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Adsorption is a promising technology for capturing nitrogen oxides (NO x) from humid flue gases, for which as the preferred NO x adsorbent, zeolite with an appropriate silica to alumina (Si/Al) ratio provides the key step for success in practical applications. In this work, the effects of Si/Al ratio, temperature, relative humidity (RH), and feed gas (NO x -H 2 O(g)–CO 2 –O 2 -N 2) compositions on NO x sorption behavior on HZSM-5 zeolites were systematically investigated, based on a series of characterizations, fixed-bed adsorption and temperature programmed desorption (TPD) tests. The low-silica HZSM-5(25) showed the best performance (326.6 μmol/g and 39.2 μmol/g at dry and 90%RH) as compared to others with higher Si/Al ratios at each RH, in which the roll-up effect was positively correlated with the Si/Al ratios and humidity. O 2 enhanced NO x adsorption and reached an optimal adsorption capacity at the concentration of 14%, while CO 2 had little effect on NO x adsorption. The decrease in temperature increased NO x adsorption capacity on HZSM-5(25), benefitting from NO 2 physisorption as well as satisfactory NO oxidation within the active adsorbent structure. The facile thermal desorption of NO x and significant NO–NO 2 conversion on HZSM-5(25) was exhibited by bimodal TPD peaks at 343–353K and 533–543K respective for NO and NO 2 , in contrast to those on Silicalite-1. A potential "water-resistant" strategy via the enhancement of NO x adsorption competitiveness was revealed, providing a theoretical guideline for NO x adsorbent screening in industrial applications. [Display omitted] • Influential rules of multiple factors on NO x adsorption are systematically explored. • Low-silica HZSM-5 shows the best NO x adsorption performance at each condition. • Contributions of NO oxidation and NO 2 physisorption at varying temperatures are shown. • Greater regenerability of NO x from NO x -H 2 O(g)–CO 2 –O 2 -N 2 feed on HZSM-5 is demonstrated. • A "water-resistant" strategy for enhancing NO x adsorption competitiveness is proposed. [ABSTRACT FROM AUTHOR]

Conventional flue gas nitrogen oxides (NO x) abatement technologies commonly convert NO x into harmless compounds, while less effort has been made to recycle NO 2 as a profitable chemical in many industries. Towards this end, adsorption is a promising technology for which an advanced technique for NO 2 desorption and efficient sorbent regeneration provides the key step for success in practical applications. This work reports a novel cyclic adsorption process for NO x removal with recycling of NO 2 from iron-ore sintering flue gas of a steel plant. This process using self-prepared and validated pelletized Na-ZSM-5 zeolites as low-cost sorbents involves NO x catalytic adsorption and reversible desorption using multiple hot gas circulations (GC) within the enclosed fixed bed followed by scavenging and purge at mild conditions. In comparison to conventional cyclic processes, greater amount of recyclable NO 2 was obtained, rendering the NO x recovery of >92% and the mean NO 2 concentration of >2% significantly enriched from original 20 ppm in feed gas. A robust adsorption-desorption performance with appreciable NO x working capacity was achieved for up to 16 cycles. The key role of the segmentation of GC in boosting NO x regenerability was addressed, providing an economical three-tower strategy for continuous NO 2 production for practical use. ga1 • NO x removal and with recycling of NO 2 from flue gas was studied through field tests. • Comparisons among different adsorption cycles in NO x removal and recycling were made. • A novel technique for efficient NO 2 desorption and sorbent regeneration was proposed. • NO x recovery of 92% and recyclable desorbed NO 2 concentration of >2% were obtained. • Robust cyclic performance with NO x working capacity of >0.1 mmol/g was demonstrated. [ABSTRACT FROM AUTHOR]

High-volume production of oxygen and nitrogen from atmospheric air is accomplished by cryogenic distillation. Prior to feeding to the air separation unit, the ambient air must be pre-purified by the removal of trace impurities such as CO 2, H 2 O vapor, and light hydrocarbons (e.g., CH 4 ) to their tolerable limits of 1.0 ppm, 0.1 ppm, and to a few ppb, respectively. In this study, the adsorption characteristics of a synthetic zeolite, Li-LSX (where LSX denotes low-silica type-X zeolite where Si/Al=1), for the removal of trace amounts of CO 2 , CH 4 , and H 2 O vapor impurities were analyzed and compared with the conventional synthetic 13X zeolite that has been used for air prepurification as well as the ion-exchanged K-LSX and Ca-LSX zeolites. Isotherms to very low partial pressures (to a few ppm of 1 atm) were measured. The Tὸth, Langmuir–Freundlich (L–F), and the Dubinin–Astakhov (D–A) isotherm models were used to correlate the low pressure experimental data and the Tὸth model was found to be the better fit especially in the low pressure range. The superior adsorption properties of Li-LSX for air prepurification are demonstrated in this work. [ABSTRACT FROM AUTHOR]

• The properties of ECSCs are controllable by adjusting the fuel in SCS process. • The superb S bet , V P, and V meso of ECSCs are beneficial to improve the naphthalene adsorption capacity. • ECSCs exhibit unprecedented high capacity, fast kinetics, and low desorption energy. Sorptive capture and recycling of gaseous naphthalene from industrial emissions are of both environmental significance and economic benefit. Constructing carbonaceous sorbents with matchable pore size and adequate active sites is significant towards the trade-off between adsorption and desorption for naphthalene. In this study, we developed a series of porous carbonaceous sorbents (ECSCs) using facile, inexpensive, and effective solution combustion synthesis (SCS) with subsequent calcination and pickling. The MgO@C precursors were fabricated via a fast and self-exothermic combustion reaction, and after calcination and MgO removal by pickling, the tailored pore structure was created. The morphology, porous structure, and surface chemical properties of ECSCs are precisely controlled by adjusting the type and content of fuel in combustion. For the optimized ECSC-G14 prepared on fuel-balanced condition, its layer-by-layer network facilitates adsorption mass transfer, and its high specific surface area (1987 m2·g−1) and abundant 3–6 nm mesoporosity promotes the accessibility of active sites. Consequently, an unprecedented high naphthalene uptake (3.075 mmol·g−1 at 398 K) and fast kinetics (∼1.43 × 10−2 s−1 at 2.82 × 10−3 mol·m−3 feed concentration) were achieved. Combined characterization and molecular calculation revealed the synergistic contribution of O and N to reversible adsorption with superb regenerability (E a of 42.71 kJ·mol−1) and cyclic properties. This study provides an effective strategy and theoretical support to customize the properties of porous carbons, overcoming the adsorption–desorption dilemma for gas purification. [ABSTRACT FROM AUTHOR]

An eruptive solution combustion synthesized carbonaceous sorbent (ECSC) with unprecedented naphthalene adsorption and desorption performances is generated by introducing rational mesoporosity and nitrogen groups into a layer-by-layer porous carbon network. The integration of all key elements via careful tuning of morphological, porous, and chemical properties during the synthesis of ECSC opens up vast possibilities to overcome the adsorption–desorption dilemma for low-volatile or large-molecular gases, which offers great opportunities for gas separation and purification applications. [Display omitted] • Carbon sorbent was derived with an facile eruptive solution combustion strategy. • Layer-by-layer network, rational mesoporosity, and reversible sites were integrated. • Unprecedented high adsorption capacity and kinetics for naphthalene were achieved. • Good regenerability with low naphthalene desorption activation energy was obtained. • Moderate sorption affinity of naphthalene-pyridinic N π–π bonding was proposed. Capturing naphthalene as a valuable chemical from waste gases via adsorption on porous sorbent materials is a promising approach to tackle such an environmental health issue with additional economic benefits. However, very few sorbents have simultaneously high adsorption capacity and good regenerability for the large-molecular and low-volatile naphthalene. Here we attempt to address this challenge by integrating key fabrication elements of a layer-by-layer network, rational mesoporosity, and highly reversible sites into a carbonaceous adsorbent (ECSC) using a facile and fast eruptive solution combustion synthesis method. Adsorption breakthrough and temperature-programmed desorption experiments show that the ECSC achieves all-round superior naphthalene capture performance with unprecedented high capacity, fast kinetics, and low desorption energy. The combination of in situ DRIFTS, XPS, and DFT calculations reveals the moderate adsorption affinity of mitigated π–π stacking bonding between tilted naphthalene molecule and surface pyridinic N. This work affords new insights for designing next-generation adsorbents for naphthalene removal and presents a way of overcoming the adsorption–desorption dilemma for gas purification. [ABSTRACT FROM AUTHOR]

• Influence of coexisting nanoparticles on toluene adsorption was studied. • Competition between gas and particles in interaction with zeolites was addressed. • Reduction of toluene adsorption capacity by particles was up to 16.0 % on K-ZSM-5. • Reduction of toluene adsorption rate by particles was up to 20.3 % on Li-ZSM-5. • Adsorption site occupation and steric hindrance could be caused by nanoparticles. Adsorption as one of the most important air cleaning methods has been extensively applied during which the coexisting airborne nanoparticles (NPs) with sizes close to adsorbent pore sizes could inevitably influence gas adsorption processes. In this work, the influence of sub-20 nm NPs on toluene adsorption on ZSM-5 zeolites exchanged with different cations (Li+, Na+ and K+) were studied based on gas-and-particle coexisting adsorption/filtration tests. Affinities for both toluene and NPs on adsorbents follow Li-ZSM-5 > Na-ZSM-5 > K-ZSM-5 regarding the orders of charge density, pore size, and internal and external specific surface areas. The toluene adsorption was shown to be impaired by coexisting NPs from perspectives of thermodynamics and kinetics. For Li-ZSM-5, Na-ZSM-5 and K-ZSM-5, significant relative reductions of 10.4 %, 10.5 % and 16.0 % in toluene adsorption capacity at the lower feed concentration, and of 20.3 %, 15.2 % and 2.3 % in mass transfer coefficient at the higher feed concentration were observed, respectively. The influential mechanisms regarding competitiveness between toluene and NPs in interaction with cationic and porous surfaces were accordingly proposed, which are of practical significance for selecting robust adsorbents under realistic harsh air conditions. [ABSTRACT FROM AUTHOR]