Scanning Transmission Electron Microscopy Investigation of Differences in the High Temperature Redox Deactivation Behavior of CePrOx Particles Supported on Modified Alumina

An in-depth structural and analytical investigation of two 25 wt % Ce 0.8 Pr 0.2 O 2 /d-Al 2 O 3 catalysts, d = 3.5 wt % SiO 2, 4 wt % La 2 O 3, is performed aimed at clarifying the origin of the differences in the evolution of their oxygen storage capacity with temperature. Using a combination of transmission and scanning transmission electron microscopy techniques, the fine details of the structural and compositional changes of the two catalysts with reduction temperature has allowed us to establish the role of SiO 2 as a stabilizer of the oxygen handling properties of the Ce−Pr mixed oxide phase under high temperature reducing environments. The entire set of data clearly reveals that Pr does not fully mix with Ce during the synthesis of both catalysts, the spatial distribution of this uncombined fraction of Pr loading being in each case very different: as nanosized particles in the catalyst prepared on the SiO 2 -doped substrate and as a highly dispersed phase in the lanthana modified alumina catalyst. Therefore, SiO 2 doping provides a barrier against lanthanide element incorporation into the alumina support. This effect hinders the formation of large amounts of the LnAlO 3 (Ln = Ce, Pr) perovskite phase which, as established by HREM and XRD, is responsible of the loss of oxygen storage capacity during hydrogen treatments at temperatures above 800 °C.