective oxidation of ethylbenzene[32], and Co-N2 was much more active than Co-N4 for electroreduction of CO2 to CO33
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