Potential rare-earth modified CeO2 catalysts for soot oxidation Part III.: Effect of dopant loading and calcination temperature on catalytic activity with O2 and NO+O2

CeO2 and CeReO(x-)y catalysts are prepared by the calcination at different temperatures (y = 500-1000 degrees C) and having a different composition (Re = La3+ or Pr3+/4+. 0-90 wt.%). The catalysts are characterised by XRD, H-2-TPR, Raman, and BET surface area. The soot oxidation is studied with O-2 and NO + O-2 in the tight and loose contact conditions, respectively. CeO2 sinters between 800-900 degrees C due to a grain growth, leading to an increased crystallite size and a decreased BET surface area. La3+ or Pr3+/4+ hinders the grain growth of CeO2 and, thereby, improving the surface catalytic properties. Using O-2 as an oxidant, an improved soot oxidation is observed over CeLaO(x-)y and CePrO(x-)y in the whole dopant weight loading and calcination temperature ramge studied, compared with CeO2. Using NO + O-2, the soot conversion decreased over CeLaO(x-)y catalysts calcined below 800 degrees C compared with the soot oxidation over CeO(2-)y. CePrO(x-)y, on the other hand, showed a superior soot oxidation activity in the whole composition and calcination temperature range using NO + O-2. The improvement in the soot oxidation activity over the various catalysts with O-2 can be explained based on an improvement in the external surface area. The superior soot oxidation activity of CePrO(x-)y with NO + O-2 is explained by the changes in the redox proper-ties of the catalyst as well as surface area. CePrO(x-)y, having 50 wt.% of dopant, is found to be the best catalyst due to synergism between cerium and praseodymium compared to pure components. NO into NO2 oxidation activity, that determines soot oxidation activity, is improved over all CePrOx catalysts. (c) 2007 Elsevier B.V. All rights reserved.