Degree Of Dealumination Research Articles

The strong SDA/framework interactions and acidity study of high-silica LTA-type zeolites

The zeolite community spent 50 years in pursuing the synthesis of high-silica LTA-type zeolites, and ultimately succeeded with the pure-silica polymorph by applying specific structure-directing agents (SDA). The high-silica zeolite A has exhibited unique properties and strong potential to be applied as an adsorbent and catalyst in several novel processes. In the present study, the high-silica polymorphs of Si/Al ratios from 15 to ∞ were synthesized and subjected to thorough characterizations using multiple physicochemical methods. It has been revealed that there exists strong interactions between the organic SDAs and the framework. Therefore, removing the SDAs by calcination in air is difficult, and can only be done above 700 °C with a certain degree of framework dealumination. The retained framework structure shows connectivity defects and a unique combination of Brønsted and Lewis acidity. Using methanol-to-olefins (MTO) as a probe reaction, the catalytic performance of high-silica LTA-type zeolites has been evaluated. Compared to the well-studied CHA and MFI-type catalysts, high-silica zeolite A exhibited a shorter life-time and higher selectivity towards C4 olefins, while methane selectivity increased with the deactivation.

High-silica FAU zeolite through controllable framework modulation for VOCs adsorption under high humidity

Although FAU zeolites have been widely used as absorbents for volatile organic compounds (VOCs) removal, preparation of high-silica FAU zeolite to expand its application under high humidity is still a big challenge. Here, two high-silica FAU zeolites were successfully prepared through the controllable framework modulation strategy. By carefully matching the degrees of dealumination and Si-insertion, the zeolite (FAU-H) with an ultra-high SiO2/Al2O3 ratio of 957 was obtained. FAU-H exhibited similar high adsorption capacities of VOCs (e.g. m-xylene and toluene) under dry and humid conditions, more importantly, its adsorption capacity of m-xylene was 25% higher than the industrial high-silica FAU zeolite (HSZ-390HUA) from Tosoh Corporation. When the dealumination degree was mismatched with that of Si-insertion, imperfect FAU-M (SiO2/Al2O3 = 108) with the existence of some defect sites was obtained that becomes a good candidate for the adsorption removal of small VOCs molecules (e.g. isopropanol). The moderate interaction between VOCs and zeolite framework is proved a key factor for small molecules adsorption on basis of the DFT calculations. Moreover, the fitted kinetic models, desorption tests, and adsorption−desorption cycling tests proved the good regenerability of FAU-H and FAU-M. Therefore, the proposed high-silica FAU zeolites are promising adsorbents for VOCs removal.

Acid Resistance and Ion-Exchange Capacity of Natural Mixtures of Heulandite and Chabazite

The recovery and immobilization of metals from wastewater often occurs in an acidic environment that destroys the structure of adsorbents such as zeolites, which are porous crystalline aluminosilicates. The influence of hydrochloric acid solutions on the structure and properties of two natural mixtures of heulandite (HEU) and chabazite (CHA)—tuff from the Georgian Dzegvi-Tedzami deposit (HEU/CHA ≈ 8) and rock from the Kazakhstani deposit Chankanay (HEU/CHA≈1)—was studied by the X-ray energy dispersion spectra and diffraction patterns, as well as by adsorption of water, benzene, and nitrogen methods. It was found that acid-mediated dealumination, decationization, dissolution, and changes in systems of micro- and mesopores depend on the nature and chemical composition of the initial zeolites. It is concluded that, under the influence of acid, (i) zeolite micropores become accessible to relatively large molecules and ions, and the surface area of the adsorbent increases; (ii) the volume of mesopores decreases, and pores with a diameter of less than 4 nm become predominant; (iii) in terms of the degree of dealumination and dissolution rate, Kazakhstani zeolite is more acid-resistant than Georgian heulandite; and (iv) Kazakhstani zeolite retains a high ion-exchange capacity in an acidic environment, while Georgian heulandite, treated with dilute hydrochloric acid solutions, uptakes relatively high amounts of valuable silver, copper, and zinc.

Influence of Structural Characterization of C3S-C3A Paste under Sulfate Attack

The durability of C3S-C3A paste with varied C3A content (0%, 5%, 10%, and 20%) against sulfate attack at various attack ages (3 d, 7 d, 28 d, and 180 d) was investigated in this study through the examinations of corrosion product composition, Ca/Si and Al/Si of calcium-(aluminum)-silicate-hydrate (C-(A)-S-H) gel, formation and evolution of microstructure, migration and transformation of Al containing phase products, and pore structure. The results indicated that sulfate attack can promote the hydration reaction in C3S-C3A paste, thus accelerating the production of C-(A)-S-H gel in the paste. With the increase of C3A content, the acceleration effect becomes more significant. In addition, sulfate attack led to the dealumination and decalcification of C-(A)-S-H gel, resulting in the reduction of the gelling power of C-(A)-S-H gel. The degree of dealumination and decalcification of C-(A)-S-H gel increases with the increase of C3A content. At the same time, free Al and Ca promote the formation of expansive products such as ettringite and gypsum. Finally, under the action of sulfate, the pore characterization of C3S-C3A paste deteriorated, showing a decrease in specific surface area, cumulative pore volume and average pore diameter.

Modification of the Acidic and Textural Properties of HY Zeolite by AHFS Treatment and Its Coke Formation Performance in the Catalytic Cracking Reaction of N-Butene

Coke formation on n-butene cracking catalyst is the main reason for the reducing of its lifetime. To study the effects of acidity and textural properties on the coke formation process, a series of HY zeolite-type catalysts were prepared by ammonium hexafluorosilicate treatment (AHFS). NH3-TPD and Py-IR-TPD were used to systematically study the change law of zeolite acidity. It was found that with the increase of AHFS concentration, the acid density decreased, whereas the ratio of Brønsted acid to Lewis acid first increased and then decreased. Meanwhile, the percentage of Brønsted acid inside the supper cages increased and the strength of Brønsted acid increased with the degree of dealumination. Combined with in situ IR study on coke formation, the relationship between coking and acid site was revealed. It was found that the rate of coke formation on zeolites was affected by acid density, which is the rate of coke formation decreased with the decline of acid density. When the acid density remains at the same level, it was the acid strength that determined the coke formation rate—the stronger the acid strength, the faster the coke formation rate.

Iron mineral admixtures improve the sulfuric acid resistance of low-calcium alkali-activated cements

We investigated the sulfuric acid resistance of low-calcium alkali-activated materials (i.e., geopolymers) supplemented with an iron mineral admixture (i.e., hematite). Geopolymers without and with 5% hematite were produced at two alkali contents (Na:Al = 0.86 and 1.39). Acid degradation reactions were comprehensibly studied through three replenishes of acid. Results demonstrate that hematite is chemically active upon acid exposure yielding a short-term increase in acid neutralization capacity. Prolonged acid resistance was enhanced in high alkali content formulations with hematite. Acid exposure revealed minimal changes to mineralogy, molecular structure, and micro-scale porosity in these samples, resulting in less dealumination and silicon leaching. Thus, results indicate that the acid buffering capacity of geopolymers, specifically at higher alkali content formulations, increases due to the addition of hematite. The increased buffering capacity leads to lower degrees of dealumination of the N-A-S-H cementitious binder. These results are important as they may help explain the increased acid durability of alkali-activated materials synthesized from industrial aluminosilicate precursors (e.g., slag, fly ash, lateritic clays) that may contain iron minerals.

Dealumination of Nanosized Zeolites Y

The dealumination of nanosized zeolites is an important scientific problem, which should be solved to improve the activity of catalysts based on this zeolite in a broad range of heterogeneous catalytic reactions, particularly in commercial processes. However, the smaller the required size of the synthesized crystals, the lower the Si/Al ratio and the lower the degree of dealumination of this material can be achieved. In this study, the dealumination of zeolites Y with a crystal size of 50–1100 nm by treatment with ammonium hexafluorosilicate and steam heat treatment is discussed. It is shown that the dealumination with ammonium hexafluorosilicate is a “gentler” method in terms of structure preservation, whereas the dealumination by steam heat treatment provides a higher Si/Al ratio in the products; however, this method is inapplicable for crystals smaller than 500 nm, because it leads to the complete degradation of the structure. However, nanosized crystals can be dealuminated by treating with ammonium hexafluorosilicate. In this case, the degree of dealumination is close to 40%. A significant disadvantage of this method is the formation of a SiO2 film on the crystal surface; this feature substantially restricts the use of the ammonium hexafluorosilicate treatment in the synthesis of cracking catalysts.

Controllable structure of fibrous SiO2–ZSM-5 support decorated with TiO2 catalysts for enhanced photodegradation of paracetamol

Fibrous silica ZSM-5 (FSZ) was synthesized by a microemulsion method, and subsequent incorporation of 5 wt% of TiO2 onto it via electrolysis in varying concentrations of supporting electrolyte tetraethylammonium perchlorate (TEAP) gave TFSZ catalysts. The results verified that the degree of desilication and dealumination, for increasing the insertion of Ti ions into the FSZ framework, was directly proportional to the concentration of TEAP. In parallel, impurity levels of SiOTi bonds, defect sites and oxygen vacancies were formed and enhanced the photodegradation of paracetamol (PCT). However, excess SiOTi interactions, as a consequence of a higher degree of desilication and dealumination, decreased the number of oxygen vacancies and surface defects, resulting in a higher band gap energy. The sequence towards the degradation of PCT was in the following order: 0.2-TFSZ (96%) > 0.1-TFSZ (88%) > 0.3-TFSZ (67%). The kinetics study followed the pseudo-first-order Langmuir–Hinshelwood model. The response surface methodology revealed that the initial concentration of PCT, catalyst dosage and pH were the significant factors in the degradation of PCT. The 0.2-TFSZ maintained the photocatalytic activities after five runs and able to degrade other endocrine disrupting chemicals efficiently, indicating its potential use in the wastewater treatment of those chemicals.

Hierarchical ZSM-5 zeolite designed by combining desilication and dealumination with related study of n-heptane cracking performance

The effect of the basic (NaOH) and/or acid (citric acid and EDTA-2Na) treatment of ZSM-5 zeolite has been studied comparing the structural and acidic features and their catalytic performance in n-heptane cracking. The properties of the catalysts have been elucidated using XRD, N2 low-temperature sorption, 27Al and 29Si NMR, pyridine adsorbed FTIR, NH3–TPD, SEM and TEM analysis. The results showed that the degree of desilication and dealumination of ZSM-5 zeolites was greatly dependent on the agents. NaOH obviously created new mesopores on parent ZSM-5 zeolites by desilication. Citric acid contributed to the removal of nonframework Al species, causing the increase of micropore surface area. EDTA-2Na promoted desilication and simultaneously converted part of removed framework Al species into nonframework Al species. The treatment of ZSM-5 combined with those three agents was very effective to obtain a hierarchical structure with partial breakdown of the crystallites and high acid amounts of both Bronsted and Lewis acid sites. Catalytic tests showed that the post-treated ZSM-5 catalysts had higher activity and stability than parent ZSM-5 catalyst at the same reaction temperature. The synergetic effect of Bronsted acid and Lewis acid of ZSM-5 catalyst (Z5-ACE) probably facilitated n-heptane conversion, while more clean micropore and newly created mesopores facilitated the slight increase of olefin selectivity and suppressing the formation of coke deposition in its inherent micropores to some extent.

Structure and morphological properties of clinoptilolite modified by manganese dioxide

The chemical composition and morphological properties of сlinoptilolite-bearing materials modified by MnО2 have been studied using modern physical methods. Scanning electron microscopy, X-ray spectral microanalysis and optical reflection microscopy were applied. It was experimentally shown that MnО2-modified samples with high and low Si/Al ratios differed in such parameters as the layer thickness, the surface concentration, the degree of particle-surface dealumination, and also in morphological peculiarities of the MnО2-phase. This phase in the samples with high Si/Al ratios exhibited the structure formed by nanorods of 10–20nm in diameter and 500–700nm in length. These nanorods are intermeshed in the net which is cross-linked with the surface of clinoptilolite particles. The MnО2-modification of the samples was established to result in improving their mechanical and chemical strength as compared with the initial forms.

Tail gas catalyzed N2O decomposition over Fe-beta zeolite. On the promoting role of framework connected AlO6 sites in the vicinity of Fe by controlled dealumination during exchange

A novel route to prepare highly active and stable N2O decomposition catalysts is presented, based on Fe-exchanged beta zeolite. The procedure consists of liquid phase Fe(III) exchange at low pH. By varying the pH systematically from 3.5 to 0, using nitric acid during each Fe(III)-exchange procedure, the degree of dealumination was controlled, verified by ICP and NMR. Dealumination changes the presence of neighbouring octahedral Al sites of the Fe sites, improving the performance for this reaction. The so-obtained catalysts exhibit a remarkable enhancement in activity, for an optimal pH of 1. Further optimization by increasing the Fe content is possible. The optimal formulation showed good conversion levels, comparable to a benchmark Fe-ferrierite catalyst. The catalyst stability under tail gas conditions containing NO, O2 and H2O was excellent, without any appreciable activity decay during 70h time on stream. Based on characterisation and data analysis from ICP, single pulse excitation NMR, MQ MAS NMR, N2 physisorption, TPR(H2) analysis and apparent activation energies, the improved catalytic performance is attributed to an increased concentration of active sites. Temperature programmed reduction experiments reveal significant changes in the Fe(III) reducibility pattern with the presence of two reduction peaks; tentatively attributed to the interaction of the Fe-oxo species with electron withdrawing extraframework AlO6 species, causing a delayed reduction. A low-temperature peak is attributed to Fe-species exchanged on zeolitic AlO4 sites, which are partially charged by the presence of the neighbouring extraframework AlO6 sites. Improved mass transport phenomena due to acid leaching is ruled out. The increased activity is rationalized by an active site model, whose concentration increases by selectively washing out the distorted extraframework AlO6 species under acidic (optimal) conditions, liberating active Fe species.

Solid-state dealumination of zeolite Y: Structural characterization and acidity analysis by calorimetric measurements

Zeolite Y was dealuminated in the solid-state at several degrees (5, 10, 15 and 20%) using (NH4)2SiF6 as dealumination agent. The materials were heated to 80, 100, 120, 140, 160, 180 and 200 °C to investigate the best temperature at which the samples retain their crystallinity and acidity. The solids obtained were characterized by XRD, FTIR, TG/DTG, XRF, 27Al and 29Si MAS NMR and N2 physisorption. They were also subjected to pyridine adsorption and calorimetric experiments. Structural and textural results showed that lower temperatures (80 and 100 °C) and smaller degrees of dealumination (5 and 10%) maintained the zeolite crystallinity and increased its specific surface area, microporosity and mesoporosity. The study of the materials acidity indicated the presence of Brønsted acid sites with different strength, hydrogen bonding sites and Lewis sites originated from acid leaching. The calorimetric measurements showed higher enthalpy values for some of the dealuminated materials than for the parent zeolite. It also evidenced an increase for the number of acid sites between −160 and −140 kJ mol−1 and a reduction for the other sites, between −140 and −80 kJ mol−1.

Enhancement of indoles production and catalyst stability in thermo-catalytic conversion and ammonization of furfural with NH3 and N2 environments

Thermo-catalytic conversion and ammonization (TCC-A) is a novel and promising thermochemical conversion process for the direct production of N-heterocycles under NH3 atmosphere, which is similar to the pyrolysis technology through introducing exogenous nitrogen. Since NH3 served as the carrier gas and reactant, it played an important part in the process. The introduction of N2 into NH3 significantly enhanced the indoles production and catalyst stability in the TCC-A process of bio-derived furans. Under the optimized TCC-A conditions of furfural, NH3 being diluted by 25% N2 at 600°C with WHSV as 1.5h−1 and gas flow rate at 40ml/min, the carbon yields of N-containing chemicals and indoles reached 46.51% and 33.04%, respectively, which increased by 90.54% and 203.96% compared with those in pure NH3. Using furan derivatives as the feedstock, diluted NH3 also showed positive effect on the production of N-containing chemicals. Functional groups in the furan derivatives strongly affect the product distribution. It was found that the increase of indoles production from furfural was because the generation of 2-furonitrile via the side reaction pathway to form coke was inhibited by the dilution of NH3. The catalysts were tested via five reaction/regeneration cycles in pure and diluted NH3 atmosphere and characterized by N2 adsorption/desorption, XRD, XRF, NH3-TPD analyses and SEM. Compared in pure NH3, the catalysts in N2 diluted NH3 was more stable, which could be due to the lower degree of dealumination, structure damage, and acid site loss.

Production of γ-valerolactone from furfural by a single-step process using Sn-Al-Beta zeolites: Optimizing the catalyst acid properties and process conditions

A bifunctional Sn-Al-Beta zeolite which possesses isolated Lewis and Brønsted acid sites was prepared by a post-synthesis procedure and applied to the one-pot conversion of furfural to γ-valerolactone (GVL), a value-added chemical. Sn-Al-Beta was capable of catalyzing a cascade of the transfer hydrogenation and hydrolysis of furfural to GVL by the interplay of Lewis and Brønsted acid sites. The degree of dealumination and the tin-incorporation method largely influence the acid properties of the catalyst and the catalyst selectivity. A high yield of GVL up to 60% was obtained with Sn-Al-Beta 7 (Si/Sn=63 and Si/Al=473) at 180°C in 2-butanol.

Influence of partial dealumination of BEA zeolites on physicochemical and catalytic properties of AgAlSiBEA in H2-promoted SCR of NO with ethanol

The two-step postsynthesis method allows obtaining AlSiBEA zeolites with different degree of dealumination (Si/Al = 100 and 200). Physicochemical properties (crystallinity, hydroxyl group coverage, acidic sites and nature of silver species) of AlSiBEA and AgAlSiBEA were investigated by XRD, DR UV–vis, XPS, TEM and FT-IR with CO and pyridine as probe molecules. Catalytic properties of the zeolites were studied in the process of selective reduction of NO with ethanol in the presence of hydrogen in the reaction mixture. It was shown that level of H2-promoting effect on the SCR-process depends on the dealumination degree of Ag-containing BEA zeolites and greater effect is observed for the catalysts with higher concentration of Lewis acidic sites.

Dimethyl ether to olefins over dealuminated mordenite (MOR) zeolites derived from natural minerals

Recent development in shale gas production ensures the availability of cheap feedstock for petrochemicals. Dimethyl ether (DME) is one of the most promising derivatives from natural gas. In this work, we developed catalysts from low-cost natural minerals for the conversion of DME to olefins as one of the most important feedstocks for the petrochemical industry. The catalytic performance of a series of hierarchical mordenite zeolites derived from natural mineral by nitric acid dealumination was studied in the conversion of dimethyl ether (DME) to light olefin compounds. The degree of dealumination was strongly dependent on the treatment period. The DME conversion and olefins selectivity over these materials were investigated at 350 °C and 1 atm. The nitric acid dealumination has a positive effect on both DME conversion and ethylene to butylene selectivity. The fabrication of hierarchical zeolites from natural minerals will stimulate related studies to produce cost-effective catalysts derived from natural resources.

Impact of rare earth concentration and matrix modification in FCC catalysts on their catalytic performance in a wide array of operational parameters

Fluid catalytic cracking (FCC) is the most flexible process in the refining industry to convert residues from the atmospheric distillation of crude oils into liquefied petroleum gas (LPG), gasoline and light cycle-oil (LCO). In order to meet the varying demands for these fractions via changes in the catalytic properties of FCC catalysts, the effects of varying rare earth content and matrix modification are primarily utilized. Rare earth content variation changes the behaviour of the zeolitic part in FCC catalysts with regard to its response to the hydrothermal deactivation and contaminant metals during FCCU operation; the rare earth content primarily determines the rate of dealumination and structural collapse of the zeolite and thus the resulting equilibrium unit cell size. This parameter strongly correlates with the rates of hydrogen-transfer reactions, which in turn, have an impact on catalyst deactivation by coke formation. The degree of dealumination, structural collapse and coke-on-catalyst level affect the diffusion of the feed molecules into the zeolite and the residence time of the products in the zeolite.For the work presented here, FCC catalysts of different rare earth content were hydrothermally equilibrated in the absence and presence of contaminant metals. The interplay of the resulting structural properties with the catalytic performance was investigated by cracking a heavy vacuum gas-oil and a resid feed on these FCC catalysts at short catalyst time-on-stream and high temperature. With increasing rare earth content, the LCO selectivity decreased whereas gasoline and LPG selectivities run through maxima and minima respectively. The evaluation of the individual compounds in the gasoline fraction suggests that these observations could be attributed to mass transport limitations imposed by the structural changes of the zeolite as a function of rare earth content. However, the selectivity trade-offs which accompany the beneficial effects of increasing the rare earth levels on zeolite, as for example lower LCO selectivity, can be compensated by matrix modification. Thus all the advantages of high unit cell size catalysts such as high stability, high activity, low coke selectivity, low dry gas, high gasoline make of low olefinicity and gasoline sulfur reduction can be utilized. To put the findings into commercial perspective: amongst the criteria which impose constraints on FCCU operation are catalyst circulation, heat balance and from a legislative point of view the gasoline olefinicity. Therefore, comparisons of yields at constant catalyst-to-oil ratio, constant coke and constant product olefinicity are often more relevant to estimate commercial performance than the comparison of yields at constant conversion. Such an evaluation at constant catalyst-to-oil ratio shows substantial benefits in catalyst activity, bottoms cracking and gasoline yields at high rare-earth-on-FCC catalyst content whilst the desired reduction in gasoline olefinicity was achieved as well.

Hierarchy Brings Function: Mesoporous Clinoptilolite and L Zeolite Catalysts Synthesized by Tandem Acid–Base Treatments

Hierarchical clinoptilolite and L zeolites are prepared using optimized tandem dealumination–desilication treatments. The main challenge in the postsynthetic modification of these zeolites is the high Al content, requiring a tailored dealumination prior to the desilication step. For natural clinoptilolite, sequential acid treatments using aqueous HCl solutions were applied, while for L a controlled dealumination using ammonium hexafluorosilicate is required. Subsequent desilication by NaOH treatment yields mesopore surfaces of up to 4-fold (clinoptilolite, 64 m2 g–1; L, 135 m2 g–1) relative to the parent zeolite (clinoptilolite, 15 m2 g–1; L, 45 m2 g–1). A thorough characterization sheds light on the composition, crystallinity, porosity, morphology, coordination, and acidity of the modified clinoptilolite and L zeolites. It is elaborated that, besides the degree of dealumination, the resulting Al distribution is a critical precondition for the following mesopore formation by desilication. Adsorption exper...

Influence of the nitric acid treatment on Al removal, framework composition and acidity of BEA zeolite investigated by XRD, FTIR and NMR

Two different procedures were used to prepare dealuminated BEA zeolite. The first procedure realized in two steps consisted of first calcination of original tetraethylammonium (TEA) BEA(17) zeolite in air at 823K for 15h to remove organic template and then treatment of as resulted organic-free HAlBEA(17) zeolite with concentrated nitric acid solution for different times to remove part or all Al atoms. Two periods was distinguished in the removal of Al atoms from HAlBEA(17) framework during the first procedure. During initial period (up to 0.08h), the dealumination was very fast and 94% of Al was removed. This period corresponded to the easy removal of extra framework octahedral and framework tetrahedral aluminum from T3-T9 sites. In the second period (from 0.08 to 4h), the dealumination was much slower. It corresponded to a much more difficult removal of framework tetrahedral aluminum from T1 and T2 sites. The second procedure realized in one step consisted of direct treatment of original TEABEA zeolite with concentrated nitric acid solution to remove simultaneously organic template and Al atoms. To obtain partly or totally dealuminated BEA zeolite the treatment time was 0.08 and 4h respectively. The influence of the nitric acid treatment on Al removal, framework composition and acidity of BEA zeolite were investigated by XRD, FTIR and NMR. 2D 27Al 3Q MAS NMR allowed distinguishing two kinds of framework tetrahedral Al atoms (AlTd(2a) and AlTd(2b)) in BEA zeolite which relative amounts depended on the Si/Al ratio. The Brønsted and Lewis acidic centers were evidenced in dealuminated BEA zeolites by FTIR spectra of adsorbed pyridine and CO use as probe molecules. Their relative amounts depended on the degree of dealumination and procedure used for removal Al atoms.

Study of the effect of the acid dealumination on the physico-chemical properties of Y zeolite

The aim of the present work was to combine different physicochemical techniques, namely X ray diffraction, IR spectroscopy, and multinuclear (29Si and 27Al) solid-state NMR spectroscopy, to study the aluminum distribution and to determine the silicon–aluminum ordering in the Y-zeolite framework when the latter was submitted to acid leaching (HCl, HNO3, H2SiF6). It was shown that all acids were effective in removing Al from the framework. Moreover, the extra-framework Al extraction from the lattice was dependent on the nature and the concentration of the acid. After the dealumination treatment, different species (silanol nest, six-coordinated non-framework Al) were detected. The investigation showed that the breakdown of the parent Y-zeolite mainly depends on the degree of dealumination.