Treatment Of Zeolites Research Articles

Heat-acid treatment of georgian and kazakhstani natural heulandite-chabazites

The article considers the processes leading to a change in the structure and properties as a result of thermal treatment followed by acid treatment of natural zeolites from the Rkoni plot of the Tedzami deposit, Georgia, containing up to 80% of heulandite and 10% of chabazite, and from the Chankanay deposit, Kazakhstan, containing up to 70% of heulandite-chabazite mixture, selected for the creation of new bactericidal zeolite filter materials for purification and desinfection of water from various sources. The influence of preliminary heat treatment of the studied natural zeolites on weight loss, the processes of dealumination and decationization during subsequent acid treatment, and the adsorption properties of the final products is described. It has been shown that mass loss is minimal for amorphized samples, dealumination and the participation of sodium ions in the decationization process slow down significantly, and the adsorption capacity for water and benzene sharply decreases with increasing calcination temperature; all these effects are clearly pronounced for heulandite-containing Rkoni tuff, and for the more acid-resistant Chankanay zeolite they are manifested to a lesser extent.

Modulating acid sites in Y zeolite for valorisation of furfural to get γ-valerolactone.

Furfural is a biomass-derived platform molecule that can be converted into a variety of useful products. Catalysts having appropriate balance between Lewis and Brønsted acid sites are suitable for valorisation of furfural. Lewis acidic metal ion incorporated zeolites were studied for this purpose. However, incorporating Lewis acidic metal ions into an alumino-silicate framework of a zeolite is a cumbersome process. Hence, an attempt has been made in this work to modulate the acid sites of Y zeolite via thermal treatment to effect controlled dealumination and use it for valorisation of furfural using isopropyl alcohol, which is a cascade transformation. The thermal treatment of zeolites changed the distribution of acid sites and increased the weak plus moderate to strong acid site ratio. Among the thermally dealuminated Y, beta and mordenite zeolites, with SiO2/Al2O3 ratio 5.2, 25 and 20, only Y zeolite could yield γ-valerolactone, the final product of the aimed cascade transformation. Complete conversion of furfural and 52% γ-valerolactone yield could be achieved under the optimized conditions using NH4Y zeolite thermally dealuminated at 700 °C (TY700). The better catalytic activity of TY700 could be correlated to a combination different factors such as framework structure, suitable weak plus moderate to strong acid site ratio, presence of both penta-coordinated and octahedral Al sites and balance between Brønsted and Lewis acid sites.

Thermal treatment of Georgian, Kazakhstani and Armenian natural heulandite-clinoptilolites

The article considers the processes leading to a change in the structure and properties as a result of thermal treatment of natural zeolites from the Rkoni plot of the Tedzami deposit, Georgia, containing up to 80% of heulandite and 10% of chabazite, from the Chankanay deposit, Kazakhstan, containing up to 70% of heulandite-chabazite mixture, and from the Nor Kokhb deposit, Armenia, containing over 80% of clinoptilolite, selected for the creation of new bactericidal zeolite filter materials for purification and desinfection of water from various sources. The thermal stability of the samples is determined, the parameters of dehydration, amorphization and the effect of heat treatment on micro- and mesoporous systems of zeolites are established.

Application of Surfactant Modified Natural Zeolites for the Removal of Salicylic Acid—A Contaminant of Emerging Concern

This work aimed to test composites (surfactant modified zeolites prepared by treatment of natural zeolites—clinoptilolite (IZ CLI) and/or phillipsite (PHIL75)-rich tuffs with two different amounts of cationic surfactants: cetylpyridinium chloride (CPyCl) and Arquad® 2HT-75 (ARQ)) for the adsorption of salicylic acid (SA)—a common contaminant of emerging concern. Adsorption of SA was studied at different initial drug concentrations (in the range of 2–100 mg/L) in water solution. The Langmuir isotherm model showed the highest adsorption was achieved by bilayer composite of IZ CLI and CPyCl—around 11 mg/g. Kinetic runs were performed by using the initial drug concentration of 20 mg/L in the time interval from 0 to 75 min and pseudo-second order had good correlation with experimental data. The influence of the four different temperatures on the SA adsorption was also investigated and thermodynamic parameters suggested that the adsorption drug onto composites is an exothermic and nonspontaneous process, followed by the decrease of randomness at the solid/liquid interface during the adsorption. Zeta potential and Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) had been performed for the characterization of composites after adsorption of SA confirming the presence of the drug at composite surfaces.

Fluoride etching of AlZSM-5 and GaZSM-5 zeolites

The post-synthesis treatment of AlZSM-5 and GaZSM-5 zeolites by etching with buffer solution of ammonium fluoride and 0.25 M HF acid was carried out. The treatment is applied in order to obtain secondary pores in crystals and to provide easier access to the catalytically active zeolite centers. Hydrothermal synthesis of these zeolites was performed from systems containing tetrapropylammonium bromide as a template. The reaction parameters of synthesis conditions for both zeolites were optimized in order to obtain pure crystalline phases. The zeolites obtained were characterized by X-ray diffraction, IR spectroscopy, scanning electron microscopy, physical adsorption–desorption of nitrogen and solid-state NMR spectroscopy. It has been found that the result materials remain with high crystallinity while new mesoporous are created in their structure. The volume due to the presence of mesopores increases by up to 67% from the total volume, which is a drastic increase compared with the parent solids. The investigations with FTIR spectroscopy of low-temperature CO adsorption and solid-state NMR spectroscopy show that the treatment is slightly selective toward dissolution of heteroatom (aluminum or gallium). This phenomenon is observed for the first time for gallium-substituted zeolites. In order to study the influence of the metal atom in zeolite structure and the efficacy of the acid attack on the catalytic activity, the samples obtained were tested in reaction of m-xylene and toluene transformation.

Steam‐Induced Coarsening of Single‐Unit‐Cell MFI Zeolite Nanosheets and Its Effect on External Surface Brønsted Acid Catalysis

AbstractCommonly used methods to assess crystallinity, micro‐/mesoporosity, Brønsted acid site density and distribution (in micro‐ vs. mesopores), and catalytic activity suggest nearly invariant structure and function for aluminosilicate zeolite MFI two‐dimensional nanosheets before and after superheated steam treatment. Yet, pronounced reaction rate decrease for benzyl alcohol alkylation with mesitylene, a reaction that cannot take place in the zeolite micropores, is observed. Transmission electron microscopy images reveal pronounced changes in nanosheet thickness, aspect ratio and roughness indicating that nanosheet coarsening and the associated changes in the external (mesoporous) surface structure are responsible for the changes in the external surface catalytic activity. Superheated steam treatment of hierarchical zeolites can be used to alter nanosheet morphology and regulate external surface catalytic activity while preserving micro‐ and mesoporosity, and micropore reaction rates.

Methods for Modifying a ZSM-5 Type Zeolite to Alter the Activity of the System of Hydrogen Transfer Reactions in the Cracking of Lower Aliphatic Alcohols

The influence of the alkali treatment of ZSM-5 zeolites with a silica ratio of 30 within the NaOH : SiO2 molar ratio of 0 : 230, as well as the modification of a ZSM-5 zeolite with phosphorus in the range of 0–8 wt %, on the physicochemical properties and activity in hydrogen transfer reactions in the case of conversion of aliphatic alcohols has been studied. The alkali treatment of the zeolite leads to a decrease in the zeolite silica ratio and a growth in the hydrogen transfer coefficient in the case of transformation of aliphatic alcohols. The modification of the zeolite with phosphorus is equivalent to an increase in the zeolite silica ratio, which leads to a decrease in the hydrogen transfer coefficient.

Time-Resolved Dynamics of Intracrystalline Mesoporosity Generation in USY Zeolite

The treatment of zeolites with surfactants in alkaline media is an effective and versatile technique to impart intracrystalline well-defined mesoporosity in these materials. In this study, the dynamics of surface reconstruction that occurs during the treatment of USY zeolite by surfactant-templating was monitored in situ by atomic force microscopy. The development of surfactant-templated mesoporosity and the concurrent healing of defects that are characteristic of steamed zeolites occur in less than 1 h at room temperature, which emphasizes the low energy barriers needed to reorganize the crystalline structure of this zeolite. This transformation was also followed by X-ray diffraction, N2 adsorption, and transmission electron microscopy analysis of ultramicrotomed samples to confirm that the rapid formation of surfactant-templated mesoporosity and the reconstruction of the zeolite crystals occur not only on the surface of the zeolite but also homogeneously throughout the whole zeolite. This process involv...

The modification of aluminium content of natural zeolites with different composition

A series of natural zeolites with different compositions were modified by formation of hydrated aluminium oxide onto the zeolite structure after NaOH treatment of the natural zeolites. Natural and modified zeolites were characterized by XRD, SEM, N2 adsorption-desorption, FTIR, zeta potential and temperature-programmed desorption of ammonia (NH3-TPD). The treatment with NaOH and then aluminium loading significantly alter zeolite characteristics depending on zeolite composition and structure. The treatment with NaOH causes significant desilication and partial dealumination of the zeolites irrespective of their compositions. The presence of quartz and feldspar phases in the zeolites increases their stability towards alkali treatment. Aluminium introduction into the zeolites treated with NaOH leads to reorganisation of zeolite structure and surface characteristics. The introduction amount of aluminium is strongly related with zeolite composition that aluminium oxide phase is detected on zeolites undergone highly desilication with NaOH treatment. Both alkali treatment and aluminium loading dramatically alter distribution of acid sites in the zeolites that while alkali treatment increases mostly strong acid sites of zeolites, aluminium loading enhances weak and medium acid sites. Enhanced aluminium content of zeolites improved its manganese adsorption capacity depending on their composition.

Effects of alkali-treated hierarchical HZSM-5 zeolites on the production of aromatic hydrocarbons from catalytic fast pyrolysis of waste cardboard

The effects of hierarchical porous HZSM-5 zeolites on improving the yield of aromatic hydrocarbons during catalytic fast pyrolysis (CFP) of waste cardboard (WCB) were investigated. Desilicated HZSM-5 zeolites were successfully prepared by alkaline treatment using NaOH solution with different concentrations (0.1M–0.7M). A Py-GC/MS apparatus was adopted to carry out the CFP experiments. Results showed that under mild alkaline treatment (NaOH concentration ≤0.3M), the micropores and crystallinity of HZSM-5 were preserved, while the mesopores and weak acid sites increased. The desilicated HZSM-5 zeolites increased the total yield of pyrolytic products from WCB. With regard to the product distribution, carbon yield of aromatics increased dramatically, while that of sugars, carbonyl compounds and other oxygenates decreased obviously. Specifically, HZSM-5 treated by 0.3M NaOH solution (HZ-0.3M) was proved to be the most effective catalyst, resulting in a 44% increase of carbon yield of aromatics and an 82% increase of carbon yield of BTX (benzene, toluene and xylenes) comparing to the parent HZSM-5. In addition, the amount of coke deposited on HZ-0.3M decreased by 29% compared to that on the parent HZSM-5. The retained micropores and the created mesopores of desilicated HZSM-5 zeolites contributed to the enhancement of catalytic performance. However, harsh alkaline treatment of HZSM-5 zeolites (NaOH concentration ≥0.5M) resulted in the grave collapse of zeolitic crystallinity and the obvious loss of micropores. As a result, the catalytic activities of HZSM-5 zeolites had been weakened.

Effect of Silica Alumina Ratio and Thermal Treatment of Beta Zeolites on the Adsorption of Toluene from Aqueous Solutions

The adsorption of toluene from aqueous solutions onto hydrophobic zeolites was studied by combining chromatographic, thermal and structural techniques. Three beta zeolites (notated BEAs, since they belong to BEA framework type), with different SiO2/Al2O3 ratios (i.e., 25, 38 and 360), before and after calcination, were tested as adsorbents of toluene from aqueous media. This was performed by measuring the adsorbed quantities of toluene onto zeolites in a wide concentration range of solute. The adsorption data were fitted with isotherms whose models are based on surface heterogeneity of the adsorbent, according to the defective structure of beta zeolites. The thermal treatment considerably increases the adsorption of toluene, in the low concentration range, on all BEAs, probably due to surface and structural modifications induced by calcination. Among the calcined BEAs, the most hydrophobic zeolite (i.e., that with SiO2/Al2O3 ratio of 360) showed the highest binding constant, probably due to its high affinity for an organophilic solute such as toluene. The high sorption capacity was confirmed by thermogravimetric analyses on BEAs, before and after saturation with toluene.

Thermal Transformation of NH4-Clinoptilolite to Mullite and Silica Polymorphs

Clinoptilolite is a natural zeolite used for the abatement of ammonium in the treatment of urban wastewater. By considering that mullite was obtained through thermal treatment of NH4-exchanged synthetic zeolites, this work aimed to evaluate if this phase can be obtained from NH4-clinoptilolite. A material containing about 90 wt % of clinoptilolite, prepared using a Sardinian zeolite-rich rock, was NH4-exchanged and subjected to treatments up to 1200 °C. After dehydration, de-ammoniation, and dehydroxylation processes, the clinoptilolite structure collapsed at 600 °C. An association of mullite, silica polymorphs, and glass, whitish in color, was obtained for treatments between 1000 and 1200 °C. The higher degree of crystallinity was reached after a 32 h heating at 1100 °C: mullite 22 wt %, cristobalite 59 wt %, tridymite 10 wt %, glass 9 wt %. It is possible to speed up the kinetics of the transformation by increasing the temperature to 1200 °C, obtaining the same amount of mullite in 2 h, but increasing the residual amorphous fraction (16 wt %). These results indicate that NH4-clinoptilolite could represent a raw material of potential interest in the ceramic field, in particular in the production of acid refractory, opening scenarios for a possible reuse of clinoptilolite-based exchangers employed in ammonium decontamination.

Adsorption of the mycotoxin zearalenone by clinoptilolite and phillipsite zeolites treated with cetylpyridinium surfactant

In this study, organozeolites were prepared by treatment of the natural zeolites (clinoptilolite and phillipsite) with cetylpyridinium chloride (CP) equivalent to 50 and 100% of their external cation exchange capacities (ECEC). Organoclinoptilolites (ZCPs) and organophillipsites (PCPs) were characterized by FTIR spectroscopy, thermal analysis, determination of the point of zero charge and zeta potential. Adsorption of zearalenone (ZEN) by ZCPs and PCPs at pH 3 and 7 was investigated. Results showed that adsorption of ZEN increases with increasing amounts of CP at the zeolitic surfaces for both ZCPs and PCPs but the adsorption mechanism was different. Adsorption of ZEN by ZCPs followed a linear type of isotherm at pH 3 and 7 while ZEN adsorption by PCPs showed non linear (Langmuir and Freundlich) type of isotherm at both pH values. Different interactions between the ZEN molecule (or ion) and ZCPs and PCPs occurred: partition (linear isotherms) and adsorption in addition to partition (non linear isotherms), respectively. For the highest level of organic phase at the zeolitic surfaces, the maximum adsorbed amount of ZEN was 5.73mg/g for organoclinoptilolite and 6.86mg/g for organophillipsite at pH 3. Slightly higher adsorption: 6.98mg/g for organoclinoptilolite and 7.54mg/g for organophillipsite was achieved at pH 7. The results confirmed that CP ions at both zeolitic surfaces are responsible for ZEN adsorption and that organophillipsites are as effective in ZEN adsorption as organoclinoptilolites.

Treatment of Natural Zeolites for Increasing the Sorption Capacity

This article describes the results ofthe research on determination of activity and sorption capacity of modified zeolites. Activation processes of sorbents were compared including thermal dehydration and ion-plasma treatment of zeolites. Mineralogical composition of investigated zeolites as well as the results of ion-plasma treatment on the structure of natural zeolites are presented. The obtained results have shown high effectiveness of ion-plasma treatmentof sorbents compared with thermal treatment method.

Adsorption and Thermal Stabilization of Pb2+ and Cu2+ by Zeolite

In recent years, zeolite has been proven to be a cost-effective adsorbent for treating wastewater containing heavy metal ions. However, few studies have investigated the subsequent treatment of metal-laden zeolites after adsorption, which may become a source of secondary pollution if not properly dealt with. To fill the knowledge gap, the adsorption behavior of Pb2+ and Cu2+ on zeolite was examined in the present study. The adsorption process was fast and reached equilibrium within 60 min, with adsorption data fitted better with the Langmuir equation than the Freundlich equation. After thermal treatment for metal-adsorbed zeolites, X-ray diffraction results showed that Pb2+ and Cu2+ adsorbed on zeolites can be readily stabilized into PbAl2Si2O8 and CuAl2O4, and the best temperatures for formation of PbAl2Si2O8 and CuAl2O4 were 950 and 1000 °C, respectively. Finally, a prolonged leaching test (at pH 2.9 for 22 d) demonstrated that the Pb2+ and Cu2+ concentrations in the leachate of calcined samples were ap...

Effect of the nature of promoters, the alkaline treatment of ZSM-5 zeolites, and the method of their synthesis on the conversion of C3–C4 alkanes

The zinc and chromium copromotion of an industrial ZSM-5 zeolite and its structural analogues synthesized under laboratorial conditions by the hydrothermal and microwave-assisted hydrothermal methods increases the selectivity towards the formation of aromatics from a mixture of C3-C4 alkanes. The formation of additional mesopores in the structure of ZSM-5 also improves the selectivity to aromatic hydrocarbons.

Dissolution and Absorption: A Molecular Mechanism of Mesopore Formation in Alkaline Treatment of Zeolite

With the aim to optimize alkaline treatment of zeolites to obtain hierarchical zeolites, dissolution and absorption mechanisms relevant to mesopore formation were investigated at an atomistic scale by density functional calculations. In the dissolution processes, dealumination is energetically more favorable than desilication, though both processes can occur. The dissolved Al species prefer to be absorbed back onto zeolite surfaces whereas the dissolved Si species tend to aggregate in solution. The dissolution process promotes but the absorption process hampers the mesopore formation, laying foundation for understanding the mesoporosity influenced by the variations of zeolite framework and solution.

Liquid and Gaseous Fuel from Waste Plastics by Sequential Pyrolysis and Catalytic Reforming Processes over Indonesian Natural Zeolite Catalysts

In this study, the performance of several differently treated natural zeolites in a sequential pyrolysis and catalytic reforming of plastic materials i.e. polypropylene (PP) and polystyrene (PS) were investigated. The experiments were carried out on two stage reactor using semi-batch system. The samples were degraded at 500°C in the pyrolysis reactor and then reformed at 450°C in the catalytic reformer. The results show that the mordenite-type natural zeolites could be used as efficient catalysts for the conversion of PP and PS into liquid and gaseous fuel. The treatment of natural zeolites in HCl solution showed an increase of the surface area and the Si/Al ratio while nickel impregnation increased the activity of catalyst. As a result, liquid product was reduced while gaseous product was increased. For PP, the fraction of gasoline (C 5 -C 12 ) increased in the presence of catalysts. Natural zeolite catalysts could also be used to decrease the heavy oil fraction (>C 20 ). The gaseous products were found that propene was dominated in all conditions. For PS, propane and propene were the main components of gases in the presence of nickel impregnated natural zeolite catalyst. Propene was dominated in pyrolysis over natural zeolite catalyst. The high quality of gaseous product can be used as a fuel either for driving gas engines or for dual-fuel diesel engine.

Germanosilicate Precursors of ADORable Zeolites Obtained by Disassembly of ITH, ITR, and IWR Zeolites

Structure transformation of germanosilicate zeolites ITH, ITR, and IWR containing hydrolytically unstable interlayer Ge–O bonds was investigated and is related to the conditions of acidic treatment (i.e., concentration of hydrochloric acid, temperature, duration). The disassembly of ITH (Si/Ge = 2.5), ITR (Si/Ge = 2.4), and IWR (Si/Ge = 6.9) zeolites under appropriate acidic treatment was demonstrated. Low-concentration acid solutions (e.g., 0.01 M HCl) and low temperatures favor the hydrolysis of the zeolites under study. The chemical composition of the parent zeolites strongly influences the efficiency of hydrolysis. For zeolites having sufficient fraction (ca. 50%) of Ge in D4R units (Si/Ge ≤ 6 for ITH and IWR, Si/Ge ≤ 3.7 for ITR), transformation into layered materials (two-dimensional zeolites) was successful while the lowering of Ge concentration resulted in only a partial separation of the ITH and ITR crystalline layers. The acidic treatment of medium-pore ITR and ITH zeolites with HCl at ambient temperature for 24 h is optimal for selective cleavage of almost all interlayer Ge–O bonds, while transformation of large-pore IWR zeolite into layered material was observed even after only 5 min of the treatment. These results evidence the general applicability of the ADOR mechanism for the synthesis of new zeolites.

Hierarchical Zeolites by Desilication: Occurrence and Catalytic Impact of Recrystallization and Restructuring

The manifestation of zeolite recrystallization and the formation of amorphous aluminosilicate species during desilication are examined to better understand the properties of alkaline-treated hierarchical zeolites and their catalytic performance. This is achieved using a systematic experimental strategy, starting from treating the filtrate of alkaline-treated silicalite-1 in the presence of various external additives. No recrystallization is evidenced upon addition of tetrapropylammonium (TPA+) and/or aluminum hydroxide ions [Al(OH)4–], confirming the low probability of zeolite nucleation and/or growth during desilication. Conversely, ordered mesoporous materials (OMMs) form upon addition of cetyltrimethylammonium (CTA+) to the filtrate. By using other silicon sources, i.e., tetramethyl orthosilicate or the organosilane dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium, we verify the facile formation of amorphous materials during alkaline treatment of USY zeolites in the presence of hydrophobic micelle-forming alkyl moieties. A systematic characterization by X-ray diffraction, transmission electron microscopy, N2 and Ar adsorption, inductively coupled plasma optical emission spectroscopy, and Fourier transform infrared spectroscopy of pyridine adsorbed, demonstrates that zeolites exposed to base solutions containing CTA+ display weaker zeolitic properties, compared to those prepared using TPA+, and should be considered as hierarchical zeolite/OMM composites. Catalytic tests in the alkylation of toluene with isopropyl alcohol or benzyl alcohol evidence that CTA+-derived composites do not outperform the conventional USY zeolite. Only the hierarchical USY zeolite prepared by alkaline treatment in the presence of TPA+ yielded a superior catalytic performance.