Nanocrystalline Zeolite Research Articles

Aqueous phase reactions of pentoses in the presence of nanocrystalline zeolite beta: Identification of by-products and kinetic modelling

Furfural, a valuable platform chemical that has the potential to replace a variety of oil/coal/gas derived materials and chemical products, is produced by the dehydration of d-xylose, which in turn is obtained from lignocellulosic biomass. Herein, the conversion of xylose in the presence of nanocrystalline zeolite beta in the H+-form, using water as solvent, was investigated. Detailed batch kinetic studies and products identifications techniques (1H, 13C NMR and comprehensive two-dimensional gas chromatography (GC×GC) combined with time-of-flight mass spectrometry (ToFMS)) provided mechanistic insights into the overall reaction process. The conversion of xylose to furfural is accompanied by several side reactions, forming complex reaction mixtures. A pseudo-homogeneous kinetic model was proposed that fitted quite well the experimental data.

Effects of ultrasound on the synthesis of silicalite-1 nanocrystals

Application of power ultrasound, offers potential in the degree of control over the preparation and properties of nanocrystalline zeolites, which have become increasingly important due to their diverse emerging applications. Synthesis of silicalite-1 nanocrystals from a clear solution was carried out at 348K in the absence and presence of ultrasound of 300 and 600W, in an attempt to investigate the effects of sonication, in this respect. Variation of the particle size and particle size distribution was followed with respect to time using a laser light scattering device with a detector set to collect back-scattered light at an angle of 173°. Product yield was determined and the crystallinity was analyzed by X-ray diffraction for selected samples collected during the syntheses. Nucleation, particle growth and crystallization rates all increased as a result of the application of ultrasound and highly crystalline silicalite-1 of smaller average particle diameter could be obtained at shorter synthesis times. The particle size distributions of the product populations, however, remained similar for similar average particle sizes. The rate of increase in yield was also speeded up in the presence of ultrasound, while the final product yield was not affected. Increasing the power of ultrasound, from 300 to 600W, increased the particle growth rate and the crystalline domain size, and decreased both the final particle diameter and the time required for the particle growth to reach completion, while its effect on nucleation was unclear.

Synthesis of Nano-crystalline Zeolites and Applications to Zeolite Membranes

Synthesis of Nano-crystalline Zeolites and Applications to Zeolite Membranes

Microscopic Investigation of Nanocrystalline Zeolite L Synthesized from Rice Husk Ash

An investigation of aluminosilicate zeolite L (structure code LTL) nanocrystals converted from rice husk ash in template‐free system is reported. Crystallization evolution of the zeolite L was monitored and followed by X‐ray diffraction, high‐resolution transmission electron microscopy, scanning electron microscopy, atomic absorption spectroscopy, and infrared spectroscopy techniques. It was found that fully crystalline zeolite L (Si/Al = 3.0) with square tablet morphology was nucleated at 4 h, and the crystals with a mean particle size of 210 nm was completely transformed from amorphous silica after 24 h of hydrothermal treatment.

Effect of nanocrystalline zeolite Na-Y on meta-xylene separation

The adsorption process for separation of meta-xylene from xylene mixture on binder-free nanocrystalline and microcrystalline zeolite Y modified with sodium cation was investigated in the liquid phase. X-ray diffraction, scanning electron microscopy (SEM), nitrogen adsorption and in situ Fourier transform infrared (FTIR) spectroscopy were also performed to study the type of adsorbed species and their thermal stabilities. The adsorption process was carried out at temperature of 110–160 °C and pressure of 6–10 atm. The effect of zeolite water content on the adsorption process was investigated. The influence of SiO 2/Al 2O 3 ratio on selectivity factor of meta-xylene to other C 8 aromatic isomers was also studied. The adsorption isotherms for each isomer of C 8 aromatics and desorbents illustrated the typical Langmuir type. It was observed that selectivity of meta-xylene was increased with decreasing the particle size of crystalline zeolite Y from micro to nano-scale. The best selectivity factor of meta-xylene to para-xylene, ortho-xylene and ethylbenzene on nanocrystalline zeolite Na-Y reached to be 2.90, 3.16 and 6.88, respectively, and compared with those obtained with microcrystalline zeolite Na-Y. Desorbents like toluene and indan were also tested to optimize the process.

Production of biofuel from waste cooking palm oil using nanocrystalline zeolite as catalyst: Process optimization studies

The catalytic cracking of waste cooking palm oil to biofuel was studied over different types of nano-crystalline zeolite catalysts in a fixed bed reactor. The effect of reaction temperature (400–500°C), catalyst-to-oil ratio (6–14) and catalyst pore size of different nanocrystalline zeolites (0.54–0.80nm) were studied over the conversion of waste cooking palm oil, yields of Organic Liquid Product (OLP) and gasoline fraction in the OLP following central composite design (CCD). The response surface methodology was used to determine the optimum value of the operating variables for maximum conversion as well as maximum yield of OLP and gasoline fraction, respectively. The optimum reaction temperature of 458°C with oil/catalyst ratio=6 over the nanocrystalline zeolite Y with pore size of 0.67nm gave 86.4wt% oil conversion, 46.5wt% OLP yield and 33.5wt% gasoline fraction yield, respectively. The experimental results were in agreement with the simulated values within an experimental error of less than 5%.

Hydrothermal synthesis of nanocrystalline zeolite Beta by acid-catalyzed hydrolysis of teraethylorthosilicate

Nanocrystalline zeolite Beta was synthesized via the acid-catalyzed hydrolysis of teraethylorthosilicate (TEOS) under static hydrothermal conditions. Various parameters, such as pH value for hydrolyzing TEOS, SiO 2/Al 2O 3 ratio, template content, crystallization temperature and time, were investigated to obtain the suitable synthesis conditions. The produced samples were characterized by XRD, SEM, TEM, IR, ICP, surface areas, pore volumes and pore distributions. Compared with the traditional base-catalyzed hydrolysis of TEOS, the silicate precursors created by the acid-catalyzed hydrolysis of TEOS are proved to be favorable to the formation of nanocrystalline zeolite Beta.

Influence of crystal size and probe molecule on diffusion in hierarchical ZSM-5 zeolites prepared by desilication

The improvement of molecular transport properties of hierarchical H-ZSM-5 obtained by desilication was evidenced by studying the desorption of o-xylene and isooctane by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). This technique enabled monitoring simultaneously bands associated with the molecular probes and the zeolite, using powdered sample masses as low as 1 mg. Two H-ZSM-5 samples with markedly different crystal sizes were investigated. The first sample was commercial and consisted of small crystallites ( ca. 250 nm). The second sample were laboratory-made large crystals with coffin-like shape ( ca. 17 × 4 × 4 μm 3). The hierarchical derivatives of the small and large zeolite crystals displayed 250 and 120 m 2 g −1 of mesopore surface area, respectively, in contrast to the 62 and 5 m 2 g −1 of the parent counterparts. The data based on o-xylene desorption were partly disguised by site-desorption limitations. Desorption experiments using isooctane evidenced a 4-fold reduction in the characteristic diffusion path length on both mesoporous small and large zeolites with respect to their purely microporous analogues. These results confirm the substantial potential for improvement of commercial nanocrystalline zeolites in diffusion-limited reactions upon the introduction of intra-crystalline mesoporosity by post-synthesis modification.

Enhanced activity of hierarchical zeolitic material with ZSM-5 structure for the tert-butylation of phenol

Nanocrytsalline phase of hierarchical zeolite structure with ZSM-5 was successfully synthesised via a facile and new method using NR latex as a polymer macrotemplate for the liquid phase alkylation of phenol with tert-butanol. X-ray diffraction pattern, FT-IR spectrum and TEM observations confirm the formation of pure and nanocrystalline zeolite ZSM-5 phase. Catalysis measurements show that the prepared zeolite ZSM-5 phase leads to high phenol conversion and 2,4-di-TBP selectivity which is mainly due to the presence of the hierarchical porosity within the zeolite ZSM-5 phase as confirmed by FESEM and pore size analyses.

Ionic Vibration Spectrum of Nanocrystalline MEL Pure Silica Zeolite Film

Skeletal siloxane bonding structure of nanocrystalline MEL pure silica zeolite film was investigated. Nanocrystalline zeolite (nc-zeolite) suspension was prepared by the two-stage hydrothermal treatment, and thin film was obtained by spin-coating. After a quantitative analysis of Fourier-transform infrared spectra with the variable incidence angles of light probe, skeletal complex dielectric function concerning the siloxane bond vibration was derived in the 1400–400 cm–1 range. Then, the widening of the AS1-(LO-TO) frequency splitting width and the enhancement of the normalized integrated oscillator strength of AS vibration mode were observed in the nc-zeolite film in comparison with those of sol–gel derived amorphous silica film. Those improvements must be attributed to the increased siloxane network connectivity and the crystal structure of zeolite. The effect of the UV assist anneal was also discussed.

Influences of Mesoporosity Generation in ZSM-5 and Zeolite Beta on Catalytic Performance During n-Hexane Isomerization

Catalytic performance of Pt impregnated parent and desilicated nano-crystalline zeolites, ZSM-5 and Beta for n-hexane isomerization was studied. Difference in channel systems of the zeolites and absence/presence of mesopores therein were found to be reflected in product distributions. ZSM-5 was desilicated by NaOH and zeolite Beta with tetramethylammonium hydroxide (TMAOH.) Desilication was found to afford comparable catalytic performance to that of the parent counterpart at reaction temperature lower by 25 °C. Observed product distributions could be substantiated with characterizations such as ammonia TPD, surface area determination and SEM. Desilicated zeolite Beta was seen to be less prone to coking as deduced from the TGA study. Location of Pt with reference to proton sites within the channels and that inside the pores viz a viz external surface also have been discussed briefly. Pt impregnated Zeolite Beta desilicated by TMAOH affords comparable isomer yields at temperature lower by 25 C to that by the parent zeolite. The modification also led to improved catalyst life.

Synthesis of high-quality nanocrystalline zeolite Y using pseudoboehmite as aluminum source

High-quality nanocrystalline zeolites Y were hydrothermally synthesized using pseudoboehmite as aluminum source. The influence of pseudoboehmite on the crystallization kinetics, composition, morphology and yield of the samples was investigated. The samples were characterized by XRD, BET, ICP OES, FT-IR, TG and TEM techniques. XRD results indicated that the samples had a short crystallization period and high crystallinity. TEM and BET results showed that the samples were in size range of 40–90 nm and exhibited an external surface area of 87 m2 g−1. Moreover, ICP OES analysis showed that the samples had high Si/Al ratio, which resulted in the high thermal stability proved by TG analysis. In present studies, pseudoboehmite was found to be better raw material for optimal preparation of nanocrystalline zeolites Y with desired characteristics and better yield.

Nanocrystalline Zeolite Y: Synthesis and Characterization

Nanocrystalline zeolite has received significant attention in the catalysis community. Zeolites with a crystal size smaller than 100 nm are the potential replacement for existing zeolite catalysts due to its unique features with added advantages. 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. The present paper covers the synthesis of nanocrystalline zeolite Y under hydrothermal conditions from clear synthesis mixtures. The crystal size of zeolite Y is influenced by temperature, aging time, alkalinity, and water content. The synthesized Y is characterized by X-ray diffraction (XRD), Fourier Transmission Infrared Sprectroscopy (FTIR), Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM) and Nitrogen Adsorption.

Nanocrystalline zeolite beta and zeolite Y as catalysts in used palm oil cracking for the production of biofuel

Nanocrystalline zeolites with crystal size smaller than 100 nm are potential replacement for conventional zeolite catalysts due to their unique characteristics and advantages. In this study, the synthesis of nanocrystalline zeolite Y (FAU) and nanocrystalline zeolite beta (BEA) under hydrothermal conditions is reported. The effect of crystal size on the physico-chemical characteristics of the zeolite, Y (FAU), and beta (BEA) is reported. The properties of nanocrystalline zeolites Y and Beta with crystal size around 50 nm are compared with the microcrystalline zeolite Y and microcrystalline zeolite beta, respectively. The performance of the nanocrystalline zeolite as a catalyst was investigated in the cracking of used palm oil for the production of biofuel. The nanocrystalline zeolite catalytic activity was compared with the activity of microcrystalline zeolite in order to study the effect of crystal size on the catalytic activity. Both nanocrystalline zeolites gave better performance in terms of conversion of used palm oil as well as selectivity for the formation of gasoline fraction. The increase in surface area and improved accessibility of the reactant in nanocrystalline zeolites enhanced the cracking activity as well as the desired product selectivity.

ChemInform Abstract: Synthesis, Characterization and Environmental Applications of Nanocrystalline Zeolites

AbstractReview: 84 refs.

Study of the mechanism of formation of nano-crystalline zeolite X in heterogeneous system

Aggregates of nano-sized zeolite 13X were synthesized at 373 K in order to study the mechanism of the nucleation and crystal growth processes of its formation. For this purpose solid phase (gel) separated from freshly prepared hydrogel having the batch molar composition: 10.94Na 2O·Al 2O 3·5.03SiO 2·417.90H 2O as well as the solids drawn off the reaction mixture, during its hydrothermal treatment at 100 °C and the crystallization end product (1.66 Na 2O·Al 2O 3·2.5SiO 2·6.6H 2O) were analyzed by different methods such as powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning-electron microscopy (SEM), electron diffraction (ED), atomic force microscopy (AFM), 29Si nuclear magnetic resonance spectroscopy ( 29Si-NMR) and thermal analysis methods (DTG, DSC). AFM analysis has shown that the freshly prepared gel is mainly composed of disc-shaped primary particles having height 0.6 nm and average diameter 2.4 nm. AFM analysis of the solids separated from the hydrogel at various stages of its hydrothermal treatment (heating at 100 °C) indicates that the particles of the partially and/or fully crystalline phase detected in gel are nuclei for further crystallization of zeolite, consisting mainly of D6Rs. Such observation was also confirmed by the other used methods.

Catalytic cyclodehydration of xylose to furfural in the presence of zeolite H-Beta and a micro/mesoporous Beta/TUD-1 composite material

The batch-wise and aqueous phase cyclodehydration of d-xylose to furfural (FUR) at 170 °C has been investigated in the presence of a composite material consisting of zeolite Beta nanocrystals (Si/Al = 12) embedded in a purely siliceous TUD-1 mesoporous matrix (BEATUD), characterised by elemental analysis, powder XRD, TEM and N 2 sorption. After 8 h the xylose conversion reached 98% and the FUR yield was 74%. The initial reaction rates for BEATUD and the bulk nanocrystalline zeolite Beta (BEA) were similar when expressed on the basis of the total amount of acid sites (Lewis + Brønsted) determined through FTIR analysis of adsorbed pyridine. However, the FUR yields at high xylose conversions of ca. 98% were higher for BEATUD (74%) than for bulk BEA (54%). TGA and DSC analyses for recovered catalysts showed that BEATUD possessed a lower amount of carbonaceous matter after a catalytic run, suggesting that the improved performance of the composite may be due to favourable competitive adsorption effects caused by the surrounding silica matrix. By thermally removing the carbonaceous matter between consecutive batch runs, BEATUD could be repeatedly reused without loss of catalytic performance.

Deactivation and coke combustion studies of nanocrystalline zeolite beta in catalytic cracking of used palm oil

Nanocrystalline zeolite beta was synthesized and its catalytic cracking activity for the production of biofuel from used palm oil was determined. The catalyst was characterized for its crystallinity, surface properties and morphology. The effect of reaction temperature on the catalytic cracking activity of nanocrystalline zeolite beta was also studied. The catalyst deactivation was monitored with the time on stream data by varying the palm oil to catalyst ratio of 6–14 at different temperatures. The deactivation data were analyzed using activity models and the deactivation parameters were obtained. The combustion behavior of the coked nanocrystalline zeolite beta derived at various coking temperature was studied by thermogravimetric analysis (TGA). The regeneration of the cracking catalyst was strongly correlated with the coke combustion kinetics. The coke combustion kinetics was studied and activation energy for coke combustion was determined.

Simultaneous n-hexane isomerization and benzene saturation over Pt/nano-crystalline zeolite beta

Hydroisomerization of n-hexane simultaneously proceeding with benzene saturation over platinum impregnated nano-crystalline zeolite beta (Si/Al = 25) at 1.0 MPa and 573–673 K was studied. The feed contained 30 wt% benzene. The synthesized catalyst was characterized by various techniques, e.g., powder X-ray diffraction, IR spectroscopy, thermal analysis, scanning electron microscopy and nitrogen adsorption. At the operating conditions used, total saturation of benzene with 95% selectivity to cyclohexane (CH) and methylcyclopentane (MCP) was observed. n-Hexane conversion increased with temperature whether benzene was present or not during the reaction. However, in the presence of benzene, n-hexane conversions as well as isomer selectivities were observed to be lower. This was attributed to reduced availability of acid sites by predominating benzene adsorption. Formation of carbenium ion on an acid site is questioned and plausible mechanism has been suggested.

Framework Stability of Nanocrystalline NaY in Aqueous Solution at Varying pH

Nanocrystalline zeolites are emerging as important materials for a variety of potential applications in industry and medicine. Reducing the particle size to less than 100 nm results in advantages for nanocrystalline zeolites relative to micrometer-sized zeolite crystals, such as very large total and external specific surface areas and reduced diffusion path lengths. Understanding the physical and chemical properties of zeolite nanocrystals is imperative for further development and application of nanocrystalline zeolites. In this study, the framework stability of nanocrystalline NaY zeolite with a crystal size of 66 nm and Si/Al = 1.74 was investigated at pH 7.4, 4, 2, and 1. The solids and solutions were analyzed using several different analytical techniques. The relative crystallinity and crystal size and morphology of the solids were examined by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The aluminum content, Si/Al, and coordination were monitored by inductively coupled plasma/optical emission spectroscopy (ICP/OES), X-ray photoelectron spectroscopy (XPS), and aluminum-27 solid-state magic-angle spinning NMR. As the acidity of the medium increased, the framework stability of nanocrystalline NaY decreased. Treatment of the zeolite samples at pH 1 resulted in complete degradation of the zeolite framework after 1 h. An increase in Si/Al was also observed, suggesting the selective removal of aluminum at low pH.