Nanocrystalline Zeolite Research Articles

Studies on the Selectivity Between O-Alkylation versus C-Alkylation of Phenol with Cyclohexene Using Nanocrystalline Beta Zeolite

The alkylation of phenol with cyclohexene using acid catalysts results in the generation of both O-alkylated and C-alkylated products, all of which hold significant utility across diverse industries. Cyclohexyl phenyl ether is utilized as a fragrant compound in perfumery applications. Through dehydrogenation, it transforms into diphenyl oxide (DPO), a significant chemical intermediate. In the current research nanocrystalline zeolite Beta was synthesised by vacuum-concentration coupled hydrothermal technique using tetraethyllammonium hydroxide templates and the catalytic performance was analysed for the alkylation of phenol with cyclohexene. Various parameters like reactant mole ratio, catalyst amount and temperature were assessed for better conversion of cyclohexene and desired product selectivity. The findings demonstrate that the catalyst effectively improves the conversion of cyclohexene while enhancing the selectivity of desired products. High efficiency of the catalyst is attributed due to its favourable structural characteristics, including its nano sized particles with open pore structure. The catalyst displayed up to ~96% conversion of cyclohexene ~55% selectivity towards the major product, cyclohexyl phenyl ether at optimal reaction conditions. Activation energy of the phenol alkylation with cyclohexene was calculated from the measured rate constant at various temperatures and was found to be 22.9 kJ/mol. There is negligible decline in percent conversion after reusing the catalyst for up to five runs.

Synthesis of hierarchical ZSM‐5 using polymer macro template for selective C‐alkylation of m‐cresol with tert‐butanol

AbstractThe present study reports nanocrystalline hierarchical zeoite ZSM‐5 as a potential alternative to homogeneous catalysts for the liquid phase tert‐butylation of m‐cresol. Polydiallyldimethylammonium chloride macro‐template was used to develop vacuum‐concentration dual template nano‐precursors by hydrothermal process. The catalytic performance was analyzed for the given reaction and the high percent conversion of reactants with excellent selectivity towards the ortho isomer, 2‐tert‐butyl‐5‐methylphenol was recorded. In contrast, the low activity and selectivity towards the tert‐butylation of m‐cresol, and the selectivity towards the desired product are noticed with the nanocrystalline zeolite ZSM‐5 synthesized without macro‐template. In addition, the catalyst is recoverable due to its robust nature, which indirectly reduces industrial wastage. Various parameters that affect the rate of the reaction were optimized. Kinetic analysis studies showed that the reaction followed first‐order kinetics with respect to tert‐ and the reaction obeyed the Langmuir‐Hinselwood mechanism. The activation energy was determined as 43.0 ± 0.2 kJ/mole. The study reveals that nanocrystalline hierarchical zeolite ZSM‐5 is an efficient, selective, simple, economical and environment‐friendly catalyst for the tert‐butylation of m‐cresol.

Hollow STW‐Type Zeolite Single Crystals with Aluminum Gradient for Highly Selective Production of p‐Xylene from Methanol‐Toluene Alkylation

AbstractZeolites with uniform micropores are important shape‐selective catalysts. However, the external acid sites of zeolites have a negative impact on shape‐selective catalysis, and the microporosity may lead to serious diffusion limitation. Herein, we report on the direct synthesis of hierarchical hollow STW‐type zeolite single crystals with a siliceous exterior. In an alkalinous fluoride medium, the nucleation of highly siliceous STW zeolites takes place first, and the nanocrystals are preferentially aligned on the outer surface of the gel agglomerates to grow into single crystalline shells upon crystallization. The lagged crystallization of the internal Al‐rich amorphous gels onto the inner surface of nanocrystalline zeolite shells leads to the formation of hollow cavities in the core of the zeolite crystals. The hollow zeolite single crystals possess a low‐to‐high aluminum gradient from the surface to the core, resulting in an intrinsic inert external surface, and exhibit superior catalytic performance in toluene methylation reactions.

Hollow STW-Type Zeolite Single Crystals with Aluminum Gradient for Highly Selective Production of p-Xylene from Methanol-Toluene Alkylation.

Zeolites with uniform micropores are important shape-selective catalysts. However, the external acid sites of zeolites have a negative impact on shape-selective catalysis, and the microporosity may lead to serious diffusion limitation. Herein, we report on the direct synthesis of hierarchical hollow STW-type zeolite single crystals with a siliceous exterior. In an alkalinous fluoride medium, the nucleation of highly siliceous STW zeolites takes place first, and the nanocrystals are preferentially aligned on the outer surface of the gel agglomerates to grow into single crystalline shells upon crystallization. The lagged crystallization of the internal Al-rich amorphous gels onto the inner surface of nanocrystalline zeolite shells leads to the formation of hollow cavities in the core of the zeolite crystals. The hollow zeolite single crystals possess a low-to-high aluminum gradient from the surface to the core, resulting in an intrinsic inert external surface, and exhibit superior catalytic performance in toluene methylation reactions.

Method for Healing Corrosion-Caused Degradation of Concrete and Causes of Efflorescence

The emergence of efflorescence may be traced back to a complex web of interconnected processes that include many different paths. Efflorescence, in its most fundamental form, is the consequence of bringing water containing dissolved salts to the surface of masonry, letting the water to evaporate, and then allowing the salts to remain on the surface of the brickwork after the water has evaporated. Salt solutions have the potential to migrate either over the surfaces of masonry units, through the spaces between mortar and brick units, or via the pores of the mortar or brick units. In addition to this, salt solutions have the potential to seep through the pores of the mortar or the brick units.Alkaline solutions (often alkali metal silicates or hydroxides) combine with solid alumina-silicate precursors to create these binders (Davidovits, 1991, 2008). The transformation of a solid alumina-silicate precursor into a synthetic amorphous or nano-crystalline binder has been modelled in a simplified fashion by Provis et al. (2005). Their scenario begins with the oligomerization of silicate and aluminate monomers following the dissolution of a solid alumina-silicate source in an alkali-activator. Polymerization and gelation of the generated alumina-silicate oligomers can result in either an amorphous alumina-silicate phase or a Nano-crystalline zeolite phase, depending on the processing circumstances.

Steam catalytic cracking and lump kinetics of naphtha to light olefins over nanocrystalline ZSM-5 zeolite.

This study investigates the reaction pathways and kinetics to comprehend the catalytic cracking of dodecane, a heavy naphtha model compound, over the nanocrystalline ZSM-5 catalyst in the presence and absence of steam with the aim of increasing olefin production. The nanocrystalline zeolite was characterized using XRD and BET, and the surface acidity was measured by NH3-TPD and Py-FTIR. The steam treated ZSM-5 contributed to an increase in pore volume with extra-framework alumina, resulting in highly catalytic active sites and hence higher olefin selectivity. The high conversion of dodecane (>90%) was achieved during catalytic cracking in the presence and absence of steam. In the presence of steam, the short pores of nano ZSM-5 led to an increase in the naphtha-to-olefin conversion with lesser dry gas and coke formation. The activation energies of primary cracking in the presence and absence of steam were slightly different. Lower activation energies through secondary cracking routes and higher reaction rate constants were obtained via assisted-steam catalytic cracking, promoted the selectivity towards light olefin products. Meanwhile the hydrogenation and alkylation reactions toward LPG and C5+ were favored in the absence of steam. Moreover, the ZSM-5 nano zeolite pores promoted more β-scission reactions, resulting in higher selectivity towards ethylene and dry gas.

Facile synthesis of mesoporous ZSM-5 aided by sonication and its application for VOCs capture

Application of ultrasound power to the mother liquor is popular pretreatment for zeolite synthesis which offers a simple way of accelerating crystallization process and finetuning the properties of nanocrystalline zeolites. In this work, sonication-aided synthesis of mesoporous ZSM-5 at low temperature and ambient pressure was systematically studied, in an attempt to reach efficient and benign synthesis of zeolites with hierarchical pore structure, which has wide applications as catalysts and sorbents. The effects of sonication duration, power density, sonication temperature and seeding on the crystallization of ZSM-5 were investigated. The obtained samples were characterized by XRD, SEM, BET and VOCs capture. High quality mesoporous ZSM-5 can be obtained by a facile 5 d synthesis at 363 K, much faster than conventional hydrothermal synthesis. The reduced synthesis time was mainly attributed to the enhanced crystallization kinetics caused by the fragmentation of seeds and nuclei, while sonication radiation had little impact on the nucleation process. Compared with control sample, mesoporous ZSM-5 prepared by sonochemical method had higher surface area and mesoporosity which demonstrated improved adsorption performance for the capture of isopropanol.

Beneficial effect of steam on synthesis of hierarchically porous zeolite‐templated carbons

AbstractHierarchically meso‐/microporous carbons were synthesized using nanocrystalline beta zeolite as a sacrificial template. The zeolite template possessed intercrystalline mesopores in addition to ordered micropores of the nanocrystals. Various amounts of steam were used with a carbon source, such as ethylene, propylene or acetonitrile, to generate a carbon structure inside the template. The synthesis results showed that adding a suitable amount of steam gave rise to faithful replication of the ordered microporous structure, while the intercrystalline mesopores were retained. That is, the carbon structure was formed selectively inside nanocrystalline zeolites rather than at the exterior by the steam addition. Microscopic observation and thermogravimetric analysis revealed that steam oxidized the carbon species deposited at the external surface of zeolite nanocrystals, and hence inhibited the undesirable carbon deposition. Furthermore, such a beneficial effect of steam could be applied for the carbon synthesis using other type zeolite templates.

Synthesis of nano-crystalline zeolite-A and zeolite-X from Indian coal fly ash, its characterization and performance evaluation for the removal of Cs+ and Sr2+ from simulated nuclear waste

Phase pure zeolite-A and zeolite-X were synthesized using coal fly ash (CFA) obtained from Indian thermal power plants by employing alkali fusion method followed by hydrothermal technique. The fusion of fly ash with Na2CO3 was accomplished by heating at 800 °C/2 h by maintaining fly ash to Na2CO3 ratio at 1.2. The fused mass was found to be nepheline (Na4Al4Si4O16); and on subsequent treatment of the fused mass with 3 M NaOH under hydrothermal condition transformed to zeolite-A (Na12Al12Si12O48.27H2O) and zeolite-X (Na88Al88Si104O384.194H2O). The effluent solution from zeolite-A synthesis was utilized to prepare cancrinite. The zeolites were characterized by XRD, FTIR, TG-DTA, SEM and surface area of the powders were measured by BET technique. The specific surface area of the zeolite-A and zeolite-X were found to be 58.29 ± 0.20 and 164.34 ± 5.4 m2g−1 respectively. The TG-DTA studies showed the conversion of nano-crystalline to micro-crystalline zeolites with loss of adsorbed water. The ion exchange capacities of these nano-crystalline zeolites were evaluated by using simulated nuclear waste solutions containing Cs+or Sr2+ ions. The adsorption capacity of zeolite-A was found to be 95.74 mg/g and 54.12 mg/g respectively for Sr2+ and Cs+ions. Similarly, zeolite-X shows the adsorption capacity of 93.14 mg/g and 53.14 mg/g respectively for Sr2+ and Cs+ ions.

Effect of Binder Content on the Properties of Nanocrystalline Zeolite BEA-based Catalysts for Benzene Alkylation with Propylene

Effect of Binder Content on the Properties of Nanocrystalline Zeolite BEA-based Catalysts for Benzene Alkylation with Propylene

Enhanced Room-Temperature Catalytic Decomposition of Cumene Hydroperoxide into Phenol and Acetone

ABSTRACTPhenol is an important industrial chemical that was manufactured by the Hock process. The sulphuric acid used in the Hock process to break cumene hydroperoxide into phenol and acetone suffers from environmental problems along with low selectivity towards the desired products. There are several solid acid catalysts have been tried in cumene hydroperoxide decomposition into an ecofriendly process. In the present work, an efficient environmentally friendly and economically benefitted zeolite-based catalyst was synthesized and tested for breaking cumene hydroperoxide (CHPO) into phenol and acetone. Beta zeolite and ZSM-5 zeolite were synthesised with nano crystalline geometry by hydrothermal method and tested their efficiency to break CHPO. The morphology and structure of nanocrystalline zeolite materials was investigated by Dynamic Light Scattering (DLS), X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) methods. From DLS studies it is documented that the zeolite particle size is tuneable as evidenced from particle size growths with the ageing time under hydrothermal treatment process. XRD analysis confirms the zeolite Beta and ZSM-5. The mean crystal size of Beta and ZSM-5 obtained from SEM analysis are 45 nm and 18.3 nm respectively. The optimization of reaction conditions for CHPO decomposition such as catalyst quantity and initial concentration of CHPO has been done using nanocrystalline Beta catalyst. The optimum catalyst amount and concentration of CHPO are 0.03 g and 15 mmol respectively. The results showed that the nanocrystalline Beta zeolite catalyst exhibits exceptional activity with 100% conversion of CHPO and yielded exclusively phenol and acetone at room temperature. No other by-products are detected. Also, the catalyst is stable and exhibits high product selectivity for phenol and acetone. The nature of the enhanced activity at room temperature for the decomposition of CHPO is suggested that higher accessibility of the active sites that are proposed to be associated with the zeolite with nano configuration with higher surface area and short distances for diffusion inside the channels in the nanocrystalline zeolite particles. The possibility of commercialization of beta zeolite is proved by complete conversion of CHPO with selective formation of phenol and acetone.

Cerium Incorporated Nanocrystalline ZSM-5: An Efficient Catalyst for Friedel Crafts Acylation of Toluene.

In this paper, the application of cerium modified nanocrystalline zeolite ZSM-5 as catalyst for Friedel Crafts acylation of toluene was investigated and compared with nanocrystalline ZSM-5. The acylating agent used was acetic anhydride. The zeolite samples were characterized by means of Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), Thermal analysis, ammonia temperature-programmed desorption (NH₃-TPD) and Nitrogen sorption analysis. The results show an enhanced Lewis acidity, pore volume and surface area for cerium modified ZSM-5 providing a superior accessibility for acetic anhydride and toluene to the active sites compared to the unmodified one, thereby leading to 93% conversion of acetic anhydride, which was higher than that of unmodified ZSM-5 sample.

Comprehensive Understanding of the Eco-Friendly Synthesis of Zeolites: Needs of 21st Century Sustainable Chemical Industries.

Zeolites have taken a leading position in petrochemical, fine, and bulk chemical industries due to their porous architecture, pore sizes, tunable acidity, and thermal stability. Various strategies of zeolites preparation, including template-free, solvent-free, and toxic mineral-free strategies are summarized. Moreover, the zeolite synthesis using naturally occurring minerals and sustainable natural templates is also discussed, which involves the synthesis of nanocrystalline zeolites of different framework structures using plant-based natural templates and biomass-derived renewable chemicals. Overall this personal account provides the fundamentals of various sustainable synthetic strategies reported in the literature for the synthesis of zeolites with suitable examples that will be useful for the students and will motivate experienced researchers to develop various novel sustainable methods for the synthesis of zeolites and other inorganic materials of industrial relevance.

Studies on the Potential of Nonmodified and Metal Oxide-Modified Coal Fly Ash Zeolites For Adsorption of Heavy Metals and Catalytic Degradation of Organics for Waste Water Recovery

A nanocrystalline zeolite of Na-X type (CFAZ) was synthesized by ultrasonic-assisted double stage fusion-hydrothermal alkaline conversion of lignite coal fly ash. Modified CFAZ with magnetic nanoparticles (MNP-CFAZ) was obtained by adding presynthesized magnetic nanoparticles between the synthesis stages. CFAZs loaded by particles of copper (Cu-CFAZ) and cobalt (Co-CFAZ) oxides were prepared by postsynthesis modification of the parent CFAZ, applying a wet impregnation technique. The parent and modified CFAZs were examined for their phase composition by X-ray diffraction, morphology by scanning electron microscopy, and surface characteristics by N2 physisorption. Comparative studies have been carried out on the adsorption capacity of the starting CFAZ and its derivatives with respect to Cd2+- and Pb2+-ions from aqueous solutions. Adsorption isotherms of Cd2+-ions on the studied samples were plotted and described by the adsorption equations of Langmuir, Freundlich, Langmuir–Freundlich, and Temkin. The best correlation between the experimental and model isotherms for the parent and modified CFAZ was found with the Langmuir linear model, assuming a monolayer adsorption mechanism. Parent and modified CFAZs were also studied as catalysts for heterogeneous thermal Fenton oxidation of methylene blue. At 90 °C, the higher catalytic activity exhibits the nonmodified sample, but with the decrease in temperature to 60 °C, the modified samples are more effective catalysts.

Synthesis and characterization of zeolite Linde Type W and its metal oxide composite Ag-O-LTW used for the decontamination of chemical warfare agent simulant

In this study, we have evaluated the performance of novel adsorbent zeolite Linde Type W and modified LTW with AgO metal oxide composite for the decontamination of chemical warfare agent simulant 2-chloroethylphenylsulphide (CEPS). Zeolites are nanoporous aluminosilicate minerals composed of silicon, aluminum and oxygen framework with cations and water molecules within the pores. The synthesized zeolite LTW and its composites Ag-O-LTW was characterized by XRD, FTIR, SEM-EDS and BET analytical techniques. The decontamination study of CWA simulant, CEPS was monitored by using GC-FID technique. The nanocrystalline zeolite LTW and Ag-O-LTW composites were found powerful adsorbents and showed great decontamination potential toward CWA simulant CEPS. The Ag-O-LTW showed better results (∼98 % decontamination in 7 hours) than LTW zeolite.

New zeolite-like RUB-5 and its related hydrous layer silicate RUB-6 structurally characterized by electron microscopy.

This study made use of a recently developed combination of advanced methods to reveal the atomic structure of a disordered nanocrystalline zeolite using exit wave reconstruction, automated diffraction tomography, disorder modelling and diffraction pattern simulation. By applying these methods, it was possible to determine the so far unknown structures of the hydrous layer silicate RUB-6 and the related zeolite-like material RUB-5. The structures of RUB-5 and RUB-6 contain the same dense layer-like building units (LLBUs). In the case of RUB-5, these building units are interconnected via additional SiO4/2 tetrahedra, giving rise to a framework structure with a 2D pore system consisting of intersecting 8-ring channels. In contrast, RUB-6 contains these LLBUs as separate silicate layers terminated by silanol/sil-oxy groups. Both RUB-6 and RUB-5 show stacking disorder with intergrowths of different polymorphs. The unique structure of RUB-6, together with the possibility for an interlayer expansion reaction to form RUB-5, make it a promising candidate for interlayer expansion with various metal sources to include catalytically active reaction centres.

Decoupling nucleation from crystal-growth for the synthesis of nanocrystalline zeolites.

The increasing demands for catalysts with improved accessibility to reactants call for a rational synthesis of nanosized zeolites. Herein we developed a facile approach for highly crystalline MFI-type (Silicalite-1 and ZSM-5) and beta zeolites with variable Si/Al ratios and high yield. This was achieved by kinetically decoupling the nucleation from the growth process of the zeolites in a highly concentrated gel system via a temperature-staged treatment. The carefully controlled low-water environment ensures only nucleation in stage I (aging), and hence the generation of abundant nuclei for the subsequent rapid crystallization within a self-confined space at stage II (growth). The method, without using expensive templates or additives, allows the syntheses of nanosized, well-isolated ZSM-5 (Si/Al = 100-∞, 36-88 nm, yield >85%) and Beta (Si/Al = 25-100, 21-66 nm, yield >95%). The ultra-small crystal size endows ZSM-5 zeolites with good catalytic activity, product selectivity and remarkably longer lifetime in methanol conversion reactions.

Benzene Alkylation with Propylene in the Presence of Nanocrystalline Zeolites BEA with Different Compositions

The effect of the chemical composition of nanocrystalline zeolites BEA on their physicochemical and catalytic properties in benzene alkylation with propylene is studied. It is shown that a decrease in the Al2O3 content in the reaction mixture during the synthesis of nanocrystalline zeolites leads to a decrease in the size of both the primary nanocrystals and their aggregates. The acidic properties of nanocrystalline zeolites BEA correlate with the aluminum concentration in the samples. The high concentration of acid sites of about 1400 μmol/g and the developed surface of zeolites BEA represented by nanocrystal aggregates provide a high activity of the samples and a high selectivity for the target product—cumene—owing to a decrease in the contribution of side reactions, namely, the secondary alkylation and oligomerization of propylene.

Mechanical Properties of Geopolymers Synthesized from Fly Ash and Red Mud under Ambient Conditions

Aluminosilicate gels form geopolymers and nanocrystalline zeolites which have comparable strength properties, making them a potential replacement for ordinary Portland cement. The study explores the use of two untreated industrial wastes, Class-F fly ash and red mud, for synthesizing geopolymeric material at ambient synthesis conditions. The high alkalinity present in the red mud was exploited for the dissolution of silica in the fly ash and red mud. The mechanical, mineralogical, microstructural, and pore characteristics were analyzed and the contributions of curing period, Si/Al, Na/Al, and liquid-to-solid (L/S) ratios on the compressive strength of the end products were also investigated. The alkalinity of the system due to the red mud was adequate for the dissolution of raw fly ash and the subsequent formation of aluminosilicate gels. The strength of the end product was directly proportional to the initial Si/Al ratio and the specimens with highest fly ash content exhibited highest compressive strength values after 28 days of curing. Furthermore, fly ash contributed to the formation and distribution of interstitial and capillary pores in the aluminosilicate matrix. The lowest L/S ratio of the initial mix resulted in the end product with the highest unconfined compressive strength.

Improved catalytic performance of mesoporous ZSM-5 nanocrystalline zeolite prepared by the cationic surfactant-ammonium salt mixed agent method in the methanol to gasoline reaction

A mixed organic agent system was employed to achieve mesoporous highly crystalline ZSM-5 zeolite. Decyltrimethylammonium bromide (DeTAB) and tetramethyl ammonium hydroxide (TMAOH) were used as the mesogenous and molecular templates respectively in the synthesis gel with a composition of 60SiO2: 1Al2O3:12Na2O:3150H2O:xDeTAB:8TMAOH. The sole presence of DeTAB as the mesogenous template in the synthesis gel led to the high degrees of mesoporosity in the ZSM-5/xD samples but negatively affected the intrinsic properties of zeolites. At the high concentration of DeTAB (x = 0.7), the mesopore volume dramatically increased while the relative crystallinity and the total acid sites critically decreased. By adding the TMA+ ions as a microporous template to the ZSM-5/0.7D synthesis gel, not only a zeolite with well-developed mesoporosity was obtained but also its crystal structure and the intrinsic acidity were preserved. The catalyst samples were characterized by FESEM, TEM, XRD, FT-IR, nitrogen adsorption–desorption isotherms, NH3-TPD and TGA techniques. The ZSM-5/0.7D/T exhibited higher surface area, higher mesopore volume, higher crystallinity and more acid sites than the ZSM-5/0.7D. The catalytic conversion of methanol to gasoline was conducted in a fixed bed reactor at T = 390 °C and WHSV = 4.74 h−1. In ZSM-5/0.7D/T catalyst the mesoporosity formation without severely damaging the crystal structure and the acidity of the zeolite led to the best catalytic performance including the highest liquid hydrocarbon yield, most stable catalytic performance and longest catalytic lifetime.