The styrene epoxidation on Au38 and Au55 clusters, which could be a benchmark to probe high catalytic activity of gold clusters, has been studied by using density functional theory. Results suggest that epoxidation proceeds via a surface oxametallacycle intermediate (OME structure). Two parallel reaction pathways coexist on the Au38 cluster: O2 dissociates before epoxidation and O2 directly reacts with styrene, whereas only the latter pathway is found on the Au55 cluster, which is induced by different geometries of the Au38 and Au55 clusters. The mechanism of O2 directly reacting is essentially determined by the electronic resonance between electronic states of adsorbed intermediates and Au atoms at reaction sites. Moreover, Au atoms correlated with the reaction on the Au38 cluster are more electropositive than those on the Au55 cluster, which leads to a higher catalytic activity of the former. Thus, the Au38 cluster should be the size threshold for epoxidation catalysis, being consistent with the obtained barrier values.

Fe/N/C electrocatalysts are attractive for electrocatalytical applications in fuel cells due to their low cost and high electrocatalytic activity. Because of its complex nature, the mechanism of CO oxidation on Fe/N/C electrocatalysts remains largely unknown. Aiming to provide insight into the mechanism of CO oxidation, we have performed extensive density functional theory calculations for the elementary steps in CO oxidation on Fe/N/C active sites, including Fe-N4 and Fe-N3 porphyrin-like carbon nanotube (T-FeN4 and T-FeN3), Fe-N4 porphyrin-like graphene (G-FeN4), and Fe-N2 nanoribbon (R-FeN2). It is found that CO adsorption and oxidation are very sensitive to the active site structures. CO adsorption is energetically more favorable than O2, and CO oxidation to CO2 hardly occurs on T-FeN4 and G-FeN4. In comparison, O2 prefers to adsorb and CO can easily be oxidized on T-FeN3 and R-FeN2, suggesting the CO tolerant property of T-FeN3 and R-FeN2.

SYNOPSISThe effect of interaction between carbon black and polymer on electrical behavior was studied using the ESR method. The polymer matrices used were HDPE, LDPE, and ethylene/vinyl acetate (EVA). Two kinds of carbon blacks (CB) , high structure CSF-I11 and low structure FEF, were used as a conductive filler. Compared to that of the HDPE/FEF compound, the positive temperature coefficient ( PTC ) intensity is lower and electrical reproducibility is worse for the HDPE/CSF-I11 compound; however, it can be improved significantly by radiation cross-linking. On the other hand, the cross-linking has no practical effect on the PTC intensity of the LDPE/CSF-I11 compound while it can be achieved by mixing the compound for a longer time. The great PTC intensity was obtained in the HDPE/EVA/CSF-I11 compound, and it is greater than that of HDPE/CSF-I11 or EVA/ CSF-111. We explain these results using the concept of interaction between the filler and matrix. The absorption of the polymer on the carbon black surface may be physical or chemical; the latter is caused by the free-radical reaction between the polymer and carbon black, and it can occur during the radiation or preparation process of the compound. These "bound polymers" are essentially important for materials to have a great PTC intensity and good reproducibility.

Single atom catalysts (SAC) are highly desirable to maximize atom efficiency, while fabricating them is largely dependent on choosing a suitable substrate to effectually fasten them. Here, in terms of strong metal–metal interaction, first-principle calculations have been performed to study the possibility of monolayer polymeric transition metal–phthalocyanines (TM–Pcs, M from Sc to Zn) as the substrate in an effect to obtain evenly distributed single Pt atom catalyst. We found that Ti–Pc is the most appropriate compound by virtue of high binding strength of Pt/Ti–Pc system and high diffusion energy barrier of Pt catalyst atom, which jointly prevent the formation of Pt clusters. CO oxidation on Pt/Ti–Pc presents some unexpected behaviors, where a presorbed CO (pCO) molecule could activate the catalyst and reduce the reaction barrier. Examining the electronic structure evolution in the reaction process demonstrates that the presence of a pCO promotes O2 adsorption and activation. Our results demonstrate that two-dimensional (2D) TM–Pcs provide a unique platform to fabricate regularly and separately distributed SAC with high activity.

Graphene-based device applications such as ultrafast transistors and photodetectors benefit from precise control over its carrier type and concentration as well as a combination of both high-quality p-and n-doped components with spatial control and seamless connection (p-n junctions/superlattices). However, this remains experimentally a challenge for an atom-scale control over the doping in graphene and the attendant formation of p-n junctions/superlattices. Here, we demonstrate that sandwiching a janus material (a functionalized graphene layer with one side by H atoms and another side by F atoms, defined as H-G-F) between MoSe 2 (BN) substrate and graphene allows us to effectively control the carrier type in graphene, where the janus material acts as an electron pump, facilitating the electron tunneling between MoSe 2 (BN) and graphene. Appropriate functionalization of the janus material would open the possibility of creating well ordered and atomically sharp graphene p-n junctions/superlattices in a single layer of graphene. Furthermore, upon applying an external electric field, the charge concentration in both n-type and p-type regions can be continuously tuned except for a platform area. A comprehensive and detailed picture built by density functional theory calculations sheds light on the physical mechanism of the observed doping course as well as its response to an external field. Our results not only introduce single-layer H-G-F as a new 2D Janus material with the ability of electron extraction, but also open up a new direction for local control over the properties of graphene without destroying its intrinsic structure.