Effects of Hydrothermal Treatment on Mesopore Structure and Connectivity in Doped Ceria-Zirconia Mixed Oxides

Pore size and pore connectivity control diffusion-based
transport
in mesopores, a crucial property governing the performance of heterogeneous
catalysts. In many cases, transition-metal oxide catalyst materials
are prepared from molecular precursors involving hydrothermal treatment
followed by heat treatment. Here, we investigate the effects of such
a hydrothermal aftertreatment step, using an aqueous ammonia solution,
on the disordered mesopore network of CexZr1–x–y–zYyLazO2−δ mixed oxides. This procedure is
a common synthesis step in the preparation of such ceria-based oxygen
storage materials applied in three-way catalysis, employed to improve
the materials’ thermal stability. We perform state-of-the-art
Ar-physisorption analysis, especially advanced hysteresis scanning,
to paint a detailed picture of the alterations in mesopore space caused
by the hydrothermal aftertreatment and subsequent aging at 1050 °C.
Furthermore, we investigate the network characteristics by electron
tomography in combination with suitable statistical analysis, enabling
a consistent interpretation of the desorption scans (physisorption).
The results indicate that the hydrothermal aftertreatment enhances
the mesopore connectivity of the continuous 3D network by widening
pores and especially necks, hence facilitating accessibility to the
particles’ internal surface area and the ability to better
withstand high temperatures.