Nanocrystalline Zeolite Research Articles

A novel gold nanoparticle decorated nanocrystalline zeolite based electrochemical sensor for the nanomolar simultaneous detection of cysteine and glutathione

High electrocatalytic activity of the sensor can be attributed to the highly dispersed gold nanoparticles on the nanocrystalline zeolite matrix.

Synthesis of hierarchical nano-crystalline zeolite beta using biomass-derived hard templates

Mesoporous nano-crystalline zeolite beta was prepared via hydrothermal synthesis and the effect of carbohydrates as a hard template was studied. The monosaccharide, disaccharide, polysaccharide and cyclic oligosaccharide type of carbohydrates were used as a secondary template. These modified beta zeolites were characterised by XRD, SEM and N2 physisorption. The polysaccharide and oligosaccharide types of carbohydrates show a significant mesoporosity generation in nano-crystalline zeolite beta where as monosaccharide and disaccharide types of carbohydrates alter the pH of gel and lead to the amorphous phase. The XRD and SEM results confirmed the formation of nano-crystalline zeolite beta. N2 adsorption/desorption results showed the generation of the mesoporosity in nano-crystalline zeolite beta. Advantages of using the biomass-derived hard-templates have been brought out.

Simple and Economical Synthesis of Alkyl Phenyl Ethers by the Reaction of Phenols and Alkyl Esters Using Nanocrystalline Beta

A simple, economical, and recyclable catalytic route is developed for the synthesis of alkyl phenyl ethers by the liquid phase reaction of phenol derivatives with alkyl esters using conventional and nanocrystalline zeolite Beta. A wide range of alkyl phenyl ethers can be prepared using this catalytic protocol. Nanocrystalline zeolite Beta exhibited higher activity than conventional zeolite Beta.

Photocatalytic Oxidation of Phenolic Pollutants and Hydrophobic Organic Compounds in Industrial Wastewater Using Modified Nonosize Titanium Silicate-1 Thin Film Technology

Nanocrystalline Titanium Silicate-1 (TS-1) with attractive physical and chemical properties is being explored for the degradation of phenol. A fully dispersible nanocrystalline zeolite TS-1 was prepared. The catalyst was characterized by DLS, XRD, TEM and BET analyses. XRD analysis confirmed that the diffraction pattern of the NPs (CP-0) was very similar to that of amorphous silica and the aged concentrated precursor sample CP-48 showed peaks characteristic of MFI. TEM analysis confirmed that the size of the crystal is about 30 nm. The photocatalytic oxidation of phenol was studied over nanocrystalline Titanium silicate-1 thin film flow reactor. The experimental parameters such as aeration, flow rate, solution pH and phenol concentration were optimized. The degradation efficiency of choro-substituted phenols are compared at optimum conditions. In addition, photocatalytic degradation efficiency of simulated phenolic waste water was studied. The results are significant, as the method adopted here can be extended for the treatment and purification of waste water and air using nanocrystalline Titanium silicate-1 thin film flow reactor.

Methylcellulose-Directed Synthesis of Nanocrystalline Zeolite NaA with High CO₂ Uptake.

Zeolite NaA nanocrystals with a narrow particle size distribution were prepared by template-free hydrothermal synthesis in thermo-reversible methylcellulose gels. The effects of the amount of methylcellulose, crystallization time and hydrothermal treatment temperature on the crystallinity and particle size distribution of the zeolite NaA nanocrystals were investigated. We found that the thermogelation of methylcellulose in the alkaline Na2O-SiO2-Al2O3-H2O system played an important role in controlling the particle size. The synthesized zeolite nanocrystals are highly crystalline, as demonstrated by X-ray diffraction (XRD), and scanning electron microscopy (SEM) shows that the nanocrystals can also display a well-defined facetted morphology. Gas adsorption studies on the synthesized nanocrystalline zeolite NaA showed that nanocrystals with a size of 100 nm displayed a high CO2 uptake capacity (4.9 mmol/g at 293 K at 100 kPa) and a relatively rapid uptake rate compared to commercially available, micron-sized particles. Low-cost nanosized zeolite adsorbents with a high and rapid uptake are important for large scale gas separation processes, e.g., carbon capture from flue gas.

Selective, Nanomolar Electrochemical Determination of Environmental Contaminants Dihydroxybenzene Isomers Found in Water Bodies Using Nanocrystalline Zeolite Modified Carbon Paste Electrodes

AbstractNanocrystalline zeolites of different framework structures were prepared by the addition of suitable structure directing agents in the synthesis composition of conventional zeolites. Zeolite modified carbon paste electrodes were constructed for the simultaneous determination of dihydroxybenzene isomers. Nanocrystalline zeolite Beta modified carbon paste electrode exhibited the highest electrocatalytic activity. Under optimum conditions, wide linear range was obtained from 150 nM to 400 µM with lower detection limit of 100, 130, and 100 nM for hydroquinone, catechol, and resorcinol, respectively. The analytical performance of the proposed sensor was demonstrated in the simultaneous determination of dihydroxybenzene isomers in different environmental water samples.

Synthesis of ionic liquids coated nanocrystalline zeolite materials and their application in the simultaneous determination of adenine, cytosine, guanine, and thymine

In this study, ionic liquids coated nanocrystalline zeolite based inorganic-organic hybrid materials were synthesized. Nanocrystalline ZSM-5 zeolite was prepared under hydrothermal condition in the presence of propyltriethoxysilane as an additive in the synthesis composition of conventional ZSM-5. Ionic liquids (methylimidazolium chloride and 1-butyl-3-methylimidazolium chloride) were coated on the surface of nanocrystalline ZSM-5 by the post synthesis method. For comparative study, ionic liquids coated conventional ZSM-5 based inorganic-organic hybrid materials were also prepared. Ionic liquids coated nanocrystalline ZSM-5/ZSM-5 modified electrodes were constructed for the simultaneous determination of all four DNA bases such as adenine, cytosine, guanine, and thymine. Difference in the electro-catalytic activity of the modified electrode is explained with the help of textural properties, conductivity, and density functional theory. The analytical performance of the proposed method was demonstrated in the simultaneous determination of all four DNA bases in calf thymus DNA sample.

Synthesis of nanocrystalline zeolite NaY by hydrothermal method and investigation of its structure and morphology

Zeolite FAU type-Y is one of the most studied framework of all zeolites, and has been used as catalysts for number of reactions in the refinery and petrochemical industry. In this research, nanocrystalline zeolite Y was synthesized by hydrothermal method. The crystal size of zeolite Y is influenced by temperature, aging time, alkalinity, and water content. The synthesized zeolite NaY is identified and characterized by Brunauer-Emmett-Tell (BET), Fourier Transmission Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). The mean crystallites size was measured by transmission electron microscopy (TEM) and it was determined also by Rietveld's method using Scherrer's equation; with similar results estimated was about 50 nm.

Zeolite–sepiolite nanoheterostructures

Zeolite–sepiolite inorganic nanoheterostructures have been hydrothermally synthesized by adding a dispersion of colloidal sepiolite to a solution able to produce a nanocrystalline zeolite (silicalite). The obtained product could be recovered in good yield by simple filtration only when the relative sepiolite concentration exceeded a threshold of 1.8 wt% in the synthesis mixture (amounting to 1:3 sepiolite:zeolite wt. ratio in the recovered product). The resulting heterostructures were characterized by XRD, FTIR, thermal (TG–DTA) and chemical analyses, N2 adsorption, TEM, SEM, 29Si NMR, and methylene blue adsorption. The intimate zeolite–sepiolite interaction at the surface produced a good dispersion of zeolite particles and prevented their sintering upon calcination to remove the organic structure-directing agent. Experiments in conditions yielding microcrystalline silicalite support the idea that the sepiolite surface acts as nucleation sites for the zeolite crystallization. The textural properties of the nanozeolite–sepiolite heterostructure are not a linear combination of their components’.

High catalytic performance of surfactant-directed nanocrystalline zeolites for liquid-phase Friedel–Crafts alkylation of benzene due to external surfaces

Beta zeolite is known as an efficient catalyst for Friedel–Crafts alkylation. In liquid phase reactions, however, beta zeolite catalyst is often deactivated rapidly. We discovered that the maximum possible catalytic turnovers in benzene alkylation with benzyl alcohol could be increased by six times by using a beta zeolite with a nanosponge-like morphology, in comparison to bulk beta zeolites. The nanomorphic zeolite was obtained using a hydrothermal synthesis method which uses multiammonium surfactants as a meso–micro hierarchical structure-directing agent. The origins of the high catalytic performance were investigated by measuring the catalytic conversions after selectively poisoning acid sites located on external surfaces and in internal micropores selectively. The result indicated that the high catalytic performance was due to the alkylation reactions occurring on external surfaces. External active sites were able to perform the catalytic function even after active sites inside the zeolite micropores were deactivated. Similar results were obtained with other nanomorphic zeolites such as MFI nanosheets, MTW nanosponge and MRE nanosponge.

Highly Efficient Nanocrystalline Zirconosilicate Catalysts for the Aminolysis, Alcoholysis, and Hydroamination Reactions

Nanocrystalline zirconosilicates and titanosilicates with MFI framework structure were hydrothermally synthesized by the addition of organosilanes in the synthesis composition of conventional zirconosilicate and titanosilicate materials. Materials were characterized by a complementary combination of X-ray diffraction, nitrogen sorption, scanning/transmission electron microscopy (S/TEM), ammonia temperature-programmed desorption (TPD), Fourier transform infrared (FT-IR) spectroscopy, and ultraviolet–visible (UV-vis) spectroscopic investigations. Nanocrystalline zeolite catalysts of the present study are reusable. They exhibit significantly higher catalytic activities in aminolysis and alcoholysis compared with the hitherto known catalysts. A range of β-amino alcohols/β-alkoxy alcohols with high regioselectivity were synthesized using zirconosilicates. Application of these materials was also extended in the synthesis of aminoesters by the hydroamination reaction of methyl acrylates and amines. Structure act...

New bifunctional Ni–H-Beta catalysts for the heterogeneous oligomerization of ethylene

The development of sustainable active and stable heterogeneous catalysts for the oligomerization of ethylene to replace the unfriendly homogenous systems based on transition metal complexes currently applied in the industry still remains a challenge. In this work we show that bifunctional catalysts comprised of Ni loaded on nanocrystalline zeolite H-Beta can efficiently catalyze the oligomerization of ethylene with high stability and selectivity to liquid oligomers under mild reaction conditions. Ni-Beta catalysts were prepared starting from a commercial nanocrystalline H-Beta sample with Si/Al ratio of 12 via both ionic exchange (1.0–2.5wt% Ni) and incipient wetness impregnation (1.1–10.0wt% Ni) using aqueous Ni(NO3)2 solutions, followed by air-calcination at 550°C. The Ni-Beta catalysts exhibited no signs of deactivation under the studied conditions (T=120°C, Ptot=3.5MPa, PC2H4=2.6 MPa, WHSV=2.1h−1, TOS=0–9h). The conversion of ethylene increased linearly with increasing Ni loading up to ca. 2.5wt%, irrespective of the method of Ni incorporation. Then, the conversion leveled off and attained a value of ca. 87% at higher Ni loadings (impregnated series), concurring with the development of large, XRD-visible, NiO crystallites sizing ca. 7–16nm. Interestingly, the disappearance of Brønsted acid sites upon Ni incorporation increased linearly up to Ni contents of ca. 2.5wt% and then leveled off, thus paralleling the activity trend. This fact indirectly suggests that Ni2+ cations replacing H+ in ion exchange positions could be the active sites responsible for the activity of Ni-Beta catalysts. Direct evidence for the nature of the active Ni sites was obtained from low temperature (−20°C) CO adsorption and ethylene–CO co-adsorption experiments followed by FTIR. CO-FTIR results ruled out the participation of Ni+ ions and provided support for the assignation of ion exchanged Ni2+ species as the likely active sites in Ni-Beta catalysts. Additionally, most active Ni-Beta catalysts displayed a non-Schulz–Flory product distribution with high selectivity to liquid oligomers (≥60wt%) and high degree of branching due to the contribution of the hetero-oligomerization pathway involving zeolite Brønsted acid sites.

Tailoring zeolite morphology by Charge Density Mismatch for aromatics processing

Nano-crystalline zeolites UZM-5 and UZM-14 were synthesized via the Charge Density Mismatch (CDM) approach and were shown to have distinct morphologies that significantly impact aromatic alkylation and transalkylation reactions. UZM-5 has surface structure features and thin plate morphologies favorable for catalyzing the alkylation of benzene with ethene. The alkylation activity depends on the crystallinity and morphology, which affect acidity and access to surface cups and internal pores. Nano-crystalline mordenite, UZM-14, was characterized in terms of crystallite length in the direction of the 12-MR channels, mesoporosity, and accessibility of acid sites. Aromatics transalkylation performance was shown to correlate with mesoporosity and crystallite length along the pore direction. This was rationalized in terms of decreased diffusion path length in the micropores and improved accessibility of feed molecules to acid sites in the interior of the zeolite crystals.

Incorporation of germanium into the framework of nanocrystalline faujasite

Due to their large surface area and accessible pore network, research on nanocrystalline zeolites is a rapidly developing area. Incorporation of tetravalent elements into the zeolite framework beyond the traditional silicon and aluminum is one facet of this research and development. Another important facet of nanocrystalline zeolite research is minimizing waste and improving product yield towards greener chemistry synthesis. The study reported here incorporates both of these facets as germanium containing FAU type zeolites with Si/Al ratios below 1.5 were synthesized with recycling methods in order to increase zeolite yield. Sub 40nm nanocrystalline FAU type zeolites with germanium incorporated into the framework were synthesized from clear reaction mixtures with systematically varied synthesis conditions. The zeolite products were characterized with transmission electron microscopy (TEM) for crystal size and morphology, inductively coupled plasma optical emission spectroscopy (ICP-OES) for elemental ratios, powder XRD for crystallinity and framework type, nitrogen adsorption for BET surface area, and both 29Si and 27Al NMR to study framework coordination.

Conversion of furfuryl alcohol to ethyl levulinate using porous aluminosilicate acid catalysts

The following porous aluminosilicates were tested as acid catalysts in the reaction of furfuryl alcohol (FA) with ethanol, at 140°C: micro/mesoporous composite Beta/TUD-1 and the correspondent nanocrystalline (large pore) zeolite H-Beta; ITQ-2 and its zeolite counterpart (medium pore) H-MCM-22; mesoporous Al-TUD-1. The target product ethyl levulinate (EL) was formed with a yield up to 80%, at 24h reaction (100% FA conversion). Relationships between the catalytic results and the acid and texture properties of the catalysts were established. Comparative studies for the aluminosilicates and the well-known sulfonic acid resin Amberlyst™-15 were reported on the basis of EL yields, the undesirable formation of diethyl ether, and catalyst stability (regeneration and reuse). A study of the reaction products was carried out by comprehensive two-dimensional gas chromatography combined with time-of-flight mass spectrometry.

Nanocrystalline Zeolite Tetraethylammonium‐Beta Membrane for Preferential Sorption and Transport of CO2 over N2

AbstractCO2/N2 gas separation was performed over a nanocrystalline zeolite tetraethylammonium (TEA)‐beta membrane prepared on a stainless‐steel porous disc by repeated hydrothermal crystallization. Two to three consecutive hydrothermal syntheses were required to form a membrane comprised of a continuous and compact layer of zeolite beta nanocrystals on the support. The membrane TEA‐BEA3 obtained by three consecutive syntheses, in which the membrane from two consecutive syntheses was used as support, exhibited the highest structural order. When the separation experiment was performed over this membrane without applying any external applied pressure, 100 % selectivity of CO2 over N2 was observed. The separation was driven by differences in chemical potentials of the molecules generated only by the adsorption‐desorption behavior of the gases into the membrane. The novel zeolite TEA‐beta membrane provided promising results for the separation of small gas molecules due to the combined influence of diffusion and sorption selectivity.

Hierarchical Zeolite Beta: An Efficient and Eco-Friendly Nanocatalyst for the Friedel–Crafts Acylation of Toluene

P-Methyacetophenone, the acylated product of toluene finds a wide range of applications in the flavors and fragrance industry. It is typically produced on an industrial scale by Friedel-Crafts acylation of toluene with acetic anhydride using homogeneous, corrosive and polluting acid catalysts such as aluminium chloride. The pollution problems related to this process such as the disposal of catalyst and treatment of acidic effluent needs to be replaced by a green process. The current work reports on the activity of hierarchical zeolite Beta in the liquid phase acylation of toluene with acetic anhydride. The liquid phase reactions were carried out in the temperature range of 60-140 degrees C in an autoclave. The effect of various reaction parameters such as time-on-stream (TOS), mole ratio of reactants, catalyst loading, and reaction temperature on the rates of reaction has been investigated. Under the optimum reaction conditions the performance of hierarchical zeolite Beta was compared with nanocrystalline zeolite Beta. It was found that hierarchical zeolite Beta catalyst exhibit higher activity, which is due to the hierarchical porosity and to the nano size of the Beta zeolite catalyst particles allows faster diffusion of the products out of the catalyst.

Preparation of a novel PAN–zeolite nanocomposite for removal of Cs+ and Sr2+ from aqueous solutions: Kinetic, equilibrium, and thermodynamic studies

In this research a novel nanocomposite adsorbent consisting of nanocrystalline zeolite A and polyacrylonitrile (PAN) was prepared. Nanocrystalline zeolite A was synthesized by a new method using tetra methyl ammonium hydroxide and tetra methyl ammonium bromide as templating agents. The sample was characterized by X-ray diffraction, X-ray fluorescence spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and differential thermogravimetric technique. The nanocomposite was evaluated for removal of Cs+ and Sr2+ from aqueous solutions. The effect of different variables such as pH, initial concentration, contact time, and temperature was studied and optimized. The kinetic studies showed that the process was quite rapid and 90% of equilibrium capacity was achieved within 30min. The process followed the pseudo-second-order kinetic model with k2 values of 0.1912 and 0.1839gmmol−1min−1 for Cs+ and Sr2+ respectively. Positive ΔH° and negative ΔG° were indicative of the endothermic and spontaneous nature of Cs+ and Sr2+ removal. The Langmuir, Freundlich, and Dubinin–Radushkviech (D–R) isotherm models were also used to describe the equilibrium data.

Effects of Hydrothermal Parameters on the Synthesis of Nanocrystalline Zeolite NaY

AbstractSynthesized zeolites are extremely important as industrial minerals and are most commonly prepared using organic templates. Because these organic templates present undesirable environmental hazards, a synthesis method which avoids their use is desirable. The objective of the current study was to develop such a synthesis method. Zeolite NaY was synthesized hydrothermally starting from a mixture of 1.0 Al2O3:10 SiO2:4.6 Na2O:180 H2O molar gel composition, without adding any organic additives. Experiments were carried out to investigate the effects of molar compositions including water content (H2O/SiO2), crystallization conditions including temperature, and time on the crystal size and yield of NaY-type zeolite. The results showed that increasing the crystallization time from 5 to 12 h increased the crystal size, while increasing the crystallization temperature from 80 to 100°C also increased crystallinity. The crystal species of zeolite NaY were characterized by X-ray diffraction, X-ray fluorescence, and scanning electron microscopy analysis. Zeolite NaY crystals in the size range 25–150 nm were synthesized successfully over a period of 8 h at 100°C.

Synthesis of a novel magnetic zeolite nanocomposite for removal of Cs+ and Sr2+ from aqueous solution: Kinetic, equilibrium, and thermodynamic studies

In this study, a novel magnetic zeolite nanocomposite (MZNC) was prepared by nanozeolite A and iron oxide. Nanocrystalline zeolite A was synthesized, and then, iron oxide nanocrystals were prepared in the presence of nanozeolite. The prepared nanocomposite was characterized by XRD, XRF, FT-IR, DTG, VSM, and TEM methods. The applicability of the synthesized nanocomposite for removal of Cs+ and Sr2+ from aqueous solutions was assessed, and the effective parameters such as initial concentration, initial pH, contact time, and temperature on the sorption process were studied and optimized. The composite was able to remove 95.2% and 81.4% of Sr+2 and Cs+1 from 0.01N aqueous solutions, respectively. The kinetic studies showed that the process was quite rapid, and 90% of equilibrium capacity was achieved within 30min. Experimental kinetic data were found to be well fitted with pseudo-second-order kinetic model with rate constant of 0.2845 and 0.2722gmmol−1 min−1 for Cs+ and Sr2+, respectively. The Langmuir, Freundlich, and D–R isotherm models were used to describe the equilibrium data. The saturation magnetization of nanocomposite was measured as 19.50emug−1, which facilitated magnetic separation of the sample after adsorption process.