Composite Molecular Sieve Research Articles

Catalytic pyrolysis of hydrolyzed lignin using HZSM-5/MCM-41 supported transition-metal to produce monocyclic aromatic hydrocarbons

Hydrolyzed lignin (HL), one kind of organic solid wastes, comes from the production of hydrolysis of lignocellulosic biomass for high-value chemicals, unsuitable treatment of which not only meaning the waste of resources but also resulting environmental pollution. The pyrolysis of HL has the problem of high oxygen-containing compounds and low hydrocarbons in the products. The HZSM-5/MCM-41 (HM) meso-microporous composite catalyst, containing nickel and molybdenum, was synthesized through impregnation to enhance the production of monocyclic aromatic hydrocarbons (MAHs) during the in-situ catalytic pyrolysis of hydrolyzed lignin. Different transition metals loaded on composite molecular sieves were prepared for comparison. The relationship between catalyst structure and pyrolysis efficiency was studied based on characterization techniques including SEM, BET, and XRD. This study investigated the catalytic properties of modified composite molecular sieves with Ni and Mo at different loaded ratios on the pyrolysis of hydrolyzed lignin. Results indicated that HM loaded with different metals had different catalytic pyrolysis selectivity. The relative yield of MAHs on 3 %Ni-HM was the highest, at 27.78 %, while that of phenolic on 5 %Mo-HM was 51.02 %. Thus, by modifying the co-loading ratios between Ni and Mo, the combined catalytic pyrolysis of hydrolyzed lignin was performed, achieving a 39.24 % yield of MAHs on the catalyst Mo1Ni2-HM, markedly surpassing the 17.69 % yield from unaltered HZSM-5/MCM-41. In addition, the improvement of active sites was caused by transition metals loaded and the synergistic effect between bimetals enhanced the catalytic activity and stability. HZSM-5/MCM-41 loaded with metal oxides promoted the depolymerization of macromolecules in the intermediate products of pyrolysis, and thus improved the relative yield of MAHs among pyrolysis products of hydrolyzed lignin.

Comprehensive study of alkali lignin pyrolysis catalyzed by composite metal-modified molecular sieves for the preparation of hydrocarbon liquid fuels

Catalytic lignin pyrolysis for hydrocarbon liquid fuel production offers a viable alternative to fossil fuels. This study investigated the effects of transition metal (Fe, Co, Ni, Cu) modified composite molecular sieve catalysts on the pyrolysis product distribution and behavior of alkali lignin (AL). AL pyrolysis achieved the highest liquid product yield of 24.50 % at 600 °C, with high temperatures favoring hydrocarbon product formation. Volatile gaseous products from AL pyrolysis included H2, CO, CO2, phenolic compounds, heteroatomic compounds, and hydrocarbons. Molecular sieve catalyst additions were all favorable to the increase in hydrocarbon content. Compared with ZSM-5 and SBA-15, catalysts processed through acid etching and metal modification exhibited optimized pore structure, acid site distribution, and catalytic performance. Metal-modified composite molecular sieve catalysts (FeZS, CoZS, NiZS, and CuZS) generated more liquid products and promoted hydrocarbon formation. Notably, Cu-modified ZS catalysts exhibited superior acid site distribution and specific surface area, considerably reducing oxygenated compounds in the products. A higher catalyst-to-feedstock ratio increased the number of catalytically active sites, facilitating the cracking and deoxygenation of oxygenated components and generating more hydrocarbon products. The highest hydrocarbon yield for AL with a catalyst-to-biomass ratio of 10:1 under CuZS was 92.25 %, with 66.07 % being monocyclic aromatic hydrocarbons (MAHs) and 61.72 % benzene, toluene, ethylbenzene, and xylenes (BTEX). Additionally, kinetic and thermodynamic analyses revealed a substantial decrease in the average activation energy (Eα) of AL and a reduction in entropy value with the CuZS catalyst, indicating enhanced pyrolytic reactivity of AL. Therefore, the proposed method is highly effective for producing highly selective hydrocarbons through catalytic pyrolysis of AL.

The Fenton catalyst prepared via ZSM-5/MOR composite molecular sieve supported Fe/La duplex metal and its dye degradation performance

The Fenton catalyst prepared via ZSM-5/MOR composite molecular sieve supported Fe/La duplex metal and its dye degradation performance

Composite Molecular Sieve ZSM-5/MCM-48-Based Impregnation Modification for Efficient Adsorption of CO2

Micro/mesoporous materials are low-cost functional materials with the potential for CO2 adsorption. Modifying micro/mesoporous materials is significant for enhancing CO2 adsorption and their high-value utilization. Herein, the micro/mesoporous material of composite molecular sieve ZSM-5/MCM-48 (ZM) was synthesized by a two-step crystallization method using cetyltrimethylammonium bromide as a template, tetraethyl orthosilicate as a silicon source and ZSM-5 seed as part of silicon aluminum source. Tetraethylenepentamine (TEPA) and polyethyleneimine (PEI) were used as impregnation modifiers to modify ZM with amine groups. The results showed that with the increase of amine loadings, both ZM-T60 (Impregnated with TEPA) and ZM-P60 (Impregnated with PEI) functionalized adsorbents exhibited the best adsorption capacities of [Formula: see text] and [Formula: see text] at 60, respectively, when the loading of ZM sample was 60%. The adsorption kinetic analysis showed that the adsorption of CO2 by ZM-T60 and ZM-P60 was a chemisorption-dominated process accompanied by physical adsorption. After 10 adsorption/desorption cycles, the CO2 adsorption capacity of ZM-T60 and ZM-P60 decreased by 8.7% and 2.6%, respectively. This work demonstrates that impregnation modification of the composite molecular sieve to achieve efficient CO2 adsorption has practical application significance.

Effects of mesopore size on ethyl acetate adsorption–desorption behaviors over hierarchical ZSM-5/MCM-41 molecular sieves

A series of micro-mesoporous structure ZSM-5/MCM-41 composites with different mesopore sizes were successfully fabricated through surfactant-mediated recrystallization method using the template agents with different alkyl chain length. Mesopore pore sizes were tuned from 2.11 nm to 5.09 nm. Taking ethyl acetate as the VOC probe molecule, the adsorption and desorption properties were evaluated by the dynamic adsorption breakthrough curves and TPD experiments. Results showed that the adsorption capacity was enhanced under dry and humid condition owing to the introduction of mesopore size structure. Especially for ZSM-5/MCM-41 (C12), its adsorption capacity reached up to 208.92 mg·g−1 and 82.29 mg·g−1 at dry and saturated humidity (4 v/v% H2O). Simultaneously, the hierarchical molecular sieves exhibited an excellent regeneration performance. Even after the fifth cycle, above 86% adsorption capacity remained under humid condition. Moreover, the adsorption kinetics of ethyl acetate on ZSM-5/MCM-41 composites followed the Bangham model. The results indicated that hierarchical composite molecular sieve can be considered as a potential adsorbent for VOCs removal.

Performance characterization and comparison study of silver molecular sieve hydrogen adsorbents in liquid hydrogen vessels

Four commercially available silver molecular sieve (SMS) hydrogen adsorbents were tested and characterized in terms of both material characterization and hydrogen adsorption performance, and an attempt was made to establish the constitutive relationship between material structure and hydrogen adsorption. The results show that the four SMS products have an average Ag content between 33 and 36 wt%, with the SBET between 200 and 400 m2/g and the cumulative hydrogen adsorption capacity in the range of 10–20 cm3(STP)/g. The two SMS products with the best hydrogen adsorption performance can replace or even surpass PdO in the vacuum interlayer of liquid hydrogen vessels. Their hydrogen adsorption capacity at an equilibrium pressure of 2 × 10−2 to 10 Pa is about two orders of magnitude greater than that of PdO. The constitutive relationship between material characterization and hydrogen adsorption performance suggests that the realization of new efficient SMS hydrogen adsorbents requires micro-mesoporous composite molecular sieves with large specific surface area and pore volume, and further improvements in the silver ions exchange process to load more silver ions into the internal pores of the molecular sieve microspheres.

ZSM‐5@KIT‐6‐encapsulated composite molecular sieves for the catalytic cracking of waste cooking oil model compound to produce light olefins

AbstractBACKGROUNDA series of ZSM‐5@KIT‐6 composite molecular sieve catalysts was prepared by encapsulating ZSM‐5 as a substrate in the mesoporous material KIT‐6. The intent was to use these catalysts to promote the catalytic cracking of a waste cooking oil model compound (WCOMC) to produce light olefins.RESULTSThe morphology, structural characteristics and acidity of each of the resulting catalysts were characterized by X‐ray diffraction, transmission electron microscopy, N2‐Brunauer–Emmett–Teller (N2‐BET) surface area analysis and temperature‐programmed ammonia desorption. The results showed that ZSM‐5 was successfully coated with KIT‐6. The BET surface areas of these catalysts ranged from 345 to 792 m2 g−1 and the specimens had average pore sizes in the range of 2.37–5.51 nm. Total acidity increased with increases in the mass‐based proportion of ZSM‐5 in the material.CONCLUSIONThe catalytic cracking of WCOMC was studied in a lab‐scale fixed‐bed apparatus. Trials at a reaction temperature of 600 °C using the material having a mass‐based ZSM‐5 proportion of 80.0% (ZK‐80) gave the highest gas‐phase yield of light olefins of 43.8%. After 6000 min, the catalytic performance of this material remained stable, demonstrating a resistance to carbon deposits. The superior activity of the present composite catalysts can be ascribed to improvements in pore structure and acid strength distribution. © 2023 Society of Chemical Industry (SCI).

HBEA/MTW composite molecular sieves with shape-selectively catalyzed alkylation of 2-methylnaphthalene with methanol for the synthesis of 2,6-dimethylnaphthalene

The methylation of 2-methylnaphthalene (2-MN) and methanol is a highly promising approach to synthesize 2,6-dimethylnaphthalene (2,6-DMN). However, it is difficult to control the target product selectivity. Herein, a series of HBEA/MTW composite molecular sieves by secondary crystallization were produced by hydrothermal method and further applied for the alkylation of 2-MN. The results showed that composite molecular sieves had higher specific surface area and porosity than mechanically mixed molecular sieves, and the secondary crystallization reduced acid amount and acid density. The composite molecular sieve performed better in the alkylation of 2-MN with methanol, improving reaction conversion and selectivity of 2,6-DMN. To further improve the catalytic performance, we used Mg to modify the pure molecular sieve. The selectivity of 2,6-DMN over 1%Mg-BEA/MTW catalyst can be further increased with the 2,6-/2,7-DMN ratio of 1.5. Therefore, the composite molecular sieves have a high potential for application in the methylnaphthalene alkylation reaction.

Appealing sheath-core spun high-performance composite carbon molecular sieve membranes.

Carbon molecular sieve (CMS) membranes are attractive candidates to meet requirements for challenging gas separations. The added ability to maintain such intrinsic properties in an asymmetric morphology with a structure that we term a "Pseudo Wheel+Hub & Spoke" asymmetric form offers new opportunities. For CMS membrane, specifically, the structure provides both selective layer support and low flow resistance even for high feed pressures and fluxes in CO2 removal from natural gas. This capability is unavailable to even rigid glassy polymers due to the much higher modulus of CMS materials. Combining precursor asymmetric hollow fiber formation and optimized pyrolysis creates a defect free CMS proof-of-concept membrane for this application. Facile formation of the sheath-core spun precursor with a 6FDA-DAM sheath and Matrimid® core also avoids the need to seal defects before or after the carbonization of the precursors. The composite CMS membrane shows CO2 /CH4 (50 : 50) mixed gas feed with an attractive CO2 /CH4 selectivity of 64.3 and CO2 permeance of 232 GPU at 35 °C. A key additional benefit of the approach is reduction in use of the more costly high performance 6FDA-DAM in a composite sheath-core CMS membrane with the "Pseudo Wheel+Hub & Spoke" structure.

Efficient-selective-catalytic aromatization of methanol over Zn-HZSM-5/SAPO-34: Action mechanism of Zn

To improve the performance and stability of catalytic methanol aromatization, the Zn-modified HZSM-5/SAPO-34(Zn-ZS) composite molecular sieve was synthesized by hydrothermal synthesis, and the modified composite molecular sieve was characterized using XRD, SEM, N2 isothermal adsorption-desorption, NH3-TPD, and XPS, and the catalysts were evaluated in catalytic methanol aromatization reactions. The results showed that the introduction of in-situ Zn greatly changes the morphology of the molecular sieve, presenting a polycrystalline stacked bloom-like structure, which brings abundant micro-pore channels to the molecular sieve, but at the same time, the introduction of metallic Zn also will cause more meso-pore channels losses. The introduction of secondary external Zn brought a large number of weak strong acidic sites, and the amount of molecular sieve acid was nearly doubled; weak acidic sites were strengthened, and the ratio of weak to strong acid amount became smaller. The BTX selectivity of the Zn-doped molecular sieve was significantly enhanced and the anti-coking performance was improved. The composite molecular sieve doped with 2% Zn achieves a 41% selectivity for the BTX within the 47 h lifetime, showing good reaction stability.

Synthesis of ZSM-22/SAPO-11 composite molecular sieve-based catalysts with small crystallites and superior n-alkane hydroisomerization performance

To improve oil quality, ZSM-22/SAPO-11 composite molecular sieves were synthesized by adding ZSM-22 into a synthetic gel of SAPO-11 for n-decane hydroisomerization. The mass ratios of ZSM-22/(ZSM-22+SAPO-11) in the composite molecular sieves were optimized and the optimal ZSM-22/SAPO-11 composite (ZS-9) was obtained. The electrostatic repulsions between the ZSM-22 precursors and the SAPO-11 crystalline nuclei produced small ZSM-22 and SAPO-11 crystallites in ZS-9, which increased the specific surface area and mesopore volume and thereby exposed more acid sites. In comparison with conventional SAPO-11, ZSM-22 and their mechanical mixture, ZS-9 with smaller crystallites and the optimal medium and strong Brønsted acid centers (MSBAC) content displayed a higher yield of branched C10 isomers (81.6%), lower cracking selectivity (11.9%) and excellent stability. The correlation between the i-C10 selectivity and the MSBAC density of molecular sieves indicated that the selectivity for branched C10 isomers first increased and then decreased with increasing MSBAC density on the molecular sieves, and the maximum selectivity (87.7%) occurred with a density of 9.6 × 10−2 μmol m−2.

Preparation and Characterization of Free-Standing Composite Cellulose-Based Carbon Molecular Sieve Membranes

Carbon membranes with excellent strength and mechanical stability were prepared using a cellulose precursor regenerated from an ionic liquid solution with a low loading of boehmite ceramic nanoparticles, ca. 0.1 wt. %. The precursor films show an asymmetrical structure while, after carbonization, the corresponding carbon molecular sieve membranes (c-CMSM) show a dense structure with a uniform thickness of ca. 22 µm. The c-CMSM exhibited excellent separation performance, well above the Robeson Upper Bound. The permeability of the c-CMSM to hydrogen increased from 300 to 530 barrer and the H2/CH4 permselectivity increased to 473, after adding boehmite nanoparticles. Boehmite nanoparticles act as a microporosity-forming agent without compromising the width of the ultramicropores. The prepared c-CMSM is extremely promising for several applications, namely for hydrogen recovery from methane – H2/CH4 (Robeson index:θ=13.5); biogas upgrading – CO2/CH4 (θ=6.5); CO2 removal from combustion flue gas – CO2/N2 (θ=1.7); and hydrogen recovery from ammonia processes – H2/N2 (θ=4.8).

Preparation of FeMn-ZSM-5/MOR composite molecular sieves: combination of adsorption/oxidation and Fenton-like reaction

Preparation of FeMn-ZSM-5/MOR composite molecular sieves: combination of adsorption/oxidation and Fenton-like reaction

Preparation, surface acidity and catalytic performance of Beta/ZSM-5 composite molecular sieve

• Beta/ZSM-5 was synthesized by seeding method. • The crystal structure and surface acidity of the composites were adjusted by changing the secondary crystallization time. • The propylene oxide rearrangement over composite molecular sieve was affected by acid type and acid amount. Beta/ZSM-5 composite molecular sieves were successfully prepared by seeding method and characterized by XRD, FTIR, BET, NH 3 -TPD, Py-FTIR. The crystal structure and surface acidity of the samples can be adjusted by changing the crystallization time. Beta/ZSM-5 shows good catalytic performance for the rearrangement of propylene oxide. The results show that when the crystallization time is 24 h, the proportion of BEA type and MFI type structure in the sample reaches equal, and the amount of Lewis acid is 18.1 mmol/g, while that of B acid is only 6.48 mmol/g, which is more conducive to the rearrangement of epoxy propane to produce propionaldehyde.

Carbon molecular sieve hollow fiber membranes derived from dip-coated precursor hollow fibers comprising nanoparticles

We report a novel approach to economically fabricate dual-layer composite nanoparticle-containing carbon molecular sieve (CMS) hollow fiber membranes having excellent gas separation performance. The economically favored process comprises dip coating engineered support layer fibers to form a dense skin layer in a CMSCMS precursor. The coated fibers are then pyrolyzed to form a high-performance CMS hollow fiber membrane. The nano-particle containing composite carbon molecular sieve hollow fiber membranes showed very attractive selectivities and productivities. This work shows how to produce high performance CMS hollow fiber membrane by coating, which exceeds that achieved with the standard sol-gel support stabilization technique. • Dual-layer nanoparticle containing precursor fiber membranes were developed. • Precursor membranes dip-coated with two polyimide polymers were employed to fabricate carbon molecule sieve (CMS) membranes. • CMS membranes generated from coating at low relative humidity (RH) have very attractive CO 2 /CH 4 separation performance. • No sol-gel support stabilization was required for the pyrolysis.

Gas separation performance and physical aging of tubular thin-film composite carbon molecular sieve membranes based on a polyimide of intrinsic microporosity precursor

We present a study on the fabrication of tubular thin-film composite CMS membranes based on an intrinsically microporous polyimide of intrinsic microporosity (PIM-PI), PIM-6FDA-OH. Besides the inherent structural similarity between the PIM-PI and CMS membranes (i.e. microporosity with pores <20 Å), the unique feature of the chosen precursor is its ability to undergo a thermal rearrangement (TR) reaction which constitutes an additional mechanism of microporosity evolution in addition to the pyrolysis process. By using Raman spectroscopy and in-situ thermal spectroscopic ellipsometry we tracked the structural TR- and pyrolysis-related evolution in CMS films as thin as 100 nm. Our study revealed a pronounced acceleration of the microstructure collapse (densification) due to physical aging that occurred in ultra-thin films. These, and our previous findings, suggest that excessive reductions in selective layer thickness in microporous amorphous materials, such as PIMs or CMS, may not be beneficial to obtaining highly efficient membranes. Instead, we have shown that excellent and stable separation properties could be achieved by PIM-PI-derived CMS membranes with thicker, ∼3 μm, selective layers (e.g. CO2, H2 permeances of >200 GPU, with CO2/CH4, CO2/N2, and O2/N2 selectivities of 43.0, 41.0, and 7.5, respectively) even after 3 months of aging.

Vapor/gas separation through carbon molecular sieve membranes: Experimental and theoretical investigation

The separation of H2O vapor from (hydrogen-rich) gaseous streams is a topic of increasing interest in the context of CO2 valorisation, where the in situ water removal increases product yield and catalyst stability. In this work, composite alumina carbon molecular sieve membranes (Al-CMSM) were prepared from phenolic resin solutions loaded with hydrophilic boehmite (γ-AlO(OH)) nanosheets (0.4–1.4 wt. % in solution) which partially transform to γ-Al2O3 nanosheets upon thermal decomposition of the resin, improving the hydrophilicity and thus the adsorption-diffusion contribution of the H2O permeation. The γ-Al2O3 nanosheets showed no influence on the pore size distribution of the membranes in the range of micropores, but they increased the membrane hydrophilicity. In addition, the use of boehmite in the resin solution causes an increase in the viscosity and thus an increase in the carbon layers thickness deposited on the porous α-Al2O3 support (from 1 to 3.3 μm). Furthermore, the alumina sheets introduce defects in the carbon matrix, increasing the tortuosity of the active layer, as concluded via phenomenological modelling and parametric fitting of the experimental results. As a consequence, the water permeability exhibits a maximum (1.3ꞏ10−6 molꞏs−1 Pa−1 m−1 at 150 °C) with boehmite/alumina content of ca. 0.8 wt. %, as the combined effects of increasing hydrophilicity (which favour H2O permeability) and increasing thickness and tortuosity (which hamper permeability) upon increasing boehmite loading. Similarly, the H2O/gas perm-selectivity is optimum at 1.2 wt. % boehmite loading. We further investigated the H2O permeation mechanism by modelling the mono- and multi-layer adsorption and capillary condensation of water in microporous media, which result as the main transport mechanisms in the explored conditions.

Preparation of core-shell ZSM-5@Beta molecular sieve and catalytic alkylation to 2,6-Dimethylnaphthalene

ZSM-5@Beta core-shell molecular sieve was prepared by dynamic hydrothermal synthesis method using ZSM-5 adhered Beta seed crystals as the core phase, and polydiallyl dimethyl ammonium chloride (PDDA) was used as a coupling agent to adhere Beta seed crystals on the surface of ZSM-5. The structure and physical properties of composite molecular sieves were characterized by XRD, N2 adsorption-desorption, SEM, TEM, ICP, NH3-TPD and Py-FTIR. The catalytic performance of composite molecular sieves for alkylation of 2-methylnaphthalene (2-MN) with methanol was investigated. The results showed that ZSM-5@Beta composite molecular sieve prepared by this method had a core-shell structure, and the particle size was about 500 nm. Compared with mechanically mixed binary molecular sieve, core-shell molecular sieve had higher specific surface area and external surface area, lower acid strength and stronger acid center density. Through the construction of core-shell interface and hierarchical porous, the catalytic activity was improved by shell phase Beta molecular sieve with 12-membered ring channel, and the catalytic selectivity was improved by core phase ZSM-5 molecular sieve with 10-membered ring channel in the alkylation reaction of 2-MN with methanol. The 2,6-/2,7-DMN ratio in the products reached 1.35, and the yield of 2,6-DMN reached 4.29%.

Effective adsorption of zeolite/carbon composite molecular sieve synthesized from spent bleaching earth.

Spent bleaching earth (SBE) as anindustrious solid rubbish seriously causes the environmental pollution problem. The resourceful utilization of SBE has become increasingly important. In this work, silicon and carbon ingredients derived from SBE were coincidently employed to synthesize a 4A zeolite/carbon composite molecular sieve (4A/CMS). Therein, the graphite carbon components in the form of porous lamellar scattering among the interlayer, surface, and periphery of 4A zeolite promote the rate of mass transfer for the lipophilic gas, which can effectively improve the adsorption property for the volatile organic compounds. The obtained 4A/CMS has large specific surface area, hierarchical pore structure, satisfactory adsorption capacity, and regeneration performance, and its equilibrium adsorption capacity of p-xylene can achieve 209.57mg·g-1. The pseudo-first-order rate equation is appropriate for the adsorption kinetics. In the end, the formation mechanism of 4A/CMS was illuminated in detail. □ Spent bleaching earth (SBE) as anindustrious solid rubbish were utilized resourcefully. Silicon and carbon ingredients from SBE were coincidently employed to synthesize 4A/CMS. Graphitic carbon with hierarchical pore promoted the rate of mass transfer of organic gas. 4A/CMS exhibited excellent adsorption capacity and regeneration performance of p-xylene.

Catalytic and deactivated behavior of SAPO-34/ZSM-5 composite molecular sieve synthesized by in-situ two-step method

This work aims at revealing the reaction and carbon behavior of SAPO-34/ZSM-5 composite molecular sieve (SZ-TS) in MTO reaction, which is synthesized via in situ two-step crystallization method. Several tests are used to explore the structure–activity relationship of the SZ-TS. The results show that the strength of weak and medium-strong acid is suitable, the particle size of two-phase molecular sieve is decreased, the hierarchical pore structure with abundant mesoporous is formed. By using the SZ-TS in MTO reaction, the methanol conversion and light olefins selectivity are 98% and 92.7%, respectively. These results can be attributed to the interface phase effect produced by etching and dissociation on the skeleton of the nuclear phase SAPO-34. The result of in situ IR and analysis of carbon deactivation indicate that polymethylbenzene is generated as the active intermediate of MTO reaction.SZ-TS with appropriate acid sites and rich mesoporous distribution could alleviate the formation rate of methyl-substituted benzene and polycyclic aromatic hydrocarbons, smaller particle size can avoid the occurrence of secondary reactions of olefins, therefore displaying the excellent resistance to the carbon deposition inactivation, with a catalytic lifetime up to 1380 min.