查看更多>>摘要：? 2022 Elsevier Inc.Zeolite-templated carbon (ZTC) can be prepared by chemical vapor deposition (CVD), which involves the coupled mass transport and chemical reaction of carbon precursors. Combining theoretical and experimental approaches, this work demonstrated that reducing the particle size of the template enhanced both the inward and outward mass transport during zeolite-templated CVD, which, in turn, improved the structural properties of the resulting ZTC. Specifically, the inward diffusion of the carbon precursor was modelled quantitatively by fitting the deposition mass of pyrolytic carbon measured in zeolite templates of different particle sizes (d = 4, 0.8 and 0.002 mm). This model revealed that the inward diffusion of the carbon precursor was enhanced in smaller zeolite particles, allowing more uniform deposition of pyrolytic carbon inside the zeolite and better replication of the zeolite's pore structure in the resulting ZTC. For the outward mass transport, semi-quantitative analysis was conducted on the intermediate components that were responsible for the external deposition of pyrolytic carbon. In particular, the concentration of the intermediate components was predicted to increase with the particle size of the zeolite. This prediction was confirmed by the experimental characterization results, where ZTC samples prepared with larger zeolite particles showed thicker external layers of quasi-crystalline graphitic carbon.
查看更多>>摘要：? 2022 Elsevier Inc.Pure UZM-5 zeolite with either nanosheet or rosette-shaped morphology have been successfully synthesized by a charge density mismatch (CDM) method under a corresponding tumbling or static conditions. The synthesis parameters were fully investigated to abstain from commonly accompanying by-products, including SOD or amorphous phase which greatly interfered with the use of UZM-5. The crystalline phases and relative crystallinity of resultant products were carefully substantiated by using scanning electron microscope and X-ray diffraction. As a result, the molar ratios of water and structure directing agents thereof were deemed to be two vital parameters which had significant effects on the well-defined pure-phase UZM-5 zeolite production. Trace ethanol added in the reagent solution was found to play a role in zeolite purification. There is an urgent need in electrocatalytic reduction of nitrate to ammonia. In this work, pure UZM-5 zeolite with Lewis acid sites served as catalyst matrix for the application to produce this valuable chemical. Excellent ammonia production rate with high faradaic efficiency was achieved by using the obtained novel UZM-5-based catalyst for the reduction reaction, strongly proving the great potential of this young zeolite in catalysis applications.
查看更多>>摘要：? 2022 Elsevier Inc.Modulation of the porosity and acidity of zeolites is a very attractive subject for designing highly efficient solid-acid catalysts. In this work, Beta nanozeolite aggregates with hierarchical porous structure were synthesized via steam-assisted conversion (SAC) of dry gel in presence of seeds and a cationic polymer of polydiallyldimethylammonium chloride (PDAD). The influence of various synthesis parameters, such as the alkalinity, the contents of PDAD and zeolite seeds, and the crystallization conditions (temperature, water/dry gel ratio and time) on the formation of Beta zeolites was studied by combining a variety of characterization techniques. The SAC-synthesized Beta zeolites (S-Beta) are assembled from ultra-small nanocrystals around 10 nm to form self-sustaining micron-sized zeolitic aggregates, and possess abundant interconnected mesopores and relatively mild acidity. Compared with the conventional Beta zeolite, S-Beta aggregates show much higher catalytic activity for the Friedel-Crafts acylation of anisole with acetic anhydride. The excellent catalytic performance of S-Beta should be mainly attributed to the enhanced mass transport ability for reagents as well as the mild acidity that can avoid the rapid deactivation of the catalyst under the test conditions.
查看更多>>摘要：? 2022The present work describes the synthesis and characterization of a zeolite type LTA-clay composite membrane on pre-existing locally organized aluminosilicate in clay support and its application to the removal of heavy metals. X-ray diffraction reveals that the natural clay consists essentially of quartz, kaolinite, illite, dolomite, and calcite phases. Flat discs, membrane supports are prepared by uniaxial pressing of natural clay with 160 ≤ Ф < 250 μm as optimal grain size mixed with 3% w/w activated carbon as porogen agent. Membrane supports are consolidated by sintering to final temperatures of 1000 °C. Zeolite Linde type A (LTA) is deposited on the clay supports using the hydrothermal method. Nitrogen adsorption analysis of the support using Brunauer–Emmett–Teller (BET) theory showed pores with 35.5 nm, which is narrowed to 14.2 nm after zeolite-A deposition. X-ray analysis of the composite membrane (MZA) reveals the growth of new diffraction peaks characteristic of zeolite-A. Prior to water filtration analysis of the MZA composite membrane, the pzc is found to be 9.8 using the titration method. The efficiency of the MZA composite membrane is evaluated by filtration tests of solutions containing heavy metals using a flow loop developed specifically for dead-end filtration. The retention of heavy metals studied follows the order Pb2+> Al3+ > Co2+ > Cd2+ > Zn2+ with 99.7, 99, 89.5, 88.3 and 81.8 retention percent, respectively. The retention mechanism seems to be controlled by the charge of the membrane's surface, which is demonstrated using the linear wave anodic stripping voltammetry (LWASV).
查看更多>>摘要：? 2022 Elsevier Inc.Porous organic frameworks entirely composed of organic building blocks are attracting more and more attention owing to their tunable porosity, lightweight and hydrolytic stability. Three novel porous aromatic frameworks (PAFs) based on the [4 + 3] design strategy have been synthesized from spirobifluorene building block as square node and various triangle nodes respectively via imine condensation. These materials are all semiconductors and permanently microporous amorphous polymer with high thermal stabilities. The Brunauer-Emmett-Teller (BET) surface areas of these PAFs are between 389 and 698 m2/g. More importantly, these frameworks exhibit good CO2 uptake (4.0 mmol/g for PAF-131) and outstanding ideal adsorption selectivities for CO2/N2 (121 for PAF-131) and CO2/CH4 (327 for PAF-131) at 273 K and 1 bar, thus showing that they are good candidates for CO2 capture.
查看更多>>摘要：? 2022 Elsevier Inc.The template used in synthesis of the zeolites needs to be removed in order to activate the zeolite micropores. High-temperature calcination is a common process, but it is associated with high energy consumption, and often induces thermal shocks to the zeolite. In this study, a new approach for SSZ-13 zeolite detemplation is investigated as a viable alternative for conventional calcination at high temperature (>500 °C). The SSZ-13 zeolite is exposed to ozone gas at 180, 190 and 200 °C which are much lower than the required temperature for the calcination. SEM, TGA, FTIR, BET experiments and CO2/CH4 adsorptive performance analyses, the Langmuir isotherm, and the IAS theory were utilized to evaluate the efficiency of this process compared to the calcination approach. SSZ-13 zeolite was successfully detemplated using ozonication process, showing porosity characteristics close to that of a thermally calcined sample. According to results, the best detemplation was achieved at 200 °C and O3 concentration of 41 g Nm?3. The BET surface area of zeolite was 441 m2 g?1 during the mentioned condition while that of calcined powder was 513 m2 g?1. Just a 14.03% drop in surface area is acceptable when a considerable amount of energy is saved compared to the calcination. For the mentioned ozonicated sample, a 28% reduction in CO2 adsorption was resulted while selectivity of 61.62 for CO2/CH4 binary system was estimated using the IAS theory which is an increase about 28.59% compared to calcined sample.
查看更多>>摘要：? 2022 Elsevier Inc.The sustainable production of p-xylene (PX), via Diels-Alder cycloaddition between biomass-derived 2,5-dimethylfuran (2,5-DMF) and ethanol followed by subsequent dehydration, was catalyzed by a series of nitric acid and phosphoric acid modified H-Beta zeolites. It is tentatively suggested that the multifold increase of p-xylene selectivity and reduction of coke amount for NPB-2 (H-Beta zeolite modified by 2 M HNO3 combining with H3PO4) was attributed to existence of acid sites with appropriate amount and strength. NH3-TPD and multiple ss MAS NMR results revealed that nitric acid can remove framework and extraframework Al species effectively, leading to the decrease of total acid amount. While by further phosphoric acid modification, not only P species was introduced in the crystal, the tetrahedrally coordinated framework Al was also turned into octahedrally coordinated framework Al, resulting in the reduction of strong acid sites and increase of weak acid sites, which can slow down the dehydration reaction rate of 2,5-hexanedione (2,5-HDO) to 3-methyl-2-cyclopentenone (MCO) and promote dehydration of cycloaddition to p-xylene. Besides, the N2 physical adsorption showed the specific surface area and pore volume were increased after modification, further enhancing accessibility and utilization efficiency of acid sites. This study promotes the development and application of P-containing zeolite in acid catalyzed reactions.
查看更多>>摘要：? 2022 Elsevier Inc.MnO2/TiO2 core-shell structure photocatalyst was prepared by a two-step microwave method. Under visible light irradiation, this core-shell photocatalyst exhibited enhanced catalytic activity for the degradation of organic dye Rhodamine B and the oxidative removal of gaseous heavy metal Hg0. The MnO2 shell not only enhanced the visible light absorption of TiO2, but also increased its specific surface area to 227.94 m2 g?1. In addition, the formation of core-shell heterojunction promotes the migration of carriers and the separation of photo-generated electron-hole pairs, and improves the stability of the composite, thus enabling it to exhibit enhanced photocatalytic performance.
查看更多>>摘要：? 2022 The Author(s)Zeolite Y was prepared by a dense-gel method and subsequently modified either by treatment with diethylamine (DEA), sodium hydroxide (NaOH) or disodium ethylenediaminetetraacetate (Na2H2EDTA), or by sequential treatment (H4EDTA-NaOH or H4EDTA-NaOH-Na2H2EDTA). Individual treatment did not succeed in introducing mesoporosity in the parent zeolite Y, while the sequential treatment lead to formation of mesopores. After introduction of Cu2+ ions, the obtained materials were studied as catalysts for the selective catalytic reduction of NOx by NH3 (NH3-SCR, DeNOx). The catalytic investigations reveal a similar NO conversion for all Cu-containing catalysts up to 450 °C, independent of the introduced mesoporosity. Insights into the dynamics of NH3-SCR intermediates through rapid scan FT-IR show that for Cu–Y, the rate-determining step is the formation of the mixed [Cu(O?)(NH3)n-1(NO)]2+ complexes, which initiate the NH3-SCR reaction.
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