Transition metal single atom catalysts (SACs) with M1-Nx coordination configuration have shown outstanding activity and selectivity for hydrogenation of nitroarenes. Modulating the atomic coordination structure has emerged as a promising strategy to further improve the catalytic performance. Herein, we report an atomic Co1/NPC catalyst with unsymmetrical single Co1-N3P1 sites that displays unprecedentedly high activity and chemoselectivity for hydrogenation of functionalized nitroarenes. Compared to the most popular Co1-N4 coordination, the electron density of Co atom in Co1-N3P1 is increased, which is more favorable for H2 dissociation as verified by kinetic isotope effect and density functional theory calculation results. In nitrobenzene hydrogenation reaction, the as-synthesized Co1-N3P1 SAC exhibits a turnover frequency of 6560 h−1, which is 60-fold higher than that of Co1-N4 SAC and one order of magnitude higher than the state-of-the-art M1-Nx-C SACs in literatures. Furthermore, Co1-N3P1 SAC shows superior selectivity (>99%) toward many substituted nitroarenes with co-existence of other sensitive reducible groups. This work is an excellent example of relationship between catalytic performance and the coordination environment of SACs, and offers a potential practical catalyst for aromatic amine synthesis by hydrogenation of nitroarenes.
Developing a cost-effective and highly efficient electrocatalyst with superior catalytic activity is crucial for clean and green water splitting, including the hydrogen evolution reaction (HER), the oxygen evolution reaction (OER), and the oxygen reduction reaction (ORR). The single-atom catalyst (SAC) is a breakthrough in industrial catalysis because of the advantages of maximum metal atom utilization, single active sites, strong metal−support interactions, and great potential to accomplish high catalytic performance and selectivity. Herein, we investigate the electrocatalytic performance of a series of SACs supported on a phosphomolybdic acid (PMA) cluster for the HER, OER, and ORR by using first-principles-based calculations. It has been found that the most plausible binding site for the single-metal adatoms is the 4-fold hollow (4H) site over the PMA cluster. Due to the higher stability and catalytic activity of single-metal adatoms, fast electron transfer kinetics is permissible through catalysis. Mainly, Pt 1 /PMA, Ru 1 /PMA, V 1 /PMA, and Ti 1 /PMA realized decent catalytic performance toward the HER due to nearly ideal (ΔG H* = 0) ΔG H* values via the Volmer−Heyrovsky pathway. The Co 1 /PMA (0.45 V) and Pt 1 /PMA (0.49 V) can be active and selective catalysts for the OER with their overpotentials comparable those of to MoC 2 , IrO 2 , and RuO 2 . Among the considered candidates, a non-noble metal Fe 1 /PMA SAC is a promising electrocatalyst for the ORR with an overpotential of 0.42 V, which is lower than that for the most favorable Pt (0.45 V) catalyst. Furthermore, Pt 1 /PMA is an auspicious multifunctional electrocatalyst for overall water splitting (−0.02 V for the HER and 0.49 V for the OER) and a metal-air battery (0.79 V for the ORR) catalyst. The current study is further extended to calculate the kinetic potential energy barrier for the excellent catalytic performance of Co 1 for the OER and Fe 1 for the ORR. The results suggest that the kinetic activation barrier values in all proton-coupled electron transfer steps are in good agreement with the thermodynamic results. It was revealed that the PMA cluster is a promising single-atom support for the HER, OER, and ORR and provides low-cost and highly efficient electrocatalytic activity under normal reaction conditions.
For understanding the catalytic activity of Fe 3 O 4 -supported gold catalysts, the adsorption structures and energies of a single Au atom on the six terminations of the Fe 3 O 4 (111) surface have been computed at the level of density functional theory (GGA+U). For the most stable adsorption configurations, correlation has been found between the surface stability and the Au atom adsorption energy; that is, the more stable the surface, the lower the Au atom adsorption energy. It is also found that the adsorbed Au atom is reduced and has a negative charge on the ironterminated surfaces, whereas it is oxidized and has a positive charge on the oxygen-terminated surfaces, and the latter is in agreement with the experimental observation. No correlation between the transferred charge and the adsorption energy has been found. Regarding the experimentally observed oxidation of gold nanoparticles on the iron oxide surface, it is possible to produce an oxygen-terminated surface for gold adsorption by synthetic tuning.
The discovery of borospherenes unveiled the capacity of boron to form fullerene-like cage structures. While fullerenes are known to entrap metal atoms to form endohedral metallofullerenes, few metal atoms have been observed to be part of the fullerene cages. Here we report the observation of a class of remarkable metallo-borospherenes, where metal atoms are integral parts of the cage surface. We have produced La 3 B 18and Tb 3 B 18and probed their structures and bonding using photoelectron spectroscopy and theoretical calculations. Global minimum searches revealed that the most stable structures of Ln 3 B 18are hollow cages with D 3h symmetry. The B 18-framework in the Ln 3 B 18cages can be viewed as consisting of two triangular B 6 motifs connected by three B 2 units, forming three shared B 10 rings which are coordinated to the three Ln atoms on the cage surface. These metalloborospherenes represent a new class of unusual geometry that has not been observed in chemistry heretofore.
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