Mesoporous superacids S2O82–-Fe2O3/SBA-15(SFS)with active nanoparticles are prepared by ultrasonic adsorption method.This method is adopted to ensure a homo-dispersed nanoparticle active phase,large specific surface ...Mesoporous superacids S2O82–-Fe2O3/SBA-15(SFS)with active nanoparticles are prepared by ultrasonic adsorption method.This method is adopted to ensure a homo-dispersed nanoparticle active phase,large specific surface area and many acidic sites.Compared with bulk S2O82–-Fe2O3,Br?nsted acid catalysts and other reported catalysts,SFS with an Fe2O3 loading of 30%(SFS-30)exhibits an outstanding activity in the probe reaction of alcoholysis of styrene oxide by methanol with 100%yield.Moreover,SFS-30 also shows a more excellent catalytic performance than bulk S2O82–-Fe2O3 towards the alcoholysis of other ROHs(R=C2H5-C4H9).Lewis and Bronsted acid sites on the SFS-30 surfaces are confirmed by pyridine adsorbed infrared spectra.The highly efficient catalytic activity of SFS-30 may be attributed to the synergistic effect from the nano-effect of S2O82–-Fe2O3 nanoparticles and the mesostructure of SBA-15.Finally,SFS-30 shows a good catalytic reusability,providing an 84.1%yield after seven catalytic cycles.展开更多
The rate determining step and the energy barrier involved in hydrogen adsorption on Pt/WO3- ZrO2 were studied based on the assumption that the hydrogen adsorption occurs only through Pt sites. The rate of hydrogen ads...The rate determining step and the energy barrier involved in hydrogen adsorption on Pt/WO3- ZrO2 were studied based on the assumption that the hydrogen adsorption occurs only through Pt sites. The rate of hydrogen adsorption on Pt/WOa-ZrO2 was measured in the adsorption temperature range of 323-573 K and an initial hydrogen pressure of 50 Torr. The rates of hydrogen uptake were very high for the initial few minutes and the adsorption continued for more than 5 h below 523 K. The hydrogen uptake far exceeded the H/Pt ratio of unity for all adsorption temperatures, indicating that the adsorption of hydrogen involved the dissociative adsorption of hydrogen on Pt sites to form hydrogen atoms, the spillover of hydrogen atoms onto the surface of the WO3-ZrO2 catalyst, the diffusion of spiltover hydrogen atom over the surface of the WO3-ZrO2 catalyst, and the formation of protonic acid site originated from hydrogen atom by releasing an electron in which the electron may react with a second hydrogen atom to form a hydride near the Lewis acid site. The rate determining step was the spillover with the activation energy of 12.3 kJ/mol. The rate of hydrogen adsorption cannot be expressed by the rate equation based on the assumption that the rate determining step is the surface diffusion. The activity of Pt/WO3-ZrO2 was examined on n-heptane isomerization in which the increase of hydrogen partial pressure provided positive-effect on the conversion of n-heptane and negative-effect on the selectivity towards iso-heptane.展开更多
摘要Mesoporous superacids S2O82–-Fe2O3/SBA-15(SFS)with active nanoparticles are prepared by ultrasonic adsorption method.This method is adopted to ensure a homo-dispersed nanoparticle active phase,large specific surface area and many acidic sites.Compared with bulk S2O82–-Fe2O3,Br?nsted acid catalysts and other reported catalysts,SFS with an Fe2O3 loading of 30%(SFS-30)exhibits an outstanding activity in the probe reaction of alcoholysis of styrene oxide by methanol with 100%yield.Moreover,SFS-30 also shows a more excellent catalytic performance than bulk S2O82–-Fe2O3 towards the alcoholysis of other ROHs(R=C2H5-C4H9).Lewis and Bronsted acid sites on the SFS-30 surfaces are confirmed by pyridine adsorbed infrared spectra.The highly efficient catalytic activity of SFS-30 may be attributed to the synergistic effect from the nano-effect of S2O82–-Fe2O3 nanoparticles and the mesostructure of SBA-15.Finally,SFS-30 shows a good catalytic reusability,providing an 84.1%yield after seven catalytic cycles.
摘要The rate determining step and the energy barrier involved in hydrogen adsorption on Pt/WO3- ZrO2 were studied based on the assumption that the hydrogen adsorption occurs only through Pt sites. The rate of hydrogen adsorption on Pt/WOa-ZrO2 was measured in the adsorption temperature range of 323-573 K and an initial hydrogen pressure of 50 Torr. The rates of hydrogen uptake were very high for the initial few minutes and the adsorption continued for more than 5 h below 523 K. The hydrogen uptake far exceeded the H/Pt ratio of unity for all adsorption temperatures, indicating that the adsorption of hydrogen involved the dissociative adsorption of hydrogen on Pt sites to form hydrogen atoms, the spillover of hydrogen atoms onto the surface of the WO3-ZrO2 catalyst, the diffusion of spiltover hydrogen atom over the surface of the WO3-ZrO2 catalyst, and the formation of protonic acid site originated from hydrogen atom by releasing an electron in which the electron may react with a second hydrogen atom to form a hydride near the Lewis acid site. The rate determining step was the spillover with the activation energy of 12.3 kJ/mol. The rate of hydrogen adsorption cannot be expressed by the rate equation based on the assumption that the rate determining step is the surface diffusion. The activity of Pt/WO3-ZrO2 was examined on n-heptane isomerization in which the increase of hydrogen partial pressure provided positive-effect on the conversion of n-heptane and negative-effect on the selectivity towards iso-heptane.