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
A series of CeO2-ZrO2-WO3 catalysts for the selective catalytic reduction （SCR） of NO with NH3 were prepared by hydrothermal method. The influence of calcination temperature on the catalytic activity, microstructure...A series of CeO2-ZrO2-WO3 catalysts for the selective catalytic reduction （SCR） of NO with NH3 were prepared by hydrothermal method. The influence of calcination temperature on the catalytic activity, microstructure, surface acidity and redox behavior of CeO2-ZrO2-WO3 catalyst was investigated using various characterization methods. It was found that the CeO2-ZrO2-WO3 catalyst calcined at 600 ℃ showed the best catalytic performance and excellent N2 selectivity, and yielded more than 90% NO conversion in a wide temperature range of 250-500 ℃ with a space velocity （GHSV） of 60000 131. As the calcination temperature was increased from 400 to 600 ℃, the NO conversion obviously increased, but decreased at higher calcination temperature. The results implied that the higher surface area, the strongest synergistic interaction, the superior redox property and the highly dispersed or amorphous WO3 species contributed to the excellent SCR activity of the CeO2-ZrO2-WO3 catalyst calcined at 600℃.展开更多
基金supported by the National Natural Science Foundation of China(21273043,21077026)Science and Technology Commission of Shanghai Municipality,China(13DZ2275200)~~
文摘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.
基金Project supported by the National Natural Science Foundation of China(21377048,21307047)the Opening Project of Key Laboratory of Green Catalysis of Sichuan Institutes of High Education(LYJ1309)
文摘A series of CeO2-ZrO2-WO3 catalysts for the selective catalytic reduction （SCR） of NO with NH3 were prepared by hydrothermal method. The influence of calcination temperature on the catalytic activity, microstructure, surface acidity and redox behavior of CeO2-ZrO2-WO3 catalyst was investigated using various characterization methods. It was found that the CeO2-ZrO2-WO3 catalyst calcined at 600 ℃ showed the best catalytic performance and excellent N2 selectivity, and yielded more than 90% NO conversion in a wide temperature range of 250-500 ℃ with a space velocity （GHSV） of 60000 131. As the calcination temperature was increased from 400 to 600 ℃, the NO conversion obviously increased, but decreased at higher calcination temperature. The results implied that the higher surface area, the strongest synergistic interaction, the superior redox property and the highly dispersed or amorphous WO3 species contributed to the excellent SCR activity of the CeO2-ZrO2-WO3 catalyst calcined at 600℃.
