First-Principles Kinetic Study for Ostwald Ripening of Late Transition Metals on TiO2(110)

Supported transition metal (TM) particles on oxides severely deactivate because of sintering. Investigation of the dependence of Ostwald ripening kinetics on the composition and size of the metal particles is essential for understanding the sintering mechanism. On the basis of the first-principles kinetics simulation, we study here the ripening kinetics of TiO2(110)-supported late TMs (including Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au) in a wide range of particle size. Density functional theory calculations show that the total activation energies of ripening are decided by the corresponding formation energy of the metal monomer on TiO2(110) and vary in the range of 3 eV following the order of Ag < Cu < Pd < Au < Ni < Rh < Pt < Ru < Ir. Isothermal and temperature ramping kinetic simulations are performed, and the corresponding half-life time and onset temperature of ripening are extracted, respectively. The results show that the half-life time of ripening exponentially increases with the total activation energy of the metal from Ag to Ir. The onset temperature of ripening increases more than hundreds of kelvin, which is consistent with variation in the melting points of the bulk counterpart. The ripening rate is found to dramatically increase with the decrease of the particle size, and the corresponding size effect increases pronouncedly with the total activation energy from Ag to Ir. This work provides valuable insights into the ripening kinetics of oxide-supported metal particles and is helpful in designing stable nanocatalysts.