查看更多>>摘要：? 2021 Elsevier Inc.Bi-doped ZnSnO3/CuO composite (Bi–ZnSnO3/CuO) was synthesized by in situ precipitation in this study. The material structure, morphology, size, specific surface area, and surface composition were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), the Brunauer-Emmett-Teller (BET) method, and X-ray photoelectron spectroscopy (XPS). Bi–ZnSnO3/CuO composite had a profoundly porous structure. CuO was bolstered on the surface of cubic ZnSnO3. The addition of Bi and CuO effectively expanded the substance of oxygen vacancies and chemisorbed oxygen of ZnSnO3/CuO. Gas-sensing test results appeared that Bi–ZnSnO3/CuO had excellent gas-sensing performances for acetone, with a 386.19 sensitivity to 100 ppm acetone under an optimal operating temperature of 375 °C and a response/recovery time of 4 s/12.5 s. The excellent improvement in the gas-sensing performances of Bi–ZnSnO3/CuO over those of ZnSnO3 can be due to the rich mesoporous structure and the arrangement of a large number of oxygen defects and p-n heterojunctions. Excellent gas-sensing performances make Bi–ZnSnO3/CuO an ideal sensing material for acetone gas.
查看更多>>摘要：? 2021 Elsevier Inc.Dual templating approach, using hexadecyltrimethylammonium bromide (CTAB), was employed in an attempt to synthesize hierarchical ZSM-5 zeolite. Amount of mesoporogen and the duration of aging of the precursor were varied. Majority of the synthesis routes resulted in phase separation, yielding separate ZSM-5 and amorphous mesoporous material. The relative amounts of the two phases were dependent on the CTAB amount ratio and also significantly on the duration of precursor aging before CTAB addition. One particular combination of the two factors led to the formation of a homogeneous hierarchical form of ZSM-5 with leafy morphology, consisting of intergrown thin crystalline sheets which formed flower-like structures. The hierarchical ZSM-5 possessed significant microporous (≈95 m2/g) and highly developed mesoporous surface (≈470 m2/g), with a relatively broad distribution of mesopore sizes (<20 nm). The acidity of all samples was studied in detail. Isothermal microcalorimetry/volumetry of ammonia adsorption provided quantitative data on the number and distribution of strength of acidic sites. In situ FTIR of pyridine and collidine adsorption was used to quantify Br?nsted and Lewis acid sites, and to provide information on their location - in the micropores or mesopores/external surface. The hierarchical ZSM-5 possessed both Lewis and Br?nsted acidity, with Br?nsted sites located mainly in the micropores. All samples were fully characterized using XRD, low temperature nitrogen adsorption, FESEM and EDS. The synthetic route used for obtaining the ZSM-5 zeolite with flower-like morphology is a simple strategy for preparing hierarchical ZSM-5 forms targeting enhanced diffusivity and accessibility of catalytically active sites.
查看更多>>摘要：? 2021Ordered mesoporous silicas are widely used in separation science and catalysis, however, their slow batch synthesis is a barrier to scale-up and new applications. SBA-15 is one of the most extensively studied and commercially available mesoporous silicas, whose textural properties can be readily tuned through judicious choice of synthesis conditions. Here we demonstrate the continuous flow synthesis of SBA-15 in high yield at 80 °C using a simple tube reactor without any mixing device. The resulting SBA-15 exhibits excellent textural properties, with a BET surface area of 566 m2 g?1 and ordered 5.1 nm mesopore channels in a p6mm arrangement, akin to those from conventional batch synthesis, but with far higher productivity than previously reported in batch or flow (5.3 g L?1 h?1 versus 0.4 and 0.6 g L?1 h?1 respectively).
查看更多>>摘要：? 2021 Elsevier Inc.Different vanadium supported beta zeolites modified with Cs and K, were used as catalysts for the conversion of glycerol, in gas phase, without any external reductant. The catalytic data show that all the catalysts studied are active in the conversion of glycerol and that the presence of vanadium oxide species promotes the formation of allyl alcohol. Moreover, modification of the vanadium-based catalysts with Cs or K changes the vanadium species and puts in evidence the importance of the acidity in this process. A low density of acid sites favors the formation of allyl alcohol, in detriment of acrolein one. The data also indicate that the formation of these compounds is closely related and could be explained using the same mechanistic path.
查看更多>>摘要：? 2021 Elsevier Inc.Zeolites are the catalytic materials that are widly applied in the processing of conventional and renewable fuels and chemicals. The present study provides a comprehensive analysis of the factors controlling the acidic medium synthesis of high silica silicalite-1 zeolite. The effect of various silica sources (TEOS, fumed and colloidal silica) and alkali metal cations (Na and K) on the silicalite-1 formation is studied. The efficiency of different types of seeds (micron-sized, nanosized, and silicalite-1 amorphous colloidal precursor) on the silicalite-1 crystal growth kinetics and crystal size formed under acidic conditions is also investigated. Further, the zeolite crystallization kinetics under acidic, neutral, and basic conditions is compared. The obtained highly crystalline samples are used to compare the physicochemical properties of zeolites synthesized in acidic, neutral, and basic medium. Thus, the crystallinity, thermal stability, and local order in silicalite-1 samples synthesized in the (2–12) pH range are evaluated.
查看更多>>摘要：? Elsevier Inc.Hierarchical macro/microporous ZSM-5 zeolite (defined as ZSM-5(MM)) was successfully synthesized by using silica spheres as silica source. The effects of template, sodium ions, hydroxyl ions, aluminum and water contents as well as crystallization temperature on the morphology and pore structure of ZSM-5 were investigated in detail. The formation mechanism was studied by XRD, SEM, N2 sorption, ICP-AES, XPS, 27Al MAS NMR and 29Si MAS NMR, confirming that the silica spheres during synthesis process were served as not only silica nutrients to accelerate the generation of crystal nucleus, but also morphology guiding agents that induce the formation of macro/microporous structure followed by quasi solid hydrogel transformation mechanism. The prepared ZSM-5(MM) zeolite exhibited much longer catalytic lifetime and higher light olefins selectivity in the methanol to olefins (MTO) than those of the conventional microporous sample. This is because the hierarchical macro/microporous structure can effectively improve the diffusion of feedstocks and products, suppressing the rapid coke deposition. Meanwhile, the contribution of alkene cycle in MTO is enhanced and it produces more propene and butene.
查看更多>>摘要：? 2021 Elsevier Inc.ZIF-8 nanocrystals were synthesized in the presence of cetyltrimethylammonium bromide, as a cationic surfactant, (ZIF-8@CTAB) and then modified by iron promoter (ZIF-8@Fe-CTAB) through a wet impregnation process. Self-assembly of surfactant in the synthesis route changed morphology of ZIF-8 nanocrystals from rhombic dodecahedron (RD) to truncated rhombic dodecahedron (TRD). The structural modifications significantly changed the adsorption properties of the nanocrystals for CO2 and CH4, so that ZIF-8@Fe-CTAB nanocrystals provided the highest CO2/CH4 adsorption selectivity (～19) compared to values have ever been reported in the literature. The nanocrystals were also employed for preparation of mixed matrix membranes (MMMs) using Matrimid?5218 as the polymeric matrix. Investigation of gas transport properties of the MMMs confirmed promising separation performance of ZIF-8@Fe-CTAB nanocrystals for CO2/CH4 separation.
查看更多>>摘要：? 2021 Elsevier Inc.The removal of lead in drinking water has attracted considerable attention of researchers in recent years, especially, the trace characteristic of lead is a challenge to water treatment. Herein, 13X zeolite/reduced graphene oxide composite material (13X-rGO) with hierarchically porous structure was successfully prepared using graphene oxide (GO) and 13X zeolite via a chemical reduction method and presented great performance for removing trace Pb(II) from drinking water. The influence of some important parameters including adsorbent dosage, contact time, initial lead concentration, coexisting competing ions, solution pH value, etc. on the removal of Pb(II) was systematically investigated. The composite material showed better adsorption properties compared with a single component and their physical mixture, confirming the synergistic effect of rGO and 13X zeolite on Pb(II) adsorption. The effluent lead concentration could be decreased to the level permitted by World Health Organization (WHO) (<10 ppb) within 30 s under calcium content of 20 ppm and initial lead concentration of 150 ppb. Simultaneously, the as-prepared 13X-rGO performed excellent adsorption capacity meeting WHO standard (6.07 mg/g), which was about 2.23 times that of single 13X zeolite (2.72 mg/g). In the presence of interfering ions, the lead concentration could still be reduced to safe drinking water standard. Moreover, the adsorbent could be effectively regenerated by saturated sodium chloride solution. Therefore, 13X-rGO can be introduced as a promising adsorption material for the purification of drinking water contaminated with trace lead owing to rapid adsorption, low cost and recycling potential.
查看更多>>摘要：? 2021Sustainable fabrication of LTA zeolite membranes was explored on the macroporous α-Al2O3 tubes by a simple wet gel conversion method with largely reduced gel consumption. The method was mainly composed of three steps: 1) water dipping of LTA seeded support 2) gel dipping 3) gel conversion into LTA membrane without any additional gel solution in the autoclave. LTA zeolite membrane under an optimized synthesis condition on the 5 cm support showed good permeation flux of 2.56 kg/(m2·h) with prominent separation factor of near 9000 for the dehydration of 90 wt % ethanol/10 wt % water mixture at 75 °C by pervaporation. Based on the optimized synthesis conditions, high performance large-scale tubular LTA zeolite membranes were further synthesized on the 80 cm α-Al2O3 tubes for the first time, demonstrating that this method offered exciting opportunities for the preparation of zeolite membranes with largely reduced raw materials consumption and waste production.
查看更多>>摘要：? 2021 The AuthorsTwo twin series of carbon replicas were synthesized by the acid-catalyzed precipitation polycondensation of various amounts of furfuryl alcohol in SBA-15 suspensions using water and toluene as reaction media. The textural and structural parameters, as well as the morphology of the polymer/silica carbonizates and corresponding replicas, were investigated comprehensively. It was found that the polarity of the reaction medium plays an essential role in the scenario of the deposition of poly(furfuryl alcohol) (PFA) onto the surface of the silica matrix. Namely, the water-based environment results in propagating PFA chains radially from the pore centres to the wall thereof, while in the case of toluene its growth progresses in the reverse direction. The spectroscopic studies disclosed that this is due to the competitive adsorption of monomer and solvent on the superficial silica silanol groups. In the case of the water-furfuryl alcohol system, H2O is adsorbed preferentially, hindering the formation of a homogenous polymer layer, thus precluding the formation of a hollow-type replica. Contrarily, for the toluene-furfuryl alcohol mixture, the monomer adsorption is favored. Furthermore, the forming polymer anchors to the silica surface covalently and clads it evenly, therefore facilitating the formation of a high-quality CMK-5 structure.
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