Theoretical study of N 2 O decomposition mechanism over binuclear Cu-ZSM-5 zeolites

High-Efficiency Electrocatalytic Reduction of N2O with Single-Atom Cu Supported on Nitrogen-Doped Carbon

Nitrous oxide (N2O) is a potent greenhouse gas with a high global warming potential, emphasizing the critical need to develop efficient elimination methods. Electrocatalytic N2O reduction reaction (N2ORR) stands out as a promising approach, offering room temperature conversion of N2O to N2 without the production of NOx byproducts. In this study, we present the synthesis of a copper-based single-atom catalyst featuring atomic Cu on nitrogen-doped carbon black (Cu1-NCB). Attributed to the highly dispersed single-atom Cu sites and the effective suppression of the hydrogen evolution reaction, Cu1-NCB demonstrated an optimal N2 faradaic efficiency (82.1%) and yield rate (3.53 mmol h-1 mgmetal-1) at -0.2 and -0.5 V vs RHE, respectively, outperforming previously reported N2ORR electrocatalysts. Further, a gas diffusion electrode cell was employed to improve mass transfer and achieved a 28.6% conversion rate of 30% N2O with only a 14 s residence time, demonstrating the potential for practical application. Density functional theory calculations identified Cu-N4 as the crucial active site for N2ORR, highlighting the significance of the unsaturated coordination and metal-support electronic structure. O-terminal adsorption of N2O was favored, and the dissociative adsorption (*ON2 → *O + N2) was the rate-determining step. These findings reveal the broad prospects of N2O decomposition via electrocatalysis.

DFT Study on the Combined Catalytic Removal of N2O, NO, and NO2 over Binuclear Cu-ZSM-5

The large amount of nitrogen oxides (N2O, NO, NO2, etc.) contained in the flue gas of industrial adipic acid production will seriously damage the environment. A designed binuclear Cu-ZSM-5 catalyst can be applied to decompose N2O and reduce NO and NO2, purifying the air environment. Using the density functional theory method, the catalytic decomposition mechanisms of N2O, NOX-NH3-SCR, and NOX-assisted N2O decomposition is simulated over the Cu-ZSM-5 model. The results indicate that N2O can be catalytically decomposed over the binuclear Cu active site in the sinusoidal channel. The speed-limiting step is the second N2O molecule activation process. After the decomposition of the first N2O molecule, a stable extra-frame [Cu-O-Cu]2+ structure will generate. The subsequent discussion proved that the NOX-NH3-SCR reaction can be realized over the [Cu-O-Cu]2+ active site. In addition, it proved that the decomposition reaction of NO and NO2 can be carried out over the [Cu-O-Cu]2+ active site, and NO can greatly reduce the energy barrier for the conversion of the active site from [Cu-O-Cu]2+ to the binuclear Cu form, while NO2 can be slightly reduced. Through discussion, it is found that the binuclear Cu-ZSM-5 can realize the combined removal of N2O and NOX from adipic acid flue gas, hoping to provide a theoretical basis for the development of a dual-functional catalyst.

Balance between Reducibility and N2O Adsorption Capacity for the N2O Decomposition: CuxCoy Catalysts as an Example

Cu_xCo_y (CuO-Co₃O₄ mixed oxides) catalysts were prepared via co-precipitation for the N₂O decomposition reaction. They exhibited a higher N₂O decomposition activity than that of pure CuO and Co₃O₄ because of the balance of the redox property and N₂O adsorption capacity. Co₃O₄ presented a large number of surface oxygen vacancies, increasing the N₂O chemical adsorption as "□-Co-ON₂" on the catalyst surface, whereas CuO was dispersed around Co₃O₄ and presented high reducibility on the interface of Co₃O₄-CuO_x for the N-O break of N₂O, healing oxygen vacancies by leaving one oxygen atom in the vacancy. Based on kinetic studies, the rate constant of N₂O decomposition was related to the number of surface vacancy sites ([Mⁿ⁺]) and the rate of N-O break (k₃), whereas the rate-determining step is the N-O break. Therefore, the N₂O decomposition rate is first order to the N₂O concentration. Overall, both the density functional theory calculations and kinetic results indicate that the quantities of adsorption and activation sites derived from the interaction between Co and Cu (dual-function mechanism) were accounted for the excellent N₂O decomposition performance of Cu_xCo_y catalysts.

Mechanistic insights from theory on the reduction of CO2, N2O, and SO2 molecules using tripodal diimine-enolate substituted magnesium(i) dimers

The mechanistic investigation of the reductive coupling vs. reductive disproportionation of CO2 using magnesium(i) dimers bearing tripodal ligands, [{Mg[κ(3)-N,N',O-(ArNCMe)2(OCCPh2)CH]}2] (Ar = C6H3Et2-2,6) has been carried out using DFT computational methods. We also elucidated the reduction of N2O to form a μ-oxo magnesium complex which upon addition of CO2 affords the experimentally observed carbonate complex. Finally, the interesting reactivity towards SO2 is considered and some insights into the mechanistic aspects of such activation/homo-coupling reaction are given for both "Nacnac" substituted magnesium(i) dimers ([{((Dip)Nacnac)Mg}2] ((Dip)Nacnac = [(DipNCMe)2CH](-), Dip = C6H3Pr(i)2-2,6)) and those bearing tripodal ligands. The analogy between the activation chemistry of low-valent f-block metal complexes with that of magnesium systems is highlighted.