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

Abstract

CeO2 and CeReOx_y catalysts are prepared by the calcination at different temperatures (y=500–1000°C) and having a different composition (Re=La3+ or Pr3+/4+, 0–90wt.%). The catalysts are characterised by XRD, H2-TPR, Raman, and BET surface area. The soot oxidation is studied with O2 and NO+O2 in the tight and loose contact conditions, respectively. CeO2 sinters between 800–900°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 O2 as an oxidant, an improved soot oxidation is observed over CeLaOx_y and CePrOx_y in the whole dopant weight loading and calcination temperature range studied, compared with CeO2. Using NO+O2, the soot conversion decreased over CeLaOx_y catalysts calcined below 800°C compared with the soot oxidation over CeO2_y. CePrOx_y, on the other hand, showed a superior soot oxidation activity in the whole composition and calcination temperature range using NO+O2. The improvement in the soot oxidation activity over the various catalysts with O2 can be explained based on an improvement in the external surface area. The superior soot oxidation activity of CePrOx_y with NO+O2 is explained by the changes in the redox properties of the catalyst as well as surface area. CePrOx_y, having 50wt.% 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.