Selective epoxidation of vinyl chloride on Ag（111）, Pt（111） and Rh（111） with pre-adsorbed atomic oxygen has been studied by density functional theory （DFT） calculation with the periodic slab model. The reactio...Selective epoxidation of vinyl chloride on Ag（111）, Pt（111） and Rh（111） with pre-adsorbed atomic oxygen has been studied by density functional theory （DFT） calculation with the periodic slab model. The reaction energies and activation energies of the epoxidation reaction are determined. Because of the asymmetry of vinyl chloride, three competitive reaction pathways are investigated. The results indicate that the most possible reaction pathway is pathway III. Compared the activation energies of the epoxidation reaction on Ag（111）, Pt（111） and Rh（111）, it is obvious that the reaction via OMMC（3） on Ag（111） is the most possible process. However, the selectivity to the target product over Ag（111） is the lowest among the three metals. The results also indicate that the formation of chloroacetaldehyde is more favorable than that of chloroepoxide.展开更多
In the present work, nanofibrous chitin microsphere （NCM） was prepared via sol-gel transition from a chitin solution dissolved in a NaOH/urea aqueous system at low temperatures. Ag nanoparticles （AgNPs） were synth...In the present work, nanofibrous chitin microsphere （NCM） was prepared via sol-gel transition from a chitin solution dissolved in a NaOH/urea aqueous system at low temperatures. Ag nanoparticles （AgNPs） were synthesized via an in situ reduction of silver nitrate using trisodium citrate dehydrate and were immobilized on chitin nanofibers to obtain composite microspheres that consist of nanofibers and AgNPs （NCM-Ag）. The size of AgNPs could be controlled in the range of 10 to 70 nm, depending on the concentration of AgNO3. X-ray photoelectron spectroscopy （XPS） and Fourier transform infrared （FT-IR） analyses showed that the chitin nanofibers have a strong affinity toward AgNPs, resulting from the interaction between the acetamino group of chitin and the AgNPs. The NCM-Ag exhibited a perfect nanoporous structure and high surface area, as well as high stability in organic solvents. Moreover, in the catalytic epoxidation of olefin （particularly, the conversion of styrene to styrene epoxide）, NCM-Ag exhibited an excellent selectivity of up to 90%. Converting chitin powder into chitin microspheres using an environmentally friendly technique is a green process, which is beneficial for the large-scale synthesis of industrial products. More importantly, this work provides a green synthetic pathway for the construction of size-controlled noble metal nanoparticles immobilized on nanofiber support, which have a wide range of potential applications.展开更多
文摘Selective epoxidation of vinyl chloride on Ag（111）, Pt（111） and Rh（111） with pre-adsorbed atomic oxygen has been studied by density functional theory （DFT） calculation with the periodic slab model. The reaction energies and activation energies of the epoxidation reaction are determined. Because of the asymmetry of vinyl chloride, three competitive reaction pathways are investigated. The results indicate that the most possible reaction pathway is pathway III. Compared the activation energies of the epoxidation reaction on Ag（111）, Pt（111） and Rh（111）, it is obvious that the reaction via OMMC（3） on Ag（111） is the most possible process. However, the selectivity to the target product over Ag（111） is the lowest among the three metals. The results also indicate that the formation of chloroacetaldehyde is more favorable than that of chloroepoxide.
基金This work was supported by the Major Program of National Natural Science Foundation of China （No. 21334005） and the National Natural Science Foundation of China （No. 20874079）. We gratefully acknowledge Prof. Can Li in State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, for their discussion and kind help for instrument.
文摘In the present work, nanofibrous chitin microsphere （NCM） was prepared via sol-gel transition from a chitin solution dissolved in a NaOH/urea aqueous system at low temperatures. Ag nanoparticles （AgNPs） were synthesized via an in situ reduction of silver nitrate using trisodium citrate dehydrate and were immobilized on chitin nanofibers to obtain composite microspheres that consist of nanofibers and AgNPs （NCM-Ag）. The size of AgNPs could be controlled in the range of 10 to 70 nm, depending on the concentration of AgNO3. X-ray photoelectron spectroscopy （XPS） and Fourier transform infrared （FT-IR） analyses showed that the chitin nanofibers have a strong affinity toward AgNPs, resulting from the interaction between the acetamino group of chitin and the AgNPs. The NCM-Ag exhibited a perfect nanoporous structure and high surface area, as well as high stability in organic solvents. Moreover, in the catalytic epoxidation of olefin （particularly, the conversion of styrene to styrene epoxide）, NCM-Ag exhibited an excellent selectivity of up to 90%. Converting chitin powder into chitin microspheres using an environmentally friendly technique is a green process, which is beneficial for the large-scale synthesis of industrial products. More importantly, this work provides a green synthetic pathway for the construction of size-controlled noble metal nanoparticles immobilized on nanofiber support, which have a wide range of potential applications.
