Selectivity control is a difficult scientific and industrial challenge in methanol-to-olefins(MTO)conversion.It has been experimentally established that the topology of zeolite catalysts influenced the distribution of products.Besides the topology effect on reaction kinetics,the topology influences the diffusion of reactants and products in catalysts as well.In this work,by using COMPASS force-field molecular dynamics method,we investigated the intracrystalline diffusion of ethene and propene in four different zeolites,CHA,MFI,BEA and FAU,at different temperatures.The self-diffusion coefficients and diffusion activation barriers were calculated.A strong restriction on the diffusion of propene in CHA was observed because the self-diffusion coefficient ratio of ethene to propene is larger than 18 and the diffusion activation barrier of propene is more than 20 kJ/mol in CHA.This ratio decreases with the increase of temperature in the four investigated zeolites.The shape selectivity on products from diffusion perspective can provide some implications on the understanding of the selectivity difference between HSAPO-34 and HZSM-5 catalysts for the MTO conversion.
Synthesis of functionalized mesoporous carbon by an easy-accessed method is of great importance towards its practical applications.Herein,an evaporation induced self-assembly/carbonization(EISAC)method was developed and applied to the synthesis of sulfonic acid group functionalized mesoporous carbon(SMC).The final mesoporous carbon obtained by EISAC method possesses wormlike mesoporous structure,uniform pore size(3.6 nm),large surface area of 735 m^2/g,graphitic pore walls and rich sulfonic acid group.Moreover,the resultant mesoporous carbon achieves a superior electrochemical capacitive performances(216 F/g) to phenolic resin derived mesoporous carbon(OMC,152 F/g) and commercial activated carbon(AC,119 F/g).
H+-restacked nanosheets and nanoscrolls peeled from K4Nb6O17display different structures and surface characters. The two restacked samples with increased surface areas have an amazing visible-light response for the photodegradation of dyes, which is superior to commercial TiO2(P25) and Nb2O5. By comparison, H+/nanosheets have a relatively faster photodegradation rate originated from large and smooth basal plane.The work reveals that dye adsorbed on the unfolded nanosheets can effectively harvest sunlight. Due to facile preparation, low-cost and high photocatalytic efficiency, H+/nanosheets and H+/nanoscrolls might be used for the visible light-driven degradation of organic dyes as a substitute for TiO2in industry.
