Type Zeolite Research Articles

Assessment of a new rigid wall permeameter for the slurry like barrier materials: zeolite example

Areas vulnerable to catastrophic disasters such as hurricane, landslide and earthquake require ready and sustainable solutions for the post-pollution scenarios. Clinoptilolite type zeolite re- sources of Türkiye can serve economical and sustainable solutions as a quick response. While the studies on compacted zeolite-bentonite mixture at optimum water content for the landfill liners applications or dry zeolite-sand mixtures in permeable reactive barrier (PRB)s are com- mon, the slurry form of zeolite emplacement at subsurface reactive barriers has not received an attention by the researchers. In this context, this experimental study presents the prelimi- nary findings on one-dimensional consolidation and hydraulic conductivity tests performed on crushed zeolite samples S1 and S2 with fine contents of 33 and 84%, respectively. The results indicate that S2 has a higher compression index than S1, without a significant change in swelling index attributed to less than 4% clay contents. A self-designed rigid wall type per- meameter was used to study on reconstituted slurry like materials under the benefit of back pressure saturation without the consolidation during testing that encountered in flexible wall permeameter. Falling head – rising tail water procedure was adopted under the back pressure in between 200 and 700 kN/m2. S2 samples reconstituted under 25, 50, 100 and 200 kN/m2 show a gradual decrease in kv from 3×10-8 to 2×10-9 m/s. Previous observations on the sample of S1 revealed 8 times higher kv values under the same σv'. Since the fine content of zeolite limits kv, the proposed permeameter will be beneficial to determine the proper grain size dis- tribution of fill materials considering the barrier height and in-situ stress conditions before the environmental studies with leachate.

Anion adsorption capacity from the iron hydroxyl group of Fe-modified Na-P1 type zeolite

Anion adsorption capacity from the iron hydroxyl group of Fe-modified Na-P1 type zeolite

The Effect Of Acid Treatment On The Characteristics Of Modernite Zeolite

This work investigated the use of acid treatment on the characteristics of zeolite mineral. The effects of treating zeolite with various acid solutions hydrochloric acid (HCl) and sulfuric acid (H2SO4) were measured using x-ray fluorescence (XRF), x-ray diffraction (XRD), and scanning electron microscope (SEM). The results showed an increase in the percentage of SiO2 and Al2O3 after zeolite activation, and also a decrease in the amount of impurities. The crystalline phase of the zeolite was carried out using XRD analysis, indicating the type of zeolite used is modernite. The SiO2 phase in the sample is quartz, and the Al2O3 phase is corundum. The average crystal size decreased after activation, from 14.23 nm to 6.85 nm for HCl and 5.42 nm for H2SO4. Futhermore, the surface morphology of all zeolite samples has a form of irregular spherical surface, and the surface size of the particles after activation shows a smaller particle shape. The results of this study are expected to become recommendations for further research related to natural zeolite pretreatment as a catalyst support.

The influence of deuterium on sodium mobility and viscosity of colloidal precursor suspensions yielding template-free nanosized zeolites

The isotopic substitution in chemistry is characterized by two main effects, i.e., the kinetic isotope effect (KIE), associated with differences in the reaction rates, and the geometric isotope effect (GIE) related to crystallographic features. In this work, considering the difference in the weight of deuterium (D) compared to the weight of hydrogen (H), we use the isotopic substitution to investigate the crystallisation mechanism of template-free nanosized faujasite (FAU) type zeolite in colloidal precursors. Тhe basic hydrothermal synthesis solvent - water (H2O), is substituted with heavy water (D2O), aiming to understand the isotopic influence and the effect of H-bond networks on the zeolite crystallisation. The crystallinity, viscosity, conductivity, chemical composition, morphology and local order of the FAU zeolites synthesized in both hydrated (H) and deuterated (D) medium are evaluated with X-ray diffraction, TEM microscopy, EDX and ICP analysis, FT-IR and solid-state NMR spectroscopy. The structural directing agent - Na+, exhibits a lower mobility in the deuterated medium, because of a characteristic higher viscosity compared to hydrated medium. This leads to a slower nucleation and crystallisation in the initial stages of hydrothermal treatment in the colloidal suspensions but also to a significant difference in the Al distribution.

Humidity- and temperature-dependent study of YUG type zeolite. A new dehydrated topology

The dehydration and hydration behaviour of a natural zeolite with YUG framework type was investigated as a function of water vapour pressure (PH2O) and temperature (T) by in situ single crystal X-ray diffraction. The chemical composition of the sample is CaAl2Si6O16∙nH2O, with n varying as a function of T and PH2O. Under ambient conditions (T = 302 K and relative humidity RH = 60%) the structure contains 4 H2O per formula unit. After exposure to dry air for 30 min, 1 H2O is released. Prolongation of the exposure time to 60 min does not induce further dehydration. The H2O can easily be up taken by exposing the crystal to ambient conditions for few minutes.The temperature-dependent experiments were conducted under N2 flow from 299 to 673 K, in steps of 50 K. In the investigated T range, the unit-cell volume is reduced by 13% and the space group Pc is maintained. Two main structural changes were observed: i) at 523 K, the release of 2.5 H2O is accompanied by the doubling of one unit-cell parameter (a-axis); ii) at 573 K, the structure becomes anhydrous, the c-axis triples, and two T-O-T connections of the framework break, leading to the formation of an interrupted framework. This topology (called HT-B phase) was never reported before. Moreover, the breaking process takes place by a different mechanism with respect that reported for other zeolites, and it is here described for the first time.

Aromatization of HDPE and PP over Ga-promoted zeolite: Effects of pretreatment and zeolite type

The effects of pretreatment and structure of zeolite on aromatization of high-density polyethylene (HDPE) and polypropylene (PP) over different Ga-promoted zeolites (HZSM-5, hierarchical HZSM-5, HY, Hβ, and USY) were investigated. Hydrogen reduction of Ga-promoted HZSM-5 resulted in a higher yield of alkenes during HDPE pyrolysis but did not lead to increased production of total aromatic hydrocarbons. The reduction and subsequent oxidation of Ga/Z5 led to the formation of GaO+ species with high dehydrogenation activity. This resulted in a remarkable 65% yield of aromatics, with a BTEX (benzene, toluene ethylbenzene and xylene) overall yield of 60% and a selectivity of 90% of the liquid product. Increasing the Ga loading decreased the BTEX yield due to pore blockage and a decrease in the amount of Brønsted acid sites. The BTEX yield over Ga-promoted zeolites was found to be strongly related to the pore size of the zeolite, whereas its yield over the parent zeolite was not strongly dependent on the pore size. Diffusion of the cracking intermediates was found to have a more significant impact on the aromatization of PP than HDPE. The highest BTEX yield for HDPE was achieved with Ga-promoted HZSM-5, while Ga-promoted hierarchical HZSM-5 exhibited the highest BTEX yield for PP. Furthermore, Ga(1)/Hβ-Redox demonstrated remarkable selectivity (90%) towards ethylene and propylene in the gas phase, surpassing other zeolites (37%-68%).

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.

Recent trends on sewage sludge transesterification: review

The need for non-existent or low-cost sources to be a feedstock for the biodiesel industry as a source of lipids has led to the trend of sewage sludge (containing high fat content) and thinking about it and finding ways to benefit from it. On the other hand, he use of sludge is an environmental treatment, as it rids the environment of tons of sludge produced daily and a solution to a problem for treatment plants that were looking for ways and solutions to get rid of it and save the cost of getting rid of it and converting it into clean and promising energy. It was found that the sewage sludge in all its primary and secondary types is a feedstock rich in free fatty acids (FFA), which is the raw material for the production of biodiesel, while treating it with one of the types of catalyst alcohols. According to a review of previous studies, it was found that acidic catalysts are most suitable for biodiesel production from sewage sludge, because sewage sludge has a free fatty acid content of 65-70%, which is a high percentage. It is a severely high percentage of free fatty acids found in pure vegetable oils that do not exceed 5%. The heterogeneous acid catalysts were preferred over the homogeneous ones because of the satisfactory results they provided and the high productivity of biodiesel compared to the homogeneous ones, and they are more economical as they can be reused more than once, but also many times. Reacting sewage sludge lipids with a type of catalyst alcohol and forming biodiesel called transesterification or esterification, and it may be traditional or in-site, and in-site is more important and economical than conventional. It was found from previous references that heterogeneous catalysts in general and zeolite types in particular are the most suitable for oil extracted from sewage sludge. Where The yield reached 100% using a type of zeolite.

Evidence of electronic influence in the adsorption of cationic and zwitterionic dyes on zeolites

The adsorption of a cationic dye, Methylene blue (MB), and a zwitterionic dye, 8-Hydroxyquinoline (8-HQ), onto zeolites synthesized from different clays has been investigated. The presence of certain metals and the Si/Al ratio of the parent clay has an overall effect on the type of zeolites produced. Zeolites LTA and FAU Y were obtained using the hydrothermal method. X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) spectral analysis was used to study the adsorption phenomena of the adsorbates on the adsorbents. The adsorption profile of MB (Topological Polar Surface Area (TPSA) 43.9 Å2 and 8-HQ (TPSA 33.1 Å2) compared favourably with a Freundlich isotherm with R2 > 0.9 for all the zeolitic materials synthesized. Adsorption capacities of zeolite FAU was significantly different from zeolite LTA for MB removal. The higher adsorption capacity of zeolite FAU was attributed to geometric effects resulting in greater shrinkage in the inter lattice spacing of zeolite LTA leading to a reduction in surface area. Adsorption of the relatively smaller 8-HQ however, did not show significant difference in the two zeolite types. Surface and structural characterization showed that adsorbates/adsorbents interactions were driven by both geometric (inter lattice spacing which imparts higher surface area of the adsorbent) and electronic (electrostatic repulsions through electron back donation from metals in the zeolitic structure) considerations.

A comprehensive parametric study of factors that influence synthesis of high-quality ZTC using Ca2+ exchanged zeolite Y as the template

We achieved the synthesis of an ordered 3D microporous graphene architecture via chemical vapor deposition using the faujasite type zeolite as the template, i.e., “zeolite templated carbon” (ZTC). We found that implanting Ca2+ in this zeolite effectively catalyzed the growth of ZTC and greatly lowered the growth temperature. To further improve the ZTC, we investigated the influence of various synthetic parameters on its growth: Ca2+ amount, growth temperature, growth time, growth pressure, stabilization temperature and stabilization time, and describe these in detail. High-quality ZTC samples having regions of what are likely continuous single-layer carbon structures composed of trivalently bonded carbon were grown and characterized. This effective and practical synthetic method should benefit synthesis of other ZTCs and the evaluation and exploration of the structural characterization and application of ZTCs.

Adsorption and Desorption Behaviors of Ammonia on Zeolites at 473 K by the Pressure-Swing Method.

Adsorption and desorption behaviors of ammonia on the zeolites were investigated using the pressure-swing method to utilize the ammonia adsorbent at 473 K. For various (Y, A, L, and mordenite) types of zeolites, the effects of their pore sizes, countercation species, and number of adsorption sites on the ammonia adsorption behavior were evaluated. The adsorption capacity increased with increasing the pore size. The differences in the countercation species and the number of adsorption sites contributed to the ammonia adsorption process on the zeolites. Sodium cations strongly adsorb ammonia molecules. The adsorption/desorption of ammonia expanded and shrunk the zeolite crystal, suggesting that the pores in the zeolite were enlarged by the adsorption of ammonia molecules. Despite repetitive lattice expansion and shrinkage, the morphologies of the zeolite particles were not degraded. These results confirm that the zeolite showed high durability for the adsorption and desorption of ammonia at 473 K.

Dehydrogenation–cracking synergistic pathway of n–pentane by core–shell MFI zeolite to produce light olefins

A core@shell MFI type zeolite supporting PtZn alloys catalyst was prepared by dry gel conversion method, which is used for catalytic cracking of n–pentane. The shell and core of catalyst is composed of nanosheet silicalite–1 and microporous ZSM–5, respectively. A proposed dehydrogenation–cracking pathway was demonstrated, which facilitate the generation of light olefins. At 600 °C with WHSV of 6.26 h−1, the yield of ethylene and propylene in the product attained up to 35.3 wt% and 33.4 wt%, respectively.

Lean methane combustion over zeolite-supported Pd catalysts: Structure-performance relationship and deactivation mechanism

Zeolites are a promising support for Pd catalysts in lean methane (CH4) combustion. Herein, three types of zeolites (H-MOR, H-ZSM-5 and H-Y) were selected to estimate their structural effects and deactivation mechanisms in CH4 combustion. We show that variations in zeolite structure and surface acidity led to distinct changes in Pd states. Pd/H-MOR with external high-dispersing Pd nanoparticles exhibited the best apparent activity, with activation energy (Ea) at 73 kJ/mol, while Pd/H-ZSM-5 displayed the highest turnover frequency (TOF) at 19.6 × 10−3 sec−1, presumably owing to its large particles with more step sites providing active sites in one particle for CH4 activation. Pd/H-Y with dispersed PdO within pore channels and/or Pd2+ ions on ion-exchange sites yielded the lowest apparent activity and TOF. Furthermore, Pd/H-MOR and Pd/H-ZSM-5 were both stable under a dry condition, but introducing 3 vol.% H2O caused the CH4 conversion rate on Pd/H-MOR drop from 100% to 63% and that on Pd/H-ZSM-5 decreased remarkably from 82% to 36%. The former was shown to originate from zeolite structural dealumination, and the latter principally owed to Pd aggregation and the loss of active PdO.

Catalytic Cracking of Fischer-Tropsch Wax on Different Zeolite Catalysts

Fisher-Tropsch synthesis (FTS) is a promising method to make alternative hydrocarbons from biomass or other resources. Upgrading the primary FTS products is of considerable interest. Cracking FT wax is economically attractive to produce light olefins. Herein, the effects of the zeolite type, Si/Al ratio of ZSM-5, and reaction condition on the catalytic cracking of FT wax were investigated. It was found that the pore structure and acid properties of zeolites had a significant impact on the product selectivity. USY was beneficial for the production of gasoline and diesel, while β was suitable for the production of propylene and butenes, and ZSM-5 was conductive to producing ethylene and propylene. Increasing the Si/Al ratio of ZSM-5 can suppress the hydrogen transfer reaction and increase the selectivity of light olefins. When the Si/Al ratio of ZSM-5 was 140, the mass yields of ethylene, propylene, and butenes were 6.40%, 26.83%, and 20.10%, respectively.

Non-Destructive Examination for Cavitation Resistance of Talc-Based Refractories with Different Zeolite Types Intended for Protective Coatings.

In many industrial processes that include fluid flow, cavitation erosion of different engineering structures (pumps, turbines, water levels, valves, etc.) during their operation is expected. Metallic, ceramic, and composite materials are usual candidates considered for application in such extreme conditions. In this study, the idea is to synthesize refractory ceramic material based on talc with the addition of zeolite for utilization as protective coatings in cavitating conditions. Two talc-based refractories with zeolites from two Serbian deposits were produced. The behaviors of the samples in simulated cavitation conditions were examined by an advanced non-destructive methodology consisting of monitoring mass loss and surface degradation using image analysis compiled with principal component analysis (PCA), interior degradation by ultrasonic measurements, and the microstructure by a scanning electron microscope (SEM). Lower mass loss, surface degradation level, and modeled strength decrease indicated better cavitation resistance of the sample with Igros zeolite, whereby measured strength values validated the model. For the chosen critical strength, the critical cavitation period as well as critical morphological descriptors, Area and Diameter (max and min), were determined. A Young's elasticity modulus decrease indicated that surface damage influence progressed towards interior of the material. It can be concluded that the proposed methodology approach is efficient and reliable in predicting the materials' service life in extreme conditions.

Direct imaging of local atomic structures in zeolite using optimum bright-field scanning transmission electron microscopy.

Zeolites are used in industries as catalysts, ion exchangers, and molecular sieves because of their unique porous atomic structures. However, direct observation of zeolitic local atomic structures via electron microscopy is difficult owing to low electron irradiation resistance. Subsequently, their fundamental structure-property relationships remain unclear. A low-electron-dose imaging technique, optimum bright-field scanning transmission electron microscopy (OBF STEM), has recently been developed. It reconstructs images with a high signal-to-noise ratio and a dose efficiency approximately two orders of magnitude higher than that of conventional methods. Here, we performed low-dose atomic-resolution OBF STEM observations of two types of zeolite, effectively visualizing all atomic sites in their frameworks. In addition, we visualized the complex local atomic structure of the twin boundaries in a faujasite (FAU)-type zeolite and Na+ ions with low occupancy in eight-membered rings in a Na-Linde Type A (LTA) zeolite. The results of this study facilitate the characterization of local atomic structures in many electron beam-sensitive materials.

Advantages and limitations of hydrogen peroxide for direct oxidation of methane to methanol at mono-copper active sites in Cu-exchanged zeolites

The efficiency of direct catalytic oxidation of methane to methanol (DMTM) is significantly influenced by oxidants. However, realizing a one-pot DMTM using dioxygen remains challenging. Hydrogen peroxide is still the most frequently reported green oxidant for DMTM, with high selectivity for methanol. To gain insight into the influence of oxidants on DMTM performance, we computationally investigated the reaction mechanisms involved in DMTM using H2O2 at mono-copper sites in three types of Cu-exchanged zeolites with different micropore sizes. We identified the advantages and limitations of H2O2 as an oxidant. In contrast to the O–O bond in O2, the O–O bond in H2O2 can be easily broken to produce reactive surface oxygen species, which enable the facile C–H bond activation of methane at a low temperature. However, because of the radical-like process of C–H bond activation at mono-copper sites, actualizing the preferential C–H bond activation of methane is kinetically challenging compared to that of methanol. Moreover, the lower O–H bonding energy of H2O2 would result in self-decomposition of H2O2. Despite these bottlenecks, kinetic analysis shows that improving catalysts to boost the DMTM performance using H2O2 is a promising approach.

Hydrogen storage behavior of zeolite/graphene, zeolite/multiwalled carbon nanotube and zeolite/green plum stones-based activated carbon composites

In this study, novel zeolite/carbon composites were synthesized to determine hydrogen storage properties. Activated carbon (AC), graphene (GR) and multi-walled carbon nanotubes (MWCNT) were used as carbon sources in the preparation of the composites with faujasite type zeolite. AC was prepared from green plum stones by using ultrasound assisted chemical activation with the use of potassium hydroxide. In order to compare the textural and hydrogen storage properties of the prepared zeolite/activated carbon, zeolite/graphene and zeolite/multiwalled carbon nanotube composites were prepared from commercial GR and MWCNT, respectively. The structures of the obtained AC and composite samples were characterized using BET, DFT, t-plot and SEM-EDX techniques. AC was synthesized with a relatively high BET surface area (1694 m2/g), total pore volume (1.023 cm3/g) and micropore volume (0.780 cm3/g). Zeolite/activated carbon composite (ZAC) has the highest surface area, total pore volume and micropore volume, and zeolite/multiwalled carbon nanotube composite (ZNT) has the highest average pore width (6.64 nm) among all composite samples. Hydrogen sorption processes have been performed for composite samples at −196 °C and ambient pressure. The relationship between hydrogen sorption capacities, BET surface areas and pore volumes of ZAC, ZGR and ZNT composites have been investigated. The hydrogen storage capacity of the ZAC was found to be 1.3 wt%. This value is 1.47 times the hydrogen storage capacity of AC and 4.16 times the hydrogen storage capacity of zeolite. Results indicated that ZAC is a promising adsorbent for hydrogen storage.

Synthesis of Na-LSX type zeolite from Polish fly ash

Synthesis of Na-LSX type zeolite from Polish fly ash

CO2-Induced Gate-Opening Adsorption on a Chabazite/Phillipsite Composite Zeolite Transformed from a Faujasite Zeolite Using Organic Structure-Directing Agent-Free Steam-Assisted Conversion.

Organic structure-directing agent-free steam-assisted conversion and Cs+ ion exchange were used to transform the faujasite (FAU)-type zeolite to the Cs+-type chabazite/phillipsite (CHA/PHI) composite zeolite. Compared with the pure PHI-type zeolite, the Cs+-type CHA/PHI zeolite showed gate-opening CO2 adsorption behavior and good thermal stability. In situ powder X-ray diffraction (PXRD) of the CO2 adsorption was measured to elucidate the mechanism for the gate-opening adsorption on the CHA/PHI zeolite. The Na+-type CHA/PHI zeolite did not show such adsorption behavior, and the PXRD pattern of the Na+-type CHA/PHI zeolite did not change with increasing CO2 partial pressure, which suggests that this unique adsorption behavior was caused by the PHI framework transition or Cs+ ions moving in both the CHA and PHI frameworks. Furthermore, in situ Fourier-transform infrared spectra of CO2 adsorption and CO2 breakthrough measurement on the Cs+-type CHA/PHI zeolite suggest that the CHA and PHI frameworks in the CHA/PHI zeolite shared eight-membered-ring windows and that CO2 molecules could easily diffuse from a CHA cage to a PHI framework. The ideal adsorbed solution theory was used to calculate the CO2/N2 separation selectivity for the Cs+-type CHA/PHI zeolite. At 298 and 318 K, the Cs+-type CHA/PHI composite zeolite showed a high CO2/N2 separation coefficient of >10,000 compared with other zeolites with high CO2 adsorption capacity. Furthermore, the CO2 working capacity was calculated for the Cs+-type CHA/PHI zeolite in both the pressure- and temperature-swing processes, and the results showed that the CHA/PHI composite zeolite could selectively separate CO2 from the CO2/N2 gas mixtures released from power generation plants operating using these processes.