Insight into coupled Ni-Co dual-metal atom catalysts for efficient synergistic electrochemical CO_(2)reduction

The development of highly active,selective,and stable electrocatalysts can facilitate the effective implementation of electrocatalytic CO_(2)conversion into fuels or chemicals for mitigating the energy crisis and climate problems.Therefore,it is necessary to achieve the goal through reasonable material design based on the actuality of the operational active site at the molecular scale.Inspired by the stimulating synergistic effect of coupled heteronuclear metal atoms,a novel Ni-Co atomic pairs configuration(denoted as NiN_(3)?CoN_(3)-NC)active site was theoretically screened out for improving electrochemical CO_(2)reduction reaction(CO_(2)RR).The structure of NiN_(3)?CoN_(3)-NC was finely regulated by adjusting Zn content in the precursors Zn/Co/Ni-zeolite imidazolate frameworks(Zn/Co/Ni-ZIFs)and pyrolysis temperature.The structural features of NiN_(3)?CoN_(3)-NC were systematically confirmed by aberration-corrected HAADF-STEM coupled with 3D atom-overlapping Gaussian-function fitting mapping,XAFS,and XRD.The results of theoretical calculations reveal that the synergistic effect of Ni-Co atomic pairs can effectively promote the*COOH intermediate formation and thus the overall CO_(2)RR kinetic was improved,and also restrained the competitive hydrogen evolution reaction.Due to the attributes of Ni-Co atomic pairs configuration,the developed NiN_(3)?CoN_(3)-NC with superior catalytic activity,selectivity,and durability,with a high turnover frequency of 2265 h^(-1)at-1.1 V(vs.RHE)and maximum Faradaic efficiency of 97.7%for CO production.This work demonstrates the great potential of DACs as highly efficient catalysts for CO_(2)RR,provides a useful strategy to design heteronuclear DACs,exploits the synergistic effect of multiple metal sites to facilitate complex CO_(2)RR catalytic reactions,and inspires more efforts to develop the potential of DACs in various fields.

Synergism of Plasma and Catalyst on the Dehydrogenative Coupling of Methane

At atmospheric pressure and ambient temperature, pulse corona induced plasma was used as a new method for dehydrogenative coupling of methane. The synergism of plasma and catalyst on dehydrogenative coupling of methane was investigated. Experimental results have revealed that the synergism does exist, when positive corona within a suitable power range and an intermediate pulse repetition frequency (PRF) for a loaded 7-Mn2O3/7-A12O3 catalyst were chosen. In respect to the mechanism approach, a tentative model for general pathway was proposed to explain the role of plasma and catalyst partaking in the process of methane decomposition and C2 products formation.

METHANE OXIDATIVE COUPLING OVER METAL OXYFLUORIDE CATALYSTS

The MOC reaction over ZrO_2/LaF_3, CeO_2/LaF_3 and ThO_2/LaF_3 catalysts indicated that these catalysts had high activity and high C_2 selectivity at low temperature. In the temperature range 480℃ to 650℃. The methane conversion was 24. 4% to 30. 8% and the C_2 selectivity was 40. 0% to 55. 4%. The XRD characterization of the catalysts indicated that O^2. and F exchang happened and LaOF was formed.

CFD modeling of catalyst pellet for oxidative coupling of methane:Heat transfer and reaction

This study deals with the phenomena occuring at single-pellet catalyst scale for the oxidative coupling of methane where heat transfer plays an important role. Computational fluid dynamics （CFD） is used for obtaining detailed rate and temperature profiles through the porous catalytic pellet where reaction and diffusion compete, lntra-particle temperature and concentration gradients were taken into account by solving heat transfer coupled with continuity equations in the catalyst pellet. In heat transfer, the energy term due to highly exothermic reaction was considered. Two external programs were successfully implemented into the CFD-code as kinetic and heat of reaction terms. Simulation results showed that reaction was favored at the beginning for the pellet, followed by diffusion predomination. The results of CFD simulation indicate that temperature variation within the catalyst pellet is 〈2 K due to exothermic oxidation. The results showed further that exothermic oxidation reactions occurred prior to endothermic coupling reaction in the pellet.

A green access to supported cinchona alkaloid amide catalysts for heterogeneous enantioselective allylsilylation of aldehydes and process intensity evaluation in batch and flow

We report herein a new class of polystyrene-supported cinchona alkaloid amide catalysts for enantioselective allylation of various aldehydes using allyltrichlorosilane under both batch and continuous flow conditions.The supported catalyst was synthesized using an environmentally benign coupling agent with a surfactant in aqueous media.Under batch conditions,consistently high yields and enantioselectivity were obtained for the allylation of aliphatic aldehydes with recycling and reuse of the catalyst for more than 10 runs.Subsequently,this catalytic system was successfully implemented into a packed bed flow reactor with similar efficiency and enantiose-lectivity.While flow is a viable option,the batch methodology has better potential for application at a larger-scale setting upon the comparison of space-time yield and catalyst loadings.With the sustainable synthesis and great recyclability of our polymeric catalyst,this methodology holds great potential for the large-scale delivery of valuable enantiopure homoallylic alcohols.

Catalysts and thermodynamic coupling of chemical reactions

The condition of occurrence of the thermodynamic coupling of chemical reactions is analysed from kinetics. It is found that the thermodynamic coupling is impossible for those reactions which obey kinetically the mass action law. The thermodynamic coupling of chemical reactions is further analysed in the case with catalyst. It is found that the thermodynamic coupling which is impossible without catalyst may become possible by introducing proper catalyst into the system. This implies that the catalysts can change not only the rates of chemical reactions, but also the behaviors of thermodynamic coupling of chemical reactions, including the direction of some reactions. Such role of catalysts comes into play not by changing the total free energy of the system, but by changing the reaction mechanism.