查看更多>>摘要：This paper reports on the control of strong acid sites in SAPO-11 molecular sieve crystals using different silica sources.The crystallization process of the SAPO-11 molecular sieves was performed using silicon sources with different particle sizes,i.e.,fumed silica(200 nm),colloidal silica(22 nm),and SiO2 sol prepared by the sol-gel method(4 nm).The SiO2 sol proved to have a significant effect on the acidic properties,morphology and crystal size of SAPO-11 molecular sieve.Moreover,more efficient incorporation of silicon is achieved,providing an increased concentration of acid sites.The SAPO-11 intergrown crystals with a size of 100-300 nm exhibited hierarchical pore structure(Sbet-250 m~2/g and V_(meso)-0.27 cm~3/g)were synthesized using the SiO2 sol precursor.The SAPO-11 molecular sieves were tested in the reaction of a-methylstyrene dimers synthesis.The SAPO-11 samples,synthesized by SiO2 sol showed the highest monomer conversion and linear dimer selectivity.
查看更多>>摘要：Immobilized enzymes on silica nano-carriers are stable biocatalysts with the potential for use in a plethora of applications.Studying how the structural characteristics of silica nano-carriers influence the performance of immobilized enzymes allows for the optimization of performance.This work investigates the influence of the pore architecture of silica nanospheres on enzyme loading,release,and reusability.Compared to dendritic mesoporous silica nanospheres(DMSN)with funnel-shaped wide-open pores,fractal silica nanoparticles(FSN)have a far more complex pore structure.FSN showed significantly higher immobilization capacity,sustained release,and enhanced reusability towards two model enzymes.The knowledge gained from this work paves the way for the rational design of enzyme nano-carriers for various applications.
查看更多>>摘要：A facile polymer heat treatment and reflux method are used for developing growth of flower-like BiOCl(BiOCl NFs)on 3D honeycomb-like N-doped graphitic carbon(N-GC)to form BiOCl/N-GC composites.The N-GC hierarchical structure effectively heightened the dispersion of BiOCl NFs,which increased the contacted area for the NOx gas molecule.Benefiting from the hierarchical structure,the(102)plane of BiOCl has a suitable adsorption energy for NOx,synergistic effect of large specific surface area and mesopores of N-GC,the formation of p-p heterojunctions,Bi-C interfacial bond,N-doping and the role of chemisorbed oxygen.The BiOCl/N-GC composites have satisfactory response and selectivity for NOx gas at room temperature.It reveals an exceptionally excellent response and response time of 52.54 and 3.2 s for NOx gas.It also exhibits a low detection limit(10 ppb)and a long-stability of 12 weeks.Thus,the BiOCl/N-GC nanocomposites are one of the most potential materials in gas sensor.
查看更多>>摘要：The accessibility to sodalite(SOD)cages in nanosized zeolite X(FAU-type framework)is tuned by varying the nature and location of extra-framework exchangeable cations(Na~+,Li~+,Cs~+,K~+ and Rb~+).Hyperpolarized(HP)and Exchange Spectroscopy(EXSY)~(129)Xe NMR experiments highlight the connectivity between SOD-and super(SUP)-cages,in particular that its diffusion pathway from sodalites to supercages depends mainly on the size and location of extra-framework cations present in the zeolite.These ~(129)Xe NMR results are supported by DFT simulations.Based on the computed adsorption energies of Xe in both SOD and SUP cages of zeolite X with different cationic compositions,it is concluded that xenon penetration in SUP cages is always favorable while the adsorption in the SOD cages is possible only if small cations(Na~+,Li~+,K~+)are present.
查看更多>>摘要：The TiO2 nanoclusters were modified into the pores of silica core-shell particles(SiO2@dSiO2)by the sol-gel method,and the loading amount reached 47%.Based on the Ostwald ripening theory,by simply extending the reaction time,a part of the TiO2 in the pores of the shell was dissolved and then re-deposited on the outer surface of the shell to form a TiO2 layer.Using this method,TiO2 crystalline grains of different sizes were obtained simultaneously inside and outside the shell of silica core-shell spheres.Small-sized crystalline grains were located in the pores of the shell,and they had a strong quantum size effect.The large crystalline grains were located in the TiO2 layer on the outer surface of the shell of SiO2@dSiO2.Due to the formation of larger-sized crystalline grains,the recombination probability of photogenerated electron-hole pairs was reduced.When used as photocatalysts for the degradation of Rhodamine B under UV irradiation,the catalytic activity of SiO2@dSiO2@TiO2 was 5.4 times higher than that of the commercial P25 TiO2 photocatalyst.
查看更多>>摘要：This work is aimed at the preparation and investigation of Cr(VSiO2 catalysts of oxidative propane dehydrogenation in the presence of carbon dioxide.The mesoporous silicas used as carriers were prepared via a sol-gel method using a beta-cyclodextrin and urea mixture as a template.The amounts of water added during Si(OEt)4 hydrolysis and chromium oxide loading were varied.The obtained catalysts were characterised via nitrogen low-temperature adsorption-desorption,XRD,SAXS,SEM with EDX,TEM,XPS,UV-Vis diffuse reflectance spectroscopy and the catalytic tests.The obtained mesoporous silicas have monomodal narrow pore size distributions with the maxima at 7,9,10 nm increasing when the amounts of water used during the synthesis increase,and large surface areas of 680,460,410 m2g~(-1),respectively.All the samples do not contain micropores.Chromium oxidation states +6 and + 3 were found according to XPS and UV-Vis diffuse reflectance spectroscopy data.The catalytic tests revealed that there is a correlation between the catalytic activity and synthesis conditions.The catalytic activity in the reaction of oxidative propane dehydrogenation in the presence of CO2 decreases in the series with a pore diameter of 9 > 10 > 7 nm.The most active and selective sample showed the selectivity to propylene up to 80% while the conversion was 20%.
查看更多>>摘要：UiO-66 supported metal catalysts have shown high catalytic activity and selectivity to cinnamyl alcohol(COL)in the selective hydrogenation(SHYD)of cinnamaldehyde(CAL),but the roles of missing-linker defects(MLDs)in UiO-66 on the catalytic performance of the UiO-66 supported metal catalysts have less been reported.Here,UiO-66 supports with the different amount of MLDs were used as the supports,and three series of UiO-66 supported Pt(Pt/U)catalysts were prepared by sol-impregnation,wet-impregnation as well as in-situ encapsulation methods,respectively.The influences of the MLDs in UiO-66 on the catalytic properties of the prepared Pt/U catalysts in the SHYD of CAL were investigated.The series of Pt/U-720 catalysts with the more MLDs showed higher CAL conversion and selectivity to COL than the corresponding Pt/U-F catalysts with fewer MLDs.The different preparing methods affect the location and dispersion of Pt species on UiO-66 supports and the metal-support interaction,but the location of the supported Pt species on UiO-66 is the critical factor affecting the catalytic properties of Pt/U catalysts.The presence of the MLDs in UiO-66 is the key to preparing UiO-66 supported Pt catalysts with high SHYD performance.
查看更多>>摘要：Realumination of dealuminated HZSM-5 zeolites by acid treatment has always been controversial and puzzling.Through characterizations of XRD,nitrogen adsorption,NH3-TPD,IR,XPS and ~(27)Al MAS NMR,this work confirmed realumination of dealuminated HZSM-5 zeolites could indeed be achieved after treated with HC1 solution.And it was found mainly a portion of the penta-coordinated extra-framework aluminia(EFA1)were reinserted into the framework during the process of realumination.Moreover,the characterizations of ICP-AES and UV-Vis-DRS of Co~(2+)-exchanged zeolites indicated the realumination capacity was closely related to the distribution of framework Al(Alp).Realumination was more likely achieved when there was lower content of Al pairs and less AlF located in the channel intersections in HZSM-5.Finally,realuminated zeolites exhibited a higher conversion of n-octane due to its more Br0nsted acid sites than dealuminated HZSM-5 in catalytic cracking reaction.The significantly lower content of Al pairs in realuminated zeolites compared to parent HZSM-5 inhibits the hydride transfer process to a certain extent,resulting in a higher selectivity of propylene.
查看更多>>摘要：Hydrothermal synthesis of SSZ-13 zeolite from precursors comprises many unanswered fundamental questions,in which understanding the effects of alkali metal cations on the structural rearrangement during the crystallizing period is an active and expanding area of research.Experimental results showed that the continuous crystallization process of SSZ-13 crystals can be easily hindered by the amorphous gel during the synthesis process.Accordingly,we carefully explored and repeated the crystallization period of SSZ-13 zeolite with different K~+ mole ratios,which demonstrated significant effects on their crystallization behaviors with the easy breaking of amorphous gel state.The crystallization time was obviously shortened to 18 h.Theoretical calculation results also demonstrated that K~+ cation in the precursor solution is more inclined to control the successive deprotonation process due to the higher activation energies for Si-O-Al bonds formation.Accordingly,the SSZ-13 zeolite sample tend to realize fast synthesis and transform into scattered crystals without aggregation by addition of K~+ cation.
查看更多>>摘要：Herein,zeolitic imidazolate framework-8 capped gold nanoclusters(AuNCs@ZIF-8)was fabricated and developed as an"on-off-on"fluorescent nanoprobe for selectively and sensitively detecting KMnO4 and ascorbic acid(AA).The prepared AuNCs@ZIF-8 initially exhibited strong fluorescence at 595 nm KMnO4 could quench the fluorescence of AuNCs@ZIF-8,rendering the fluorescence signal of AuNCs@ZIF-8 in the"off state.The probe allows KMnO4 to be detected with a 10 nM detection limit and the linear analytical range was 0.05-2 uM.When AA was added into the AuNCs@ZIF-8/KMnO4 system,the fluorescence of the AuNCs@ZIF-8 recovered due to the redox reaction between KMnO4 and AA,and the fluorescence signal of the system turned"on".The detection limit of AA was 37 nM in a good linear concentration range of 0.05-5 uM.Furthermore,this AuNCs@ZIF-8 nanoprobe was successfully used for AA detecting in fresh orange juices with the recoveries ranged from 96.6% to 108.2%,which validates the potential applicability of this strategy.
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