Original ZSM-5 Research Articles

Enhanced hydrophobic ZSM–5 with high capacity for toluene capture under high-humidity conditions

Industrial volatile organic compounds (VOCs) have the characteristics of large displacement and high humidity. The problem of water resistance of the adsorbent in treating VOCs by adsorption method under high humidity conditions needs to be solved urgently. Herein, methyl triethoxysilane (CH3Si(C2H5O)3) and methyl trimethoxysilane (CH3Si(CH3O)3) are used for hydrophobic modification of ZSM-5, and its adsorption properties for toluene are studied under high-humidity conditions. Fourier infrared spectroscopy and X-ray photoelectron spectroscopy indicate that the hydrophobic groups –CH3 and –CH2– are successfully grafted onto the surface of the ZSM-5. The adsorption–desorption results of toluene show that the hydrophobicity of the modified ZSM-5 is remarkably improved, and the adsorption capacity for toluene is almost 6.5 times higher than that of original ZSM-5 at 80 % relative humidity. The mechanism of surface hydrophobicity modification of ZSM-5 was further investigated and found that the silicone hydroxyl group on the surface of the material reacted with the modifier to graft the hydrophobic group onto the surface of the material, which improved the hydrophobic property of the material. Moreover, the universality of the hydrophobic modification method has been proved feasible in commercial ZSM-5. Therefore, this work provides an important theory and reference for improving the hydrophobic properties of ZSM–5 molecular sieve.

One-step microwave synthesis of micron-sized ZSM-5/MCM-41 hierarchical porous materials for phenol hydroxyl alkylation

• ZSM-5/MCM-41 hierarchical porous materials are synthesized through a one-step approach. • Microwave irradiation accelerates the formation of the composite zeolites. • ZSM-5/MCM-41 hierarchical porous materials catalytic performance better than pristine ZSM-5. The application of micron-sized zeolites ZSM-5 in industrial complex reaction system, despite of its high crystallization and stability and low price, is limited due to their single microporous structures. This study explores the one-step microwave synthesis of ZSM-5/MCM-41 hierarchical porous materials under low alkaline conditions and with the assistance of microwave, and examines their catalytic performance by the synthesis of anisole with phenol and methanol as probe reaction. The results show that the prepared ZSM-5/MCM-41 layered porous materials exhibit typical characteristics of micro-mesoporous composites. They have higher surface area and pore capacity, and good connectivity between micropores and mesopores, compared with the original ZSM-5. The above-mentioned advantages enable prepared ZSM-5/MCM-41 materials to produce higher phenol conversion, selectivity and catalyst stability of anisole. Through systematic investigations, this study develops a low-cost synthesis method for micron-sized ZSM-5/MCM-41 hierarchical porous materials, which facilitates their industrial application in complex reaction systems.

Research on propene oligomerization reaction over the Fenton's reagent modified ZSM-5

ZSM-5 zeolite was modified by Fenton's reagent, FeSO4 and H2O2 aqueous solutions using impregnation method, respectively. All these catalysts were characterized by XRD, ICP-OES, N2 adsorption-desorption, NH3-TPD, Py-FTIR and evaluated in propene oligomerization process. The results demonstrated that the framework of the parent ZSM-5 was well preserved after modification with Fenton's reagent, FeSO4 or H2O2 solutions. However, the SiO2/Al2O3 ratios for all the modified ZSM-5 samples increased due to the dealumination. Furthermore, Fe was detected in Fenton-ZSM-5 while no Fe was observed for FeSO4-ZSM-5 catalyst. The BET surface areas and total pore volumes of three modified catalysts significantly increased compared with the original ZSM-5 sample. Among them, the BET surface area of the Fenton-ZSM-5 increased by 17.86%. The increase of mesopores was probably caused by the removal of the residual organic template in the catalysts due to the generation of ·OH radicals by Fenton's reagent and H2O2. The Fenton-ZSM-5 catalyst formed new acid sites of Brønsted (B) and Lewis (L) with little change in the total calculated amount, which significantly changed the B/L ratio. Compared with the parent ZSM-5, the Fenton-ZSM-5 catalyst exhibited the best activity and stability for propene oligomerization reaction. The initial propene conversion and diesel selectivity were as high as 98.3% and 92.4%, respectively, and kept at >80% and >82% for about 24 h, respectively.

Preparation of bio-oil derived from catalytic upgrading of biomass vacuum pyrolysis vapor over metal-loaded HZSM-5 zeolites

The Fe-, Co-, Cu-loaded HZSM-5 zeolites were prepared via impregnation method. The upgrading by catalyst on biomass pyrolysis vapors was conducted over modified zeolites to investigate their catalytic upgrading performance and anti-coking performance. The Brønsted acid sites amount on Cu-,Co-loaded HZSM-5 decreased sharply, while that of Lewis both increased. The yield of liquid fraction and refined bio-oil over metal loaded ZSM-5 catalysts decreased, while that of char almost kept constant. The physical property of refined bio-oil was promoted in terms of pH value, dynamic viscosity and higher heating value (HHV). FT-IR analysis revealed that the chemical structure of refined bio-oil obtained over Fe-, Co-, Cu-loaded HZSM-5 zeolites was highly similar. The yield of monocyclic aromatic and aliphatic hydrocarbon over Fe-,Co-loaded HZSM-5 were boosted by around 2.5 times compared with original ZSM-5 zeolites. Data analysis revealed that Cu/HZSM-5 presented the worst deoxygenation ability. The anti-coking capability of Fe/HZSM-5 was obviously better, i.e., the coke content showed an approximate decrease of 38%. Thus, this study provided an efficient Fe/HZSM-5 catalysts for preparation of bio-oil derived from catalytic upgrading of biomass pyrolysis vapor.

Beneficial Use of Ultrasound in Rapid-Synthesis of SAPO34/ZSM-5 Nanocomposite and Its Catalytic Performances on MTO Reaction

SAPO-34 is highly selective and hydrothermally stable for MTO reactions but it is rapidly deactivated by the formation of coke through its micropores. The promising SAPO-34/ZSM-5 nanocomposite catalyst with a different ratio was synthesized by the ultrasonic-assisted hydrothermal method and it obtained products that were characterized to further investigate their catalytic performance. Utilization of the ultrasound method led to a faster synthesis time, a decrease of crystallite size, an increase of surface area, and a dominant mesopore structure. The physicochemical properties of the product were extensively investigated by XRD, FESEM, TEM, FT-IR, N2 adsorption–desorption techniques, and NH3-TPD. Results indicate that the composite had high conversion and selectivity compared to that of the original ZSM-5 and SAPO-34. When composite structures due to the synergic effect between ZSM-5 and SAPO-34 acted as promoted catalysts, they improved catalytic properties of composite catalysts. Moreover, the SAPO-34/...

Catalytic conversion of biomass-derivates by in situ DRIFTS: Evolution of coke

Coke deposition in the catalytic fast pyrolysis of biomass includes active coke and inert coke, which promote or inhibit the formation of hydrocarbons. This study aims at the evolution of coke formation on various catalysts in the catalytic conversion of furan as an important intermediate from biomass fast pyrolysis. The functional groups on the surface of each catalyst at every moment were recorded by in situ diffuse reflectance Fourier transform infrared spectroscopy. The results indicated that the coke formation was closely related to the structure and acid property of the catalysts combined with catalytic tests in a fixed-bed reactor. Though dealumination only changed the acid distribution, it increased the hydrocarbon yield and introduced different chemical component of active coke. Because MCM-22 had a large internal space and small windows, its coke content should be quite large. However, the coke on MCM-22 did not show large molecules in this study because of the wide acid distribution, and similar active coke species with ZSM-5 were detected of polymethyl benzaldehyde. The coke content of HY was small because of large quantities of weak acid, although HY showed a significantly large internal space. The main components of active coke on HY and Hβ were diolefinic alcohols and polymethyl benzenes. The understanding of coke formation on various catalysts will provide guidelines for catalyst design, i.e., it is suggested that 3-dimensional structures such as MCM-22 with large supercages and small windows can be introduced into the original ZSM-5 system to form a core-shell catalyst to increase the hydrocarbon yields.

Microwave-assisted catalytic fast pyrolysis of spent edible mushroom substrate for bio-oil production using surface modified zeolite catalyst

In order to minimize coke yield and improve hydrocarbon production during microwave-assisted catalytic fast pyrolysis of spent edible mushroom substrate, ZSM-5 zeolite catalyst is modified with pre-coking treatment, chemical vapor deposition of SiO2, and ethylene diamine tetraacetie acid (EDTA) chemical modification method, respectively (labeled PC-ZSM-5, SiO2-ZSM-5 and EDTA-ZSM-5). Experimental results show that all the modification methods result in a loss of external acid sites of ZSM-5. Among the three modified catalysts, the maximum oil fraction yield and the minimum coke yield are obtained with SiO2-ZSM-5. The relative content of hydrocarbons in oil fraction increases in the following order: SiO2-ZSM-5>EDTA-ZSM-5>PC-ZSM-5>original ZSM-5. Moreover, SiO2-ZSM-5 shows the highest relative contents of toluene and xylene, whereas original ZSM-5 produces the lowest ones. Besides, the selectivity of benzene in aromatics follows the order of original ZSM-5>EDTA-ZSM-5>PC-ZSM-5>SiO2-ZSM-5, while the selectivity of toluene+xylene presents the opposite trend.

Catalytic Conversion of Biomass Derivates over Acid Dealuminated ZSM-5

The present study describes the catalytic performance of acid treated HZSM-5 catalyst for the conversion of biomass derivates to olefins and aromatics. The ZSM-5 catalysts were prepared by changing several modifying parameters, such as the leaching agent, H+ concentration, processing temperature, and time. Fresh and modified catalysts were characterized by X-ray diffraction, scanning electron microscopy, surface area analysis, and NH3 temperature programmed desorption. The results show that modified ZSM-5 (leaching agent of H3PO4, H+ concentration of 2 mol/L, temperature of 20 °C, and time of 4 h) produced the maximum yield of chemicals (13.9% olefins and 31.8% aromatics), which are much higher than that obtained with the original ZSM-5 catalyst (9.8% olefins and 24.5% aromatics). The coke yield decreased from 44.1% with original ZSM-5 to 27.4% with modified ZSM-5. At the optimized dealumination condition, the selectivities of ethylene, propylene, and toluene increased, while those of butylene, C5, and be...

Storage of molecular hydrogen into ZSM-5 zeolite in the ambient atmosphere by the sealing of the micropore outlet

The storage of molecular hydrogen into ZSM-5 zeolite in the ambient atmosphere was examined by hydrogen filling into the micropore and the following sealing of the micropore outlet to prevent the release of hydrogen to the outside. The surface grafting of 1,4-bis(hydroxydimethylsilyl)benzene onto ZSM-5 zeolite was applied to the sealing of the micropore outlet. Pressurized hydrogen (10MPa) was filled into the micropore of ZSM-5 at liquid nitrogen temperature (−196°C), and then the sample was heated at 150°C for forming strong binding between the zeolite surface and the disilane compound under the hydrogen pressure. The hydrogen sorption isotherm at −196°C showed that the adsorption of hydrogen onto the disilane-grafted ZSM-5 thus obtained was reduced to less than 20% from the original ZSM-5. The remarkable hysteresis between the adsorption and desorption branches of the isotherm indicated that the kinetic trap of hydrogen occurred by the narrowed outlets of the micropores of ZSM-5 with the disilane compound. Even after exposing the disilane-grafted ZSM-5 to the atmosphere over a few months, hydrogen could be discharged by heating over 150°C. This result demonstrated that molecular hydrogen was successfully stored into ZSM-5 zeolite in the ambient atmosphere for a long time.

Catalytic conversion of biomass pyrolysis-derived compounds with chemical liquid deposition (CLD) modified ZSM-5

Chemical liquid deposition (CLD) with KH550, TEOS and methyl silicone oil as the modifiers was used to modify ZSM-5 and deposit its external acid sites. The characteristics of modified catalysts were tested by catalytic conversion of biomass pyrolysis-derived compounds. The effects of different modifying conditions (deposited amount, temperature, and time) on the product yields and selectivities were investigated. The results show KH550 modified ZSM-5 (deposited amount of 4%, temperature of 20°C and time of 6h) produced the maximum yields of aromatics (24.5%) and olefins (16.5%), which are much higher than that obtained with original ZSM-5 catalyst (18.8% aromatics and 9.8% olefins). The coke yield decreased from 44.1% with original ZSM-5 to 26.7% with KH550 modified ZSM-5. The selectivities of low-molecule-weight hydrocarbons (ethylene and benzene) decreased, while that of higher molecule-weight hydrocarbons (propylene, butylene, toluene, and naphthalene) increased comparing with original ZSM-5.

Synthesis of Micro/Mesoporous Composites and Their Application as CO<sub>2</sub> Adsorbents

We synthesized a series of micro/mesoporous composites of S-β-MCM41(c), P-β-MCM41(c), P-ZSM-MCM41(c), P-ZSM-C through a two-step crystallization process. During this process, the microporous zeolite precursor solution (S) or the zeolite powder (P) was first synthesized and treated with NaOH solution with different concentration (c), and then the mesopores were induced by hexadecyltrimethylammoniumbromide (CTAB) as a soft template or mesoporous carbon as a hard template. The effects of the type of inorganic precursor, the base concentration, and the type of mesoporous template on the structure and property of the micro/mesoporous composites were investigated. The results of X-ray diffraction (XRD), transmission electron microscopy (TEM), and nitrogen adsorption-desorption isotherms showed that the products contained micropores and mesopores, simultaneously. The CO2 adsorption capacities of these micro/mesoporous composites were obviously improved compared to the pure microporous or mesoporous materials. Among them, P-ZSM-MCM41(2) had the highest CO2 adsorption capacity of 1.51 mmol ·g-1, which was almost twice that of the original ZSM-5.

Síntese da zeólita ZSM-5 e suas propriedades estruturais após troca iônica com cobre

A zeólita ZSM-5 foi sintetizada utilizando sílica "Aerosil-Degussa -- 380 m²/g" como fonte de silício, em substituição ao trisilicato de sódio, que é normalmente utilizado na síntese dessa zeólita. Subseqüentemente, foi incorporado cobre à ZSM-5 através do método convencional de troca iônica. Técnicas de difração de raios X, microscopia eletrônica de varredura, área superficial e análise elementar por absorção atômica foram utilizadas para verificar a formação da zeólita sintetizada e suas propriedades após troca com cobre. Os resultados mostraram que houve a formação da ZSM-5 nas condições de síntese empregadas e que a amostra modificada pelo processo de troca manteve as propriedades da zeólita original.

Origin of boron mobility over boron-impregnated ZSM-5. A combined high-resolution–solid-state 11B nuclear magnetic resonance/infrared spectral investigation

Boron-impregnated ZSM-5 samples have been shown by 11B n.m.r. spectroscopy to have different phases, which are dependent on the zeolite pre-treatment conditions. While the original ZSM-5 sample reveals a resonance associated with tetrahedral boron (incorporated during synthesis in the zeolite lattice at a typical location of zeolitic aluminium), the other impregnated samples show a variety of spectral patterns associated with different phases of boron. For non-pretreated impregnated samples, boron exists as H3BO3, as indicated by a very broad resonance at lower field. Pretreatment at 0.1 mPa/673 K effects the condensation of H3BO3 with the host zeolite Bronsted sites into an Si—O—B(OH2) species. If excess of boron is present it exists as amorphous B2O3. Pretreatment at 0.1 mPa/1073 K assists in a further dehydration into a surface-annealed Pyrex-like structure. This structure does not exhibit the Pyrex stability, where it reverts to the less-structured phase upon zeolite rehydration. This suggests a role for water in mobilizing boron on ZSM-5 surfaces. An i.r. investigation of methanol reaction (static conditions) over samples pre-treated at 0.1 mPa/673 K reveals and confirms the boron mobility for the impregnated samples. Methyl borate ester is shown to form at 293 K in proportions increasing linearly with the impregnated boron and is identified in the gas phase. Similar vaporization of boron or boron ester is not evident for the original sample which contains framework boron.