Removal of Organochlorine from Model Oil Using Mg-Modified ZSM-5 Zeolite:Dechlorination Performance,Regeneration,and Thermodynamics

Various metal-modified ZSM-5 zeolite adsorbents prepared by the impregnation method were applied to the removal of organic chlorides from model naphtha.The adsorption performance and regeneration stability were investigated by static adsorption experiments.The morphologies,structural features,and physicochemical properties of the adsorbents were characterized by X-ray diffraction,Brunauer-Emmett-Teller analysis,NH3 temperature-programmed desorption,scanning electron microscopy,transmission electron microscopy,and pyridine adsorption infrared spectroscopy.The Mg/ZSM-5 zeolite adsorbent possessed a relatively high specific surface area and good metal dispersion and exhibited the best dechlorination and regeneration performance.The characterization results revealed that introduction of the metal exerted a significant influence on the acidic properties of the catalyst surface.A decrease in the ratio of Brønsted acidic sites to Lewis acidic sites and an increase in the amount of moderately acidic sites were confirmed to be responsible for the excellent adsorption performance of the Mg-modified ZSM-5 zeolite.Furthermore,the Langmuir adsorption isotherm model was applied to study the adsorption equilibrium and thermodynamics of the Mg/ZSM-5 adsorbent under mild conditions.The results revealed that the removal of 1,2-dichloroethane by the Mg/ZSM-5 adsorbent was endothermic,spontaneous,disordered,and primarily involved physical adsorption.

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;]aspecies with stronger Lewis acid sites produced a better synergism with moderate Br?nsted acid sites and thus improved the selectivity to aromatic compounds. However, the impregnation results in the formation of Ga;O;phase and small amounts of GaO;species that are mainly located on the external surface（[GaO;];）, 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.,65.4 wt%） was achieved over the Ga4.2-NZ5 sample, which contained with the highest Ga content.

Adsorption of Benzene and Propylene in Zeolite ZSM-5:Grand Canonical Monte Carlo Simulations

The adsorption behavior of benzene and propylene in zeolite ZSM-5 was studied by Grand Canonical Monte Carlo（GCMC） simulations. It could be found that benzene and propylene molecules showed different adsorption behavior in the zeolite cavities. The loadings of propylene were significantly larger than those of benzene at 100 kPa. From the figures of potential energy distribution, the potential energy of benzene/zeolite was more negative than that of propylene/zeolite, so benzene could be adsorbed more stably than propylene. When the temperature was in- creased from 298 to 443 K at 100 kPa, the loading ofpropylene was reduced from 99 to 82 molecules, whereas that of benzene changed little. When benzene and propylene were adsorbed in zeolite simultaneously, the competitive adsorption of them occurred; therefore, the potential energy distribution could be changed significantly. Besides, the adsorption isotherms of benzene and propylene in ZSM-5 at 298 and 443 K were simulated. The results exhibit that the different factors influenced the molecular adsorption at various temperatures and pressures, leading to the diffe- rent rules for the adsorption of benzene and propylene molecules in the zeolite. At a low pressure, the unfavorable energy of propylene/zeolite and the ＂commensurate freezing＂ phenomenon of benzene would make the loadings of itself higher than those of propylene. When pressure was higher than 5 kPa, the adsorption of benzene in ZSM-5 would nearly reach saturation.

Seed-Assisted Synthesis and Catalytic Performance of Nano-sized ZSM-5 Aggregates in a One-Step Crystallization Process

Hierarchical nano-sized ZSM-5 aggregates were successfully synthesized via a seed-assisted method in the presence of cetyltrimethylammonium bromide(CTAB)through a facile one-step crystallization process.Commercial ZSM-5 zeolites with a SiO2/Al2O3 ratio comparable to that of ZSM-5 products were treated with alkali and used as the seed particles.The influences of crystallization conditions were investigated,and the possible synthesis mechanism was proposed.ZSM-5 zeolites with diff erent amounts of CTAB added were characterized using many techniques and evaluated in toluene alkylation with methanol.The results showed that a trace amount of CTAB signifi cantly promoted the crystallization of ZSM-5 zeolite,with the morphology changing from hexagonal-shape crystals to uniform spherical aggregates.CTAB may act as the structure-directing agent and assemble the primary crystallites to generate hierarchical ZSM-5 aggregates.The ZSM-5 zeolite with the smallest primary particles of 50-80 nm exhibited large specific surface area,abundant mesopores,and the greatest microporosity.The hierarchical nano-sized ZSM-5 aggregate showed higher toluene conversion and a longer lifetime without compromising the selectivity to xylene and p-xylene in toluene alkylation with methanol.

Synthesis of ZSM-5 zeolite membranes without organic templates using a varying-concentration technique

Template-free nanosized ZSM-5 seeds with an average size of 15 nm were prepared from a synthesis solution with the composition 12Na2O∶100SiO2∶2Al2O3∶2500H2O. By the use of these seeds, thin ZSM-5 zeolite membranes were prepared on the outer surface of a porous α-alumina tube with a pore size of 2 μm in a gel system by varying-concentration synthesis with organic-free template. The first composition synthesis sol-gel was the same as seeds of molar composition and the second one was 12Na2O∶100SiO2∶2Al2O3∶5000H2O at 180 ℃ for 10 h, respectively. XRD shows that the film consists of well-crystallized ZSM-5 zeolite. SEM investigation indicats that the zeolite films on the supports are defect free and the film thickness is approximately 8 μm. The permeances for H2, N2, CH4 and CO2 are 8.94×10-7, 3.27×10-7, 3.9×10-7, 3.14×10-7 and 0.874×10-7 mol·m2·s-1·Pa-1, respectively. The ideal selectivity of membrane at room temperature for H2/CO2, H2/N2, H2/CH4 are 2.84, 2.73 and 2.29, respectively.

Synthesis and Characterization of ZSM-5/β Co-Crystalline Zeolite

ZSM-5/β co-crystalline zeolites with different content of ZSM-5 have beensynthesized by adding different amount of ZSM-5 to the synthetic system of β zeolite with NaAlO_2,silica sol as the source of aluminum and silica, respectively, and TEA^+ as the template undercontrolled condition of the synthesis. The ZSM-5/β co-crystalline zeolite was studied by XRD, SEM,BET and NH_3-TPD. The reaction activity of toluene alkylation was investigated with a mixture oftoluene-methanol as the feedstock in a pulse micro-reactor over the ZSM-5/β co-crystalline zeolite.It is found that ZSM-5/β co-crystalline zeolite has two kinds of zeolite structure including ZSM-5and β zeolite, not in the form of a physical mixture. The pore structure of ZSM-5/βco-crystalline zeolites is different from that for β zeolite, ZSM-5 and their physical mixture. Inaddition, the peaks of both high and low temperature desorption of ammonia over the ZSM-5/βco-crystalline zeolite shift 23℃ to lower temperatures and the acid amount of its strong acid is 3%more than the physical mixture. So the ZSM-5/β co-crystalline zeolite produces the highest contentof xylene, which is 10.4% higher than the physical mixture. And the ZSM-5/β co-crystalline zeolitehas better selectivity for toluene alkylation and weaker de-methylation than β zeolite, ZSM-5 andtheir physical mixture.

Effect of Alkali Treatment on the Structure and Catalytic Properties of ZSM-5 Zeolite

Catalytic properties of ZSM-5 zeolite samples pretreated with NaOH solution have been investigated. The samples are characterized by XRD, SEM, chemical analysis, and N2 adsorption. The results indicate that mesopores are created in ZSM-5 crystals under alkali treatment without change the microporous structure and acidic strength of the zeolite, but the crystallinity is greatly decreased under severe treatment. IR indicates that the concentration of silanol is greatly enriched by alkali treatment. The etherification activities of ZSM-5 zeolites are greatly increased by alkali-treatment. The noticeably improved catalytic activity of treated samples is ascribed to the formation of mesopores and greatly enriched silanol group.

Catalytic Desulfurization of n-Butyl-sulfide over HZSM-5 Zeolite in the Presence of a Hydrogen Provider

The catalytic desulfurization of a model organic sulfurous compound n-butyl-sulfide in a fixed bed microreactor is studied in the presence of catalyst and a hydrogen provider. The experimental results show that the appropriate reaction conditions are： a mixed catalyst of HZSM-5 zeolite and Co-Mo/Al2O3-TiO2, a reaction temperature of 300℃, atmosphere pressure, a feed speed of 50 mL/h and a mass hourly space velocity of 3.0 h^-1 A higher catalytic property and desulfurization efficiency of the mixed catalyst of HZSM-5 zeolite and Co-Mo/Al2O3-TiO2 is achieved. The adsorption and desulfurization efficiency of the FCC gasoline from Shenghua Refinery, which is affiliated to China University of Petroleum （East China）, is 53.0 %.

Pore Structure and Catalytic Performance of Steam-Dealuminated ZSM-5/Y Composite Zeolites

For investigating the effect of dealumination on the pore structure and catalytic performance, ZSM-5/Y composite zeolites synthesized in situ from NaY gel were dealuminated by steaming at different temperatures. XRD (X-ray diffraction) characterization indicates that the relative crystallinity of the composite zeolites decreases with the increase in Si/Al ratio after steaming. N2 adsorption-desorption suggests that more mesopores are formed while the BET (Brunauer, Emmett and Teller) specific surface area and the micropore specific surface area decrease as the temperature of steaming rises. Daqing heavy oil was used as feedstock to test the catalytic cracking activity of ZSM-5/Y composite zeolites. The experimental results of the catalytic cracking performance reveal that the distribution of products differs due to the different conditions of hydrothermal treatment. Further hydrothermal treatment leads to an increase in the yield of light oil, and a decrease in the yield of gas products and coke.

Preparation of Mesoporous ZSM-5 Zeolite under Double Ester Base Long Carbon Chains Organosilane Quaternary Ammonium Salt Template Agent

The pore sizes of traditional zeolites are in the range of0. 3-1. 5 nm,which strongly hinder the diffusion of large reactant and product molecules within the zeolite pores. To compensate for it,we tried to create mesopores in traditional microporous zeolites and retain all advantages of microporous zeolites. Mesoporous Zeolite Socony Mobile-Five( ZSM-5) zeolite was synthesized by a new double ester base long carbon chains organosilane quaternary ammonium salt as the soft template agent in hydrothermal method.The structure of the acquired zeolite crystals was confirmed by fieldemission scanning electron microscopy( FE-SEM), transmission electron microscopy( TEM), nitrogen adsorption-desorption measurements and X-ray diffraction( XRD),which indicated that their structure had the same characteristics as traditional ZSM-5 zeolites. Compared with traditional ZSM-5 zeolite,there were 4 nm and 15 nm mesopores in the crystal. The prepared hierarchical porous ZSM-5 zeolite was expected to be effective catalytic materials for chemical reactions involving large molecules.

EPR AND HIGH RESOLUTION SOLID-STATE NMR STUDIES ON Fe^(3+) SUBSTITUTED ZSM-5 ZEOLITE

Fe^(3+) substituted ZSM-5 zeolite was studied using EPR and ^(27)A1,^(29)Si MAS-NMR spectroscopy.The results showed that the synthe- sized sample has the typical ZSM-5 structure with Fe^(3+) ionsincorporated in tetrahedric sites in the zeolite framework and there are some para- magnetic centers in the samples.

Preparation of hierarchical ZSM-5 zeolite and its application in synthesis of tributyl citrate

First,the hierarchical ZSM-5 zeolite was prepared by hydrothermal method using mesoporous template cetyltrimethylammonium bromide(CTAB).The physical and chemical properties of the hierarchical ZSM-5 zeolite were characterized by X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR)and N2 adsorption-desorption and Scanning electron microscope(SEM).Then,the as-prepared hierarchical ZSM-5 zeolite and ion exchange resin were used as catalysts to evaluate the reaction performance of the synthesis of tributyl citrate.Compared with the ion exchange resin,the as-prepared ZSM-5 has a microporous and mesoporous composite structure and a large specific surface area,so that significantly improving the catalytic performance of synthesizing tributyl citrate and increasing the esterification rate of the reaction 8.7%.

Synthesis of ZSM-5 Zeolite with Small Crystallite and its Application in Aromatiration of Propane

By optimizing the orystallization condition, a procedure for the synthesis of small crystallite zeolite ZSM-5 was developed. Compared with the larger crystallite ZSM-5. the smaller one exhibits higher catalytic performance in aromatization reaction of propane.

SYNTHESIS AND PROPERTIES OF A NOVEL COMPOSITE ZSM-5 ZEOLITE/VERMICULITE CATALYST

The composite ZSM—5 zeolite/vermiculite catalyst,in which tiny ZSM—5 zeolite parti- cles embedded in the vermiculite substrate,has been synthesized by hydrothermal method with vermiculite as silicon source.The catalytic behavior of resulting catalyst for xylene isomerization,propylene aromatization and toluene disproportionation is better than that of HZSM—5 zeolite.

Core-shell-structured Composite ZSM-5@MCM-41 Catalysts:Fabrication,Characterization,and Enhanced Performance in Hexane Catalytic Cracking

A series of core-shell zeolites with a ZSM-5 zeolite core and a MCM-41 shell with varying shell thicknesses were successfully fabricated via a cetyltrimethylammonium bromide(CTAB)-directed sol-gel coating method in an ultradilute solution. Extensive characterization techniques, including XRD, TEM, N_(2) adsorption-desorption, NH_(3)-TPD, and IR measurements, confirmed the successful coating of a microporous ZSM-5 core with a mesoporous MCM-41 shell layer and were further employed to explore the textural properties and acidic properties of the samples. The hexane cracking results revealed a significant enhancement in olefin yields after introducing the MCM-41 shell to ZSM-5. Interestingly, a volcanic trend in olefin yields was observed with the increase in the shell thickness. In particular, the highest olefin yield of 51.5%, exceeding that of the core catalyst by 17.1%, was achieved when the shell thickness was controlled at 40 nm.Moreover, the catalyst lifetime investigation revealed that the core-shell composite catalyst exhibited a minimal reduction in hexane conversion of merely 3.8% over a 120 h reaction period, significantly outperforming the 11.3% reduction exhibited by the core catalyst. This remarkable catalytic performance was attributed to the passivation of external acid sites and the introduction of more developed pore channels by the shell, which effectively mitigated unwanted side reactions. The successful synthesis of these core-shell structured catalysts presents a novel strategy for improving catalytic performance in hexane cracking, in addition to serving as a solid foundation for the design of industrial catalysts for light naphtha cracking.

ZSM-5沸石结晶度对乙苯叔丁基化对位选择性的影响(英文)

Highly crystalline ZSM-5 zeolites are important for para-selective alkylation of alkyl aromatics, because they carry few external acid sites for isomerization of p-dialkyl products. Such zeolites (Si/Al = 25, 50, and 75) were synthesized in a fluoride medium between pH 4 and 6. Their crystallinities, crystal sizes, and surface areas were higher than those of a commercial ZSM-5 zeolite. Their para selectivities in alkylation were tested for vapor-phase tert-butylation of ethylbenzene between 200 and 400 °C. As expected, all the catalysts showed more than 90% para selectivity. At 300 °C, ethylbenzene conversion decreased in the order ZSM-5(25, commercial) > ZSM-5(25) > ZSM-5(50) > ZSM-5(75). The catalysts had weak, medium, and strong acid sites, but all the acid sites of ZSM-5(75) were weaker than those of ZSM-5(25) and ZSM-5(50). The high activity of commercial ZSM-5 was caused by its strong acid sites being stronger than those of the synthesized zeolites. Although the activity of the commercial catalyst was higher than those of the present catalysts, the selectivity for 4-t-butylethylbenzene (4-t-BEB) was low. The optimum feed ratio (ethylbenzene:t-butyl alcohol) was 2:1 and the feed rate was 1.65 h?1 for high ethylbenzene conversion and 4-t-BEB selectivity. Time-on-stream studies showed slow catalyst deactivation. Highly crystalline ZSM-5 zeolites are therefore better than a commercial zeolite for para-selective alkylation of alkyl aromatics. They do not require much post-modification for high para selectivity. A fluoride medium is therefore better than an alkaline medium for obtaining highly crystalline para-selective ZSM-5 zeolites.

CrOx supported on high-silica HZSM-5 for propane dehydrogenation

Industrial propane dehydrogenation(PDH)catalysts generally suffer from low catalytic stability due to the coke formation onto the catalyst surface to cover the active sites.The exploitation of an efficient catalyst with both high catalytic selectivity and long-term stability toward PDH is of great importance but challenging to make.Herein CrOx supported on high-silica HZSM-5 with a SiO2/Al2O3 ratio of 260(Cr/Z-5(260)is synthesized by a simple wet impregnation method,which exhibits high catalytic activity,good selectivity and excellent stability for PDH.At a weight hourly space velocity(WHSV)of 0.59 h-1,a propylene formation rate of 4.1 mmol g-1cath-1(~32.6% propane conversion and ~94.2% propylene selectivity)can be maintained over the 5%Cr/Z-5(260)catalyst after 50 h time on stream,which is much better than commercial Cr/Al2O3(Catofin process,catalyst life is several hours)at the same reaction conditions.With increasing the WHSV to 5.9 h-1,a high propylene formation rate of 27.9 mmol gcat-1h-1can be obtained over the 5%Cr/Z-5(260)catalyst after 50 h time on stream,demonstrating a very promising PDH catalyst.Characterization results and Na+doping experiments reveal that the Cr species combined with Br?nsted acid sites in Cr/HZSM-5 catalysts are responsible for the high catalytic performance.In particular,the Br?nsted acid sites in HZSM-5 zeolite could increase the propane adsorption and enhance the C–H bond activation.Furthermore,the high surface area and well-defined pores of HZSM-5 zeolite can provide a special environment for the dispersion and stabilization of Cr species,thus guaranteeing high catalytic activity and stability.

ZSM-5/MAPO Composite Catalyst for Converting Methanol to Olefins in a Two-Stage Unit with a Dimethyl Ether Pre-Reactor

A ZSM-5/MAPO composite catalyst was prepared by adding ZSM-5 zeolite powder to a conventional molecular sieve synthesis system, followed by modification with NH_4H_2PO_4. The samples were characterized by XRD, SEM, IR, NH_3-TPD, and BET analyses. The catalytic property of the samples toward the methanol-to-olefin(MTO) reaction was evaluated in a connected in series two-stage unit equipped with a continuous flow(once-through) fixed-bed tubular reactor similar to an industrial reactor. The first reactor mainly converted methanol into dimethyl ether and water, followed by being subject to continuous reaction in the second reactor, in which DME was converted to hydrocarbons. The composites exhibited the typical framework topology of MFI, AEI and AFI, which represented the ZSM-5 zeolite, the molecular sieves AlPO-18 or SAPO-18, AlPO-5 or SAPO-5, respectively. The composites showed several advantages for optimizing the zeolite acidity, enhancing the mass transfer, and restraining the side reactions. Catalytic reaction results showed that the composites exhibited higher selectivity to light olefins(84.0%) and lower selectivity to C_2―C_4 alkanes and C_5^+ hydrocarbons than pure ZSM-5. Moreover, the composite zeolite loaded with 3% of P demonstrated improved catalytic activity and stability for the conversion of methanol to propylene, because the coking rate was obviously suppressed.

Effect of Morphological Structure of PtSnNa/ZSM-5 on Its Catalytic Performance in Propane Dehydrogenation

The ZSM-5 zeolite with flower-shaped crystallites(marked as ZFS)was synthesized through the hydrothermal preparation method.The properties of ZFS as a supporting material have been investigated in comparison with the traditional ZSM-5 zeolite.The prepared samples were characterized by XRD,N2 adsorption-desorption,TEM,NH3-TPD,XRF,and XPS techniques.The results showed that the formation of the flower-shaped crystallites directly influenced the physicochemical properties of ZFS material.In ZFS,the pore structure was changed,the acid content was decreased,and the surface properties were promoted.Besides,in the PtSnNa/ZFS catalyst,the amount of oxidized Sn species was remarkably increased and the dispersion of Pt was relatively improved.Meanwhile,due to these modifications,the capacity of the catalyst supported on ZFS to accommodate coke was greatly improved and the coke deposits on PtSnNa/ZFS were migrated from active metals to the support.Furthermore,as expected,the catalytic performance of the PtSnNa/ZFS catalyst for propane dehydrogenation to propylene and the stability of catalyst were significantly improved.