Catalytic combustion of chlorinated ethylenes over H‐zeolites

Several H‐zeolites (H‐Y, H‐ZSM‐5 and H‐MOR) were investigated for the catalytic combustion of chlorinated ethylenes, namely 1,1‐dichloroethylene and trichloroethylene. Conversion was inversely related to the chlorine content of the feed molecule. H‐ZSM‐5 zeolite was the most active catalyst in 1,1‐dichloroethylene combustion whereas H‐MOR was the most effective zeolite for trichloroethylene destruction. Temperature‐programmed desorption of ammonia and diffuse reflectance FT‐IR measurements of adsorbed pyridine revealed that strong Brønsted acidity plays an important role in controlling the activity of H‐zeolites. The main combustion products were CO, CO₂, HCl, and Cl₂. Additionally, small amounts of highly chlorinated by‐products were also detected, namely trichloroethylene and tetrachloroethylene. H‐zeolites showed a great selectivity to HCl formation. © 2002 Society of Chemical Industry     

Effect of Phosphate Modification on the Brønsted Acidity and Methanol‐to‐Olefin Conversion Activity of Zeolite ZSM‐5

Phosphate‐modified ZSM‐5 zeolites were studied by standard characterization techniques and solid‐state nuclear magnetic resonance spectroscopy, and in the methanol‐to‐olefin (MTO) conversion. Considering the physicochemical properties of the ZSM‐5 zeolites, the most important effects of the phosphate modification are a deposition of polyphosphates in the pore system and a decrease of the acid site density, but not of the acid site strength. The significant increase in the selectivity to C₂ – C₄ alkenes and the decrease of C₅₊ formation in the MTO reaction for a phosphate coverage of about 5 wt % are explained by extra‐framework phosphate species near the crossing intersections of the ZSM‐5 pore system, which hinder the formation of large intermediates and reaction products.     

Transferring polypropylene into carbon nanotubes via combustion of PP/zeolites (H‐ZSM‐5 or H‐beta)/Ni2O3

In a simple device, two kinds of zeolites were successfully used as synergistic additive to promote formation of the multi‐walled carbon nanotubes (MWNTs) from polypropylene (PP) via combustion. More importantly, this kind of process may potentially act as a new approach for recycling plastic wastes, because it could effectively transfer polyolefin wastes into valuable carbon materials. Experimental results demonstrated that the higher quality of MWNTs can be obtained from the mixture (PP/H‐Beta/Ni₂O₃) than that from the mixture (PP/H‐ZSM‐5/Ni₂O₃). At the same time, the yield of MWNTs from PP/H‐ZSM‐5/Ni₂O₃ system is much lower than that from PP/H‐Beta/Ni₂O₃ under the same condition. The reason for the different effects of both types of zeolites on the morphology and the yield of the MWNTs was analyzed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The versatile synthesis method for hierarchical micro‐ and mesoporous zeolite: An embedded nanocarbon cluster approach

In this work, we are reporting for the first time the synthesis of hierarchical micro‐ and mesoporous zeolite using silica–carbon (SiO₂/C) composites prepared by pyrolysis of carbonaceous gases in the presence of silica gel. The pyrolysis effectively yielded carbon deposited onto the raw silica material. The obtained SiO₂/C composites were utilised as a bifunctional material, mesoporous template and silica source, for the zeolite synthesis. Tetrapropylammonium hydroxide (TPAOH) was used as a microporous template. The combination of the obtained composites and the TPAOH for the hydrothermal synthesis resulted in the formation of hierarchical micro‐ and mesoporous ZSM‐5. The results from the SEM, TEM, and N₂ adsorption/desorption isotherms, and ²⁷Al MAS NMR characterisations of the synthesised samples obtained after the removal of the templates confirmed the successful formation of the micro‐ and mesoporous zeolites. The mesoporosity of the zeolites could be controlled by adjusting the carbon content in the SiO₂/C composites while the carbon content could be controlled by varying the deposition time and the concentration of the carbonaceous gases used. This controllable and efficient synthesis method is considered to be a promising method for creating hierarchical micro‐ and mesoporous zeolites. © 2011 Canadian Society for Chemical Engineering     

Synthesis of modified catalyst and stabilization of CuO/NH4‐ZSM‐5 for conversion of methanol to gasoline

In this article, the catalytic conversion of methanol to gasoline range hydrocarbons has been studied over CuO/ NH₄‐ZSM‐5(3,5,7,9%) catalysts prepared via sono‐chemistry methods. In order to improve, copper oxide can be used as a booster on NH₄‐ZSM‐5 this catalyst property. Accordingly, the conversion process of Methanol to Gasoline (MTG) was conducted under a pressure of 1 atm and temperature of 400°C by a fixed‐bed reactor on copper oxide catalysts which were prepared based on synthetic NH₄‐ZSM‐5. The synthetic catalyst was investigated by such analyses as BET, XRD, FT‐IR, and SEM. Formation of copper oxide phase and proper distribution of copper oxide were proven on the basic level of using XRD analysis. BET analysis showed the reduction in catalyst level and SEM images depicted the proper distribution of particles. The present investigation is to study the effect of CuO loading on NH4‐ZSM‐5 support for conversion of methanol to gasoline range hydrocarbons. A series of CuO/ NH4‐ZSM‐5 catalysts were prepared, characterized, and experimented for their performance on methanol conversion and hydrocarbon yield.     

Migration of Potassium in an Fe2O3/H‐ZSM‐5 Composite Catalyst

The migration of potassium in an iron/H‐ZSM‐5 bifunctional system was investigated by pressing K/Fe₂O₃ and H‐ZSM‐5 in a pellet using 2 t of pressure. These pellets were heated at 350 °C in air for a number of days. Migration of potassium was visualized using energy‐dispersive X‐ray profiling. The distribution of potassium in the Fe₂O₃ phase and the H‐ZSM‐5 phase was approximately constant, with a step change over the phase boundary. The step change varied as a function of the heating time. The amount of potassium migrated from the Fe₂O₃ phase to the H‐ZSM‐5 phase was quantified using NH₃‐TPD. It is shown that an equilibrium distribution between potassium in the Fe₂O₃ phase and the H‐ZSM‐5 phase is obtained after ca. 7 days of heating.     

Ethanol perm‐selective B‐ZSM‐5 zeolite membranes from dilute solutions

Boron‐substituted MFI (B‐ZSM‐5) zeolite membranes with high pervaporation (PV) performance were prepared onto seeded inexpensive macroporous α‐Al₂O₃ supports from dilute solution and explored for the separation of ethanol/water mixtures by PV. The effects of several parameters on microstructures and PV performance of the B‐ZSM‐5 membranes were examined systematically, including the seed size, synthesis temperature, crystallization time, B/Si ratio, H₂O/SiO₂ ratio and silica source. A continuous and compact B‐ZSM‐5 membrane was fabricated from solution containing 1 tetraethyl orthosilicate/0.2 tetrapropylammonium hydroxide/0.06 boric acid/600 H₂O at 448 K for 24 h, showing a separation factor of 55 and a flux of 2.6 kg/m² h along with high reproducibility for a 5 wt % ethanol/water mixture at 333 K. It was demonstrated that the incorporation of boron into mobile five (MFI) structure could increase the hydrophobicity of B‐ZSM‐5 membrane evidenced by the improved contact angle and amount of the adsorbed ethanol, and thus enhance the PV property for ethanol/water mixtures. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2447–2458, 2016     

Production of olefins from ethanol by Fe and/or P‐modified H‐ZSM‐5 zeolite catalysts

BACKGROUND: Much attention has been paid to the catalytic conversion of ethanol to olefins, since biomass resources such as ethanol are carbon‐neutral and renewable, and olefins are useful as both fuels and chemicals. It has been reported that zeolite H‐ZSM‐5 is effective for converting ethanol to hydrocarbons, with the chief products being aromatic compounds. RESULTS: Successive addition of Fe and P to the H‐ZSM‐5 improved the initial selectivity for propylene, while the sole addition of Fe or P and co‐addition of Fe and P showed medium initial selectivity. In general, catalysts showing higher initial selectivity for propylene exhibited a steeper decrease in propylene selectivity with time on‐stream. The cause of the change in product selectivity may be carbon deposition during reaction. Addition of Fe and P can improve catalytic stability when processing both neat and aqueous ethanol. The catalytic performance was regenerated by calcination in flowing air. CONCLUSION: Fe‐ and/or P‐modified H‐ZSM‐5 zeolite catalysts efficiently produced olefins (especially propylene) from ethanol. Effective catalyst regeneration was achieved by calcination in flowing air. Copyright © 2010 Society of Chemical Industry     

One‐pot synthesis of sheet‐like MFI as high‐performance catalyst for toluene disproportionation

In this study, one‐pot hydrothermal synthesis of sheet‐like ZSM‐5 as a high‐performance catalyst for toluene disproportionation was carried out using binary surfactants. In the dual template, tetraethylammonium hydroxide was used to construct the microporous structure of ZSM‐5, and cationic surfactant (e.g., octadecyltrimethylammonium chloride (C₁₈TMAC), hexadecyltrimethyl ammonium bromide (C₁₆TMAB), and tetradecyltrimethylammonium bromide, (C₁₄TMAB)) can change the growth habits of the ZSM‐5 crystals by hindering the regular stacking of zeolite layers from their longer hydrophobic chain. From the XRD pattern of the as‐synthesized samples which were hydrothermally treated for different time, it was found that a lamellar mesostructured intermediate gradually transformed into the sheet‐like ZSM‐5 during hydrothermal process. With a proper amount of cationic surfactant, the thickness of the sheet‐like ZSM‐5 could be controlled to less than 30 nm. Concerning the catalyst application, the toluene disproportionation performance over the sheet‐like ZSM‐5 is 1.5 times higher than that of the commercial ZSM‐5. The higher conversion is ascribed to the faster diffusion amount due to the sheet‐like ZSM‐5.     

Synthesis of ZSM‐5 by hydrothermal method with pre‐mixing in a stirred‐tank reactor

This work proposed a synthesis route of ZSM‐5 via the hydrothermal method with premixing in a stirred tank reactor (STR). Effects of various operating conditions, including pre‐mixing time, molar ratio of SiO₂/Al₂O₃, TPAOH (organic template agents) concentration, NaCl (alkali metal cations) concentration, crystallization temperature, and crystallization reaction time, on the average particle size (PS) and particle size distribution (PSD) were investigated. It was found that the pre‐mixing time in the STR significantly affect the formation of proto‐nuclei in premixing process and crystal growth in hydrothermal reaction process, and consequently influence the PS and PSD of the prepared ZSM‐5. ZSM‐5 with good thermal stability, a PS of 380 nm, PSD of 0.17–0.9 µm, pore diameter of 2.31 nm, pore volume of 0.19 cm³ · g^?1 and specific surface area of 337.25 m² · g^?1 were obtained under the optimal conditions of a crystallization reaction time of 24 h, a crystallization temperature of 130 °C, a molar ratio of SiO₂/Al₂O₃ of 200, a TPAOH concentration of 3.5 mol · L^?1, NaCl concentration of 0.3 mol · L^?1, and a pre‐mixing time of 5 h. This work indicated that the operating conditions including premixing time have a significant effect on its PS and PSD.     

High performance ZSM‐5 membranes on coarse macroporous α‐Al2O3 supports for dehydration of alcohols

High‐performance ZSM‐5 membranes with a low Si/Al ratio of 10.3 were prepared on cheap coarse macroporous α‐Al₂O₃ tubes by fluoride route without organic template. The effects of crystallization time and aluminum source on the growth, morphology and pervaporation (PV) performances of the as‐synthesized membranes were investigated. The feasibility of preparing ZSM‐5 membranes with different Si/Al ratio which was implemented by using different Al₂(SO₄)₃·18H₂O content in synthesis gel were discussed. It was found that the aluminum source had significant effect on the synthesis of membranes. The ZSM‐5 membranes prepared by using Al₂(SO₄)₃·18H₂O as an aluminum source from synthetic gel with composition of 1SiO₂/0.05Al₂O₃/0.17Na₂O/0.9NaF/45H₂O showed high reproducibility and high PV performance with flux of 3.85 kg/(m²·h) and separation factor of higher than 10,000 in dehydration of 90 wt % i‐PrOH/H₂O at 348 K. Moreover, the ZSM‐5 membranes exhibited high water perm‐selectivity performance for dehydration of 90 wt % n‐PrOH/H₂O, n‐BtOH/H₂O, and i‐BtOH/H₂O mixtures, respectively. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2813–2824, 2016     

The State of the Art in Selective Catalytic Reduction of NOx by Ammonia Using Metal‐Exchanged Zeolite Catalysts

An overview is given of the selective catalytic reduction of NO_x by ammonia (NH₃‐SCR) over metal‐exchanged zeolites. The review gives a comprehensive overview of NH₃‐SCR chemistry, including undesired side‐reactions and aspects of the reaction mechanism over zeolites and the active sites involved. The review attempts to correlate catalyst activity and stability with the preparation method, the exchange metal, the exchange degree, and the zeolite topology. A comparison of Fe‐ZSM‐5 catalysts prepared by different methods and research groups shows that the preparation method is not a decisive factor in determining catalytic activity. It seems that decreased turnover frequency (TOF) is an oft‐neglected effect of increasing Fe content, and this oversight may have led to the mistaken conclusion that certain production methods produce highly active catalysts. The available data indicate that both isolated and bridged iron species participate in the NH₃‐SCR reaction over Fe‐ZSM‐5, with isolated species being the most active.     

Experimental study on the solvent regeneration of a CO2‐loaded MEA solution using single and hybrid solid acid catalysts

The performance of a hybrid solid acid catalyst consisting of a physical mixture of γ‐Al₂O₃ and H‐ZSM‐5 in terms of the rate and heat duty for solvent regeneration (i.e., CO₂ stripping) of a CO₂‐rich MEA solution was compared with the individual performance of γ‐Al₂O₃, H‐ZSM‐5, and H‐Y solid acid catalysts using MEA (2–7 mol/L), with initial CO₂ loading of 0.5 mol CO₂/mol MEA at 378 K. It was observed that any catalyst significantly decreased the energy required for CO₂ regeneration. The performance of the catalysts investigated ranked as follows: γ‐Al₂O₃/H‐ZSM‐5 = 2/1 > γ‐Al₂O₃ > H‐ZSM‐5 > H‐Y if the process is in the lean CO₂ loading region whereas it was H‐ZSM‐5 > γ‐Al₂O₃/H‐ZSM‐5 = 2/1 > γ‐Al₂O₃ > H‐Y if the process is in the rich CO₂ loading region. These results highlight the joint dependence on Brønsted/Lewis acidity and mesopore surface area of heat duty for solvent regeneration. © 2015 American Institute of Chemical Engineers AIChE J, 62: 753–765, 2016     

Removal of methylene blue from coloured effluents by adsorption onto SBA‐15

Adsorption has been proven to be the most efficient method for quickly lowering the concentration of dissolved dyes in an effluent. In this regard, activated carbon is the most widely used adsorbent for removal of dyes from aqueous solution. However, the high cost of production and regeneration make it uneconomical. Therefore, inorganic adsorbents (e.g. zeolites) with high surface areas have been used as alternatives to carbon adsorbents. Microporous zeolites ZSM‐5, NH₄‐Beta, MCM‐22 and mesoporous materials MCM‐41 have been investigated for the removal of dyes from aqueous solutions and they show effective adsorption performance. SBA‐15 possesses a larger pore size and pore wall thickness than MCM‐41. As a result, SBA‐15 has greater potential for the adsorption of methylene blue with larger molecule size and higher hydrothermal stability than the M41S family. SBA‐15 is an excellent adsorbent for methylene blue (MB), exhibiting 280 mg g^?1 adsorption capacity and about 100% fading rate for MB. The adsorptive process is so fast that adsorption equilibrium is achieved in 5 min. In addition, SBA‐15 can be effectively recovered by calcination and reused 10 times without significant loss in removal of MB from aqueous solution. The efficient adsorption of MB molecules onto SBA‐15 was ascribed to MB adsorbed into the pore channels of SBA‐15, which was confirmed by nitrogen physisorption analysis of the adsorbent before and after adsorption. The long reuse life of the adsorbent suggests a high potential for application in industry. Copyright © 2010 Society of Chemical Industry     

Selective Catalytic Reduction of NO by Ammonia over Raney‐Ni Supported Cu‐ZSM–5 I. Catalyst Activity and Stability

Composite materials containing Raney Ni and Cu‐ZSM‐5 are highly active catalysts for the selective catalytic reduction (SCR) of NO by NH₃. Their catalytic properties were studied with particular attention to the influence of moisture and SO₂ in the feed, and to effects of catalyst shaping operations. Composite materials (16–20 wt‐% zeolite) were prepared by mixing the components, with different degree of segregation in the resulting pressed particles, or by growing ZSM‐5 crystallites on the surface of leached Raney Ni, which were then exchanged with Cu ions. Catalytic tests were performed with 1000 ppm NO, 1000 ppm NH₃, 2 % O₂ in He, at 3–6.5 · 10⁵ h^–1 (related to zeolite component). With physical mixtures, the catalytic behaviour strongly depended on the mixing strategy, particles containing both Ni and zeolite being inferior to mixed Ni‐only and zeolite‐only particles. The SCR activity was promoted by 2 % H₂O in the feed, SO₂ (200 ppm) was a moderate poison at low temperatures, but indifferent or slightly promoting at high temperatures. A catalyst prepared from ZSM‐5 grown on Raney Ni, which was ranked intermediate in dry feed, was promoted to excellent performance in H₂O and SO₂ containing feed at T > 700 K and was stable for 38 h at 845 K. The results suggest that SCR catalysts containing highly active zeolites should be produced avoiding shaping operations e.g. by use of zeolite crystallites grown on wire packings.     

Kinetic Reaction Models for the Selective Reduction of NO by Methane over Multifunctional Zeolite‐based Redox Catalysts

Kinetic measurements of the selective catalytic reduction (SCR) of NO by methane were performed over CeO₂/H‐ZSM‐5, In‐ZSM‐5, and CeO₂/In‐ZSM‐5 catalysts. The parameter space covered NO, CH₄, and O₂ concentrations varying from 250 to 1000 ppm, from 500 to 2000 ppm, and from 0.5 to 10 vol.‐%, respectively, space velocities between 5000 and 90000 h^–1 and temperatures between 573 and 873 K depending on the catalyst activities. With CeO₂/In‐ZSM‐5 an additional series of measurements was performed with moistened feed gas (0.5–10 vol.‐% H₂O). On the basis of a pseudo‐homogeneous, one‐dimensional fixed‐bed reactor model, the data were fitted to a kinetic model that includes power rate laws for the reduction of NO and for the unselective total oxidation of methane. From analyses of isothermal data sets, almost all reaction orders were found to vary significantly with changing temperature, which indicates that the simple kinetic model cannot reflect the complex reaction mechanism correctly. Nevertheless, the data measured with In‐ZSM‐5 could be modeled with good accuracy over a wide range of reaction temperatures (150 K) while the accuracy was less satisfactory with the remaining data sets, in particular for data with the moist feed over CeO₂/In‐ZSM‐5. With the latter catalyst it was not possible to represent the data measured in dry and in moist feed in a single model even upon confinement to fixed reaction temperatures. A comparison of the separate models established showed strong changes in the reaction orders in the presence of water, which occur apparently already at a very low water content (≤ 0.5 vol.‐%). The kinetic parameters found are in agreement with earlier conclusions about the reaction mechanisms. With In‐ZSM‐5, both reaction orders and the activation energy show a rate‐limiting influence of NO oxidation on the NO reduction path which is removed by the presence of the CeO₂ promoter. A difference in the reaction mechanism over CeO₂/In‐ZSM‐5 and CeO₂/H‐ZSM‐5 is reflected in different kinetic parameters. The differences of the kinetic parameters between dry‐feed and moist‐feed models for CeO₂/In‐ZSM‐5 reflect adsorption competition between the reactants and water.     

Catalytic para‐xylene maximization: III. Hydroisomerization of meta‐xylene on H‐ZSM‐5 catalysts containing different platinum contents

Hydroisomerization of meta‐xylene was carried out using catalysts containing 0.15–0.60 wt% Pt on H‐ZSM‐5 zeolite, in a pulsed microreactor system connected to a gas chromatograph at a flow of hydrogen of 20 cm³ min⁻¹ and temperatures of 275–500 °C. Increasing temperature, increased isomerization with low rates. Increasing Pt content of the catalyst, decreased hydrodealkylation considerably via masking strong acid sites as revealed by temperature programmed desorption of ammonia measurements. Formation of trimethylbenzenes was inhibited by Pt incorporation in the H‐ZSM‐5 zeolite. The activation energies obtained for meta‐xylene hydroisomerization were relatively low (24.4–61.6 kJ mol⁻¹) on all catalysts under study. Para‐xylene yields in the xylenes mixture of product relative to the corresponding thermodynamic equilibrium values amount to about 0.8–0.9 at temperatures of 400–500 °C but were lower at lower temperatures. © 1999 Society of Chemical Industry     

Hydrocracking of Fischer‐Tropsch Wax with Tungstovanadophosphoric Salts as Catalysts

The synthesis of liquid hydrocarbons from CO₂ and H₂, based on renewable energy and H₂O electrolysis, respectively, in a power‐to‐liquid process is a promising concept for the substitution of fossil fuels. Such a process is based on Fischer‐Tropsch synthesis followed by hydrocracking to convert waxy products into transportation fuels such as gasoline and diesel oil. Heteropolyacid cesium salts as catalysts show appropriate activity for hydrocracking, and the selectivity in cracking model hydrocarbons and Fischer‐Tropsch wax can be tuned by the vanadium content of the catalyst. Thermal stability and surface properties were investigated, and the catalysts are compared with a classical H‐Y‐type zeolite used for hydrocracking.     

The Kinetics and Equilibrium of Ethanol Adsorption from Aqueous Phase Using Calcined (Na‐1,6‐Hexanediol)‐ZSM‐5

Na‐ZSM‐5, synthesized using 1,6‐hexanediol as the structure directing agent, has been found to have a suitable selectivity and adsorbing capacity for ethanol adsorption from aqueous solutions. In contrast to quaternary ammonium based Na‐ZSM‐5 zeolites, this Na‐ZSM‐5 did not show any catalytic interaction with ethanol during thermal desorption. The dynamics of the adsorption process were investigated using the finite volume “uptake rate” route. The data predicted from the governing relations of the process were correlated with experimental results. The micro‐diffusion coefficient was determined as a function of temperature.The macropore diffusional mass transfer contribution for biporous zeolite particles was found to be negligible.     

Esterification of Renewable Levulinic Acid to n‐Butyl Levulinate over Modified H‐ZSM‐5

The synthesis of n‐butyl levulinate, one of the most important biodiesel additives, by catalytic esterification of biomass‐derived levulinic acid (LA) with n‐butanol over modified H‐ZSM‐5 (micro/meso‐HZ‐5) in a closed‐batch system is reported for the first time. The optimization of the reaction conditions such as the reactant molar ratio, the catalyst loading, the reaction time and the temperature was performed in view to maximize the yield of n‐butyl levulinate. Micro/meso‐HZ‐5 was found to be the most efficient catalyst, with 98 % yield of n‐butyl levulinate and a reusability for six cycles, which is higher than reported in the literature. A possible catalytic mechanism for the esterification reaction is also proposed. A second‐order pseudo‐homogeneous model with R² > 0.97 confirmed that the esterification reaction is performed in the kinetic regime due to the high activation energy of 23.84 kJ mol^?1.