| CeO2 is known to be an efficiently assistant catalyst or a support. Itis not only related to its oxygen storage and release property, but also tothe ability of improving dispersion of the activity phage. Therefore, CeO2has attracted much attention in recent years. In this master thesis, a seriesof high surface area nanosized CeO2 and Ce-based composite oxides wereparepared by a surfactant-templated method, and their catalyticperformances were tested for the CO oxidation. This method increasedthe surface area of the catalysts, so as to improve their catalyticperformance. The catalysts were characterized by XRD, Ramanspectroscopy, TPR, BET, TEM and XPS techniques.1. The high-surface area nano-CeO2 was prepared using Ce(NO3)3 asprecursor by precipitation method, taking surfactants CTAB astemplating agent. The effects of the precipitators, reaction temperature,ageing time and calcination temperature on the surface area as well as onthe pore structure and the mean crystallite size of nano-CeO2 were studied.It was found that the reaction of Ce(NO3)3 With NaOH in the presence ofCTAB at 90℃for 12 h gived a cerium oxide/surfactant mixture, whichafter calcined at 400℃results in nano-CeO2 particles with high surfacearea. The mean crystallite size of CeO2 was about 6 nm, BET surface areawas more than 200 m2·g-1, pore size was about 9 nm, and-the poredistribution was narrow. Moreover, after calcined at 700℃the BETsurface area still can reach 147 m2.g-1, which showed the good thermalstability of the conducted material. The number of oxygen vacancies inthe structure of CeO2 was strongly related to the surface area of CeO2 andthe high surface area was propitious to the formation of oxygenvacancies. 2. The high-surface area nanosized CuO-CeO2 catalysts withdifferent CuO content were prepared using Ce(NO3)3 and Cu(NO3)2 asprecursors by precipitation method, taking surfactants CTAB astemplating agent. Their catalytic activities for CO oxidation were tested.The highest BET surface area of the catalysts is 215 m2·g-1(3.3 mol%CuO catalyst). These high-surface area nanosized catalysts were found tobe very active for CO oxidation reaction and the lowest Temperature for90% CO conversion (T90) was 80℃over a 12.0 mol% CuO catalyst. Inaddition, the CuO-CeO2 catalysts also showed high catalytic activity forselectiye oxidation of CO in excess of H2 at a relatively low temperature.The H2-TPR results revealed three reduction peaks for these catalysts,which could be attributed to reduction of the highly dispersed CuO, theCu2+ in the CeO2 lattice and the bulk CuO. Removal of the finelydispersed CuO in the catalyst by HNO3 treatment resulted in decline incatalytic activity for CO oxidation, indicating that the finely dispersedCuO species were the active sites for the reaction.3. The high-surface area nanosized MnOx-CeO2 catalysts withdifferent Mn content were prepared using Ce(NO3)3 and Mn(NO3)2 asprecursors by precipitation method, taking surfactants CTAB astemplating agent. Their catalytic activities for CO oxidation were tested.The highest BET surface area of the catalysts was 174 m2·g-1(34.3 mol%Mn catalyst). The CO oxidation over the catalyst with the highest BETsurface area was very active. The TOF of the catalysts decreased with theincrease of Mn content, indicating that the finely dispersed MnOx specieswere the active sites for CO oxidation.
|
PDF Full Text Request