Regulating the local environment and structure of metal center coordinated by nitrogen ligands (M‐N4) to accelerate overall reaction dynamics of the electrochemical CO2 reduction reaction (CO2RR) has attracted extensive attention. Herein, we develop an axial traction strategy to optimize the electronic structure of the M‐N4 moiety and construct atomically dispersed nickel sites coordinated with four nitrogen atoms and one axial oxygen atom, which are embedded within the carbon matrix (Ni‐N4‐O/C). The Ni‐N4‐O/C electrocatalyst exhibited excellent CO2RR performance with a maximum CO Faradic efficiency (FE) close to 100 % at −0.9 V. The CO FE could be maintained above 90 % in a wide range of potential window from −0.5 to −1.1 V. The superior CO2RR activity is due to the Ni‐N4‐O active moiety composed of a Ni‐N4 site with an additional oxygen atom that induces an axial traction effect.

A chemical absorption-biological reduction integrated process can be used to remove nitrogen oxides (NOx) from flue gas. In such a process, nitric oxide (NO) can be effectively absorbed by the ferrous chelate of ethylenediaminetetraacetate (Fe(II)EDTA) to form Fe(II)EDTA-NO, which can be biologically regenerated by denitrifying bacteria. However, in the course of these processes, part of the Fe(II)EDTA is also oxidized to Fe(III)EDTA. The reduction of Fe(III)EDTA to Fe(II)EDTA depends on the activity of iron-reducing bacteria in the system. Therefore, the effectiveness of the system relies on how to effectively bioreduce Fe(III)EDTA and Fe(II)EDTA-NO in the system. In this paper, a strain identified as Escherichia coli FR-2 (iron-reducing bacterium) was used to investigate the reduction rate of Fe(III)EDTA. The experimental results indicate that Fe(III)EDTA-NO and Fe(II)EDTA in the system can inhibit both the FR-2 cell growth and thus affect the Fe(III)EDTA reduction. The FR-2 cell growth rate and Fe(III)EDTA reduction rate decreased with increasing Fe(II)EDTA-NO and Fe(II)EDTA concentration in the solution. When the concentration of Fe(II)EDTA-NO reached 3.7 mM, the FR-2 cell growth almost stopped. A mathematical model was developed to explain the cell growth and inhibition kinetics. The predicted results are close to the experimental data and provide a preliminary evaluation of the kinetics of the biologically mediated reactions necessary to regenerate the spent scrubber solution.

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The main issue related to the deployment of the amine-based absorption process for CO capture from flue gas is its intensive energy penalty. Therefore, this study screened a novel biphasic solvent, comprising a primary amine e.g., triethylenetetramine (TETA) and a tertiary amine e.g., N, N-dimethylcyclohexylamine (DMCA), to reduce the energy consumption. The TETA-DMCA blend exhibited high cyclic capacity of CO absorption, favorable phase separation behavior, and low regeneration heat. Kinetic analysis showed that the gas- and liquid-side mass transfer resistances were comparable in the lean solution of TETA-DMCA at 40 °C, whereas the liquid-side mass transfer resistance became dominant in the rich solution. The rate of CO absorption into TETA-DMCA (4 M, 1:3) solution was comparable to 5 M benchmark monoethanolamine (MEA) solution. Based on a preliminary estimation, the regeneration heat with TETA-DMCA could be reduced by approximately 40% compared with that of MEA. C NMR analysis revealed that the CO absorption into TETA-DMCA was initiated by the reaction between CO and TETA via the zwitterion mechanism, and DMCA served as a CO sinker to regenerate TETA, resulting in the transfer of DMCA from the upper to lower phase. The proposed TETA-DMCA solvent may be a suitable candidate for CO capture.

The biphasic solvent-based absorption process has been regarded as a promising alternative to the monoethanolamine (MEA)-based process because of its high absorption capacity, phase separation behavior, and potential for conserving energy for CO 2 capture. A trade-off between the absorption capacity and phase separation ratio is critical for developing an advanced biphasic solvent. Typically, water content in the biphasic solvent can be manipulated to tune the phase separation behavior. To explore the relationship between water content and phase separation behavior, an inert organic solvent, 1-methyl-2-pyrrolidinone, was added as a substitute for water in a biphasic solvent, specifically a triethylenetetramine (TETA) and 2-(diethylamino)ethanol (DEEA) blend. Moreover, the water content−kinetics and thermodynamics relationships were also evaluated. Experimental results revealed that reducing the water content was beneficial for phase separation but adverse for adsorption capacity. Kinetic analysis indicated that the water content did not significantly affect the rate of CO 2 absorption at a rich loading. Furthermore, the regeneration heat decreased with the water content. The regeneration heat of TETA−DEEA with a water content of 20 wt % was almost 50% less than that of MEA solution. 13 C nuclear magnetic resonance analysis revealed that the water content did not affect the reaction mechanism between CO 2 and amines.