Stability of cerium-modified γ-alumina catalyst support in supercritical water

Supercritical water is emerging as a promising medium to carry out a variety of catalytic reactions. However the support material can undergo transformation in the hydrothermal environment, as shown in the figure below. In this work the stability of a common support material γ-Al 2O 3 is examined at 500–700 °C and 246 bar. Supercritical water (above 374.1 °C and 220.6 bar) is emerging as a promising medium to carry out a variety of catalytic reactions, including reforming to produce hydrogen. However, when using a heterogeneous catalyst the support material can undergo transformations in the hydrothermal environment. In this work the stability of γ-Al 2O 3 modified with 1–10 wt% Ce in supercritical water is examined, specifically in the temperature range of 500–700 °C at 246 bar. Transformations of the γ-phase were slowed but not prevented. Based on X-ray analysis, the transformation of γ-Al 2O 3 proceeded through the κ phase toward the stable α phase. Reduced cerium species were seen to be oxidized in the supercritical water environment, and low Ce-loading supports maintained the highest BET surface areas. The stabilization was greatest at 700 °C, where Ce-modified aluminas retained significantly higher specific surface areas than unmodified alumina.