Theoretical Study Of Ostwald Ripening Of TiO₂-supported Metal Nanoparticles

Metal nanoparticles have attracted a great attention for their unique property.Though small particles may expose more active low coordination sites and show quantum size effects,high surface energy destabilizes corresponding particles which tend to sinter and grow to the larger one.This would result in the decrease of the dispersion and active sites.Subsequently,metal nanoparticles would lose its unique feature.Therefore,to suppress the growth of metal nanoparticles is one of the central challenges to gain long-term stability of nanoparticles.Sintering may proceed via Smoluchowski ripening or Ostwald ripening.For Smoluchowski ripening,the process can be easily captured.However,it would take a long time to study Ostwald ripening of particles.With the development of computer technology and Ostwald ripening theory,it could save more time and cost by first principles kinetics.The first principles can give us the energy information and subsequent ripening kinetics can present the concrete picture of ripening by computer.In this paper,the first-principles kinetics are used to study Ostwald ripening of rutile TiO₂（110）-supported Pd.It is verified that the initial small size and monodispersity are beneficial to resist the growth of particles.Comparing and analyzing Ostwald ripening of different late transition metals on rutile TiO₂（110）,it is indicated that the composition of the metal can greatly influence the ripening.And a relationship formula between the onset temperature of the ripening and the melting point of the corresponding metal is suggested.The study of Ostwald ripening of anatase and rutile TiO₂-supported Pt metals indicates that the ripening of the supported metal depends on the surface structure,morphology and crystal phase of the support.These details are as follows:（1）The adsorption and diffusion of Pd on rutile TiO₂（110）were calculated by first principles.Subsequently,the size effect and monodispersity of rutile TiO₂（110）-supported Pd on the ripening were addressed by the ripening kinetics.（2）The adsorption and diffusion of different late transition metals on rutile TiO₂（110）were studied by first principles,and the effect of metals on the ripening was quantitatively analyzed.By fitting results of the simulation of Ostwald ripening,the relationship between the onset temperature of ripening and the melting point of the supported metal was obtained.（3）Ostwald ripening of Pt on different surfaces of anatase and rutile TiO₂ were presented by first principles kinetics.By comparing the ripening process of Pt on different surfaces of anatase and rutile TiO₂,the dependence of the ripening on the surface structure of anatase and rutile TiO₂ was discussed.（4）The effect of the support morphology on Ostwald ripening of supported Pt was elaborated by using the TiO₂ morphologies according to their Wulff structures.Moreover,the crystal phase effect of TiO₂（anatase and rutile）on Ostwald ripening of supported Pt was investigated by comparing the different performances of their ripening by first principles kinetics.