No abstract

Wet-kneaded binary MgO–SiO2 composite catalysts gave exceptionally high productivity of butadiene governed by a subtle balance of acid–base sites in relation to the formation of an interfacial Si–O–Mg linkage and by varying preparation methods and MgO to SiO2 ratios.

Gaining mechanistic insights into the active site is essential to rational design of a high-performance cathode catalyst for the electrochemical CO2 reduction reaction (CO2 RR). Here, by means of density functional theory and computational hydrogen electrode methods, we investigated synergy of a metallic NiCo dimer anchored on a C2N graphene matrix for promoting the CO2 RR. It is found that heterometallic NiCo@C2N (U L = −0.25 V) outperforms homometallic Co2@C2N (U L = −0.30 V) and Ni2@C2N (U L = −0.67 V) for catalyzing the CO2 RR toward CH4 formation owing to its synergy within the dimer. We emphasize the impact of co-adsorbed *H, *OH, and *CO intermediates on the CO2 RR, revealing that multiple competing reaction channels are accessible from viable co-adsorbates. Moreover, strongly-bound *H, *OH, and *CO intermediates are predicted not to deactivate metallic dimer sites for a continuous cycle of the CO2 RR. Our study could provide a theoretical basis for optimizing a metallic dimer anchored on a N-doped graphene matrix for achieving a more advanced CO2 RR cathode with enhanced activity and selectivity.

Copper is a well-known metal for catalyzing the electrochemical CO 2 reduction reaction (CO 2 RR) toward valuable hydrocarbons and alcohols. Here, using a combined density functional theory and microkinetic modeling approach, we systematically investigated 11 bimetallic M@Cu(211) single-atom stepped surface alloys for their CO 2 RR activity. It is revealed that the stepped M edge is most likely to be the active site for CO 2 RR. The primary reaction pathway is identified as *COOH → *CO → *CHO with the potential-determining step of *CO + H + + e − → *CHO, leading to either CH 4 or CH 3 OH formation at more negative potential. Especially, Ru@Cu(211) and Fe@Cu(211) are both predicted to be most efficient in promoting CO 2 RR toward CH 4 owing to their breaking of the coupled scaling relations of key intermediates' binding at the active site. Furthermore, the binding strength of *CO and *OH can be used as a good descriptor for differentiating various M@ Cu(211) for CO 2 RR activity and selectivity, and specifically, the moderate oxophilic and carbophilic elements of M are preferred. Our study highlights the utmost importance of breaking the linear scaling relations of key intermediates' binding at the active site for boosting CO 2 RR performance.

An intrinsically microporous fluoropolymer has been successfully synthesized through thermo-cross-linking of a functional monomer having a quaternary carbon center and thermopolymerizable trifluorovinyl ether groups as the side chains. Because the monomer has a tetrahedral configuration, the thermo-cross-linking produces spontaneously formed micropores with an average size of 8 Å in the polymer. Because of the existence of the micropores, the fluoropolymer exhibits excellent dielectric properties with dielectric constant (D k ) of 2.36 and dissipation factor (D f ) of 1.29 × 10 −3 at a frequency of 5 GHz. Moreover, the polymer shows very low water uptake (<0.08% in water of 99 °C for 72 h) and high transparency (transmittance of 93% varying from 400 to 1100 nm). TGA and DMA data show that the polymer has 5 wt % loss temperature of 492 °C (in N 2 ) and Young's modulus of 4.95 GPa, respectively. These results suggest that the polymer is very suitable as the matrix resin for the production of the composites utilized in high-frequency printed circuit boards (HF-PCBs). In particular, this work is the first example for the production of a low D k and D f polymer using a strategy of spontaneously forming pores. Because HF-PCBs have a broad range of applications, this contribution is of considerable industrial importance.