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

Abstract

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 TiO 2 (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 TiO 2 (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.

Porous Hybrid Nanofibers Comprising ZnSe/CoSe₂/Carbon with Uniformly Distributed Pores as Anodes for High-Performance Sodium-Ion Batteries

“…The elemental mapping images shown in Figure 2e reveal uniform distributions of Co, Se, and C components, and not Zn, over the entire structure. During the selenization process, Zn metal, with its lower melting point (419.5 °C) compared to that of Co metal (1495 °C) was phase-separated from other elements, which caused the separation of ZnSe in the composite [18]. From the high-resolution nanoparticle HR-TEM image in Figure 2f, it can be seen that the lattice fringes were clearly separated, by 0.33, 0.29, and 0.31 nm, which correspond to the (111) lattice plane of cubic ZnSe, the (200) lattice plane of cubic CoSe₂, and the (011) lattice plane of orthorhombic CoSe₂.…”

Enhancing Au/TiO2 Catalyst Thermostability and Coking Resistance with Alkyl Phosphonic-Acid Self-Assembled Monolayers

“…Weaker binding of Au adatoms to the TiO2 surface is thought to lead to greater Au mobility on the TiO2 and thus increased ripening during the calcination step of synthesis. 7,[32][33][34][35] Following the synthesis of Au/TiO2 and Pt/TiO2, a series of alkyl PA SAMs were deposited on both catalysts. Table 1 shows the structures and surface densities for each of the PA precursors as well as their surface densities as determined by ICP analysis.…”

Stabilizing Highly Dispersed Halo Sites in Thermally Restructured Palladium Core@shell Nanoparticles for Improved Catalyst Activity and Durability

“…This suggests that total particle migration and coalescence is not the dominant restructuring mechanism in core@shell architectures. Several computational 33,38 and experimental [39][40][41][42][43] works suggest that the decomposition or disintegration of larger clusters into smaller mobile species can also occur in 800°C aging conditions. As such, it appears that encapsulation promotes active metal disintegration and transport, which is a process that is limited by the emission of mobile species.…”