Effect of Nd content on the energetics of H2O adsorption and defect structure in the Ce(1−x)NdxO(2−0.5x) system
Nd-doped CeO2 nanopowders were prepared using the non-aqueous sol–gel method. The effect of Nd content on the defect structure of the powders and their water adsorption energetics was investigated. The effect of Nd doping on the thermal stability and electrical properties of CeO2 is well established, but there has only been limited study of the influence of Nd addition on the interaction of gases with the surface of the doped materials. In particular, there is limited knowledge about the impact of Nd doping on the surface interaction with water vapor, which is of great significance for many catalytic applications. The present work explores these water–surface interactions by implementing a combination of methods, including thermal gravimetry, water adsorption calorimetry, and computational modeling. Results show that water uptake increases with increasing amounts of Nd doping, but the normalized integral adsorption enthalpy is not affected. Analysis using density functional theory (DFT) shows that adding Nd to CeO2 not only increases the number of adsorption sites but also creates a wider distribution of adsorption energies. The DFT calculations provide an explanation of the apparently anomalous experimental finding that Nd addition increases the heat of adsorption (ΔHads) of the first water molecule compared to undoped CeO2.