The fast adsorption kinetics of zeolitic imidazolate frameworks (ZIFs) enable a wide range of sorption applications. The most commonly used framework, ZIF-8, is relatively non-polar. Increasing the ...polarity of ZIF-8 through the encapsulation of different polar species shows promise for enhancing the sorption performance for pure COsub.2. Recently, the outlook has re-focused on gas mixtures, mostly in the context of post-combustion COsub.2 capture from wet flue gasses. While water is known to sometimes have a synergistic effect on COsub.2 sorption, we still face the potential problem of preferential water vapor adsorption. Herein, we report the preparation of three ZIF-8/organic dye (OD) composites using Congo red, Xylenol orange, and Bromothymol blue, and their impact on the sorption properties for COsub.2, water, and a model wet COsub.2 system at 50% RH. The results show that the preparation of OD composites can be a promising way to optimize adsorbents for single gasses, but further work is needed to find superior ZIF@OD for the selective sorption of COsub.2 from wet gas mixtures.
Two series of MCM-36 zeolites intercalated with various pillars and modified with iron were synthesized, analyzed with respect to their physicochemical properties, and tested as catalysts for the ...NHsub.3-SCR process. It was found that the characteristic MWW morphology of MCM-36 can be obtained successfully using silica, alumina, and iron oxide as pillars. Additionally, one-pot synthesis of the material with iron resulted in the incorporation of monomeric Fesup.3+ species into the framework positions. The results of catalytic tests revealed that the one-pot synthesized sample intercalated with silica and alumina was the most efficient catalyst of NO reduction, exhibiting ca. 100% activity at 250 °C. The outstanding performance of the material was attributed to the abundance of Lewis acid sites and the beneficial influence of alumina on the distribution of iron species in the zeolite. In contrast, the active centers originating from the Fesub.2Osub.3 pillars improved the NO conversion in the high-temperature range. Nevertheless, the aggregated particles of the metal oxide limited the access of the reacting molecules to the inner structure of the catalyst, which affected the overall activity and promoted the formation of Nsub.2O above 300 °C.
Fe(III)-modified clinoptilolites (Fe-CPs) were prepared by hydrothermal treatment. The collapse of the heulandite skeletons was avoided by adjusting the pH value using HCl solution, showing the ...maximum relative crystallinity of the Fe-CPs at an optimal pH of 1.3. The competitive exchange performances between Fesup.3+ ions and Hsup.+ with Nasup.+ (and Ksup.+) suggested that the exchange sites were more easily occupied by Hsup.+. Various characterizations verified that the hydrothermal treatments had a strong influence on the dispersion and morphology of the isolated and clustered Fe species. The high catalytic activity of the oxygen evolution reaction indicated the insertion of Fesup.3+ into the skeletons and the occurrences of isomorphic substitution. The fractal evolutions revealed that hydrothermal treatments with the increase of Fe content strongly affected the morphologies of Fe species with rough and disordered surfaces. Meanwhile, the Fe(III)-modified performances of the CPs were systematically investigated, showing that the maximum Fe-exchange capacity was up to 10.6 mg/g. Their thermodynamic parameters and kinetic performances suggested that the Fe(III)-modified procedures belonged to spontaneous, endothermic, and entropy-increasing behaviors. Finally, their adsorption capacities of COsub.2 at 273 and 298 K were preliminarily evaluated, showing high COsub.2 adsorption capacity (up to 1.67 mmol/g at 273 K).
Globally, there is a growing concern about air pollution due to rapid industrialization and urbanization. Therefore, in this study, an experimental study was conducted to evaluate the performance of ...reducing nitrogen oxides, a precursor to fine dust, in mortars coated with a titanium dioxide (TiOsub.2) photocatalyst, which has the effect of decomposing pollutants. In particular, in this study, zeolite and activated red clay were used as cement substitutes to improve the fine dust reduction performance of the TiOsub.2 photocatalyst. A total of 14 different mixtures were designed, considering the substitution rates of zeolite and activated red clay (30%, 40%, and 50%) and the cement–fine aggregate ratio (1:2 and 1:3) as experimental variables. A TiOsub.2 photocatalyst was employed in this study to evaluate the NOsub.x reduction performance. As zeolite and activated red clay were added, the compressive strength and flexural strength of the mortars decreased by 15% to 60%, while the absorption rate increased by 5% to 16%. The NOsub.x reduction efficiency of up to 67.4% was confirmed in the H50-3 specimen with the TiOsub.2 catalyst. The NOsub.x reduction performance of mortars with the TiOsub.2 photocatalyst sprayed on their surface improved as the substitution ratio of zeolite and activated red clay increased. Additionally, it was confirmed that the NOsub.x reduction effect of specimens using activated red clay was superior to those using zeolite. Therefore, through this study, it was confirmed that the NOsub.x reduction performance of the TiOsub.2 photocatalyst can be improved when zeolite and activated red clay are used as cement substitutes.
The present work studies the adsorption of COsub.2 using a zeolitic industrial molecular sieve (IMS) with a high surface area. The effect of the COsub.2 feed concentration and the adsorption ...temperature in conjunction with multiple adsorption–desorption cycles was experimentally investigated. To assess the validity of the experimental results, theoretical calculations based on well-established equations were employed and the values of equilibrium, kinetic, and thermodynamic parameters are presented. Three additional column kinetic models were applied to the data obtained experimentally, in order to predict the breakthrough curves and thus facilitate process design. Results showed a negative correlation between temperature and adsorption capacity, indicating that physical adsorption takes place. Theoretical calculations revealed that the Langmuir isotherm, the Bangham kinetic model (i.e., pore diffusion is the rate-determining step), and the Thomas and Yoon–Nelson models were suitable to describe the COsub.2 adsorption process by the IMS. The IMS adsorbent material maintained its high COsub.2 adsorption capacity (>200 mg gsup.−1) after multiple adsorption–desorption cycles, showing excellent regenerability and requiring only a mild desorption treatment (200 °C for 15 min) for regeneration.
The single-component adsorption of COsub.2, CO, Nsub.2, and Hsub.2 at 25 and 35 °C was studied using microporous faujasite-framework zeolites (NaY and NaX), activated carbons (GCN and MSP), and ...metal–organic frameworks (A100 and Z1200) as starting points for the separation of COsub.2 from syngases produced by gasifying biomass-based solid wastes. The indicated adsorption isotherms and uptake of the adsorbates strongly depended on the adsorbates themselves as well as on the adsorbents because of significant differences in the surface features, such as surface nonuniformity, and in the molecular properties. The selectivity of COsub.2 to the other gases also varied with the adsorbents due to the distinctive energetic characteristics. The surfaces of the zeolites were the most energetically heterogeneous ones, yielding higher COsub.2 uptake at low pressures, while the two activated carbons and A100 had moderate surface heterogeneities, and MSP showed the highest COsub.2 uptake at high pressures, such as 6 bar, at which the micropore volume and surface area are important. Z1200, which has highly homogeneous surfaces and no high-affinity-binding sites, exhibited the lowest COsub.2 adsorption capacity regardless of equilibrated pressure. The surface nonuniformities of the six sorbents were consistent with the calculated isosteric heats of COsub.2 adsorption. COsub.2 could be reversibly adsorbed on NaY and MSP but not on GCN, with some metal impurities, although all these adsorbents showed a fully reversible process for CO adsorption. The estimated working capacity for COsub.2 adsorption at 25 °C was 0.78–6.50 mmol/g, depending on the sorbents used. The highest value was disclosed for MSP, the surface energetic heterogeneity of which was between that of zeolites and Z1200. Such a high working capacity bodes well for use in our later applications.
Due to their interfacial defects between inorganic fillers and polymer matrices, research into mixed matrix membranes (MMMs) is challenging. In the application of COsub.2 separation, these defects ...can potentially jeopardize the performance of membranes. In this study, aminosilane functionalization is employed to improve the nano-sized zeolite Y (ZeY) particle dispersion and adhesion in polyether block amide (Pebax). The performance of COsub.2/CHsub.4 separation of Pebax mixed matrix composite hollow fiber membranes, incorporated with ZeY and aminosilane-modified zeolite Y (Mo-ZeY), is investigated. The addition of the zeolite filler at a small loading at 5 wt.% has a positive impact on both gas permeability and separation factor. Due to the COsub.2-facilitated transport effect, the performance of MMMs is further improved by the amino-functional groups modified on the ZeY. When 5 wt.% of Mo-ZeY is incorporated, the gas permeability and COsub.2/CHsub.4 separation factor of the Pebax membrane are enhanced by over 100% and 35%, respectively.
The textural, structural, morphological, and acidic properties of TiOsub.2/Al-ZSM-12 zeolite synthesized viathe hydrothermal method and using methyltriethylammonium chloride as a template were ...studied in this study. The structure, size, and shape of the crystallites, and the acidity of the synthesized materials were investigated in detail using the following methods: XRD, low-temperature nitrogen adsorption-desorption, XRF, FTIR, Raman spectroscopy, DRS UV-Vis, DRIFTS, PL, SEM, TEM, solid-state NMR spectroscopy on sup.27Al, sup.1H, sup.29Si, sup.1H-sup.29Si and sup.23Na nuclei, NHsub.3-TPD, TG, DSC, DTA, FTIR-Py, FTIR-2,6-dTBP, FTIR-CDsub.3CN, and DRIFTS-acid. The presence of tetrahedral titanium in the TiOsub.2/Al-ZSM-12 zeolite was confirmed by Raman spectroscopy, DRIFT, and sup.29Si NMR. It was revealed that the crystallites of the TiOsub.2/Al-ZSM-12 zeolite, elongated along the b axis, had a higher acidity compared to the unsubstituted zeolite Al-ZSM-12. The oxidative catalytic activity of the TiOsub.2/Al-ZSM-12 zeolite was studied in the photoinduced decomposition of the crystal violet dye and it was found that the reaction proceeds most efficiently in the presence of Hsub.2Osub.2 as an oxidizing agent and TiOsub.2/Al-ZSM-12 as a catalyst (PCA = 0.157%∙minsup.−1).
This manuscript deals with the synthesis of different types of zeolites from natural kaolinite samples for COsub.2 adsorption. A zeolite A was prepared from kaolinite by means of an alkaline fusion ...process, followed by hydrothermal treatment, whereas a highly crystalline zeolite X was synthesized by optimizing the previously mentioned synthetic procedure. In detail, the SiOsub.2/Alsub.2Osub.3 molar ratio in the preliminary mixture was modified with the addition of a secondary silicon source (sodium silicate) in order to obtain the one required for zeolites X. The physicochemical properties of the pristine clay and of the different zeolites were investigated by means of a multi-technique approach, including XRPD; SEM-EDX; sup.23Na, sup.27Al and sup.29Si MAS NMR spectroscopy; and Nsub.2 physisorption analysis at 77 K. Since the Si and Al molar ratios and reactivities are key parameters for the synthesis of zeolites, these aspects, primarily related to the use of a naturally occurring aluminosilicate as the raw material, have been investigated for their correlation with the physicochemical properties of the synthetic products. Moreover, by means of a custom-built volumetric apparatus, the COsub.2 adsorption capacity of the resulting zeolites at low gas pressures (<1 bar) and at 25 °C was assessed.
![Evaluation of the NO[sub.x]...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1996-1944/small "Evaluation of the NO[sub.x] Reduction Performance of Mortars Containing Zeolite/Activated Red Clay Coated with a TiO[sub.2] Photocatalyst")
![Adsorption of CO[sub.2], CO...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/2071-1050/small "Adsorption of CO[sub.2], CO, H[sub.2], and N[sub.2] on Zeolites, Activated Carbons, and Metal-Organic Frameworks with Different Surface Nonuniformities")
