Effect of the Number of Methyl Groups in DMOF on N2O Adsorption and N2O/N2 Separation

Nitrous oxide (N2O), as the third largest greenhouse gas in the world, also has great applications in industry, so the purification of N2O from N2 in industrial tail gas is a crucial process for achieving environmental protection and giving full play to its economic value. Based on the polarity difference of N2O and N2, N2O adsorption was researched on DMOF series materials with different polarities and methyl numbers of the ligand. N2O adsorption at 0.1 bar is enhanced, attributed to an increase of the methyl group densities at the benzenedicarboxylate linker. Grand canonical Monte Carlo simulations demonstrate the key role of methyl groups within the pore surface in the preferential N2O affinity. Methyl groups preferentially bind to N2O and thus enhanced low (partial) pressure N2O adsorption and N2O/N2 separation. The result shows that DMOF-TM has the highest N2O adsorption capacity (19.6 cm3/g) and N2O/N2 selectivity (23.2) at 0.1 bar. Breakthrough experiments show that, with an increase of the methyl number, the coadsorption time and retention time also increase, and DMOF-TM has the best N2O/N2 separation performance.

Non-CO2 greenhouse gas separation using advanced porous materials

Global warming has become a growing concern over decades, prompting numerous research endeavours to reduce the carbon dioxide (CO2) emission, the major greenhouse gas (GHG). However, the contribution of other non-CO2 GHGs including methane (CH4), nitrous oxide (N2O), fluorocarbons, perfluorinated gases, etc. should not be overlooked, due to their high global warming potential and environmental hazards. In order to reduce the emission of non-CO2 GHGs, advanced separation technologies with high efficiency and low energy consumption such as adsorptive separation or membrane separation are highly desirable. Advanced porous materials (APMs) including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs), porous organic polymers (POPs), etc. have been developed to boost the adsorptive and membrane separation, due to their tunable pore structure and surface functionality. This review summarizes the progress of APM adsorbents and membranes for non-CO2 GHG separation. The material design and fabrication strategies, along with the molecular-level separation mechanisms are discussed. Besides, the state-of-the-art separation performance and challenges of various APM materials towards each type of non-CO2 GHG are analyzed, offering insightful guidance for future research. Moreover, practical industrial challenges and opportunities from the aspect of engineering are also discussed, to facilitate the industrial implementation of APMs for non-CO2 GHG separation.

Inverse Adsorption Separation of N2 O/CO2 in AgZK-5 Zeolite

Nitrous oxide (N2 O), as the third largest greenhouse gas in the world, also has great applications in daily life and industrial production, like anesthetic, foaming agent, combustion supporting agent, N or O atomic donor. The capture of N2 O in adipic acid tail gas is of great significance but remains challenging due to the similarity with CO2 in molecular size and physical properties. Herein, the influence of cation types on CO2 -N2 O separation in zeolite was studied comprehensively. In particular, the inverse adsorption of CO2 -N2 O was achieved by AgZK-5, which preferentially adsorbs N2 O over CO2 , making it capable of trapping N2 O from an N2 O/CO2 mixture. AgZK-5 shows a recorded N2 O/CO2 selectivity of 2.2, and the breakthrough experiment indicates excellent performance for N2 O/CO2 separation. The density functional theory (DFT) calculation shows that Ag+ has stronger adsorption energy with N2 O, and the kinetics of N2 O is slightly faster than that of CO2 on AgZK-5.

Collaborative Purification of Tert-Butanol and N2O over Fe/Co-Zeolite Catalysts

N₂O is a greenhouse gas and a candidate oxidant. Volatile organic pollutants (VOCs) have caused great harm to the atmospheric ecological environment. Developing the technique utilizing N₂O as the oxidant to oxidize VOCs to realize the collaborative purification has significant importance and practical value for N₂O emission control and VOC abatement. Therefore, the study of N₂O catalytic oxidation of tert-butanol based on zeolite catalysts was carried out. A series of molecular sieves, including FER, MOR, ZSM-5, Y, and BEA, were selected as the catalyst objects, and the 1.5% wt Fe and Co were, respectively, loaded on the zeolite catalysts via the impregnation method. It was found that the catalytic performance of BEA was the best among the molecular sieves. Comparing the catalytic performance of Fe-BEA under different load gradients (0.25~2%), it was found that 1.5% Fe-BEA possessed the best catalytic activity. A series of characterization methods showed that Fe³⁺ content in 1.5% Fe-BEA was the highest, and more active sites formed to promote the catalytic reaction. The α-O in the reaction eventually oxidized tert-butanol to CO₂ over the active site. The Co mainly existed in the form of Co²⁺ cations over Co-BEA samples; the 2% Co-BEA possessing higher amounts of Co²⁺ exhibited the highest activity among the prepared Co-BEA samples.

Generation of Phenol and Molecular Hydrogen through Catalyst-Free C-H Activation of Benzene by Water Radical Cations

Here, we report on the abundant formation of phenol and molecular hydrogen when benzene vapor was exposed to gas plasma generated by +5.5 kV corona discharge of water vapor in argon in the absence of oxygen. Systematic analysis using a series of isotopic standards (d₆-benzene, D₂O, and H₂¹⁸O) and benzene derivatives (mono-, di-, trichlorobenzene, and N,N-dimethylaniline) indicated that the formation of phenol occurred through the reaction between neutral benzene and the radical cation of water dimer, (H₂O)₂^+•. A two-step reaction mechanism was proposed based on the results of experiments and DFT calculations: (1) the formation of (C₆H₆...H₂O)^+• intermediate through electrophilic addition; (2) the formation of C₆H₅OH^+• through the release of H₂ from the (C₆H₆...H₂O)^+• intermediate. Our findings offer a novel catalyst-free method to prepare phenol from benzene with phenol selectivity >90%.

The efficient separation of N2O/CO2 using unsaturated Fe2+ sites in MIL-100Fe

It is a big challenge to separate N2O from CO2 using adsorption because they have similar physical properties. The Fe3+-F- site in MIL-100Fe transforms to an unsaturated Fe2+ site under high-temperature activation (300 °C), and the target sorbent MIL-100Fe-300 exhibits the biggest difference in CO2 and N2O adsorption capacity, and the selectivity of N2O/CO2 (50%/50%) is up to 3.00 at 298 K. According to DFT calculations, the original Fe3+-F- site has strong interaction with CO2, but the open Fe2+ site has a stronger interaction with N2O. Through a breakthrough experiment, it was confirmed that MIL-100Fe-300 has the best N2O/CO2 separation performance, making it potentially a useful material in industry.

The ZSM-5-Catalyzed Oxidation of Benzene to Phenol with N2O: Effect of Lewis Acid Sites

The oxidation of benzene to phenol (BTOP) with N2O as the oxidant has been studied with a variety of Fe/ZSM-5 catalysts. The literature has conclusively proven that Fe2+ sites are the active sites. However, some studies have suggested that the Lewis acidic sites (LAS) are responsible for the generation of the active chemisorbed oxygen. Nevertheless, there is no clear relationship between the LAS and the N2O selectivity to phenol. In an effort to elucidate the effects of LAS on BTOP with various ZSM-5 catalysts, we investigated the initial N2O selectivity to phenol. Here we show that the initial N2O selectivity to phenol is negative with the amount of LAS over a certain range. The catalyst H-ZSM-5-ST (H-ZSM-5 treated with water vapor) showed a remarkable initial N2O selectivity to phenol as high as 95.9% with a 0.021 mmol g−1 LAS concentration on the surface of the catalyst, while the Fe/ZSM-5 catalyst demonstrated the lowest initial N2O selectivity to phenol (11.7%) with the highest LAS concentration (0.137 mmol g−1). Another remarkable feature is that steaming was more effective than Fe ion exchange and high temperature calcining. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), N2-adsorption-desorption, UV-vis, NH3-TPD and pyridine Fourier transform infrared (FT-IR) techniques. Our results demonstrate how the concentration of LAS is likely to affect the initial N2O selectivity to phenol within a certain range (0.021–0.137 mmol g−1). This research has demonstrated the synergy between the active Fe2+ sites and LAS.

Metal oxide–zeolite composites in transformation of methanol to hydrocarbons: do iron oxide and nickel oxide matter?

Novel, hierarchical zeolites modified with both Fe₃O₄ and Ni_xO_y nanoparticles have been developed and studied in the methanol-to-hydrocarbon process.

Effective conversion of biomass-derived ethyl levulinate into γ-valerolactone over commercial zeolite supported Pt catalysts

Selective hydrogenation of biomass-derived ethyl levulinate into γ-valerolactone over commercial zeolite supported catalysts was performed, and high yield was obtained.

Periodic mesoporous organosilicas functionalized with iron(iii) complexes: preparation, characterization and catalysis on direct hydroxylation of benzene to phenol

Incorporation of iron(iii) complexes into hydrophobic periodic mesoporous organosilica prevents over-oxidation of phenol and hence significantly improves both the selectivity and yield of phenol compared with their corresponding homogeneous iron precursors.

Tri- and tetradentate copper complexes: a comparative study on homogeneous and heterogeneous catalysis over oxidation reactions

A comparative catalytic study between heterogeneous (zeolite-encapsulated Cu complexes) and homogeneous analogues over oxidation reactions was undertaken in detail.