Kinetics and mechanisms of enhanced ammonia abatement under synchronous process of electrochemistry and adsorption

As a kind of common nitrogen pollutants, ammonia seriously pollutes water and soil environments and threatens human health. The treatment of water contaminated with ammonia was carried out in an electrochemical-adsorption system (ECAS). This paper discusses the capacity, kinetics, and mechanism of ammonia electrosorption, which is accurately described by a pseudo-first-order model, indicating that physical adsorption is the dominating mechanism. A high adsorption capacity of 4.086 mg N/g was attributed to the formation of a large number of adsorption sites and the highly acidic nature of dealumination of zeolites during electrolysis. Fast directional migration of ammonia in the electric field weakened the negative effect of boundary layer on adsorption and accelerated adsorption procedure. Brunauer, Emmett, and Teller measurements and scanning electron microscopy indicated that the formation of new channels and surface erosion, which resulted in a large surface area and pore volume of zeolites and a low resistance towards ion migration. As a whole, this study achieved efficient ammonia removal without the addition of chemical reagents to avoid secondary pollution.

Bi2O3/BiO2 Nanoheterojunction for Highly Efficient Electrocatalytic CO2 Reduction to Formate

Heterostructure engineering plays a vital role in regulating the material interface, thus boosting the electron transportation pathway in advanced catalysis. Herein, a novel Bi₂O₃/BiO₂ heterojunction catalyst was synthesized via a molten alkali-assisted dealumination strategy and exhibited rich structural dynamics for an electrocatalytic CO₂ reduction reaction (ECO₂RR). By coupling in situ X-ray diffraction and Raman spectroscopy measurements, we found that the as-synthesized Bi₂O₃/BiO₂ heterostructure can be transformed into a novel Bi/BiO₂ Mott-Schottky heterostructure, leading to enhanced adsorption performance for CO₂ and *OCHO intermediates. Consequently, high selectivity toward formate larger than 95% was rendered in a wide potential window along with an optimum partial current density of -111.42 mA cm^-2 that benchmarked with the state-of-the-art Bi-based ECO₂RR catalysts. This work reports the construction and fruitful structural dynamic insights of a novel heterojunction electrocatalyst for ECO₂RR, which paves the way for the rational design of efficient heterojunction electrocatalysts for ECO₂RR and beyond.

Effect of acid treated HY zeolites in adsorption of mesosulfuron-methyl

PURPOSE

Pollution of surface water and groundwater by bulky molecules such as pesticides has been recognized as a major problem in many countries due to their persistence in aquatic environment and potential adverse health effects. The main purpose of this study is the development of a capable adsorbent to remove these bulky molecules from wastewater such as the pesticide Mesosulfuron-Methyl (MM) by reducing the diffusion path, to overcome the problems of diffusional limitations on microporous adsorbents.

METHODS

The adsorption of mesosulfuron-methyl (MM) from aqueous solution is curried out using treated acid HY zeolite. Batch sorption equilibrium and kinetic experiments are conducted to evaluate the efficiency of these materials. Parent zeolites and their derivatives have been characterized by nitrogen adsorption-desorption, pyridine chemisorption followed by infrared spectroscopy and X-ray fluorescence.

RESULTS

The acid treatment leads to an increase in the specific surface from 691 to 853 m2 g- 1 for HY(30) and from 631 to 806 m2 g- 1 for the HY(16.6) zeolites. It also leads to a reduction in Lewis acidity from 74 to 25 µmol g- 1 and from 135 to 31 µmol g- 1 for HY(30) and HY(16.6) zeolites respectively, and increases the adsorbent-adsorbate interaction. The adsorption capacity increased from 83 to 99 % after acid treatment. The equilibrium adsorption time is decreased from 15 h to 10 min for the HY(30)_A and from 20 h to 20 min for the HY(16.6)_A for an initial concentration of 20 mg L- 1. The adsorption capacity depends on the pH solution, and the neutral form of the MM is more easily adsorbed into zeolite than the dissociated form via the framework bridged oxygen atoms. For all the samples, the pseudo-second-order kinetic model fits very well with the experimental data. In the case of the modified zeolites, the approaching equilibrium factor R w decreases from 0.08183 to 0.00008 when the Lewis acid sites decrease; indicating that the equilibrium is reached more quickly. S-shape adsorption isotherms indicates that cooperative adsorption phenomena. Nevertheless, the shape of acid treated zeolites evolves to an L type indicating a significant enhancement of the adsorbent - adsorbate interactions inducing better adsorption efficiency.

CONCLUSIONS

Mesosulfuron-methyl adsorption has been successfully enhanced after acid treatments of zeolites HY.

Manganese supported on controlled dealumination Y-zeolite for ozone catalytic oxidation of low concentration toluene at low temperature

Low-temperature catalytic degradation of VOCs with ozone has received widespread attention recently. In this work, a combination method of steam and nitric acid was used to control the dealuminization of Y zeolite, and then manganese oxide was loaded on the Y zeolite by impregnation method. It was found that MnO_x was highly dispersed in the dealumination zeolite, and the adsorbed oxygens were more easily activated in the active oxygen vacancies. The MnO_x supported on dealumination Y zeolite showed better catalytic effect than that supported on the parent Y. At low humidity (0.8%) in 30 °C, the degradation efficiency of toluene reached above 94% by using the catalyst with mild dealumination. When more water vapor was introduced, the degradation of toluene was inhibited. However, the catalytic performance of the catalyst with deep dealumination was not affected. With the help of in-situ DRIFTS, it was observed that the intermediates and reaction by-products had changed under different humidity conditions.

Thermal effect on the leachability of extraframework Co2+ in zeolite X

A partially Co²⁺-exchanged zeolite X was thermally treated to simulate the effect of decay heat on the leachability of extraframework Co²⁺. To have a mechanistic insight into thermal effect, X-ray diffraction, scanning electron microscopy, ²⁷Al magic angle spinning nuclear magnetic resonance spectroscopy, and Co K-edge X-ray absorption spectroscopy were employed with leaching tests. Although thermal treatment at ≤ 600 °C did not lead to the collapse of zeolite framework, it removed H₂O molecules from the coordination shell of extraframework Co²⁺, which in turn changed its coordination structure in a way to strengthen the interaction between Co²⁺ and the lattice oxygens. In leaching tests, the sample treated at higher temperature for a longer period showed less remobilized Co²⁺ by forming a Co(OH)₂-like surface precipitate and a Co hydrotalcite-like phase. Notably, the formation of the latter phase indicated the abstraction of the framework Al, the extent of which increased with the treatment temperature and duration. Two mechanisms, the concurrent extraction of Al with Co²⁺ remobilization and the hydrolysis-promoted Al abstraction, were proposed to account for thermally promoted dealumination. This study suggests that the exposure of Co²⁺-exchanged zeolite X to decay heat lessen the risk of extraframework Co²⁺ to be reintroduced into groundwater.

Effect of dealumination on the acidity of zeolite Y and the yield of glycerol mono stearate (GMS)

Research on the production of Glycerol Monostearate from glycerol using dealuminated Zeolite Y catalysts has been carried out. Optimization of the dealumination process is conducted using the help of statistical software 10, where the variables used are acid concentration (5-7 M), temperature of dealumination (55-70 °C) and time of dealumination (2-6 h). The acidity characterization test of dealuminated Zeolite Y using ammonia and pyridine solution. Glycerol Monostearate yield was obtained by GC-MS test that was carried out on 2 samples zeolite Y catalyst with the highest value of total and surface acidity of zeolite Y which produced 2.18% and 4% yield of Glycerol Monostearate. The two samples showed that the greater the acidity, the GMS yield was also greater. Compared to previous studies it was found that ZSM-5 catalyst has a higher acidity value than zeolite Y so that the yield of Glycerol Monostearate is higher with the use of ZSM-5 than Zeolite Y.

Modified Jordanian zeolitic tuff in hydrocarbon removal from surface water

This work aims to investigate the potential of Jordanian raw zeolitic tuff (RZT) as oil adsorbent for oil-contaminated water. As hydrophobic properties are the primary determinants of effective oil adsorbents, the hydrophobicity of RZT was enhanced by dealumination process; since the degree of hydrophobicity of zeolites is directly dependent on their aluminum content. The microemulsion modification of the dealuminated zeolitic tuff (TZT) was also applied to increase its hydrophobicity. The raw and modified tuffs were characterized in terms of the surface area and porosity (BET), mineral composition (XRD), microstructure and morphology using scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). In this work, a mixture of water and kerosene was used to examine the hydrophobic/organophilic character of raw and modified zeolitic tuff. Water/dodecane and water/octane mixtures were used to study the kinetics of the adsorption over zeolitic tuff. The results revealed that the sorption capacity using kerosene as a mixed model (water-oil) was enhanced by three- and four-fold for TZT and micro-emulsified zeolitic (MeTZT) tuff respectively. The adsorption capacity of modified zeolitic was compared with that of activated carbon adsorbents.

Effect of vanadium contamination on the framework and micropore structure of ultra stable Y-zeolite

Y-zeolites are the main component of fluid catalytic cracking (FCC) catalyst for conversion of crude petroleum to products of high demand including transportation fuel. We investigated effects of vanadium which is present as one of the impurities in FCC feedstock on the framework and micropore structure of ultra-stable (US) Y-zeolite. The zeolite samples were prepared and characterized using standard techniques including: (1) X-ray diffraction, (2) N2 adsorption employing non local density functional theory method, NLDFT, (3) Transmittance and Pyridine FTIR, (4) Transmittance electron microscopy (TEM), and (5) (27)Al and (29)Si MAS-NMR. Results revealed that in the presence of steam, vanadium caused excessive evolution of non inter-crystalline mesopores and structural damage. The evolved mesopore size averaged about 25.0nm at 0.5wt.% vanadium loading, far larger than mesopore size in zeolitic materials with improved hydrothermal stability and performance for FCC catalyst. A mechanism of mesopore formation based on accelerated dealumination has been proposed and discussed. Vanadium immobilization experiments conducted to mitigate vanadium migration into the framework clearly showed vanadium is mobile at reaction conditions. From the results, interaction of vanadium with the passivator limits and decreases mobility and activity of vanadium into inner cavities of the zeolite capable of causing huge structure breakdown and acid sites destruction. This study therefore deepens insight into the causes of alteration in activity and selectivity of vanadium contaminated catalyst and hints on a possible mechanism of passivation in vanadium passivated FCC catalyst.

Dealumination of clinoptilolite and its effect on zinc removal from acid rock drainage

Clinoptilolite, a natural zeolite, is capable of removing heavy metals from acid rock drainage (ARD). Previous studies have neglected the dealumination of clinoptilolite and its impact during remediation. This study observed the dealumination of clinoptilolite during ARD remediation in a slurry bubble column (SBC), and investigated its impact on the capture of zinc. Uptake tests were performed with natural ARD and various sorbent average particle diameters from 300 to 1400μm, superficial gas velocities from 0.08 to 0.23ms(-1), initial aqueous pH from 2 to 6, Zn concentrations from 15 to 215ppm and sorbent/solution mass ratios from 25 to 400gkg(-1) to test zinc uptake. Dealumination of clinoptilolite was sometimes observed during the uptake process. Increased Al in the aqueous phase led to co-precipitation of Zn-Al colloid, enhanced by abundant sulfate in solution. The unit zinc uptake of the Al colloid was found to be much higher than for the raw clinoptilolite.