Research on CO2-N2O separation using flexible metal organic frameworks

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.

Exploring the Micropore Functional Mechanism of N2O Adsorption by the Eucalyptus Bark-based Porous Carbon

Nitrous oxide (N2O), recognized as a significant greenhouse gas, has received insufficient research attention in the past. In view of their low energy consumption and cost-effectiveness, the application of porous materials in adsorption is increasingly regarded as a potent strategy to reduce N2O pollution. In this study, a series of microporous porous carbons with a preeminent specific surface area (244.54-2018.08 m2 g-1), which are derived from the fast-growing eucalyptus bark, were synthesized by KOH activation at high temperatures. The obtained materials demonstrated a relatively fine N2O capture capability (0.19-0.68 mmol g-1) at normal temperature and pressure. More importantly, the optimal pore size affecting N2O adsorption (0.8 and 1.0 nm) has been detected, which is a meaningful view that has never been put forward in previous studies. The rationality of the N2O adsorption mechanism was also validated by combining the experimental analysis and Grand Canonical Monte Carlo (GCMC) simulation. The calculated results showed that 0.8 and 1.0 nm of the porous carbon were the preferred pore sizes for N2O adsorption, and the interaction force between N2O and the pore wall decreased with the increase of distance. This study provides a significant theoretical basis for the preparation of biomass porous carbon with excellent N2O adsorption performance and practical adsorption application.

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.

Materials Design for N2O Capture: Separation in Gas Mixtures

The adsorption of greenhouse gases (GHG) as a method to reduce their emissions into the atmosphere is an alternative that is easier to implement industrially and cheaper than other existing technologies, such as chemical capture, cryogenic separation, or membrane separation. The vast majority of works found in the literature have focused their efforts on capturing CO2 as it is the largest GHG. However, although N2O emissions are not as large as CO2, the impact that N2O has on the stratosphere and climate is much larger in proportion, despite which there is not much research on N2O capture. Since both gases are usually emitted into the atmosphere together (along with other gases), it is necessary to design selective adsorbents capable of capturing and separating these gases from each other and from other gases, to mitigate the effects of climate change. This review aims to compile the existing information to date on porous adsorbents, the characteristics of the N2O adsorption processes and, above all, aims to focus the reader’s gaze on the importance of designing selective adsorbents for greenhouse gas mixtures.

Metal-Organic Frameworks for NOx Adsorption and Their Applications in Separation, Sensing, Catalysis, and Biology

Nitrogen oxide (NO_x ) is a family of poisonous and highly reactive gases formed when fuel is burned at high temperatures during anthropogenic behavior. It is a strong oxidizing agent that significantly contributes to the ozone and smog in the atmosphere. Thus, NO_x removal is important for the ecological environment upon which the civilization depends. In recent decades, metal-organic frameworks (MOFs) have been regarded as ideal candidates to address these issues because they form a reticular structure between proper inorganic and organic constituents with ultrahigh porosity and high internal surface area. These characteristics render them chemically adaptable for NO_x adsorption, separation, sensing, and catalysis. In additional, MOFs enable potential nitric oxide (NO) delivery for the signaling of molecular NO in the human body. Herein, the different advantages of MOFs for coping with current environmental burdens and improving the habitable environment of humans on the basis of NO_x adsorption are reviewed.

Preparation of an interpenetrating bimetal metal–organic framework via metal metathesis used for promoting gas adsorption

Novel interpenetrating bimetallic MIL-126(Cr/Sc) has been synthesized using a metal metathesis method, and showed a higher CO2, N2O and C2H2 uptake and binding energy than the parent MIL-126(Sc) material.

Mechanistic studies on the conversion of NO gas on urea-iron and copper metal organic frameworks at low temperature conditions: in situ infrared spectroscopy and Monte Carlo investigations

Nitrogen oxide (NOx) emissions from high-temperature combustion processes under fuel-lean conditions continue to be a challenge for the energy industry. Selective catalytic reduction (SCR) is possible using metal oxides and zeolites. There is still a need to identify catalytic materials that are efficient in reducing NOx to environmentally benign nitrogen gas at temperatures lower than 200 °C. Metal-organic frameworks (MOFs) have emerged as a class of highly porous materials with unique physical and chemical properties. This study is motivated by the lack of systematic investigations on SCR using MOFs under industrially relevant conditions. Here, we investigate the extent of NO conversion with two commercially available MOFs, Basolite F300 (Fe-BTC) and HKUST-1 (Cu-BTC), mixed with solid urea as a source for the reductant, ammonia gas. For comparison, experiments were also conducted using cobalt ferrite (CoFe2O4) as a non-porous counterpart to relate its reactivity to those obtained from MOFs. Fourier-transform infrared spectroscopy (FTIR) was utilized to identify the gas and surface species in the temperature range of 115–180 °C. Computational analysis was performed using Monte Carlo simulations to quantify the adsorption energies of different surface species. The results show that the rate of ammonia production from the in situ solid urea decomposition was higher using CoFe2O4 than Fe-BTC and Cu-BTC and that there was very limited conversion of NO on the mixed solid urea-MOF systems due to site blocking. The main conclusions from this study are that MOFs have limited ability to convert NO under low-temperature conditions and that surface regeneration requires additional experimental steps.

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.