75. Byrd, Adam J.; Gupta, Ram B.. Stability of cerium-modified .gamma.-alumina catalyst support in supercritical water. Applied Catalysis, A: General (2010), 381(1-2), 177-182.
Supercritical water (above 374.1 oC 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 .gamma.-Al2O3 modified with 1-10 wt% Ce in supercrit. water is examd., specifically in the temp. range of 500-700 C at 246 bar. Transformations of the .gamma.-phase were slowed but not prevented. Based on X-ray anal., the transformation of .gamma.-Al2O3 proceeded through the .kappa. phase toward the stable .alpha. phase. Reduced cerium species were seen to be oxidized in the supercrit. 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 sp. surface areas than unmodified alumina.