Different Wetting Behaviors of Pd and Rh on the CeO2(111) Surface. A DFT and Hrtem Study

The catalysts comprising noble metals supported on ceria surfaces are widely utilized in water-gas shift reactions and automotive exhaust-gas converters. In this work we present a systematic study on the interaction of noble metals Pd and Rh with the CeO2(111) surface using density functional theory (DFT) and high-resolution transmission electron microscopy (HRTEM). HRTEM studies revealed that Pd and Rh show different wetting behaviors on the CeO2(111) surface. Rh tends to form 2-dimensional layers, while Pd can form 2-dimensional islands followed by transformation into 3-dimensional particles upon heating. Our DFT calculations indicated that for both Rh and Pd 3-dimensional clusters are energetically more favorable than 2-dimensional layers, which is a result of a delicate balance between metal-metal and metal-support interactions. However, the transformation of Rh from the monolayer to clusters is prohibitively difficult due to a significant reaction barrier.