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An in-depth understanding of the microscopic reaction mechanism on a nonmetal-doped catalytic system at the atomic level is one of the critical approaches to developing new efficient catalysts. Herein, the effects of S-doping on melon-based carbon nitride (CN) for the photocatalytic selective oxygen reduction reaction (ORR) have been comprehensively investigated by first-principles calculations. The configurations, electronic properties, optical properties, and the reaction performance of the S-doped melon-based CN have been studied and discussed. The results demonstrate that the decoration with S atoms exhibited substantial effects, involving the redistribution of the charge density and tuning of the bandgap, which promote the photocatalytic selective ORR activity. Accordingly, O2 is activated on the S-doped system with about 0.4 e of charge obtained from catalytic surfaces, leading to the thermodynamically feasible H2O2 and H2O formation, which is in good agreement with the experimental results. Our results provide theoretical insights into the design and development of polymeric carbon nitride (PCN) as well as other metal-free photocatalysts for the selective ORR.

Two-dimensional (2D) layered materials are at the forefront of research because of their unique structures and promising catalytic abilities. Here, the structural stability, electronic properties and gas adsorption of metal (V, Nb, Ta)-doped monolayer MoS 2 have been investigated by density functional theory calculations. Our results show that the metal (V, Nb, Ta)-doped monolayer MoS 2 is a stable catalyst under room temperature, due to the strong interaction between the doped metals (V, Nb, Ta) and S vacancy of monolayer MoS 2 . Compared with the gas adsorption (CO, NO 2 , H 2 O, NH 3 ) on pristine monolayer MoS 2 , doped metal (V, Nb, Ta) can significantly improve the adsorption properties, chemical activity and the sensitivity of that of adsorbed gas molecules. This effect occurs due to the strong overlap between the metal nd orbitals and gas molecule orbitals, result in activation of the adsorbed gas molecules. Analysis of Bader charge shows that, more charge transfer (−0.66 e to −0.72 e ) occur from metal (V, Nb, Ta)-doped monolayer MoS 2 to the oxidizing gas molecules (NO 2 ) acting as acceptors. While for the adsorption of CO molecules, the relative less electrons (about −0.24 e − −0.35 e ) transfer occuring from substrate to the adsorbed gases. Whereas the direction of charge transfers is reversed for the adsorption of the reducing gas (H 2 O and NH 3 ) behaving as donors, in which small electrons (0.04 e −0.09 e ) transfer from adsorbed gas to metal (V, Nb, Ta)-doped monolayer MoS 2 . Our results suggested that metal (V, Nb, Ta)-doped monolayer MoS 2 might be a good candidate for low-cost, highly active, and stable catalysts and gas sensors, providing an avenue to facilitate the design of high active MoS 2 -based two dimensional catalysts and gas sensors.

Iron-based catalysts have been widely studied for the oxidation of H2 S into elemental S. However, the prevention of iron sites from deactivation remains a big challenge. Herein, a facile copolymerization strategy is proposed for the construction of isolated Fe sites confined in polymeric carbon nitride (CN) (Fe-CNNχ). The as-prepared Fe-CNNχ catalysts possess unique 2D structure as well as electronic property, resulting in enlarged exposure of active sites and enhancement of redox performance. Combining systematic characterizations with density functional theory calculation, it is disclosed that the isolated Fe atoms prefer to occupy four-coordinate doping configurations (Fe-N4 ). Such Fe-N4 centers favor the adsorption and activation of O2 and H2 S. As a consequence, Fe-CNNχ exhibit excellent catalytic activity for the catalytic oxidation of H2 S to S. More importantly, the Fe-CNNχ catalysts are resistant to water and sulfur poisoning, exhibiting outstanding catalytic stability (over 270 h of continuous operation), better than most of the reported catalysts.

The structures and electronic properties of bimetallic oxide CrW2O9 clusters supported on the perfect and defective MgO(001) surfaces with three different color centers, FS (0), FS (+), and FS (2+) centers, respectively, have been investigated by density functional theory calculations. Our results show that the configurations, adsorption energies, charge transfers, and bonding modes of dispersed CrW2O9 clusters are sensitive to the charge states of the FS centers. Compared with the gas-phase configuration, the CrW2O9 clusters supported on the defective surfaces are distorted dramatically, which exhibit different chain structures. On the perfect MgO surface, the depositions of clusters do not involve obvious charge transfer, while the situation is quite different on the defective MgO(001) surfaces in which significant electron transfer occurs from the surface to the cluster. Interestingly, this effect becomes more remarkable for electron-rich oxygen vacancies (FS (0) center) than that for electron-poor oxygen vacancies (FS (+) and FS (2+) centers). Furthermore, our work reveals a progressive Brønsted acid sites where spin density preferentially localized around the Cr atoms not the W atoms for all kinds of FS-centers, indicating the better catalytic activities can be expected for CrW2O9 cluster on defective MgO(001) surfaces with respect to the W3O9 cluster.