Small Zeolite Research Articles

Zeolite Nanocrystals (MOR, EU-1, and ZSM-12) Synthesized Using a Versatile Diquaternary Ammonium Template as Robust Catalysts

Nanocrystals of zeolites with shortened diffusional pathways compared to bulk counterparts are attractive catalysts, but their direct synthesis often remains challenging and expensive. Here, we describe the utility of p-phenylenedimethylene–bis(trimethylammonium) dichloride, an organic diquaternary ammonium compound that can be easily prepared, as an effective organic structure-directing agent (OSDA) for obtaining several zeolites composed of agglomerated nanocrystals. By modifying the gel composition (NaOH/Si and Si/Al ratios) and crystallization time, synthesis can be tuned to obtain mordenite, EU-1, and ZSM-12 zeolites. 13C NMR spectra of the occluded OSDA reveal subtle differences in host–guest interactions between the OSDA and the respective zeolites, which derives from the flexibility of the OSDA. The relatively strong interaction between the OSDA and inorganic aluminosilicate precursor species during the induction period explains how small zeolite nanocrystals are obtained. Nanosized EU-1 and ZSM-12 significantly outperform their corresponding bulk counterparts as acid catalysts in the methanol-to-hydrocarbons reaction and the alkylation of benzene with benzyl alcohol, respectively.

Effect of Low Zeolite Doses on Plants and Soil Physicochemical Properties.

Thousands of tons of zeolitic materials are used yearly as soil conditioners and components of slow-release fertilizers. A positive influence of application of zeolites on plant growth has been frequently observed. Because zeolites have extremely large cation exchange capacity, surface area, porosity and water holding capacity, a paradigm has aroused that increasing plant growth is caused by a long-lasting improvement of soil physicochemical properties by zeolites. In the first year of our field experiment performed on a poor soil with zeolite rates from 1 to 8 t/ha and N fertilization, an increase in spring wheat yield was observed. Any effect on soil cation exchange capacity (CEC), surface area (S), pH-dependent surface charge (Qv), mesoporosity, water holding capacity and plant available water (PAW) was noted. This positive effect of zeolite on plants could be due to extra nutrients supplied by the mineral (primarily potassium—1 ton of the studied zeolite contained around 15 kg of exchangeable potassium). In the second year of the experiment (NPK treatment on previously zeolitized soil), the zeolite presence did not impact plant yield. No long-term effect of the zeolite on plants was observed in the third year after soil zeolitization, when, as in the first year, only N fertilization was applied. That there were no significant changes in the above-mentioned physicochemical properties of the field soil after the addition of zeolite was most likely due to high dilution of the mineral in the soil (8 t/ha zeolite is only ~0.35% of the soil mass in the root zone). To determine how much zeolite is needed to improve soil physicochemical properties, much higher zeolite rates than those applied in the field were studied in the laboratory. The latter studies showed that CEC and S increased proportionally to the zeolite percentage in the soil. The Qv of the zeolite was lower than that of the soil, so a decrease in soil variable charge was observed due to zeolite addition. Surprisingly, a slight increase in PAW, even at the largest zeolite dose (from 9.5% for the control soil to 13% for a mixture of 40 g zeolite and 100 g soil), was observed. It resulted from small alterations of the soil macrostructure: although the input of small zeolite pores was seen in pore size distributions, the larger pores responsible for the storage of PAW were almost not affected by the zeolite addition.

Intracrystalline Transport Barriers Affecting the Self-Diffusion of CH4 in Zeolites |Na12|-A and |Na12-xKx|-A.

Carbon dioxide must be removed from biogas or natural gas to obtain compressed or liquefied methane, and adsorption-driven isolation of CO2 could be improved by developing new adsorbents. Zeolite adsorbents can select CO2 over CH4, and the adsorption of CH4 on zeolite |Na12-xKx|-A is significantly lower for samples with a high K+ content, i.e., x > 2. Nevertheless, we show, using 1H NMR experiments, that these zeolites adsorb CH4 after long equilibration times. Pulsed-field gradient NMR experiments indicated that in large crystals of zeolites |Na12-xKx|-A, the long-time diffusion coefficients of CH4 did not vary with x, and the upper limit of the mean-square displacement was about 1.5 μm, irrespective of the diffusion time. Also for zeolite |Na12|-A samples of three different particle sizes (∼0.44, ∼2.9, and ∼10.6 μm), the upper limit of the mean-square displacement of CH4 was 1.5 μm and largely independent of the diffusion time. This similarity provided further evidence for an intracrystalline diffusion restriction for CH4 within the medium- and large-sized zeolite A crystals and possibly of clustering and close contact among the small zeolite A crystals. The upper limit of the long-time diffusion coefficient of adsorbed CH4 was (at 1 atm and 298 K) about 10-10 m2/s irrespective of the size of the zeolite particle or the studied content of K+ in zeolites |Na12-xKx|-A and |Na12|-A. The T1 relaxation time for adsorbed CH4 on zeolites |Na12-xKx|-A with x > 2 was smaller than for those with x < 2, indicating that the short-time diffusion of CH4 was hindered.

Flux and salt rejection enhancement of polyvinyl(alcohol) reverse osmosis membranes using nano-zeolite

Zeolite based membranes have been extensively studied over the past decade for enhanced reverse osmosis (RO) performances. In this study, poly vinyl alcohol (PVA)-networked cellulose (NC) membranes incorporated with nano zeolite-Y were prepared through a facile slip casting approach using various nano zeolite-Y loadings from 0.05 to 1.0 wt%. The nano zeolite was prepared through a unique ball milling process. Membrane hydrophilicity was seen to increase with increase in zeolite loading, while improved tensile strength (8.7 MPa) and tensile modulus (67 MPa) were obtained on small zeolite additions of 0.05 wt%. No prominent peak shifts were observed in differential scanning calorimeter (DSC) testifying to the thermal stability of the membranes.Membranes were tested for RO using 25,000 mg/L NaCl solution. Optimum RO performance was achieved for 0.5 wt% nano zeolite registering a salt rejection (Rs) of 99.52% with a flux increase of 34.2% compared to the bare PVA-NC membranes. Thus, addition of nano-Y to the polymer matrix provides preferential water pathways which facilitate water flow through the membrane. In addition, the irregular crystal morphology of the nano-Y, the size exclusion principle and the ion exchange mechanism provided a high salt rejection for the PVA-NC-nano Y membranes.

Synthesis of potassium-type zeolites by the reverse-micelle method with microwave heating

Potassium-type zeolites (K-zeolites) containing a chabazite phase were synthesized using the reverse-micelle method with microwave heating. The reverse micelle acts as a space-confining reactor, and treatment by microwave irradiation provides fast, homogeneous, and preferential heating of the aqueous phase where the zeolites are synthesized. As control experiments, K-zeolites were also synthesized using the reverse-micelle method with external oil bath heating, the conventional method with microwave heating, and the conventional method with external heating. Based on dynamic light scattering and scanning electron microscopy analyses, we confirmed that small zeolite crystals could be successfully prepared using the reverse-micelle method. We also found that the crystallization rate of zeolites obtained using the reverse-micelle microwave heating method was larger than those obtained using other methods. Furthermore, we evaluated the adsorption performance of the synthesized zeolites via ammonium adsorption experiments. The rates of ammonium adsorption and the maximum adsorption capacities of the zeolites obtained by the reverse-micelle method were larger than those of the zeolites obtained by the conventional method.

Study of Confinement and Catalysis Effects of the Reaction of Methylation of Benzene by Methanol in H-Beta and H-ZSM-5 Zeolites by Topological Analysis of Electron Density

In this work we studied the host–guest interactions between confined molecules and zeolites and their relationship with the energies involved in the reaction of methylation of benzene by methanol in H-ZSM-5 and H-Beta zeolites employing density functional theory (DFT) methods and the quantum theory of atoms in molecules. Results show that the strength of the interactions related to adsorption and coadsorption processes is higher in the catalyst with the larger cavity; however, the confinement effects are higher in the smaller zeolite, explaining, from an electronic viewpoint, the reason why the stabilization energy is higher in H-ZSM-5 than in H-Beta. The confinement effects of the catalyst on the confined species for methanol adsorption, benzene coadsorption, and the formed intermediates dominate this stabilization. For the transition state (TS), the stability of the TS is achieved due to the stabilizing effect of the surrounding zeolite framework on the formed carbocationic species (CH3+) which is highe...

Perlite templated Y zeolite assembly and its potential as an efficient catalytic cracking catalyst

Monolayer Y zeolite crystal morphology was obtained by hydrothermal zeolitization of expanded perlite, perlite functions as template and the only aluminum source. Y zeolite crystals with size of 200–300 nm are growing on surface of perlite. The resultant composition NaY/perlite shows microporous surface area of 538 m2/g in contrast to 0 m2/g for expanded perlite, and it has a remarkable lower bulk density characteristic compared to usual NaY zeolite. Furthermore, the morphology of NaY/perlite is unchanged after steaming and heat treatment. The lattice collapse temperature of NaY/perlite is 64 K higher than NaY. The USY/perlite zeolite prepared from NaY/perlite shows similar monolayer dispersion morphology as NaY/perlite. It was shaped by spray drying to microsphere catalyst, catalytic cracking evaluation of heavy oil showed a significantly improvement of gasoline yield compared to the reference, it is attributed to efficient diffusion of reactant and desired product which is benefited from small zeolite crystal and high porosity features of the catalyst.

Ultrasonic/microwave synergistic synthesis of well-dispersed hierarchical zeolite Y with improved alkylation catalytic activity

Well-dispersed hierarchical zeolite Y, structure-directed by ionic liquid 1-methyl-3-(3'-(trimethoxysilyl) propyl) imidazolium chloride, was synthesized for the first time using a novel ultrasonic/microwave synergistic synthe- sis (UMSS). The time required for the synthesis of zeolite Y by UMSS method was remarkably reduced to 6 h instead of 24 h under conventional hydrothermal conditions. The structures of all samples were characterized by XRD, BET, FT-IR, SEM and TEM. The results clearly demonstrated that the UMSS is a promising strategy to achieve zeolite Y with improved crystallinity, large BET surface area, bulky mesopore volume, well-dispersed morphology, small zeolite nanoparticle. The catalytic activity of hierarchically micro-mesoporous zeolite Y was evaluated by using the alkylation of o-xylene with styrene. Mesoporous zeolite Y synthesized by UMSS method showed significantly higher catalytic activity, stability and reusability, compared with conventional hydrothermal synthesis. It might be ascribed to its large mesoporous volume, small crystal nanoparticle and high surface area, minimizing the diffusion length as the reactant molecules diffuse into the pores, and correspondingly the products diffuse out of zeolites. This study suggests that UMSS method is a good alternative for the synthesis of micro-mesoporous zeolite Y, which may be of remarkable ben- efit for industrial applications.

Direct dimethyl ether synthesis from syngas on copper–zeolite hybrid catalysts with a wide range of zeolite particle sizes

This paper reports on direct dimethyl ether synthesis from syngas on hybrid bifunctional copper–zeolite catalysts. Both laboratory synthesized and commercial zeolites were used in this work. The catalyst performance is evaluated under pressure in a continuous fixed bed milli-reactor. The relationships between zeolite particle sizes, acidity and catalytic performance of the hybrid catalysts in dimethyl ether synthesis have been studied. The catalysts and catalyst precursors were characterized using a wide range of characterization techniques: nitrogen adsorption–desorption measurements, X-ray diffraction, 27Al NMR, scanning electron microscopy, transmission electron microscopy and Fourier transform infrared spectroscopy with adsorbed molecular probes.It is found that the reaction rate in direct dimethyl ether synthesis is strongly affected by the sizes of zeolite particles. The hybrid catalysts containing small individual nanosized zeolite particles (60–100nm) were much active than their counterparts with intergrown crystal agglomerates. The phenomenon is interpreted in terms of enhanced transport of methanol from the copper catalyst to the acid sites in the small zeolite particles with a shift of the thermodynamic equilibrium. The catalyst deactivation was attributed to copper sintering in the presence of the acid sites on the external surface of zeolites. It is established that the catalyst deactivation is less significant with the catalysts containing ZSM-5 zeolites with lower concentration of acid sites on the zeolite external surface. A new methodology to enhance the catalytic performance and stability of copper–zeolite hybrid catalysts for direct dimethyl ether synthesis is proposed.

Cost-effective two-stage varying-temperature rapid crystallization of zeolite T and SAPO-34

In this paper, zeolite T and SAPO-34 have been synthesized by two-stage varying temperature crystallization method (TVTC method). The feature of this method is dividing the hydrothermal process into two steps. The first step is lower temperature treatment which is favorable for the crystals nucleation and the second step is higher temperature treatment which is helpful to the crystals growth. The advantage of this method is that it greatly reduces the crystallization time and particle size compared to conventional constant temperature crystallization method (CCTC method). The influences of different initial and final temperatures on the zeolite crystallinity, morphology and particle size have been investigated in detail. Ultimately, the optimal crystallization conditions of zeolite T and SAPO-34 using this method have been summarized. The samples prepared with TVTC method and CCTC method also have been contrasted. With TVTC method, the synthesis time of zeolite T crystals is reduced from 7 days to 4 days and the synthesis time of SAPO-34 crystals is reduced from 48h to 16h. Furthermore, the sample prepared by TVTC method has higher crystallinity compared with the sample prepared by CCTC method. The particle size distributions of samples prepared by two methods have strongly confirmed that TVTC method is beneficial to form uniform and small zeolite particles. This paper provides an efficient and economical route to the industrial preparation of zeolite T and SAPO-34.

Synthesis of hierarchical zeolite Beta with low organic template content via the steam-assisted conversion method

We report the synthesis of hierarchical zeolite Beta with low organic template (tetraethylammonium hydroxide, TEAOH) content by the steam-assisted conversion (SAC) method. Neither zeolite seeds nor the secondary mesoporogen were required. Only a bit amount of organic template (denoted as TEAOH/SiO2 ratio=0.06) was used to obtain highly crystalline zeolite Beta, which was remarkably lower than the reported lowest value (0.10). Physicochemical properties of the resulting samples were investigated by comprehensive characterizations including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, solid state 27Al MAS NMR spectra, nitrogen adsorption–desorption, X-ray fluorescence, temperature-programmed desorption of ammonia and infrared spectra of pyridine adsorption. These characterization results showed that the SAC method led to hierarchical crystalline zeolite Beta aggregates assembled by 20–40nm nanosized crystals with controllable SiO2/Al2O3 ratios among 29–47 by varying the compositions of synthetic gels with the Na2O/SiO2 ratio of 0.12 and the H2O/dry gelratios at 0.20–0.30. These zeolite Beta aggregates possessed large external surface area (158–180m2/g) and mesoporous volume (0.27–0.30cm3/g) resulted from the formation of intercrystalline mesopores and of the small zeolite crystal sizes. The obtained hierarchical zeolite Beta showed 41.2% conversion in the esterification reaction of levulinic acid with ethanol and four catalytic runs without obvious decrease in conversion, which were better than those on the zeolite Beta samples from the conventional hydrothermal synthesis. This was due to the promotion of the accessibility of reactants to the acid sites distributed on the external surface of zeolite nanocrystals and of the prominent diffusion in intercrystalline mesopores.

2D Surface Structures in Small Zeolite MFI Crystals

Utilization of new hierarchical zeolites comprised of small crystallites (<50 nm) provides enhanced processing rates in separation and catalytic applications. However, molecular permeation through surface pores in small zeolite crystals has been shown to control the overall rate, resulting in apparent site-to-site intracrystalline kinetics that vary by as much as three orders of magnitude. In this work, the external surface of small zeolite MFI crystals was characterized by combining experimental kinetics and molecular simulation to evaluate the hypothesis of a two-dimensional distribution of surface pores that are either open or closed (i.e., fraction, popen). The movement of benzene through the MFI lattice and surface was evaluated with a discrete space kinetic Monte Carlo algorithm with varying particle sizes (1.0 nm ≤ R ≤ 640 nm) and fraction of surface pore openings (10–4 < popen < 100). Introduction of randomly distributed surface pore blockages was shown to increase the molecular path length for adsorbates exiting the particle while maintaining a constant apparent activation energy, consistent with additional molecular motion near the internal surface. Comparison of the dimensionless surface barrier (λ = τSurface/τBulk) obtained by simulation to experimental measurements (zero length chromatography) for silicalite-1 particles (62 nm to 3 μm, 50–110 °C) reveals that the vast majority (>99.9%) of surface pores must be blocked (popen < 10–3) to justify the observed surface permeation rate of hydrocarbon adsorbates.

Fabrication of zeolite/polymer multilayer composite membranes for carbon dioxide capture: Deposition of zeolite particles on polymer supports

Membranes, due to their smaller footprint and potentially lower energy consumption than the amine process, offer a promising route for post-combustion CO2 capture. Zeolite Y based inorganic selective layers offer a favorable combination of CO2 permeance and CO2/N2 selectivity, membrane properties crucial to the economics. For economic viability on large scale, we propose to use flexible and scalable polymer supports for inorganic selective layers. The work described in this paper developed a detailed protocol for depositing thin zeolite Y seed layers on polymer supports, the first step in the synthesis of a polycrystalline zeolite Y membrane. We also studied the effects of support surface morphology (pore size and surface porosity) on the quality of deposition and identified favorable supports for the deposition. Two different zeolite Y particles with nominal sizes of 200nm and 40nm were investigated. To obtain a complete coverage of zeolite particles on the support surface with minimum defects and in a reproducible manner, a vacuum-assisted dip-coating technique was developed. Images obtained using both digital camera and optical microscope showed the presence of color patterns on the deposited surface which suggested that the coverage was complete. Electron microscopy revealed that the particle packing was dense with some drying cracks. Layer thickness with the larger zeolite Y particles was close to 1μm while that with the smaller particles was reduced to less than 0.5μm. In order to reduce drying cracks for layers with smaller zeolite Y particles, thickness was reduced by lowering the dispersion concentration. Transport measurement was used as an additional technique to characterize these layers.

Mechanism of seeding in hydrothermal synthesis of zeolite Beta with organic structure-directing agent-free gel

The organic structure-directing agent-free synthesis of zeolite Beta was carried out using several zeolite Beta seeds that differed in SiO2/Al2O3 ratio and crystal size. The synthesis was studied using X-ray diffraction, X-ray fluorescence, scanning electron microscopy, transmission electron microscopy, ultraviolet-Raman spectroscopy, infrared spectroscopy, and N2 physisorption. Synthesis was successful using different zeolite Beta seeds including pure silica seeds. During the induction period, the seeds underwent dissolution. The SiO2/Al2O3 ratio and crystal size, pretreatment (calcination), and seed addition time had a significant influence on seed dissolution behavior, crystallization process, and product. Morphological studies revealed that the seed residues produced by dissolution (except for pure silica) resulted in the formation of “immobilized” surface nuclei, which allowed for the dense growth of fresh small zeolite Beta crystals. The dissolved small seed fragments yielded dispersed nuclei, which formed relatively scattered small zeolite Beta crystals thought to be the main nuclei source of the pure silica seed. It is suggested that the use of an appropriately high SiO2/Al2O3 ratio, small size, and precalcined zeolite Beta seed is helpful for the synthesis of highly crystalline and pure zeolite Beta from the organic structure-directing agent-free gel.

Some observations on the synthesis of fully-dispersible nanocrystalline zeolite ZSM-5.

A facile method for the rapid synthesis of fully-dispersible ZSM-5 (Si/Al = 100) of about 30 nm size in high yield (about 91%) is described. The method comprises three steps, viz., concentration of an initial clear solution, low-temperature (80 degrees C) ageing of concentrated sol, and high-temperature (175 degrees C) hydrothermal treatment or microwave heating (175 degrees C) of aged concentrated sol. A simple vacuum-concentration method was used for the extraction of pure NPs of ZSM-5 in solution. XRD, FT-IR, TGA and ASAP characterizations showed that the NPs were partially crystalline. The concentration step accelerated the aggregation of primary units, which helps in the production of a large number of nucleation centers protected by TPA+ ions against aggregation. During low-temperature ageing, the number of critical sized nuclei increases, growing into zeolite. The high-temperature heating results in the complete growth of unreacted silica, giving high yields. A key factor for generating small non-aggregated zeolite crystals is the amount of water in the synthesis sol. The three-step method presented here produces a target material of small and uniform sized, non-aggregated ZSM-5 of about 30 nm in a short reaction time. The results are significant, as the synthesis method adopted here produces much uniform, non-aggregated nanocrystalline ZSM-5 in a shorter time with high yield.

Development of Hydrocracking Catalyst Support from Kaolin of Indonesian Origin

The global shift of petroleum refinery towards heavier crude oils means an increasing demand of hydrocracking catalysts. This work studies the conversion of a kaolin originating from the Bangka island in Indonesia into a hydrocracking catalyst support consisting of zeolite-Y and amorphous alumina-silica phases. After a beneficiation process combining controlled settling and adsorption of the kaolin suspension in water with the addition of 125 ppm of 0.01% polyacrylamide solution as flocculant and 156 ppm of 0.1% calcium chloride solution as the adsorbent, the kaolinite phase content is increased from 63.6 to 74.3 %-mass. After spray drying, the kaolin is calcined at three temperatures for 2 hours each, producing calcined kaolin phases K700C at 700 °C, K1013 at 1013 °C, and K1050C at 1050 °C. Temperatures of calcination for obtaining calcined kaolin phases is determined based on result of DSC/TGA. Synthesis of zeolite-Y is done by mixing varying proportions of these three calcined kaolin products, and zeolite-Y crystal seeds. These mixtures are aged at room temperature for 11 hours prior to reaction in a hydrothermal condition at 93 °C for 15-21 hours. The best calcined kaolin composition is found to be K700C : K1013C : K1050C = 10:85:5 (%-mass), resulting in a zeolite NaY purity of 86-88 % as characterized by X-ray diffraction (XRD), average ratio of SiO2/ Al2O3 of 5.35, mean pore diameter of 23.1 Å, specific surface area of 186 m2/g, and a total pore volume of 0.107 mL/g as measured by N2 adsorption. In a parallel manner, a series of amorphous silica-alumina (ASA) synthesis experiments is done to identify the best metakaolin calcination temperature and metakaoline activation pH. These are found to be 527 °C and 8.0, respectively, producing an ASA product with a 65 %-mass amorphous phase content as estimated by XRD data processing. To prepare the hydrocracking catalyst support, the zeolite NaY is added into the ASA-forming metakaolin sol at a pH of 8.0, aged for 8 hours at 50 °C. An initial morphological characterization of the obtained zeolite-ASA composite catalyst support suggests a good dispersion of the smaller zeolite NaY particles in the ASA microspheres.

Simulation study of CO2 adsorption properties in small Zeolite Imidazolate Frameworks

Applying first principles Born–Oppenheimer Molecular Dynamics and Grand Canonical Monte Carlo simulations, we investigated three prototype Zeolite Imidazolate Frameworks to assess the role of their electronic and structural details on CO2 adsorption. We found that the regions proximal to the linkers are the preferential adsorption sites of CO2. The uptake capacity at low pressures is related to the electrostatic interaction of the adsorbate with the crystal. At higher pressures, CO2 adsorption depends linearly on the surface areas and porosities of ZIFs.

Synthesis and Characterization of Small Crystals NaY Zeolite with High Silicon

Small crystals NaY zeolite with high silicon was successfully synthesized via a two-stage temperature crystallization program, without adding any organic additives. While the effect of low temperature crystallization time and the alkalinity on the crystal size and SiO2/Al2O3 ratio of NaY zeolite were investigated. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared (FT-IR) spectroscopy, N2 adsorption, 29Si MAS NMR and thermogravimetric TG measurements. NaY zeolite, with crystal size about 100 nm and SiO2/Al2O3 ratio about 5.3, is obtained. It possesses high surface area and some amount of mecropores, and the decomposition temperature is higher than 1000 °C. The crystal size and SiO2/Al2O3 ratio of as-synthesized NaY zeolite depend on low temperature crystallization time and the alkalinity.

Synthesis of the composite material Y/ASA and its catalytic performance for the cracking of n-decane

Y/ASA composite was successfully prepared by wrapping NaY zeolite with small-crystal size in amorphous silica–alumina (ASA) gel. Characterization results show that bonding action between zeolite Y and ASA contributes new acid sites in HY/ASA, which are responsible for its higher activity in the catalytic cracking of n-decane and light diesel, comparing with the mixture-derived catalysts. HY/ASA catalyst possesses larger surface area and mesoporous volume and uniform slit-shaped mesopores, which are beneficial to the diffusion of the products and responsible for higher yield of the middle distillates. The smaller zeolite Y crystallites in Y/ASA lead to more contact points between Y crystallites and ASA and thus provide more new acid sites for the HY/ASA catalyst. The high conversion of n-decane and yield of middle distillates over the HY/ASA catalyst can be ascribed to its acid quantity and super pore structure.

Preparation of small analcime particles with narrow size distributions from acid-treated larger analcime particles

Narrowly size distributed analcime particles of 0.38–3.7μm were hydrothermally synthesized from alkaline synthesis mixtures containing seeds of acid-treated larger analcime particles (25±4.2μm). Treatment of the larger particles with dilute HCl (∼0.5N) led to fine cracking as aluminium dissolved; more concentrated HCl (>3.0N) led to larger cracks and particles’ breaking. The acid-treated analcime particles dissociated into small zeolite domains in the alkaline synthesis mixture and acted as seeds to grow analcime particles. Seeds prepared with 1.0N HCl grew into analcime particles of 0.38±0.03μm; the use of 4.0N HCl resulted in analcime particles of 2.7±0.07μm. The analcime particles’ sizes could be controlled through the concentration of HCl used in the preparation of the seeds. Narrow particle size distributions arose due to the seeds in the synthesis mixtures and the rapid hydrothermal growth of analcime particles.