Stable and Catalytically Active Shape-Engineered Cerium Oxide Nanorods by Controlled Doping of Aluminum
Shape-engineered nanocrystals (SENs) promise a better selectivity and a higher activity in catalytic reactions than the corresponding non-shape-engineered ones owing to their larger specific surface areas of desirable crystal facets. However, often, these SENs are less stable because the desirable surface facets have higher specific surface energies than other types of facets. Therefore, it is challenging to apply SENs in practical catalytic applications at high reaction temperatures to achieve favorable kinetics. In this paper, we show that atomic layer deposition of Al2O3 can modify the shape-engineered CeO2 nanorods (NRs) to not only increase their shape transition temperature from 400 ºC to at least 700 ºC, but also greatly increase their reversible specific oxygen storage capacity (srOSC) upto 700 ºC. Through Al2O3 atomic layer deposition at 200 ºC, trimethyl aluminum reduces the Ce4+ to Ce3+ and substitutes Ce3+ ions with Al3+ to form -Al-O-Ce-O- structure. The substituted Al3+ ions impede the surface diffusion of Ce ions, therefore improve the thermal stability of CeO2 NRs. The Ce ion in -Al-O-Ce-O-, a new Ce species, can be reversibly reduced and oxidized at 500 – 700 ºC. Our method presents a new strategy to improve the thermal stability and catalytic activities of SENs, thereby expand their applications into high temperature environments.