Ostwald ripening and disintegration of supported metal particles under reaction conditions has been of central importance in study of sintering and redispersion of catalysts for long term industrial implementation. An atomistic and quantitative theory taken into account of particle's size, metal-support interaction (MSI), temperature and pressure of the reactant in gas phase is presented first in this talk. Chemical potential of supported metal particles considering MSI and adsorption of reactant was formulated. We derived the criterion for reactant assisted Ostwald ripening, which depends crucially on the bonding strength between reactant and metal adatom mediated by supports. For the sintering rate equation, the Gibbs free energy of formation of the reactant on the metal adatom and the diffusivity of the complexes formed are decisive. These might not only affect dramatically the absolute rate but also change completely the mechanism of sintering rate. For reactant induced disintegration, corresponding criterion was defined, and described by the Gibbs free energy of formation of monomers of the metal-reactant complexes. We find that compared to the reactant assisted Ostwald ripening, higher chemical potential of the reactant on the disintegration is required. This theory is applied to TiO2(110) supported Rh particles under carbon monoxide, and the result rationalizes well with available experiments at wide range of CO's temperature, pressure and particle size. Most of input parameters appeared in theoretical framework developed can be obtained conveniently from the first-principles theory. This allows one to explore various metal-support systems and chemical environments. Insights obtained would help to rationalize the design of catalysts and supports under working conditions to suppress sintering and control the dispersion.

Atomistic theory of Ostwald ripening and disintegration of supported nanoparticles under reaction conditions

245th National Meeting (2013)

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