(675d) Effects of CO and NO on TiO2 Supported Pt, Pd, and Rh Nanoparticle Disintegration

Supported transition metal catalysts like Rh, Pd, and Pt are used in a broad range of economically and environmentally significant processes such as the conversion of toxic gases like NO and CO to less harmful species. Unfortunately these rare and expensive catalysts often suffer from deactivation. Thus there is a strong need to improve and understand these catalysts to increase their stability and efficiency. Due to its widespread catalytic importance, the focus of this study is to understand the effects of the presence of NO and CO on the stability of isolated Rh, Pd, and Pt nanoparticles supported on TiO₂(110). Density functional theory and ab initio thermodynamics will be applied to understand these systems under a variety of experimental conditions. Formation and binding energies of metal adatoms and adatom-reactant complexes are computed as well as the influence of CO or NO adsorption on nanoparticle surface energetics. The disintegration free energy of supported Rh, Pd, or Pt particles under a large parameter space of reaction conditions and nanoparticle sizes is explored. In agreement with previous experiments, we compute that CO and NO both cause Rh/TiO₂(110) to disintegrate at 300 K and 1 mbar via the formation of di-carbonyl or di-nitrosyl adatom-reactant complexes, and that NO is a more efficient reactant for particle redispersion than CO. On the other hand, we find that TiO₂(110) supported Pt or Pd nanoparticles are more resistant to CO or NO induced disintegration via the formation of adatom complexes. Overall, this information could lead to strategies for facilitating the redispersion of aggregated nanoparticles.