ZSM-5 Zeolite Samples Research Articles

Mesoporous configuration effects on the physicochemical features of hierarchical ZSM-5 supported cobalt oxide as catalysts in methane partial oxidation

Hierarchical porous system has become a prevalent method to overcome the diffusion limitation of conventional zeolites. Two types of mesopores characterized as intra-crystalline (mesopores in the zeolite pore wall) and inter-crystalline mesopores (meso-sized voids between nano-zeolite aggregates) could be formed in the synthesis of hierarchical zeolites. In an attempt to investigate the influence of mesopores structure on the physicochemical properties of hierarchical ZSM-5, specifically cobalt oxide impregnated ZSM-5 zeolite samples with intra- and inter-crystalline mesopores were synthesized through two different synthesis strategies. Analysis of the physicochemical properties of the as-modified hierarchical ZSM-5 catalysts were carried out using SEM, TEM, XPS, and H2-TPR which showed distinct features given by the two mesopores configurations. Co-oxide impregnated on ZSM-5 with inter-crystalline mesopores was dominated by Co(II) species, while Co-oxide/ZSM-5 showed a fair amount of Co(III) and Co(II). Furthermore, analysis of the catalytic activity was conducted using methane partial oxidation as a model reaction. With a variation in reaction time, various types of oxygenated products, i.e. methanol, formaldehyde, formic acid, and a small trace of carbon dioxide were observed. Catalytic results suggested that the Co-oxide/ZSM-5 material with inter-crystalline mesopores configuration is more active for the methane partial oxidation reaction compared to the Co-oxide/ZSM-5 with intracrystalline mesopores. This was confirmed by the formation of formaldehyde rather than methanol as the major product in the brief reaction time of 30 min.

Characterization of Zeolite ZSM-5 Synthesized from Kaolin and TPABr Using X-Ray Diffraction and Infrared Spectroscopy

Kaolin with alumina and silica content is used as the main material in this research to study the synthesis of ZSM-5 zeolite. The hydrothermal process was carried out through different aging times, namely 12, 24 and 36 hours. Tetrapropyl ammonium bromide (TPABr) was used as a template for the Mobile Five-1 (MFI) structure guide. X-ray diffraction (XRD) and infrared spectroscopy (FTIR) instruments were used to characterize the ZSM-5 zeolite formed from the synthesis results. This was done to identify the phase change from kaolin to zeolite ZSM-5. The results of the analysis using XRD for all samples showed a characteristic peak of the ZSM-5 zeolite at 2θ around 7.88°; 8.72° ;23.09°; 23.84° and 24.32°. However, samples with an aging time of 12 hours also showed peaks at 2θ around 15.84° and 26.03° which indicated an analsim phase. The absorption bands from the FTIR characterization for all samples are seen at wave numbers around 453, 542, 793, 1088 and 1221 cm−1 which are the characteristic peak points of ZSM-5 zeolite. The longer the aging time indicates that the crystallinity of the ZSM-5 zeolite is increasing. The highest crystallinity was obtained from ZSM-5 zeolite samples which were aged for 36 hours. This indicates an increasing number of ZSM-5 crystal nuclei with high purity because there is no other phase besides the ZSM-5 phase.

Synthesis and Characterization of Fe-Substituted ZSM-5 Zeolite and Its Catalytic Performance for Alkylation of Benzene with Dilute Ethylene

A series of Fe-substituted ZSM-5 zeolite samples with an almost constant Si/(Fe + Al) molar ratio of 50 but varied levels of Fe substitution were synthesized via an in situ seed-induced hydrotherma...

Determination of micropore volumes of ZSM-5 zeolite samples by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy using back-propagation artificial neural network (BP-ANN) and non-negative matrix factorization -alternating least squares (NMF-ALS) as chemometric approaches

In this paper, the proposed method has been introduced for qualitative and quantitative determination of micropore volume in nano ZSM-5 zeolite samples based on diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy along with chemometric methods.For this purpose, a total of 72 samples were provided and DR-FTMIR spectra corresponding to the samples were obtained in the range of 400–4000 cm−1. In order to estimate total surface area from a nitrogen adsorption isotherm, Brauner Emmett Teller (BET) method as a reference method was used.The results are displayed that the significant adsorption peak of the mid-IR spectroscopy in 3660 cm−1 is corresponded to the SiOH groups of the zeolite external surface that is a criterion for the intensity of the mesoporosity. The intensity of the 3745 cm−1 peak is grown up with enhancing the external surface area.These changes were evaluated by non-negative matrix factorization -alternating least squares (NMF –ALS) chemometrics approach for estimating the microporosity in nano ZSM-5 zeolite samples.Back-propagation artificial neural network (BP-ANN) as a nonlinear multivariate regression technique was also used to determine the micropore volume of zeolites based on DRIFT spectroscopy.For BP-ANN model in these samples, R and minimum mean squared error (MSE) values of the testing set data with 5 hidden nodes were 9.95 × 10−1 and 4.11 × 10−7, respectively.The achieved results are presented that DRIFT spectroscopy coupled with chemometrics approaches is a precise, explicit and easy technique to analyze the volume of the micropore in ZSM-5 nano-catalyst samples.

Synthesis and performance of ZSM-5 and HZSM-5 in desulfurization of naphtha

In this work, four ZSM-5 and HZSM-5 zeolites were synthesized hydrothermally with SiO2/Al2O3 ratio of 40 and 80 and the performance of these samples was studied in desulfurization of heavy naphtha. Samples were analyzed by X-ray diffraction, the Brunauer–Emmett–Teller, field emission scanning electron microscope (FE-SEM), and temperature-programmed desorption of ammonia (NH3–TPD). All samples were tested at 450 °C, 15 bar, H2/Oil = 150 Nml/ml, and weight hourly space velocity (WHSV) = 1 h−1 in a fixed-bed reactor (a Catatest reactor system). The standard of ASTM-D5453 was used for measuring the total sulfur of the feed and products. The result shows that the HZSM-5 zeolites have higher acidity compared to ZSM-5 zeolite samples; as a result, they are more capable of eliminating sulfuric compounds. The sample with SiO2/Al2O3 of 40 shows 87% desulfurization.

The diquaternary ammonium surfactant-directed synthesis of single-unit-cell nanowires of ZSM-5 zeolite.

Hierarchical ultrathin ZSM-5 zeolite samples with controllable crystal growth directions were realized by designing bifunctional soft templates with different hydrophobic alkyl chain groups. MFI-type crystal growth along the a-c plane and stacking along the b-axis could be controlled to form nanowires of ZSM-5, which exhibited better catalytic activity for phenol hydroxylation than nanosheets of ZSM-5.

Nanocrystal H[Fe, Al]ZSM-5 zeolites with different silica-alumina composition for conversion of dimethyl ether to gasoline

Non-petroleum route to produce transportation fuels is alternative way to address the fast depletion of the crude oil reservoir, especially in China. In this work, series of nanocrystal H[Fe, Al]ZSM-5 zeolite samples with different SiO2/Al2O3 ratio were prepared with hydrothermal method using sodium aluminate and tetraethyl orthosilicate as Al and Si sources, respectively, and the tetrapropylammonium hydroxide was used for structure-directing agent (SDA). The synthesized zeolites were characterized in detail by UV–Vis, X-ray diffraction, scanning electron microscope, N2 sorption, X-ray fluorescence, ammonia temperature-programmed desorption and pyridine-FTIR techniques. Fe species were incorporated into ZSM-5 framework, resulting in the formation of some new active sites. For the Iron-containing nanocrystal ZSM-5 samples with different SiO2/Al2O3 ratio, the B and L acid strength and amounts are determined by the coexistence and synergistic effect of Al- and Fe-based acid sites. The catalytic results illustrated that the H[Fe, Al]ZSM-5 zeolite with SiO2/Al2O3 ratio for 45 exhibited the best catalytic activity and stability due to its maximum B acid amount and higher B/L ratio. The DME conversion remains at >98% within the 135 h investigation. Moreover, the gasoline yield was up to 72.5%, and the selectivity for aromatics and durene could be reduced to 40% and 1%, respectively.

Application of diffuse reflectance near-infrared spectrometry and chemometrics in characterization of micro and mesoporous ZSM-5 zeolites.

Evaluation of porosity type of zeolites is one of the critical topics in catalysis science. The relationship between external surface area and diffuse reflectance (DR) spectra in the near-infrared spectral region has been employed to propose a method for estimation of micro or mesoporosity in ZSM-5 zeolite samples. Linear discriminant analysis (LDA) was utilized to estimate degree of porosity based on near-infrared diffuse reflectance spectra. The textural properties (surface area and pore volume) of micro and mesoporous ZSM-5 samples were measured using N2 adsorption/desorption technique at 77 K and external surface area was calculated by t-plot as a reference method in this work. Several porous ZSM-5 samples with only microporous channels or mesoporous besides them were classified in terms of external surface area and meso pore volume derived from t-plot as “Micro” or “Micro + Meso” type samples. It was concluded that LDA using the PCA for feature selection is capable of generalization and could precisely predict the type of porosity in ZSM-5 zeolites.

Aromatization over nanosized Ga-containing ZSM-5 zeolites prepared by different methods: Effect of acidity of active Ga species on the catalytic performance

Nanosized Ga-containing ZSM-5 zeolites were prepared via isomorphous substitution and impregnation followed by characterized using various techniques. The catalytic performance of the zeolites for the aromatization of 1-hexene was investigated. The results indicate that isomorphous substitution promotes the incorporation of Ga heteroatoms into the framework along with the formation of extra-framework GaO+ species ([GaO+]a) that have stronger interactions with the negative potential of the framework. In addition, based on the Py-IR results and catalytic performance, the [GaO+]a species with stronger Lewis acid sites produced a better synergism with moderate Brønsted acid sites and thus improved the selectivity to aromatic compounds. However, the impregnation results in the formation of Ga2O3 phase and small amounts of GaO+ species that are mainly located on the external surface ([GaO+]b), which contribute to weaker Lewis acid sites due to weaker interactions with the zeolite framework. During 1-hexene aromatization, the nanosized Ga isomorphously substituted ZSM-5 zeolite samples (Gax-NZ5) exhibited better catalytic performance compared to the impregnated samples, and the highest aromatic yield (i.e., 65.4wt%) was achieved over the Ga4.2-NZ5 sample, which contained with the highest Ga content.

A study on the effect of SiO2/Al2O3 ratio on the structure and performance of nano-sized ZSM-5 in methanol to propylene conversion

The effect of SiO2/Al2O3 ratio on high silica content nano-sized HZSM-5 stability and selectivity in conversion of methanol to propylene (MTP) has been investigated in a continuous flow isotherm fixed-bed reactor. Highly crystalline HZSM-5 zeolite samples with SiO2/Al2O3 ratios ranging 150–200 have been prepared and characterized using XRD, ICP-AES analytical techniques, NH3-TPD, BET surface area and SEM imaging for studying their physical and chemical behavior. The reaction was conducted at 480 °C and 1bar with WHSV = 1 h−1 and a solution with 1:1 wt% of methanol and water as feed. Over thoroughly monitoring the catalyst synthesis conditions, the nanocrystal ZSM-5 zeolite samples were fabricated with fairly close microstructural properties and crystal sizes in order to be able to study the effect of SiO2/Al2O3 ratio on the ZSM-5’s performance in MTP. Results show that although the crystal size does not considerably affect the elementary structure of the zeolite active sites, it seems to be an influential factor in bond strength of Si–O versus Al–O. The results have also showed that increase of SiO2/Al2O3 ratio leads to higher selectivity and stability of catalyst.

Simultaneous existence of defects and mesopores in nanosized ZSM-5 zeolite studied by positron annihilation and X-ray diffraction spectroscopies

Crystallization, formation, and accumulation of defects and mesopores in the ZSM-5 zeolite samples, which are synthesized from the gel composition of 1.2Na2O 0.1Al2O3 0.8 tetra-propylammonium hydroxide (TPAOH) 6SiO2 400H2O at a temperature of 140 degree Celsius (°C) in 10, 15, and 18 h, are studied by using the Positron annihilation lifetime (PALS) and X-ray diffraction (XRD) spectroscopies. The XRD is used for investigating the crystalline concentration and nano-crystal size of ZSM-5 during the crystallizing process, whereas the PALS is performed in order to determine the presence of templates, defects, and mesopores in the zeolite samples. The latter are calcined in air during 1, 2, and 3 h at a temperature of 600 °C before being measured. The results obtained indicate that there exist clusters of small crystals in the early crystalline stages of the samples. The size of these crystals increases with time and reaches approximately 100 nm after 18 h of reaction. In addition, the template (TPAOH) is found to exist not only in the channels inside the framework but also in the mesopores outside it. Finally, by analyzing the Positron lifetime spectra, we have found for the first time the simultaneous existence of defects and mesopores, which are formatted and accumulated during the crystallization of ZSM-5. Those important results contribute significantly to our understanding of the internal structure of the synthetic zeolite ZSM-5 as well as the synthetic processes for producing zeolites with special features.

Effect of SiO2/Al2O3 ratio on the performance of nanocrystal ZSM-5 zeolite catalysts in methanol to gasoline conversion

In this study, the effect of SiO2/Al2O3 ratio on the catalytic performance of nanocrystal ZSM-5 zeolite catalyst in the methanol to gasoline conversion (MTG) was investigated. A series of zeolite samples with different SiO2/Al2O3 ratios of 23, 47, 107, 217 and 411 were synthesised. Through systematically controlling the material synthesis conditions, these nanocrystal ZSM-5 zeolite samples were produced to have very similar crystal sizes and structural properties, thus providing an ideal opportunity to study the intrinsic effect of SiO2/Al2O3 ratio on the performance of the ZSM-5 samples in MTG. The MTG experimentation was carried out in a fixed-bed reactor under a set of constant conditions of temperature 375°C, pressure 1MPa and WHSV 2h−1. A steady methanol conversion was sustained with increasing the SiO2/Al2O3 ratio, and a progressive decrease in methanol conversion was found over catalysts with low SiO2/Al2O3 ratios (≤107) after 5h on stream. Decreasing the SiO2/Al2O3 ratio promoted C1-C4 selectivity and thus decreased gasoline yield. It was also found that decreasing the SiO2/Al2O3 ratio promoted aromatisation reactions and hence higher durene selectivity and more coke formation, resulting in rapid catalyst deactivation. The sample with SiO2/Al2O3 ratio of 217 showed the highest methanol conversion, gasoline yield, and very low coke formation.

Synthesis of nanosized Silicalite-1 in F−media

This paper reports on the successful crystallization of monodisperse, highly crystalline, nanosized zeolite Silicalite-1 crystals in fluoride media by using an active silica gel as silica source and tetrapropylammonium fluoride as structure directing agent. The synthesis procedure is hydrothermal dynamic crystallization. The silica/water ratio and synthesis temperature were reduced to optimize the number of crystal nuclei and control the rate of crystallization for obtaining nanosized zeolite crystals. Meanwhile, F− ions were used to partly replace OH− ions in the synthesis system to obtain zeolite products with high crystallinity. Analytical results of XRD-, SEM-, Dynamic Light Scanning- (DLS) IR-, Simultaneous Thermal Analysis- (STA) and N2 adsorption and desorption experiments show that the average particle size of zeolite Silicalite-1 product is about 45 nm and shows high crystallinity. The F− containing Silicalite-1 zeolite sample was compared with an industrial ZSM-5 zeolite sample and it shows obvious advantages in both reduced particle size and enhanced crystallinity.

Transformation of 1-hexene on Pt supported ZSM-5 zeolite modified with tin, copper or chromium

ZSM-5 zeolite samples containing Pt and a second metal (Sn, Cu or Cr) were prepared by different impregnation procedures. All these catalysts were highly active in the transformation of 1-hexene. A great variety of hydrocarbons were obtained, whose proportion depended on the particular catalyst and the reaction conditions. In general, low temperatures (250 °C) favored the double bond shift reaction, whereas medium temperatures (350 °C) predominantly led to cracking and skeletal isomerization. However, cracking was the major reaction at temperatures above 450 °C. The addition of the second metal decreased the hydrogenating activity of Pt and so olefins constituted a considerable fraction in the product. The use of nitrogen as a carrier gas instead of hydrogen favored the formation of both internal and branched olefins while reducing cracking. The reaction products are interesting for their use in gasoline blending.

Structural, morphological and catalytic investigations on hierarchical ZSM-5 zeolite hexagonal cubes by surfactant assisted hydrothermal method

Nanosized ZSM-5 zeolite hexagonal cubic micro-blocks with different Si/Al ratios were successfully synthesized by using TPAOH in the presence of nonionic surfactant (Triton X-100) by a hydrothermal method. The samples prepared with the surfactant were characterized by XRD, XRF, FT-IR, N2 adsorption, HR-TEM, HR-SEM and NH3-TPD analysis to evaluate the particle structure, size and acid strength. Pure crystalline phase of ZSM-5 is confirmed by powder X-ray diffraction. FT-IR analysis further showed that nanosized zeolite has double five rings of the MFI-type of typical absorption at about 550cm-1. The SEM images clearly show that all ZSM-5 zeolite samples possess the similar hexagonal spheres morphology with particle size of about 320–360nm. The influence of Triton X-100 in the structural, textural, morphological and catalytic properties of ZSM-5 is compared with conventional ZSM-5. The catalytic activity of ZSM-5 zeolites with different Si/Al ratios (ZSM-5-WS(x) and ZSM-5-WOS(x)) is evaluated in the selective oxidation of benzyl alcohol (BzOH) using tert-butyl hydroperoxide (TBHP) as an oxidant and water as a solvent. The Triton X-100-assisted preparation yielded a zeolite exhibiting a higher conversion than the one prepared in the absence of Triton X-100. Among the catalysts, ZSM-5-WS(28) (Si/Al=28) catalyst exhibited significantly higher conversion at optimum conditions. This catalyst can be retrieved and reprocessed for five times without a significant loss in its activity and selectivity.

Synthesis of nanosized ZSM-5 zeolite with intracrystalline mesopores

A series of nanosized ZSM-5 zeolite samples with intracrystalline mesopores has been synthesized using organosilane functioned fumed silica as silica source and tetrapropylammonium hydroxide as microporous structure directing agent. The organic moiety linked on the surface of fumed silica blocks the growth of zeolite crystal, forming the nanosized zeolite crystal and intracrystalline defects inside the nano-crystal. The formation of the mesopores is by bond-blocking function in crystallization. The XRD results indicate that the samples are high crystalline ZSM-5 and the TEM images show that the samples are nanosized with the size ca. 20nm and the intracrystalline mesopores about 3nm exist inside the nanosized crystal.

Effects of concentration on the alkali-treatment of ZSM-5 zeolite: a study on dividing points

Alkali-treatment for modification or dissolution has attracted extensive attention as an innovative means of preparing porous materials. The hierarchical porosity of modified zeolite is highly dependent on its treatment conditions. However, studies on critical alkali-treatment concentrations, specifically those that discuss the dividing points, have not yet been reported. In this article, the pore and crystalline properties of ZSM-5 zeolite samples modified by different concentrations of alkali-treatment are investigated. The experimental results show that the pore properties of the samples change as a function of the alkaline concentration. The total surface, mesopore surface area, total pore volume, mesopore volume, and average pore diameter of ZSM-5 zeolites increase and then decrease with increasing alkaline concentrations. The micropore surface area, micropore volume, and crystallinity of the samples decrease monotonously. The following dividing points are proposed: 0.40 mol/L as the threshold for alkali-modification and 1.00 mol/L as the starting point for alkali-dissolution. A possible desilication mechanism is also proposed.

Shape-controlled synthesis of monolithic ZSM-5 zeolite with hierarchical structure and mechanical stability

Columned ZSM-5 zeolite monoliths with hierarchical structure and excellent mechanical strength were successfully prepared by a hydrothermal transformation method. The pre-formed extrudates of aluminosilicate embedded with β zeolite were subjected to a hydrothermal synthesis system and the hierarchical porous ZSM-5 zeolite monoliths with the same columned shape were obtained after the hydrothermal treatment. The intra-particle hollow structure formed during hydrothermal synthesis was attributed to the digestion of inner β zeolite accompanying with the growth of ZSM-5 zeolite shell. The related data of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) analysis, N 2-sorption experiment and mercury intrusion prosimetry (MIP), showed ZSM-5 zeolite monolith had enriched multi-porosity and excellent mechanical stability, which contribute to its further application in field of catalysis and separation. The obtained hierarchical ZSM-5 zeolite monoliths showed superior catalytic performance in α-pinene isomerization for their proper acidity and good diffusion, compared with the ZSM-5 zeolite sample prepared from the precursor without β zeolite.

Preparation and characterization of nanosized ZSM-5 zeolite using kaolin and investigation of kaolin content, crystallization time and temperature changes on the size and crystallinity of products

Nano sized ZSM-5 zeolite samples were synthesized successively from kaolin clay as alumina source having a large amount of quartz (39%) and silicic acid as silica source by hydrothermal treatment with NaOH in the presence of tetrapropylammonium hydroxide as a template. Then the effect of kaolin content, crystallization temperature and time on the size and crystallinity of the products were investigated. The prepared samples were characterized using XRD, SEM, EDS and FT-IR techniques. The results showed that the synthesized ZSM-5 zeolite samples were almost pure and their crystallization was almost complete. The average particle size, as determined by Debye-Scherrer equation, was in the range of 20-42 nm. Increasing kaolin content on crystal size was more effective than increase in crystallization temperature and time. Additional evidences for the nano sized ZSM-5 zeolite were the asymmetric stretch vibration band at 1225 cm-1 in the FT-IR spectra and TEM images. The scanning electron micrographs of the synthesized zeolites showed that they are spherical shape crystals.

A spectroscopic study of the nature and accessibility of protonic and cationic sites in H- and partially exchanged Cu- and Co-MFI zeolites

A study of the nature and accessibility of internal and external protonic and cationic sites has been carried out on protonic and partially Co- or Cu-exchanged ZSM5zeolite samples through UV-Vis and FT-IR spectroscopies. The samples were prepared by ionic exchange. o-toluonitrile has been chosen as a probe for the external surface of the zeolites. The existence of Cu2+ and Co2+ sites at positions different from those exchanging the active protons of the zeolites is emphasized.