查看更多>>摘要：? 2021 Elsevier Inc.In this study, the possible applications of Cr-doped UiO-66 in adsorption heat transformation (AHT) were investigated. Four different Cr-doped UiO-66 samples were prepared to examine their structures and water adsorption properties. Results showed that Cr-doped UiO-66 samples have higher pore volume and specific surface area than pure UiO-66 samples. In particular, 0.2Cr-UiO-66 has the highest BET specific surface area (993 m2/g) and micropore volume (0.50 cm3/g), which are 31.6% and 29.6% higher than those of unmodified UiO-66, respectively. Water adsorption tests revealed that Cr doping can improve the water adsorption performances of UiO-66. At 25 °C and P/P0 = 0.9, the saturated water uptake of 1.0Cr-UiO-66 is 0.69 g/g, which is 64.3% higher than that of pure UiO-66. After 10 adsorption/desorption cycles, the water adsorption capacity of pure UiO-66 and 0.5Cr-UiO-66 samples has decreased by 3.4% and 5.7%, respectively, indicating their good cycle stability. All these results indicate that Cr doping is beneficial to UiO-66 application in AHT.
查看更多>>摘要：? 2021 Elsevier Inc.The acid compounds removal from natural gas by adsorption on zeolites is an environmentally friendly alternative technology for its purification and commercialization. However, despite numerous theoretical studies determining the adsorption energies for gases on zeolites are found, for important natural gas compounds adsorption on Y zeolite they are poorly reported, especially with respect to long range van der Waals interactions, the description of their nature and related thermodynamic properties. Thus, this work aims to pre-select transition metal-exchanged Y zeolite for selective removal of H2S and other acid compounds from natural gas streams by DFT calculations for H2S, COS, CO2 and CH4 adsorption on Fe–Y, Co–Y, Ni–Y, Cu–Y and Zn–Y zeolite clusters. Adsorption energies, thermodynamic properties, chemical hardness, electronegativity, Natural Bond Orbital (NBO) and Energy Decomposition Analysis (EDA) were determined using B3LYP hybrid functional and Grimme's D3 empirical dispersion correction. Comparison between H2S and other compounds adsorption energies indicates that Ni–Y zeolite has potential for selective removal of H2S, despite Co–Y zeolite presents stronger adsorption energy for all compounds. Moreover, the NBO and EDA analyzes reveal that there is a transfer of d electrons from H2S molecule to unoccupied orbitals of the cation. Charge transfer and polarization phenomena contribute mainly to the adsorption energy of H2S, COS and CO2 in transition metal-exchanged Y zeolite clusters, showing the presence of surface chemisorption.
查看更多>>摘要：? 2021 Elsevier Inc.The impact of the crystal size of the template zeolite on the textural properties of resulting Zeolite Templated Carbons was studied using nano- (20 nm) and micron-sized (5 μm) zeolite beta crystals. ZTCs were obtained for both nano- and micron-sized zeolite beta crystals, yet for the micron-sized sample the presence of supermicropores and small mesopores was detected, indicating a higher degree of structural defects during the templating process and hence in the final ZTC. The insights gained from nitrogen physisorption were confirmed by TEM, TGA and XPS. Despite, long range structural order, evidenced by X-ray powder diffraction (XRD) for both, nano- and micron-sized ZTCs was inferred. These results suggests that XRD patterns allow to evidence the well-ordered part of the sample but might not be the method of choice for characterizing the structural quality of ZTCs. Simulated XRD powder patterns allowed to propose a graphene-based nanoribbon structure grown in the zeolite pores as a satisfactory model for ZTCs in beta zeolite.
查看更多>>摘要：? 2021 Elsevier Inc.Highly active and recyclable sulfated silica nanocatalyst for the synthesis of hexyl levulinate (HL) is reported. The sulfated catalysts, Sn-BLA (n = 15 or 30 μL of H2SO4 added), are prepared via sulfation upon amorphous bamboo leaf ash (BLA) under non-microwave instant heating condition (100 °C, 1.5 h). The spectroscopy and microscopy results reveal that silica nanoparticles (28 nm) with Br?nsted ([Formula presented] bisulfate group) and Lewis ([Formula presented] sulfate group) acid sites are produced upon sulfation treatment. The sulfur containing acid groups covalently bound on the mesosilica surface are very active in the esterification of levulinic acid and hexanol where S30-BLA presents excellent catalytic activity (95.2% conversion, 98.0% selective to HL) at 90 °C for 7 min, which is far more superior than the previously reported catalysts. The S30-BLA catalyst is reusable with slight decrease in catalytic activity after six consecutive runs, suggesting an economical and environment-friendly route to biomass utilization.
查看更多>>摘要：? 2021 Elsevier Inc.Traditionally zeolites are produced under long aging processes and high autogenous pressure reactions associated with a lot of safety concerns and explosion risks. Herein, a facile zeolite synthesis method under atmospheric pressure using a reflux system is reported. The zeolite gel crystallizes rapidly under the synthesis conditions of heating, stirring, and reflux in an oil bath. We have successfully synthesized LTA, FAU, MFI, and BEA zeolites. This technique not only eliminates the potential risks associated with pressure vessels but also greatly improves the synthesis rate and speeds up the production cycle. This synthesis strategy provides a new, safe and rapid way of synthesizing zeolites.
查看更多>>摘要：? 2021 Elsevier Inc.Herein, a series of novel amidoxime-functionalized porous polymeric adsorbents using dimethoxymethane (FDA) as the external cross-linker and biphenyl and amidoxime-functionalized 1-(benzyloxy)-4-ethylbenzene (BP-AO) as the original monomers were synthesized in one-pot Friedel-Crafts alkylation reactions via a simple “knitting” synthetic strategy. The adsorbents were characterized by FT-IR, solid-state 13C NMR/MAS spectrum, N2 adsorption-desorption, etc. The adsorption mechanism was probed by XPS, which suggests that the η2 complexation between uranium and amidoxime, and the polymers provide an approach to synthesize novel porous materials. The batch adsorption experiments showed that amidoxime hyper-crosslinked polymer-2 (HCPA-2) displays a uranium adsorption capacity of 27.7 mg/g at pH 6. The static adsorption action was more consistent with the Langmuir model and pseudo-second-order kinetics. Ionic competition experiments showed that Kd (U(IV)) is as high as 695.94 mL/g and reusable with a removal rate up to 60% after 7 cycles when 0.1 M HNO3 was used as a stripping agent, which verifies the practical application potential of the materials.
查看更多>>摘要：? 2021 Elsevier Inc.Microporous materials, such as MOFs and ZIFs, have been proposed as adsorbents for many gas separation/purification applications. To be used in industry, their shaping is required. ZIF-8 (Basolite Z1200) and MIL-53(Al) (Basolite A100) were shaped employing the extrusion method. For that, two binders were used: alumina and carboxymethylcellulose (CMC). Loadings of 5, 10, and 15 %wt. of alumina were utilized to shape ZIF-8 and MIL-53(Al) into pellets. Additionally, pellets of ZIF-8 with 5 and 10 %wt. of CMC were also produced. The materials were characterized by SEM/EDS, N2 adsorption at 77 K, CO2 adsorption at 273 K, mercury intrusion porosimetry, and XRD to evaluate the effect of the shaping process on the materials. The shaping process does not result in significant alterations in the crystalline structure of the materials. Besides, as expected, in general, with the increase of the binder quantity the average pore diameter decreases along with the surface area of the materials. Furthermore, the mechanical strength of the material was analyzed through crush strength tests. In general, the increase of the binder amount in the pellets results in an improvement of the mechanical strength of the material. The adsorption equilibrium isotherms for CH4 and N2 were determined at 303 K up to 4 bar. Langmuir adsorption model was used to fit the experimental results. This study allows understanding the effect of shaping in the adsorption capacities of the materials. For both gases, the impact of shaping in the adsorption capacities is higher on the MIL-53(Al) materials than on ZIF-8 pellets. It also proves the extrusion method's potential to prepare structured materials to be used in CH4/N2 separation.
查看更多>>摘要：? 2021 Elsevier Inc.An efficient approach for the rapid synthesis of nanosized SSZ-13 zeolite with hierarchical structure was rationally developed by the combination of additive and seed induced crystallization. Compared with the conventional hydrothermal synthesis, the addition of additive and seed during the synthesis of SSZ-13 could significantly shorten the crystallization time from 144 h to 6 h. The obtained nanosized SSZ-13 with average crystal size of ca. 400 nm possessed abundant mesopores within the crystals. The crystal size could also be regulated in the range of 400–6000 nm by adjusting the crystallization time and the type and amount of the additives. UV–Vis results showed that the strong chelation ability of citric acid to Al ions as well as the formation of new metastable phase accelerated the crystallization rate in the synthesis of SSZ-13. The fast-synthesized hierarchical nanosized SSZ-13 exhibited prolonged catalytic lifetime and improved selectivity to light olefins in comparison with the conventional SSZ-13 catalyst in the MTO reaction. This work not only provides a simple and facile approach for the rapid synthesis of hierarchical nanosized aluminosilicate zeolite, but also might help to develop the fast synthesis methods for other aluminosilicate zeolites.
查看更多>>摘要：? 2021 Elsevier Inc.In this work, the sodium halide, e.g., NaBr, NaCl, or NaF, was added into the synthesis system of ZSM-12 zeolite. The addition of sodium halide accelerated the crystallization of ZSM-12 zeolite, and the acceleration effect of different sodium halide increased in the order of NaBr < NaCl < NaF. To understand the acceleration mechanism of sodium halide, the crystallization process of ZSM-12 zeolite synthesized with and without sodium halide was studied comparatively by using XRD, SEM, TEM, TG and FTIR characterizations. Experimental results revealed that the accelerated crystallization of ZSM-12 zeolite arose from the combined effects of sodium cation and halide anion. The sodium cation induced the coagulation of colloidal particles of initial sol and avoided the formation of gel, resulting in the improved mass transfer. The halide anion promoted the combination of tetraethylammonium cation (as structure-directing agent) with the solid phase. A ZSM-12 zeolite with abundant mesopores was finally obtained from the synthesis system containing sodium halide. The Pt/ZSM-12 catalyst using the mesoporous zeolite as the support exhibited excellent activity and isomerization selectivity in the hydroisomerization of n-dodecane.
查看更多>>摘要：? 2021 Elsevier Inc.Eutrophication has long been one of the environmental pollution problems, and excess phosphate in water bodies is the main cause of this phenomenon. To solve this problem, magnetic adsorbent with Fe/Ce-loaded zirconium-based metal-organic framework (Fe3O4/UiO-66-NH2/CeO2) was prepared by co-precipitation, microwave assisted and hydrothermal method. The results showed that different molar ratios of cerium and zirconium were the main influencing factors for phosphate adsorption, and the adsorbent exerted its maximum capturing capacity of 260.8 mg/g of phosphate when Ce:Zr = 4:1. The newly synthesized Fe3O4/UiO-66-NH2/CeO2 was characterized by SEM, XRD, FT-IR, XPS, VSM and TGA. The adsorption process was found to be consistent with the Langmuir adsorption isotherm model and the pseudo-second-order model by batch experiments, indicating that the monolayer chemisorption dominated the adsorption process. Thermodynamic parameters obtained from temperature experiments proved that the phosphate adsorption process is a spontaneous endothermic absorption process and the adsorption experiments with coexisting ions (F?, Cl?, NO3?, SO42?, HCO3?) showed that the adsorbent has a unique selectivity for phosphate. Unlike most adsorbents previously studied, Fe3O4/UiO-66-NH2/CeO2 exhibited consistently efficient adsorption performance over the pH spectrum tested (2 < pH < 10). After five cycles, the adsorbent still maintained favourable adsorption performance. Mechanism of Fe3O4/UiO-66-NH2/CeO2 adsorption on phosphate was attributed to electrostatic attraction, ligand exchange and inner-sphere complexation. Therefore, the prepared Fe3O4/UiO-66-NH2/CeO2 with wide pH suitability will be a promising option for capturing phosphate from wastewater.
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