查看更多>>摘要：Zeolite-tailored encapsulation of metal nanoparticles exhibits prominent catalytic performance in many especially for selective hydrogenation reaction due to the modulation effect of the zeolite microenviron Here,Pd nanoparticles encapsulated in MFI zeolite by an in-situ encapsulation method were first used i selective hydrogenation of nitrile into a primary amine.After introducing KOH for mediating the acic property of zeolite microenvironment,the as-synthesized Pd@S-1-K manifested an improved selectivity i synthesis of primary amine from nitrile,while outperformed both commercial catalysts and convention supported on zeolite catalyst.The remarkable performance of Pd@S-1-K could be attributed to both the property of the S-1-K zeolite for inhibiting the side reactions and the highly dispersed and ultrasmall Pd cl1 for superior catalytic activity.Besides,the best yield of 81% was achieved at 80 ℃,5 bar H2,2 h in ami solution via optimization experiments,and the moderate applicability of Pd@S-1-K catalyst was obtain substrate scope test.
查看更多>>摘要：Zeolites catalyze the hydroamination of alkenes,alkynes and dienes,yielding valuable amines,enamines and imines with high efficiency and chemoselectivity(i.e.,Markovnikov or and-Markovnikov products)thanks to the architecture of their pore system and tunable acidity.However,their micropores may impose mass-transfer constraints on reaction rates.Nevertheless,the high external surface area of hierarchical micro-mesoporous zeolites should enable them to outperform conventional zeolites.To test our hypothesis,we compared the activity of hierarchical MFI zeolites of different crystal morphologies(i.e.,nanosponge,nanosheet and micro-crystalline desilicated samples)with that of conventional medium-(MFI)and large-pore(MOR and Beta)zeolites in the hydroamination of methyl acrylate with aniline.The results showed that nanosponge MFI had the highest activity(TOF = 32.9 h"1),reaching 57% yield of the anti-Markovnikov product N-[2-(methoxycarbonyl)ethyl] aniline.Furthermore,our kinetic study revealed a pseudo-second-order rate law with respect to aniline over the most active nanosponge MFI catalyst,with an apparent activation energy of 68.9 kJ/mol.The high external surface of this catalyst(371 m~2/g)and its developed inter-crystalline mesopores(4.8 nm)suggest a kinetic-driven hydroamination reaction.Therefore,hierarchical nanosponge aluminosilicate MFI zeolites stand out as promising heterogeneous catalysts of hydroamination reactions involving bulky substrates.
Stanislav V.KonnovVladimir S.PavlovDaniil V.Bruter
9页
查看更多>>摘要：A series of MFI zeolites were synthesized in fluoride media from fumed silica hydrogel,fumed silica and TEOS to elucidate the influence of silica source on the physicochemical and catalytic properties of MFI zeolites.The materials obtained were characterized by nitrogen adsorption,XRD,SEM,TPD and ~(27)A1 NMR MAS methods and evaluated in MTO and hexane/3-methyl pentane cracking catalytic reactions.It has been demonstrated that crystallization proceeds via solution-mediated mechanism independently on silica source.However,the nature of silica source substantially affects the crystallization rate,the crystal size,the dynamics of Al incorporation into the MFI framework and Al distribution in the zeolite crystals.The application of fumed silica hydrogel and fumed silica with high polymerization degree yields crystals with an Al-enriched core and a siliceous shell.These materials demonstrate faster deactivation in the MTO reaction and higher selectivity to ethylene as compared to the MFI obtained from TEOS with a uniform Al distribution in the crystals.The effect observed is attributed to a longer diffusion path length of the reagent to active sites located mainly in the crystal core and the reaction products outside from the crystal core,resulting in a higher contribution of secondary reactions.
查看更多>>摘要：Solid electrolytes with a large number of pores can replace liquid electrolytes to effectively avoid liquid leakage as well as undertake electrochemical-mechanical functions.However,the influences of pore structure inside solid electrolytes on load transfer and capacitive nature of corresponding structural supercapacitors are usually contradictory.Here,electrochemical modulation is firstly applied to tune the pore structure of polyacrylic acid(PAA)cement electrolyte to solve the trade-off.Hierarchical network pore structure inside PAA cement electrolyte optimizes to an ideal state with an electrochemical modulation operation voltage of 1 V,achieving synchronous improvements in capacitance(increasing by 90%)and compressive strength(increasing by 20%)of corresponding structural supercapacitor.The important contribution of pore structure inside PAA cement electrolyte to capacitive nature of corresponding structural supercapacitor is introduced through experiments and molecular dynamics simulations.As the porosity,specific surface area and average pore size of pore structure inside PAA cement electrolyte increase to critical values,the capacitance of corresponding structural supercapacitor enhances to the maximum value.These surprising results provide a blueprint for optimizing pore structure inside structural supercapacitor solid electrolyte via electrochemical modulation.
查看更多>>摘要：The inhibition of ethylene exposure is necessary for preserving the quality of postharvest fruit and vegetables.In this study,we report a rational design of Pd-based MFI composite adsorbents consisting of Pd-ZSM-5 and S-l zeolites with high ethylene adsorption capacity even in the humid environment.The effects of S-l incorporation on the morphology,apparent surface area,Pd nanoparticles distribution,and the hydrophobicity of the MFI composite were investigated in relation to their ethylene adsorption performance in dry and humid environments.Our finding reveals a synergistic effect between the Si-rich layer and Pd nanoparticles on moisture protection and ethylene capture,respectively,leading to an exceptional ethylene adsorption ability of S-1/Pd-ZSM-5 under high relative humidity.Compared with the conventional ZSM-5-supported Pd adsorbent,S-1/Pd-ZSM-5 exhibited a two-fold enhancement in ethylene removal in the presence of moisture(0.195 mmol/g vs.0.416 mmol/g).In particular,the secondary crystallization of S-1 achieved by 72 h of hydrothermal treatment gave an excellent confinement over the Pd-ZSM-5 structure.This novel design of S-1/Pd-ZSM-5 provides the valuable applicability of the composite zeolite for ethylene regulation in postharvest crops in the future.
查看更多>>摘要：The vanadium(V)complexes bearing the aroylhydrazone Schiff base 2-hydroxy-N'-((2-hydroxynaphthalen-1-yl)methylene)benzohydrazide ligand[VO(OMe)L](1)and[EtsNH][VO2L](2)were synthesized,characterized and supported on porous MIL-lOO(Fe)forming the 1@MIL-100(Fe)and 2@MIL-100(Fe)composites.The outcome of such immobilizations was assessed by several characterization techniques,namely powder X-ray diffraction,UV/Vis,FTIR,SEM-EDS,ICP and BET surface area analysis,confirming the successful heterogenization of both vanadium complexes.They were screened as catalysts towards the oxidation of toluene,under homogenous(1 and 2)and heterogeneous(1@MIL-100 and 2@MIL-100)conditions.The influence of several parameters,namely the type and amount of catalyst or oxidant,reaction time,temperature,and radical trapping,was studied.The main products obtained were benzaldehyde,benzyl alcohol and benzoic acid.Under the optimized conditions,using 1 and 2 as homogeneous catalysts,total yields of 19 and 23%,respectively,were achieved at 80 ℃ after 6 h.Using l@MIL100(Fe)and 2@MIL100(Fe)composites under heterogeneous conditions,total yields up to 11% after 24 h,were achieved.
查看更多>>摘要：Here,we report the influence of the pore size in biocatalysts based on magnetically responsive mesoporous silicas on the loading of an immobilized enzyme-glucose oxidase(GOx)-and the activity and reusability of the biocatalyst in D-glucose oxidation.The choice of the silica supports was determined by their commercial availability and drastically different pores sizes:6 nm and 15 nm.In the former case,the pores are too small to accommodate GOx whose hydrodynamic diameter is 7.6 nm,while in the latter case,there is an ample room for immobilization of GOx inside the pores.Magnetic properties in both cases were imparted by the formation of magnetite nanoparticles in silica pores,whose presence did not alter the pore size distribution.We demonstrate that larger pores allow for higher enzyme loading capacity due to immobilization inside the pores,remarkable 100% relative activity,and enhanced stability in the repeated use due the conformational integrity of GOx in spacious pores.This study unambiguously shows advantages of supports with pores larger than the size of an enzyme for its immobilization in the biocatalyst synthesis.
查看更多>>摘要：The temperature behavior of the heat capacity of isostructural compounds M2(bdc)2(dabco)(M = Co,Ni,Cu,Zn)is analyzed.It is shown that all the samples are characterized by phase transitions at 12K and 60K.The phase transition observed in the Zn complex at-130K is not manifested in M2(bdc)2(dabco)(M = Co,Ni,Cu)because of the spin-phonon interaction between paramagnetic M~(2+)ions and the mobility of frameworks of these compounds.
查看更多>>摘要：The mechanochemically-assisted solvent-free(or minimal-solvent)method,compared with the traditional hydrothermal method,exhibits the merits of reduced waste generation,high yields,and fewer safety problems,thus offering new opportunities for the green fabrication of zeolitic materials.This promising synthetic strategy,however,tends to suffer from a severe aggregation of zeolite crystals.Herein,we report the synthesis of a series of well-dispersed MFI-type zeolites with various compositions via a mechanochemical route using imidazolium ionic liquids as additives.The crystal dimensions along a-,b-,and c-axis of the obtained coffin-like silicalite-1 zeolites can easily be controlled by varying the concentration of ionic liquids or the alkyl chain length of ionic liquid cations.This imidazolium ionic liquids-assisted mechanochemical approach can also work equally well with the heteroatom-containing MFI zeolites(e.g.Al-MFI and B-MFI).In addition,it is found that the imidazolium ionic liquid can be recycled for further use.
查看更多>>摘要：Themetal-organic framework(MOF)materials could exhibit advanced applications in many fields and their mechanical stability upon external stimuli is extre 1 important for the applications.Here,we discovered a Cd(II)-based metal-organic framework(Cd-MOF)exhibits a very high structural stability and the Cd MOF structure remains stable and reversible upon compression up to at least 28 GPa,a pressure that has never been reported before.Moreover,this Cd-MOF material shows an obvious change in the photoluminescence(PL)emission upon compression,which has blue-green luminance at ambient conditions,while the blue emission is preserved but the green emission is quenched at above 5 GPa.This transition in PL emission is due to a pressure-induced framework transition,which is caus d h an anisotropic compression of Cd-MOF framework under pressure,as revealed by our theoretical simulations.Our results show that such highly stable MOF framework could exhibit a potential for applications under extreme conditions as a novel optical material.
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