High-silica ZSM-5 Zeolites Research Articles

Structure and thermal properties of zeolites modified with Fe and Cu nanopowders

We have studied the thermal properties of copper and iron nanopowders supported on high-silica ZSM-5 zeolites. The results demonstrate that the attachment of metal nanoparticles to the zeolite surface improves the oxidation resistance of the metals. The oxidation onset temperature and the temperature range of the weight gain due to the oxidation of the metal nanopowders depend on the nature of the zeolite matrices and the metal.

Application of high silica zeolite ZSM-5 in a hybrid treatment process based on sequential adsorption and ozonation for VOCs elimination

In this study, a hydrophobic synthetic zeolite, namely ZSM-5 is chosen as an adsorbent/catalyst for toluene removal. Experimental results showed that toluene adsorption onto ZSM-5 was favourable, following a Langmuir adsorption isotherm model. ZSM-5 zeolite was regenerated using gaseous ozone at low temperature. Adsorbed toluene was oxidised, releasing mainly CO2 and H2O. Traces of oxidation by-products such as acetic acid and acetaldehyde were formed and remained adsorbed after the oxidativate regeneration with ozone. After four successive cycles of adsorption/ozonation, the adsorption efficiency was not affected (92%–99%). These results showed that volatile organic compound (VOC) removal by adsorption onto ZSM-5 zeolite followed by ozone regeneration could be used as a promising hybrid process for the control of VOC emissions in terms of efficiency.

Selective production of propylene from methanol over high-silica mesoporous ZSM-5 zeolites treated with NaOH and NaOH/tetrapropylammonium hydroxide

The influence of alkaline treatments with NaOH and NaOH/TPAOH mixtures on the physicochemical properties and catalytic performance of high-silica ZSM-5 zeolites (Si/Al = 175) during the methanol-to-propylene (MTP) reaction have been investigated. It was found that alkaline treatment in an NaOH/TPAOH solution with TPAOH/(NaOH + TPAOH) = 0.4 ensures the formation of narrow and uniform intracrystalline mesoporosity without severely damaging the crystal structure and the intrinsic acidity of the zeolite, leading to the best catalytic performance, including the highest propylene selectivity (47.2) and P/E ratio (4.97) as well as the longest catalyst lifetime (80 h).

Combined desilication and phosphorus modification for high-silica ZSM-5 zeolite with related study of hydrocarbon cracking performance

Mesoporosity was introduced into high-silica ZSM-5 zeolite (SiO2/Al2O3=417) by controlled desilication using the mixture of NaOH and TEAOH (tetraethylammonium hydroxide), and subsequent phosphorus modification was used to improve the structural stability and acidity reservation of the desilicated ZSM-5 samples during the procedure of severe steam aging treatment. The phosphorus modified mesoporous ZSM-5 sample along with parent ZSM-5, solo phosphorus modified ZSM-5 and mesoporous ZSM-5 were characterized by techniques of N2 adsorption-desorption, NH3-TPD (temperature programmed desorption), IR (infrared) spectroscopy of pyridine adsorption and 27Al &31P MAS NMR spectroscopy. A mechanism for underlying chemistry of the combinative treatment was proposed. The aluminophosphate formed in the steam activation could interact with the framework aluminum on zeolite, thus achieved to the textural and acidity stabilization during the steam aging. The catalytic performance of these samples was tested by different hydrocarbon cracking reactions. It turned out that owing to its reduced diffusion limitation and stabilized acidity, the phosphorus modified mesoporous ZSM-5 sample exhibited the highest conversion in the bulky molecule cracking reaction. And in the 1-octene cracking reaction under harsh reaction conditions, the steamed phosphorus modified mesoporous ZSM-5 sample exhibited higher activity and more prolonged catalyst life compared to the other steamed catalysts, which could be attributed to the improved coke tolerance capability by mesoporosity introduction and the stabilized acid sites by phosphorus modification.

Catalytic activities of K-modified zeolite ZSM-5 supported rhodium catalysts in low-temperature steam reforming of bioethanol

Recently, zeolite materials have attracted attention as efficient catalysts for low-temperature steam reforming of bioethanol (SRE). However, cost-effective zeolite ZSM-5 materials, one of the most popular industrial reforming catalysts, were rarely reported for SRE. In this study, low-load rhodium (Rh) catalysts are prepared using commercial high-silica zeolite ZSM-5 as the supports. The commercial zeolite ZSM-5 has strong acidic sites that lead to fairly extensive dehydration of bioethanol. To generate basic sites and mesoporous structure, zeolite supports are modified by K ion exchange and alkali treatment. The effect of the physicochemical properties of the modified supports on low-temperature SRE reaction is investigated by SEM, TEM, XRD, XRF, TPD, NMR and N2 adsorption. The results indicate that strong acidic sites in zeolite ZSM-5 can be effectively neutralized by K ion exchange, while basic sites in zeolite ZSM-5 are noticeably altered only by alkali treatment. The hydrogen selectivity can be significantly promoted by the alkalinity of the zeolite KZSM-5, however, only the moderate alkali-treated Rh/S2 catalyst retains its high activity during reaction. Our results appear to demonstrate the positive effect of the special zeolitic structure of the Rh/S2 catalyst with uniform mesopores, which can improve the Rh dispersion and avoid its sintering. Moreover, there seem to be a unique synergy between the Rh active component and the alkali-treated zeolite support, which might result in the lowest CO selectivity at 300–400 °C.

Catalytic conversion of methanol to propylene over high-silica mesoporous ZSM-5 zeolites prepared by different combinations of mesogenous templates

The effects of mesoporosity on catalytic performance of methanol to propylene (MTP) reaction have been investigated by using a series of high-silica nanosized hierarchical ZSM-5 zeolites with different degrees of mesoporosity, which were hydrothermally synthesized in the presence of different mesogenous templates, i.e., TPOAC, CTAB, and their combinations. The results were compared with a conventional microporous ZSM-5 catalyst. The prepared catalysts were characterized by XRD, FE-SEM, BET, NH3-TPD and FT-IR techniques. Meanwhile, their catalytic activities were evaluated in a fixed-bed reactor under atmospheric pressure, 460 °C and WHSV of 1h−1. Compared with conventional catalyst, the nanosized hierarchical porous ZSM-5 templated with a mixture of 75% TPOAC and 25% CTAB displayed reliable MTP catalytic lifetime (76 h) as well as sufficiently high propylene selectivity (43.65%) and propylene to ethylene (P/E) ratio (4.05), which were predominately attributed to its optimal combination of acidity and porosity.

State and properties of ion-exchanged cations in zeolites: 1. IR spectra and chemical activation of adsorbed molecular hydrogen

Adsorption isotherms and of adsorbed molecular hydrogen indicate that H2 is weakly adsorbed by alkali-metal forms of faujasites, mordenite, and high-silica zeolite ZSM-5. The alkaline-earth forms of the same zeolites adsorb hydrogen somewhat more strongly; nevertheless, the hydrogen molecules adsorbed by the barium form of mordenite are in the hindered rotation state. Molecular hydrogen is most strongly adsorbed by the zinc and cadmium forms of the high-silica zeolite. In this case, molecular hydrogen is strongly polarized and undergoes heterolytic dissociative adsorption, yielding acidic hydroxyl groups and cation-bound hydride ions.

Synergism in the actions of a transition metal cation and a Lewis acid in the liquid- and gas-phase catalytic conversion of alkanes over modified ZSM-5 zeolites under mild conditions

Bimetallic catalysts have been prepared by successively modifying the high-silica zeolite ZSM-5 with cobalt and aluminum salts. The performance of these catalysts in the conversion of higher alkanes at medium temperatures (130–190°C) depends on whether the reaction is conducted in the liquid or gas phase. In both cases, the transition metal and surface-anchored aluminum chloride act synergetically. In the liquid-phase reactions of n-heptane and n-dodecane, the activity of the bimetallic systems is more than one order of magnitude higher than the activity of the hydrogen form of the initial zeolite. New adsorption and catalytic sites resulting from the introduction of the two modifiers into the zeolite have been discovered by diffuse reflectance IR spectroscopy. In particular, the modifiers generate a new state of cobalt in which the transition metal atoms are linked with aluminum atoms through chlorine or oxygen atoms. The liquid-phase conversion of alkanes over the modified zeolites is unlikely to proceed via a carbocationic mechanism.

Fast Synthesis of High-Silica ZSM-5 Zeolite via a Simple Vapor-Phase Transport Method

Fast synthesis of high-silica ZSM-5 zeolite through vapor-phase transport (VPT) method was reported in this paper. The synthesized samples were characterized with XRD, FT-IR, XRF, SEM and N2 Absorption. Factors affecting the synthesis of ZSM-5 zeolite such as the alkalinity, the crystallization temperature and time, the quantity of seeds were investigated. With precipitated silica and fumed silica as silica source respectively, the appropriate ratio was studied as follows: (0.04-0.05) Na2O: 1.0SiO2: 15H2O: (0-0.0046)Al2O3: 0.01Seed, the reaction was carried out at 393-413K for 4-24h.

Highly selective formation of propylene from methanol over high-silica EU-1 zeolite catalyst

Abstract High-silica EU-1 zeolite (SiO2/Al2O3 = ~ 400) was tested in methanol to propylene (MTP) reaction and was found to be a very efficient catalyst. In comparison with the other three high-silica zeolites, i.e. ZSM-48, ZSM-5, and beta zeolites, a higher propylene selectivity (52%) and remarkably high propylene/ethylene (P/E) ratio (15) were obtained under the operating conditions of T = 450 °C, P = 0.1 MPa, and WHSV = 1.5 h− 1. Besides, a substantially low amount of C5 + hydrocarbons, especially aromatics is another prominent feature of the product distribution over high-silica EU-1 catalyst.

Desorption of butanol from zeolite material

Sorption-based recovery of 1-butanol from aqueous solution has been investigated focusing on the recovery of butanol by desorption from the sorbate. Sorption isotherm, thermogravimetric adsorption and differential scanning calorimetry experiments have been used to determine the desorption behavior of butanol and water for two high-silica zeolite adsorbents, faujasite (CBV901) and ZSM-5 (CBV28014).Carbon dioxide can be used as displacement agent for butanol recovery, with the butanol–carbon dioxide equilibria determining the carbon dioxide mass requirement for such a process.For CBV901 desorption requires 2440J/g of water and 1080J/g of butanol. The heat effects for CBV28014 are 2730J/g (water) and 1160J/g (butanol). A significant difference in water content can be seen between both zeolite materials, with CBV28014 showing the least amount of water adsorption. The desorption rate of butanol from CBV28014 is significantly slower than from CBV901.A catalytic reaction, most probably dehydration, occurs around 200°C during temperature programmed desorption of butanol from CBV28014.

Separation of succinic acid from its salts on a high-silica zeolite bed

Succinic acid production from renewable resources might replace production of several petroleum derived chemicals. This study focuses on development of a sorption process for efficient separation of succinic acid from its salts in a low pH fermentation medium. Therefore, solutions of succinic acid in water and Saccharomyces cerevisiae at pH 2.8–4.7 were eluted over high-silica ZSM-5 zeolite particles, which were packed in laboratory columns. Succinic acid adsorbed well, whereas succinate salts eluted from the column with an early breakthrough. A mathematical model, involving succinic acid dissociation, described the breakthrough behavior correctly. The presence of acetic acid slightly reduced the observed succinic acid capacity, but most acetic acid eluted during succinic acid loading, which is favorable. The adsorbed succinic acid was completely desorbed already when the temperature was increased to 80 °C. Experiments with fermentation medium decreased the column's capacity, but this was restored by calcining at 600 °C. So succinic acid was separated from its salts without use of additional chemicals such as acids or bases. Issues that require further study are modeling nonlinear mass transfer, and the prolonged use of sorbent, especially when using fermentation medium.

Reducing bromate formation with H +-form high silica zeolites during ozonation of bromide-containing water: Effectiveness and mechanisms

This paper investigated the effect of H +-form high silica ZSM-5 (HZSM-5) zeolites on bromate formation. HZSM-5 zeolites with different Si/Al molar ratios (i.e., 25−300) were tested taking ozonation alone as control. The zeolites were more effective in reducing bromate formation for the filtered surface water than CeO 2, a former reported oxide that can reduce bromate formation at slightly acidic pH. The reduction efficiencies were not closely related to their Si/Al ratios. The HZSM-5 (Si/Al = 300) selected for detailed studies effectively reduced bromate formation by 58% for the filtered water, and also enhanced the removal of dissolved organic carbon (DOC) during ozonation. The efficiency of the HZSM-5 in reducing bromate formation increased with ozone dose (0.38−1.16 mg O 3 mg −1 DOC) and pH (6.6−9.3). The HZSM-5 adsorbed OBr − (one of the critical intermediates in bromate formation) quickly with an adsorption capacity of 54 mg g −1, but had no adsorption for ozone, Br −, HOBr and BrO 3 - . It also significantly inhibited the formation of trace H 2O 2 which was generated from ozone decomposition and had been considered promoting bromate formation at low concentrations during ozonation. The reduction of bromate formation in O 3/HZSM-5 is possibly ascribed to the selective OBr − adsorption in combination with the inhibited H 2O 2 formation.

Adsorption of Carbon Dioxide on High-Silica Zeolites with Different Framework Topology

Adsorption isotherms of carbon dioxide were measured on six high-silica zeolites TNU-9, IM-5, SSZ-74, ferrierite, ZSM-5 and ZSM-11 comprising three-dimensional 10-ring (8-ring for ferrierite) at 273, 293, 313 and 333 K. Based on the known temperature dependence of CO2 adsorption, isosteric heats of adsorption were calculated. The obtained adsorption capacities and isosteric adsorption heats related to the amount of CO2 adsorbed have provided detailed insight into the carbon dioxide interaction with zeolites of different framework topology. The zeolites TNU-9 and ferrierite are characterized by pronounced energetic heterogeneity whereas due to the location of Na+ cations in the same positions the isosteric adsorption heats of CO2 adsorption on IM-5, ZSM-5 and ZSM-11 zeolites are rather constant for molecular ratio CO2/Na+ < 1. As IM-5 zeolite has a maximum adsorption capacity, it appears to have optimum properties for carbon dioxide separation.

Nonoxidative conversion of methane into aromatic hydrocarbons on Ni-Mo/ZSM-5 catalysts

The nonoxidative conversion of methane into aromatic hydrocarbons on high-silica zeolites ZSM-5 containing nanosized powders of molybdenum (4.0 wt %) and nickel (0.1–2.0 wt %) was studied. Data on the acid characteristics of the catalysts and the nature and amount of coke deposits formed on the surface of the catalysts were obtained using the thermal desorption of ammonia and thermal analysis. The microstructure and composition of Ni-Mo/ZSM-5 catalysts were studied by high-resolution transmission electron microscopy and energy-dispersive X-ray analysis. The formation of various chemical species in the samples was detected: oxide-like clusters of Mo within zeolite channels (∼1 nm), molybdenum carbide particles (5–30 nm) on the outer surface of the zeolite, and Ni-Mo alloy particles with different compositions (under reaction conditions, carbon filaments grew on these particles). It was found that, as the Ni content was increased from 0.1 to 2.0 wt %, the rate of deactivation of the catalytic system increased because of blocking pores in the zeolite structure by filamentous carbon up to the formation of condensed coke deposits.

Azacyclohexadienyl radicals in pyridine and ZSM-5 silicalite

Abstract Three muoniated azacyclohexadienyl radical isomers were produced by the addition of muonium to pyridine in liquid pyridine and in high silica ZSM-5 zeolite ( Si / Al = 450 ) at 298 K, and observed with avoided level crossing muon spin resonance. The hyperfine coupling constants of the azacyclohexadienyl radicals are similar in both environments, which indicates that the radicals do not interact strongly with the zeolite framework. The relative yield of the three radicals depends on the medium, with the yield of the para isomer being six times larger in ZSM-5.

Significant Influence of Zn on Activation of the C‐H Bonds of Small Alkanes by Brønsted Acid Sites of Zeolite

Herein, we analyze earlier obtained and new data about peculiarities of the H/D hydrogen exchange of small C(1)-n-C(4) alkanes on Zn-modified high-silica zeolites ZSM-5 and BEA in comparison with the exchange for corresponding purely acidic forms of these zeolites. This allows us to identify an evident promoting effect of Zn on the activation of C-H bonds of alkanes by zeolite Brønsted sites. The effect of Zn is demonstrated by observing the regioselectivity of the H/D exchange for propane and n-butane as well as by the increase in the rate and a decrease in the apparent activation energy of the exchange for all C(1)-n-C(4) alkanes upon modification of zeolites with Zn. The influence of Zn on alkane activation has been rationalized by dissociative adsorption of alkanes on Zn oxide species inside zeolite pores, which precedes the interaction of alkane with Brønsted acid sites.

Catalytic activity in hydrocarbon conversion of pentasil containing platinum, nickel, iron, or zinc nanoparticles

Catalyst samples containing nanosized Pt, Ni, Fe, or Zn powder were prepared on the basis of high-silica zeolite ZSM-5 by mechanical mixing. The structure and state of active centers of zeolite catalysts (freshly prepared or calcined after the reaction cycle of upgrading the petroleum straight-run gasoline fraction) were studied by means of the X-ray diffraction, UV spectroscopy, and X-ray photoelectron spectroscopy techniques. It was shown that the oxidized forms of the metals are practically absent from the freshly prepared zeolite samples. After the heat treatment of the catalysts in air, nanosized metal powders transform into oxides on the zeolite surface, with iron and nickel producing the greatest variety of oxidized forms.

Hydrophobic zeolite–silicone rubber mixed matrix membranes for ethanol–water separation: Effect of zeolite and silicone component selection on pervaporation performance

High-silica ZSM-5 zeolites were incorporated into poly(dimethyl siloxane) (PDMS) polymers to form mixed matrix membranes for ethanol removal from water via pervaporation. Membrane formulation and preparation parameters were varied to determine the effect on pervaporation performance including siloxane chain length, crosslinking agent concentration and density of reactive groups, catalyst level, solvent type, zeolite type and loading, mixing method, and presence of a porous support membrane. Uniform dispersion of zeolite was critical to the achievement of reproducible results and ultrasonication with a probe-type device was found to be effective at particle dispersal. Properties of the vinyl-terminated PDMS and methyl-hydride crosslinking agents in the polymer system had a limited effect on performance while zeolite loading had the greatest effect. The highest observed selectivity of 3.0 was observed with 65 wt% zeolite loading, the highest practicable loading for the polymer system studied. The current results are placed in the context of ZSM-5/PDMS mixed matrix membranes previously reported in the literature for ethanol–water separation.

Ethanol, Acetic Acid, and Water Adsorption from Binary and Ternary Liquid Mixtures on High-Silica Zeolites

Adsorption isotherms were measured for ethanol, acetic acid, and water adsorbed on high-silica ZSM-5 zeolite powder from binary and ternary liquid mixtures at room temperature. Ethanol and water adsorption on two high-silica ZSM-5 zeolites with different aluminum contents and a high-silica beta zeolite were also compared. The amounts adsorbed were measured using a recently developed technique that accurately measures the changes in adsorbent/liquid mixture density and liquid concentration. This technique allows the adsorption of each compound in a liquid mixture to be measured. Adsorption data for binary mixtures were fit with the dual-site extended Langmuir model, and the parameters were used to predict ternary adsorption isotherms for each compound with reasonable accuracy. In ternary mixtures, acetic acid competed with ethanol and water for adsorption sites and reduced ethanol adsorption more than it reduced water adsorption.