Untreated Zeolite Research Articles

Effect of thermal treatment on zeolite for real-time gas sensing of oxygenated volatile organic compounds

The breathable air is severally polluted due to the emission of various pollutants like volatile organic compounds (VOCs) and dust particles of submicron sizes. These pollutants have several adverse health hazards, which can cause fatal accidents and mortalities. In the current study, we have modified the FAU type of Zeolite (ZE) with the Si/Al to 1 and treated at different temperatures (300–600 °C) in a 10% H2 + 90% N2 mixture to achieve different distributions of oxygen vacancies. The presence of oxygen vacancy and electrons in the lattice is confirmed by EDAX, XPS and ESR techniques. The charge irregularities generated due to trapped electrons are exploited for detection of different VOCs like acetone, ethyl methyl ketone, isopropyl alcohol, ethanol, n-hexane, and benzene using the scanning kelvin probe (SKP) technique. The oxygen vacancies raise the distribution of Lewis and Brønsted basic sites, which impacts the interaction of VOCs with the sample surface and the amount of VOCs uptake. The untreated ZE and treated at 600 °C (ZE600) exhibited n-type behavior with 13.8% oxygen deficient sites with ∼1.9 μmol/g of total basic sites and 3 μmol/g of total acidic sites. The thermal treatment for ZE600 leads to ∼280 folds enhancement in surface photovoltage towards acetone with ∼ 67% of recovery concerning untreated ZE.

Catalytic Oxidation of VOC over Cobalt-Loaded Hierarchical MFI Zeolite

The zeolites ZSM-5 with different Si/Al ratios were modified with a buffer solution of HF and NH4F. This acidic treatment led to the obtaining of a material with secondary mesoporosity. The deposition of cobalt from an aqueous solution of cobalt acetate on the surface of treated samples generates the formation of different cobalt oxide species: bulk-like Co3O4 phases strongly interacting with the support, Co2+ in ion exchange positions (γ and β sites) and silicate-like phases. The mechanism of cobalt silicate phase formation is proposed here and includes a replacement of silanol groups and the bridging hydrogens by Co and the inclusion of the Co atoms in tetrahedral framework positions. The catalysts, obtained through use of the treated ZSM-5, exhibit higher activity in the reactions of propane, and n-hexane completes oxidation compared with the catalyst samples containing un-treated zeolite. Both the finer dispersion of metal oxide particles on the hierarchical sample and the presence of secondary mesoporosity improve the effectiveness of the active phase utilization via access to larger number of active sites.

Effect of treated clinoptilolite zeolite on alkali-silica reaction

The reactive aggregates can cause a volumetric expansion in the concrete leading to cracking and spalling due to alkali-silica reaction (ASR). The use of natural zeolite as the supplementary cementitious material can reduce the expansion due to ASR by providing physical space for the ASR gel along with the adsorption of alkalis through the cation exchange. However, the rate of reduction in expansion may sometimes not be satisfactory due to the slow rate of cation exchange along with other factors. Therefore, the present study investigates three different treatment techniques (calcination, milling, and chemical pre-treatment) on clinoptilolite zeolite to obtain an optimal method for reducing the expansion due to ASR. Calcination was done at 400 °C for 3 h to increase the amorphous contents, while milling was done for 3 h to increase the specific surface area of zeolite particles leading to increasing pozzolanic activities. The chemical pre-treatment was accomplished with a 1 M Ca(OH)2 solution to largely remove any existing sodium or potassium ions via cation exchange. To observe the physical expansion due to ASR, mortar bars were prepared with highly reactive cherty sand and up to 20% of both untreated and treated zeolite with the replacement of the portland cement. Results revealed that calcination slightly increased the amorphous contents while milling substantially increased the specific surface area of zeolite particles. The chemical pre-treatment successfully transformed the zeolite into calcium-based clinoptilolite zeolite. Results also revealed that the application of up to 20% untreated, calcined, milled, and chemically treated zeolite reduced the ASR expansion by up to 60%, 40%, 70%, and 42%, respectively, compared to the control sample at 28 days. Overall, among the three different treatment methods, milling was the most effective method to reduce the ASR expansion, while calcined and chemically treated zeolite was less effective than untreated zeolite.

Catalytic Oxidation of CO and Benzene over Metal Nanoparticles Loaded on Hierarchical MFI Zeolite.

In order to obtain highly active catalytic materials for oxidation of carbon monoxide and volatile organic compounds (VOCs), monometallic platinum, copper, and palladium catalysts were prepared by using of two types of ZSM-5 zeolite as supports—parent ZSM-5 and the same one treated by HF and NH4F buffer solution. The catalyst samples, obtained by loading of platinum, palladium, and copper on ZSM-5 zeolite treated using HF and NH4F buffer solution, were more active in the reaction of CO and benzene oxidation compared with catalyst samples containing untreated zeolite. The presence of secondary mesoporosity played a positive role in increasing the catalytic activity due to improved reactant diffusion. The only exception was the copper catalysts in the reaction of CO oxidation, in which case the catalyst, based on untreated ZSM-5 zeolite, was more active. In this specific case, the key role is played by the oxidative state of copper species loaded on the ZSM-5 zeolites.

Platinum catalysts supported on ZSM5 zeolites with a hierarchical pore structure: characterization and performance in n-hexadecane hydroconversion

HZSM5 zeolites with a hierarchical pore structure were prepared from a microporous one using the top-down methodology by treatment with a sodium hydroxide solution in optimal conditions of time, alkali concentration and temperature. These materials were used as supports for platinum to produce bifunctional hydroconversion catalysts. The activity in n-hexadecane hydroconversion was one order of magnitude larger on Pt supported on the mesoporous than on the untreated zeolite and one order of magnitude larger than that of the supports. All Pt catalysts and supports were more selective to hydrocracking than to hydroisomerization, but the initial selectivity for hydroisomerization of the Pt catalysts supported on the mesoporous supports was considerably smaller than that of all other materials, including the supports. This was attributed to a smaller mass transfer limitation with the Pt catalysts supported on the mesoporous zeolites. All supports and catalysts were extensively characterized by techniques such as X-ray diffraction, hydrogen chemisorption, TPD of ammonia, IR spectroscopy of adsorbed pyridine, MAS 29Si and 27Al solid state NMR and transmission electron microscopy.

Shaped Hierarchical H-ZSM-5 Catalysts for the Conversion of Dimethyl Ether to Gasoline

Hierarchical H-ZSM-5 zeolites are a promising class of heterogeneous catalysts that have shown encouraging results in lab-scale studies for the production of gasoline from dimethyl ether (DTG conversion). However, the influences of mesopore formation and shaping on various catalyst properties are still under debate. In this study, a series of H-ZSM-5 zeolites with hierarchical pore structures were prepared by modifying commercially available zeolites via alkaline treatment (“desilication”). The powdered zeolites were shaped into technical catalyst bodies by wet extrusion using either silica or alumina binders. All materials were extensively characterized. The different interactions during alkaline treatment were related to the observed modifications in the zeolite properties of the materials obtained. Although many properties of modified and untreated zeolite powders remained predominantly unchanged in their shaped catalyst equivalents, both binders affected certain material characteristics, particularly those related to their acidity. Finally, preliminary tests showed enhanced catalytic performance of hierarchical ZSM-5 catalysts in DTG conversion.

Impact of concentrated acid, base and salt pretreatments on the characteristics of natural clinoptilolite and its ammonium uptake from model solution and real effluents

Abstract In this study the influence of highly concentrated reagents (NaCl, 22.36%; HCl, 20%; NaOH, 32%) on the mineralogy (e.g. structure and mineral chemistry) and NH 4 + -exchange capacity of a natural zeolite (clinoptilolite) is investigated. Treatment was executed in packed bed columns and accompanied by liquid and solid analytics (ICP-MS, XRD, EPMA, BET, ion exchange). Ammonium uptake was tested in batch experiments with model solutions using different concentrations of NH 4 Cl and real effluents from mechanical sludge dewatering (sludge liquor). It turned out that the Si/Al-ratio of the zeolite minerals measured by EPMA changes to some extent because of dissolution of Si and Al during treatment. Acid treatment leads to a remarkable increase in the specific surface (from 16 to 77 m 2 /g after treatment). NH 4 + -exchange isotherms revealed a significant decrease in equilibrium loadings with HCl-treatment and an increase with NaOH-treatment (+25%) at concentrations > 1300 mg NH 4 + L −1 compared to untreated zeolite. At lower concentrations ( 4 + L −1 ) treatment with NaCl is best. Basic treatment leads to the formation of an altered outer rim on zeolite particles enriched in Na and depleted in K. Compared to model solutions, ammonium uptake from sludge liquor (712 mg NH 4 + L −1 ) was significantly lower for NaCl treated zeolite but higher for HCl and NaOH treated samples, probably as a result of the complex composition of real effluents leading to potential cross-interactions that influence NH 4 + ion exchange on treated zeolites.

Tailoring Natural Zeolites by Acid Treatments

In this study, a comparison of a variety of existing acid treatment methods for zeolite based on their abilities to modify physical properties of the particles is performed. Evaluation of the effects that four different acids have on numerous properties of the zeolites including surface area, pore size, pore volume, thermal stability, IR spectra, crystallinity, and morphology is conducted and compared with the reference untreated zeolite. Furthermore, all five zeolite particles are evaluated for their adsorption properties in column mode experiments. The importance of the examined features is discussed. The results obtained in this work are compared to similar studies to examine which conditions greatly influence the zeolite modifications.

Improved Catalytic Technology for Waste Plastic Processing: Toward Novel Remediation and Emission Control Measures

A mesoporous zeolite USY to process waste plastic, illustrated on low-density polyethylene, is presented. The technology is mobile and can be used as a remediation and control measure to the emissions in the open environment. The core of this approach lays on the catalytic material employed. It is a zeolite USY that possesses both micropores (up to 2 nm) and mesopores (between 2 and 50 nm) that was prepared by desilication using a mixture of mesopore inducing agents, tetra-butyl ammonium hydroxide and sodium hydroxide. This gives rise to a well-defined zeolite USY with double intracrystalline mesoporosity and higher intrinsic acidity. Those improvements had a positive impact on the cracking of low-density polyethylene, with a lowering of the cracking temperature, ascribed to the enhanced mass transfer of the reactant into the acid sites. The lowering of the reaction temperature reduces the energy requirements with operational savings of 0.50 MW with respect to the thermal process and 80 kW with respect to the untreated zeolite for a plant of 50 kt per year, though the scale of operation can be adjusted to the local requirements. The lower operation temperature triggered by the catalyst has also benefits in terms of lower capital investment since low-cost construction materials would be required. The zeolite preparation is industrially scalable. All these features make the deployment of this technology a realistic option.

Acid mine drainage treatment by integrated submerged membrane distillation–sorption system

Acid mine drainage (AMD), an acidic effluent characterized by high concentrations of sulfate and heavy metals, is an environmental and economic concern. The performance of an integrated submerged direct contact membrane distillation (DCMD) – zeolite sorption system for AMD treatment was evaluated. The results showed that modified (heat treated) zeolite achieved 26–30% higher removal of heavy metals compared to natural untreated zeolite. Heavy metal sorption by heat treated zeolite followed the order of Fe > Al > Zn > Cu > Ni and the data fitted well to Langmuir and pseudo second order kinetics model. Slight pH adjustment from 2 to 4 significantly increased Fe and Al removal rate (close to 100%) due to a combination of sorption and partial precipitation. An integrated system of submerged DCMD with zeolite for AMD treatment enabled to achieve 50% water recovery in 30 h. The integrated system provided a favourable condition for zeolite to be used in powder form with full contact time. Likewise, heavy metal removal from AMD by zeolite, specifically Fe and Al, mitigated membrane fouling on the surface of the hollow fiber submerged membrane. The integrated system produced high quality fresh water while concentrating sulfuric acid and valuable heavy metals (Cu, Zn and Ni).

Desilicated ZSM-5 Zeolites for the Production of Renewable p-Xylene via Diels–Alder Cycloaddition of Dimethylfuran and Ethylene

The selective production of p-xylene and other aromatics starting from sugars and bioderived ethylene offers great promise and can eliminate the need for separation of xylene isomers, as well as decreasing dependency on fossil resources and CO2 emissions. Although the reaction is known, the microporosity of traditional commercial zeolites appears to be a limiting factor. In this work, we demonstrate for the first time that simply desilication of microporous commercial zeolites by a simple NaOH treatment can greatly enhance conversion and selectivity. The [4 + 2] Diels–Alder cycloaddition of 2,5-dimethylfuran with ethylene in a pressurised reactor was investigated using a series of H-ZSM-5 catalysts with SiO2/Al2O3 ratios 30 and 80 with increasing pore size induced by desilication. X-ray diffraction, scanning electron microscopy, 27Al magic-angle spinning nuclear magnetic resonance, temperature programmed desorption of ammonia, and nitrogen physisorption measurements were used to characterise the catalysts. The enhancement of conversion was observed for all desilicated samples compared to the untreated zeolite, and increases in temperature and ethylene pressure significantly improved both dimethylfuran conversion and selectivity to p-xylene due to the easier desorption from the zeolite’s surface and the augmented cycloaddition rate, respectively. A compromise between acidity and mesoporosity was found to be the key to enhancing the activity and maximising the selectivity in the production of p-xylene from 2,5-dimethylfuran.

Catalytic conversion of hemicellulosic sugars derived from biomass to levulinic acid

Catalytic conversion of hemicellulosic sugars from biomass towards levulinic acid production was conducted using modified-zeolite Y (commercial). The zeolite was treated by NaOH of different concentration (x M) before used for the conversion of C5 sugars to levulinic acid. The modified zeolites had a larger porosity and an increased concentration of stronger acid sites compared to the untreated zeolite. Levulinic acid yield of 4.6% (conversion of C5 sugar to levulinic acid: 42.7%) was maximized at 190 °C and reaction time of 180 min (batch reactor), when using the zeolite treated with 0.25 M NaOH. In addition, with the absence of C6 sugar, the conversion of C5 sugar was higher than that of C5-C6 sugar mixture. The present work provides a new heterogeneous catalytic approach for levulinic acid production from liquid hydrolysates (by-product of biomass utilization).

Electro-elastoviscous response of polyaniline functionalized nano-porous zeolite based colloidal dispersions

The present article discusses the typical influence of grafted conducting polymers in the mesoscale pores of dielectric particles on the static and dynamic electrorheology and electro-viscoelastic behavior of corresponding colloids. Nanocrystalline meso-nanoporous zeolite has been prepared by chemical synthesis and subsequently polyaniline (PANI) coating has been implemented. Electrorheological (ER) suspensions have been formed by dispersing the nanoparticles in silicone oil and their viscoelastic behaviors are examined to understand the nature of such complex colloidal systems under electric fields. PANI-Zeolite ER fluids demonstrate higher static electroviscous effects and yield stress potential than untreated Zeolite, typically studied in literature. Transient electro-viscous characterizations show a stable and negligible hysteresis behavior when both the fluids are exposed to constant as well as time varying electric field intensities. Further oscillatory shear experiments of frequency and strain sweeps exhibit predominant elastic behavior in case of Zeolite based ER suspensions as compared to PANI systems. Detailed investigations reveal Zeolite based ER suspensions display enhanced relative yielding as well as electro-viscoelastic stability than the PANI-Zeolite. The steady state viscous behaviors are scaled against the non-dimensional Mason number to model the system behavior for both fluids. Experimental data of flow behaviors of both the ER fluids are compared with semi-classical models and it is found that the CCJ model possesses a closer proximity than traditional Bingham model, thereby revealing the fluids to be generic pseudo-linear fluids. The present article reveals that while the PANI based fluids are typically hailed superior in literature, it is only restricted to steady shear utilities. In case of dynamic and oscillatory systems, the traditional Zeolite based fluids exhibit superior ER caliber.

Effect of Type of Amine Salt and Surfactant on the Water Sorption and Flexural Properties of Modified Zeolite/Polyester Composites

Natural zeolite, an abundant clay with porous solids based on silica, is modified with amine salt and surfactant, and incorporated as filler for polyester to produce modified zeolite/polyester (MZP) composite. A general factorial design of experiment is implemented with two factors (type of amine salt and type of surfactant) varied at three levels each. The amine salts are tetra- (TDA), hexa-, and octadecyl dimethylamine chloride while surfactants are stearic acid (SA), glycerol monostearate, and cocamide diethanolamine (CDEA). Water sorption and flexural testing are performed on MZPs. Results show that natural zeolite treated with SA exhibits improved hydrophobicity of MZPs, resulting to lower water uptake as compared to untreated natural zeolite. However, water sorption in MZPs is higher than in pure polyester due to difference in hydrophobicity. Flexural modulus of MZP is highest using TDA + CDEA due to enhanced filler-to-matrix compatibility. Meanwhile, break stress is highest for untreated zeolite filler due to the high stress resistance of rigid natural zeolite. Analysis of variance shows water sorption to be significantly affected by the type of surfactant, while break stress is significantly higher using amine salt with shorter chain length.

Enhanced chromium adsorption capacity via plasma modification of natural zeolites

Natural zeolites such as mordenite are excellent adsorbents for heavy metals. To enhance the adsorption capacity of zeolite, sodium-exchanged samples were irradiated with 13.56 MHz capacitively coupled radio frequency (RF) argon gas discharge. Hexavalent chromium [Cr(VI)] was used as the test heavy metal. Pristine and plasma-treated zeolite samples were soaked in 50 mg/L Cr solution and the amount of adsorbed Cr(VI) on the zeolites was calculated at predetermined time intervals. Compared with untreated zeolite samples, initial Cr(VI) uptake was 70% higher for plasma-treated zeolite granules (50 W 30 min) after 1 h of soaking. After 24 h, all plasma-treated zeolites showed increased Cr(VI) uptake. For a 2- to 4-month period, Cr(VI) uptake increased about 130% compared with untreated zeolite granules. X-ray diffraction analyses between untreated and treated zeolite samples revealed no major difference in terms of its crystal structure. However, for plasma-treated samples, an increase in the number of surface defects was observed from scanning electron microscopy images. This increase in the number of surface defects induced by plasma exposure played a crucial role in increasing the number of active sorption sites on the zeolite surface.

Experimental study of the effect of zeolite 4A treated with magnesium hydroxide on the characteristics and gas‐permeation properties of polysulfone‐based mixed‐matrix membranes

ABSTRACTNowadays, new methods for gas‐separation processes are being quickly developed. The separation of CH4/CO2 and CH4/H2 is usually the subject of most related research studies, especially in the membrane gas‐separation process, because of their important role in industry. In this study, we attempted to improve the separation properties of a polysulfone/zeolite 4A mixed‐matrix membrane by modifying the zeolite particle surface. The method included a simple ion‐exchange reaction of magnesium chloride with ammonium hydroxide that yielded the formation and precipitation of magnesium hydroxide whiskers on the surface of the zeolites. The whiskers could omit most of the nonselective voids by interlocking the polymer chains through them and, consequently, improve the permeability, selectivity, and elastic modulus of the membranes. X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and dynamic mechanical analysis proved all the changes recorded after the particle and membrane treatments. SEM images showed the petal‐like morphology of the whiskers that formed on the surface of the particles after the reaction against the smooth surface of the untreated zeolite. At a 30 wt % loading of particles in the polymeric matrix, the selectivities for H2/CH4 and CO2/CH4 increased by 69 and 56%, respectively; in contrast, the H2 and CO2 permeabilities decreased by 2.5 and 10%, respectively. The modulus of elasticity for the treated membrane also increased by 14 and 30% compared to those of the pure and untreated membranes, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44329.

Novel pre-treatment of zeolite materials for the removal of sodium ions: potential materials for coal seam gas co-produced wastewater.

Coal seam gas (CSG) is the extraction of methane gas that is desorbed from the coal seam and brought to the surface using a dewatering and depressurisation process within the saturated coalbed. The extracted water is often referred to as co-produced CSG water. In this study, co-produced water from the coal seam of the Bowen Basin (QLD, Australia) was characterised by high concentration levels of Na+ (1156 mg/L), low concentrations of Ca2+ (28.3 mg/L) and Mg2+ (5.6 mg/L), high levels of salinity, which are expected to cause various environmental problems if released to land or waters. The potential treatment of co-produced water using locally sourced natural ion exchange (zeolite) material was assessed. The zeolite material was characterized for elemental composition and crystal structure. Natural, untreated zeolite demonstrated a capacity to adsorb Na+ ions of 16.16 mEq/100 g, while a treated zeolite using NH4+ using a 1.0 M ammonium acetate (NH4C2H3O2) solution demonstrated an improved 136 % Na+ capacity value of 38.28 mEq/100 g after 720 min of adsorption time. The theoretical exchange capacity of the natural zeolite was found to be 154 mEq/100 g. Reaction kinetics and diffusion models were used to determine the kinetic and diffusion parameters. Treated zeolite using a NH4+ pre-treatment represents an effective treatment to reduce Na+ concentration in coal seam gas co-produced waters, supported by the measured and modelled kinetic rates and capacity.

Activity of titania and zeolite samples dosed with triethylamine

Certain properties of titania and the ammonium- and proton-form of Y zeolites silica/alumina = 5.2 were explored before and after treatment by triethylamine (TEA). The effect of the triethylamine upon the physical and chemical properties of both titania and the zeolite were characterized by physical and chemical adsorption methods. BET surface area data showed enhanced surface area of the TEA-treated nanotitania over the untreated nanotitania; whereas, the TEA-treated zeolite showed a considerable decrease in surface area compared to the untreated zeolite. A lower bound on the exothermic heat release from the sol–gel generated TiO2 nanoparticle-TEA interaction has been evaluated. Temperature programmed desorption (TPD) of the TEA-treated Y zeolite showed that weakly adsorbed TEA left the surface between 150 and 300 °C; strongly adsorbed TEA decomposed to ethylene and ammonia at higher temperatures. Methanol adsorption isotherms and temperature-programmed, surface reaction (TPSR) were used to understand further the Zeolite-TEA interactions and correlations were made to CO2 adsorption. XPS, IR, and Raman spectroscopies, powder XRD, and 27Al MAS-NMR spectroscopy were used characterize the changes attending the TEA adsorption. Pre-adsorbed, triethylamine decorated acid sites so as to neutralize these sites for the reaction of methanol to dimethyl ether. Carbon monoxide and formaldehyde, products of the methanol probe reaction, were observed – suggesting that basic sites are present in this treated zeolite and titania.

Titanium dioxide/zeolite integrated photocatalytic adsorbents for the degradation of amoxicillin

Integrated photocatalytic adsorbents (IPA) prepared from TiO2 and natural zeolite were applied to amoxicillin (AMX) degradation. The acid-alkali pre-treated zeolite annealed at 300°C under nitrogen resulted in the best degradation of AMX. The superior performance of this IPA material was explained using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). SEM analysis showed an uneven surface as a result of TiO2 cluster deposition, which provides more active sites for adsorption and degradation. XRD results revealed that peaks from more photoactive anatase were more prominent in this IPA material. EDS analyses also confirmed the presence of high amounts of TiO2. Despite their large TiO2 loadings, comparison experiments with untreated zeolite suggested that the pores are still available for adsorption. The overall performance of the IPA material for the degradation of AMX was thus attributed to the adsorption capability of the zeolite carrier, the photocatalytic activity of TiO2 coating and acid-catalyzed hydrolysis (‘capture & destroy’). Degradation products resulting from TiO2/zeolite IPA-induced hydrolysis were identified by liquid chromatography-mass spectrometry (LC-MS) prior to photocatalytic treatment. AMX and its thermal degradants were almost completely removed after 240min of irradiation. The efficiency of the developed TiO2/zeolite material provides a potentially economical way of degrading pharmaceutical compounds and recovering photocatalysts simultaneously.

Biosorptive Behavior of Aerobic Biomass Biofilm Supported on Clinoptilolite Zeolite for the Removal of Copper

The aim of this study was to determine the behavior of aerobic biomass biofilm supported on untreated clinoptilolite zeolite in the biosorption process to reduce the concentration of copper from synthetic solutions. A systematic study in batch and continuous systems was carried out. In addition, biomass and zeolite were characterized before and after biosorption treatment by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). According to results, zeolite only acts as a support for biomass and the study of SEM and EDS indicated that copper was absorbed by bacteria that are present on the surface of the zeolite. This study showed that untreated zeolite clinoptilolite acts as a support material for biomass during copper removal, and it may be an alternative of great interest for the immobilization of biomass in the restoration process of sites contaminated with heavy metals.