查看更多>>摘要：Zeolites are very important catalysts in the chemical industry,but their intrinsic narrow micropore system oft(restricts the mass transport of reactant and product molecules.These mass transport limitations can be overcon by introducing a second larger pore system(meso-/macropores)into the zeolite crystals.Over the past decad desilication of zeolites has emerged as a simple post-synthetic process to implement mesoporosity into zeolite Here we present the investigation of the influence of framework topology on the formation of mesoporosity 1 the desilication process.For this purpose,the desilication behaviour of a channel-like system(ZSM-5/MFI-typ and a cage-like system(SSZ-13/CHA-type)are compared.It has been found that cage-like zeolite(SSZ-13)more susceptible to the desilication process.The desilication of SSZ-13 zeolite resulted in drastic reduction microporosity and crystallinity,while the microporosity and crystallinity of ZSM-5 gradually decreased wi desilication time.By systematically studying the influence of various desilication parameters(e.g.treatme:time,temperature and alkaline concentration),it has been found that there exists a direct correlation betwee the extraction of silicon and mesoporosity formation for the channel-like zeolite(ZSM-5)whereas in case of cag like zeolite(SSZ-13)no direct correlation has been found.
Ali A.El-SamakDeepalekshmi PonnammaMohammad K.Hassan
8页
查看更多>>摘要：Porous nanocomposite of polystyrene(PS)is fabricated by non-solvent induced phase separation,and with the addition of ZnO nanomaterials through electrospinning,the different evaporation rates of solvent/non solvent mixture causes phase separation and improves the porosity of the fiber.The spherical particles of ZnO are uniformly distributed within the polymer chains,creating a networking effect that further restricts the motion of the PS chains and higher pores generation.The specific surface area and average pore size values were respectively 48 m~2/g and 82.5 nm for the PS/ZnO with 3 wt% filler concentration,much higher than the neat polymer(23 m~2/g and 61.1 nm).The PS/ZnO composite showed 95% degradation efficiency when irradiated with natural sunlight for Azocarmine G dye.This study addresses the correlation of porous structural characteristic with the sunlight driven photocatalysis as the porous sites provide active centers for the catalysis to take place.The porous structural integrity is maintained,and improved with ZnO addition and promising catalysis efficiency is achieved.Moreover,the ZnO imparts excellent antibacterial activity against S.aureus bacteria and the PS/ZnO fibers show good functional and structural stability.
查看更多>>摘要：ITQ-34 zeolite is an interesting catalyst in FCC process due to its three-dimensional medium pore topology.Nowadays,the zeolite ITQ-34 is synthetized as ger-manosilicate with a zero acid capacity,low stability and sometimes its channels system are partial blocked by the formation of phosphate compounds during the calcination process.For these reasons,to develop a synthesis route to incorporate aluminum in its framework as well as avoid the described problems has a great interest.In the present work is described the possibility to synthesize the zeolite ITQ-34 rich in aluminum,with a low content of germanium and with the total elimination of the phosphate compounds.The zeolite Al-ITQ-34 shows a great catalytic capacity in the propylene production by FCC.
查看更多>>摘要：An environmentally friendly and inexpensive silica source,sodium silicate solution,was applied to synthesize a free-standing mesoporous silica film at the air/liquid interface,exploiting the co-assembly of cetyltrimethylammonium bromide and polyethylenimine.The effect of the composition of the solution used for the film formation on the mesostructure of the as-synthesized silica films,characterized by small angle X-ray scattering(SAXS),was investigated.The initial film formation time is estimated by the change in surface pressure with time.Additionally,a possible formation process of the mesostructured silica film is proposed using data from in situ grazing incidence small angle X-ray scattering(GISAXS)and X-ray reflectivity(XRR)measurements.A free-standing film with a wormlike structure was formed at the interface and reorganized into a 2D hexagonal ordered structure while drying at room temperature,after removal from the air/solution interface.The ordered 2D hexagonal structure,however,could only be retained to some extent during calcination,in samples where nitrate ions are present in the film formation solution.
查看更多>>摘要：In this study,sulfur compounds were removed from real diesel fuel in a continuous system employing the encapsulated mesoporous material with cobalt.The Co/MCM-41 was characterized with the help of X-ray diffraction(XRD),scanning electron microscopy(SEM),energy-dispersive X-ray spectroscopy(EDX)techniques,Fourier transform-infrared spectroscopy(FT-IR),and BET surface area.The effects of two variables,namely the height(2-6 cm)of the bed and the rate of flow(0.8-2 mL min~(-1))were investigated.The maximum capacity(1310.63 mg.g~(-1))of the bed was achieved with the following ideal values:column height of 6 cm,the rate of flow of 0.8 mL min~(-1),and a preliminary concentration of 12,000 mg.L-1 of sulfur.The bed depth influenced the time of breakthrough and exhaustion in a column apparatus operating at a low flow rate.The Thomas and Yoon-Nelson models were used to anticipate the breakthrough curves(BTC)and compute the usual laboratory continuous adsorption characteristics required for the best design of this process.According to the regression coefficient studies,the Yoon model outperformed the Thomas model.The BTC effectiveness demonstrated that Co/MCM-41 can be employed for application in fixed-bed adsorption systems for sulfur concentration removal.
查看更多>>摘要：Organic micropollutants pose a tremendous challenge to global water resources,for nonbiodegradable synthetic chemicals,especially.In this investigation,we loaded Cucurbit[5]uril on polymer BPEIH to prepare supramolecular polymer Q[5]@BPEIH with pore structure,which is used to adsorb and remove organic micropollutants in water.The experimental results show that the adsorbent can remove organic micropollutants from water quickly and with high loading,which is better effect than that of traditional activated carbon.In particular,the polymer is an excellent adsorbent for 2,7-dihydroxynaphthalene and Neutral Red pollutants.It also has classy adsorption properties for 1-naphthylamine,Amaranth,Metallic Yellow,8-hydroxy-1,3,6-trisulfonic acid pyrene,Methyl Orange and Crystal Violet.This adsorbent can also adsorb I2.When the adsorption tends to equilibrium,the calculated adsorption rate is 87.2%.These outstanding adsorption effects show that this adsorbent can help to remove a variety of micropollutants in the process of wastewater treatment.More importantly,Q[5]@BPEIH that we designed and synthesized has the characteristics of low synthesis cost,simple synthesis and preparation process,high product yield,fast adsorption speed and strong removal ability.The admirable removal ability of pollutant proved the prospect of Q[5] @BPEIH for rapid sewage disposal.
查看更多>>摘要：A ubiquitous phenomenon in zeolite synthesis is the generation of polymorphs leading to either single or multiphase products.The use of organic structure-directing agents(OSDAs)often ensures a high degree of phase purity for a desired zeolite; however,OSDAs can be economically and environmentally prohibitive.The use of alkali metals as inorganic structure-directing agents(ISDAs)is a common alternative,although reductions in polymorph specificity and/or purity in organic-free media are significant limitations.Developing more controlled,facile synthesis strategies without the aid of OSDAs relies on understanding how zeolite growth conditions impact polymorph selection and alter the physicochemical properties of crystalline products.Relatively few studies of organic-free syntheses have systematically explored potassium growth media.In this study,we examine synthesis conditions that promote the formation of five K-zeolites:CHA,LTL,MER,EDI,and BPH frameworks.Time-resolved analyses reveal distinct trends in crystallization kinetics and interzeolite transformations for potassium compared to prior studies that have largely focused on Na-zeolites.We also highlight methods to achieve nanosized crystals and markedly reduce crystallization times for zeolites,such as chabazite,which are notoriously difficult to synthesize in organic-free media at reasonable timescales.Collectively,these findings identify routes to control K-zeolite polymorphism and provide general design strategies to tailor their crystallization.
查看更多>>摘要：Simultaneous insertion of double heteroatom in the MFI framework generally gives rise to synergistic catalysis effect,however the specific origins for synergistic catalysis is still nebulous.In this study,vanadium-titanium doped MFI zeolite was synthesized via one-pot hydrothermal synthesis with the addition of(NH4)2CO3 and applied as heterogeneous catalyst for the synergistic catalysis of 1-hexene and cyclohexene epoxidation.Simultaneous incorporation of vanadium and titanium induced the partial charge transformation of titanium(IV)into titanium(III),which was verified by EPR and XPS characterizations.UV-Raman and UV-Vis spectra disclosed that partial charge transformation mainly occurred for framework titanium(IV).In addition,simultaneous insertion of vanadium and titanium gave rise to more Lewis acid sites as well as larger external surface area for VTS(0.15)zeolite in comparison to VS(0.15)and TS(0.15)zeolite.The prepared VTS(0.15)zeolite presented a TOF value of 118.8 h"1 for 1-hexene epoxidation,which is 7.8 folds and 1.3 folds of VS(0.15)and TS(0.15)respectively.Partial charge transformation of framework titanium(IV)into titanium(III),robust Lewis acid sites as large external surface area may induce the synergistic catalysis effect for VTS(0.15)zeolite in the epoxidation reactions.Moreover,the obtained VTS(0.15)zeolite particles showed good reusability for more than five cycles.
查看更多>>摘要：Reducing synthesis costs in the petrochemical industry leads to decreasing financial value of final products from raw materials.In this paper,SAPO-34 molecular sieve as a main catalyst of methanol-to-olefin process is newly synthesized by rice husk.The silica source of SAPO-34 synthesis is achieved from this agricultural waste material by calcination and leaching methods with the purity of 97% based on XRF analysis.Between the series of samples synthesized,the sample with the highest crystallinity and textural properties is obtained by Si = 0.6 M concentration and hydrothermal synthesis at 200℃ for 18 h which has been proved by XRD,SEM,BET,EDX and NH3-TPD analyses.Also,this sample showed that has relatively higher selectivity toward light olefins compared to other samples.In the case of operating conditions,using methanol/water(20 wt%)instead of pure methanol as feed increased light olefins selectivity and reached the maximum value of 83.5% at 375 ℃,however,highest light olefins mass(26 wt%)from the consumed feed acquired at 425 ℃.
Mariya A.KazakovaAlexander G.SelyutinMikhail V.Parfenov
11页
查看更多>>摘要：Gamma alumina is a widely used support for catalysts of various processes.However,in the case of aqueous-phase processes,hydrothermal conditions result in transformation of γ-Al2O3 to boehmite,which is accompanied by degradation of the porous structure and leads to rapid catalyst deactivation.Here,we demonstrate a simple approach to stabilize the textural characteristics of γ-AI2O3 under hydrothermal conditions,based on preliminary graphitization of its surface by chemical vapor deposition of ethylene.Different duration(5-240 min)revealed the optimal degree of alumina surface coverage with carbon,ensuring the preservation of its textural characteristics from collapse during hydrothermal treatment(HTT)at 200 ℃.Materials characterization was performed by X-ray diffraction,transmission electron microscopy,nitrogen physisorption,and Raman spectroscopy.It is shown that initial γ-Al2O3 during HTT transforms into boehmite with a dramatic decrease in the surface area from 217 to 42 m~2/g.Whereas the preliminary graphitization of its surface maintains high surface area of the material after HTT,which is achieved by forming a C@boehmite composite(294 m~2/g).The presented approach makes it possible to modify the surface of alumina supports with a layer of graphite-like carbon and can be used to improve or maintain the catalysts activity.
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