Nitrous Oxide Adsorption and Decomposition on Zeolites and Zeolite-like Materials

Decomposition of N2O on modified zeolites, crystalline titanosilicalites, and related amorphous systems is studied by the catalytic and spectroscopic methods. Zinc-containing HZSM-5 zeolites and titanosilicalites with moderate Ti/Si ratios are shown to exhibit a better catalytic performance in N2O decomposition as compared with conventionally used Cu/HZSM-5 zeolites and amorphous Cu-containing catalysts. Dehydroxylation of the HZSM-5 zeolite by calcination at 1120 K results in an enhancement of the N2O conversion. The mechanism of the reaction and the role of coordinatively unsaturated cations and Lewis acid sites in N2O decomposition are discussed on the basis of the spectroscopic data.

Effect of the coexistence of SO32− and PO43− on the adsorption performance of zeolite-loaded FeOOH@ZnO for S2−

The present study deals with the synthesis of zeolite-loaded FeOOH@ZnO by hydrothermal method and investigates the effects of coexisting SO32− and PO43− ions in the aqueous solution on the adsorption performance for S2−. The results showed that the HNO3-modified zeolite loaded with FeOOH@ZnO (FeOOH@ZnO/HZ) resulted in a maximum S2− removal rate of ≈98%. The adsorbent's performance on removing S2− was significantly enhanced, compared with NaOH and ZnCl2-modified zeolites loaded with FeOOH@ZnO, and the adsorption was proved to be a heat-absorbing process. When SO32− and PO43− coexisted with S2−, SO32− and PO43− had a significant influence on the adsorption properties of FeOOH@ZnO/HZ. When three ions of S2−, SO32− and PO43− were present simultaneously, the adsorption performance of FeOOH@ZnO/HZ on S2− was further, and the removal rate dropped to about 80%. Moreover, FeOOH@ZnO/HZ also adsorbed PO43− and SO32− in the system containing multiple ions, but the adsorption rate of PO43− and SO32− were much lower than S2−. This indicated that the adsorption of S2− in the presence of FeOOH@ZnO/HZ dominates under competitive conditions.

INFLUENCE OF THE NATURE OF THE MODIFIER ON THE SORPTION PROPERTIES OF SHANKANAI ZEOLITE

Sorbents modified with hydrochloric acid and chitosan based on the Shankanai bridge formation zeolite were obtained, and the effect of drying temperature on the sorption properties of sorbents was studied. It was found that 25 °C is the optimal temperature for obtaining acid-modified zeolite. A chitosan-modified sorbent with good sorption characteristics can be obtained at 25 °C with cation-exchange (COE 68.05 mg-eq/g) and 70°C with anion-exchange (SEC 70.16 mg-eq/g) properties. Physicochemical analysis of modified zeolites showed an increase in the size of voids and channels on the surface of acid-modified zeolite, and when modified with chitosan, the latter is crosslinked with the surface of natural zeolite.

OXIDATIVE DEHYDROGENATION OF BUTYL ALCOHOLS TO THE CORRESPONDING CARBONYL COMPOUNDS OVER MODIFIED ZEOLITES

The catalytic properties of modified synthetic (A, X, Y) and natural (MOR, Clp) zeolites have been studied in the reactions of oxidative dehydrogenation of butyl alcohols to corresponding carbonyl com-pounds. It has been established that bimetallic zeolite catalysts show higher activity in these reactions

Effect of Exchangeable Ions in Natural and Modified Zeolites on Ag Content, Ag Nanoparticle Formation and Their Antibacterial Activity

To broaden the application of silver nanoparticles (AgNPs), which are well-known antibacterial agents, they are supported on different substrates to prevent aggregation, increase their surface area and antibacterial efficiency, and to be separated from the system more effectively at the end of treatment. To produce nanocomposites that consist of silver nanoparticles on natural and modified zeolites, silver ions (Ag+) were loaded onto zeolite (natural, Na-modified, H-modified) and then thermally reduced to AgNPs. The effect of the exchangeable cations in zeolite on Ag+ uptake, AgNPs formation, size and morphology was investigated by the TEM, SEM, EDX, XPS, UV-vis, XRD and BET methods. The silver amount in the nanocomposites decreased in the following order Na-modified zeolite > natural zeolite > H-modified zeolite. Microscopic techniques showed formation of AgNPs of 1–14 nm on natural and Na-modified zeolite, while the diameter of metal particles on H-modified zeolite was 12–42 nm. Diffuse reflectance UV-vis and XPS methods revealed the presence of both silver ions and AgNPs in the materials indicating that partial reduction of Ag+ ions took place upon heating at 400 °C in air. Additionally, antibacterial properties of the nanocomposites were tested against Escherichia coli, and it was found that Ag–containing composites originating from the Na-modified zeolite demonstrated the highest activity.

Hydrochloric Acid Modification and Lead Removal Studies on Naturally Occurring Zeolites from Nevada, New Mexico, and Arizona

Four naturally occurring zeolites were examined to verify their assignments as chabazites AZLB-Ca and AZLB-Na (Bowie, Arizona) and clinoptilolites NM-Ca (Winston, New Mexico) and NV-Na (Ash Meadows, Nevada). Based on powder X-ray diffraction, NM-Ca was discovered to be mostly quartz with some clinoptilolite residues. Treatment with concentrated HCl (12.1 M) acid resulted in AZLB-Ca and AZLB-Na, the chabazite-like species, becoming amorphous, as confirmed by powder X-ray diffraction. In contrast, NM-Ca and NV-Na, which are clinoptilolite-like species, withstood boiling in concentrated HCl acid. This treatment removes calcium, magnesium, sodium, potassium, aluminum, and iron atoms or ions from the framework while leaving the silicon framework intact as confirmed via X-ray fluorescence and diffraction. SEM images on calcined and HCl treated NV-Na were obtained. BET surface area analysis confirmed an increase in surface area for the two zeolites after treatment, NM-Ca 20.0(1) to 111(4) m2/g and NV-Na 19.0(4) to 158(7) m2/g. 29Si and 27Al MAS NMR were performed on the natural and treated NV-Na zeolite, and the data for the natural NV-Na zeolite suggested a Si:Al ratio of 4.33 similar to that determined by X-Ray fluorescence of 4.55. Removal of lead ions from solution decreased from the native NM-Ca, 0.27(14), NV-Na, 1.50(17) meq/g compared to the modified zeolites, 30 min HCl treated NM-Ca 0.06(9) and NV-Na, 0.41(23) meq/g, and also decreased upon K+ ion pretreatment in the HCl modified zeolites.