Recent in-situ TEM as well as STM studies suggest that particle migration plays only a secondary role during catalyst sintering [1], the dominant mechanism appears to be Ostwald ripening [2]. To gain mechanistic insight into Ostwald ripening, we have studied the emission of mobile species and their trapping on catalyst supports in the context of automotive exhaust catalysts, specifically three way catalysts (TWCs) and diesel oxidation catalysts (DOCs). When heated in air, Pt forms volatile PtO2. Transport of mobile species occurs via the vapor phase as well as surface diffusion. Addition of Pd helps to slow the rates of catalyst sintering. There are two mechanisms at play: Pd helps to slow the rates of emission of adatoms [3] and PdO can trap mobile Pt species to reform Pt-Pd metallic particles [4]. Both processes work in concert helping to create a more robust diesel oxidation catalyst. Understanding these mechanisms provides insight into the design of sinter resistant heterogeneous catalysts. 1. A.T. DeLaRiva, et al. Journal of Catalysis, 2013. 308: p. 291-305. 2. T.W. Hansen, et al. Accounts of Chemical Research, 2013. 46(8): p. 1720-1730. 3. T.R. Johns, et al. Journal of Catalysis, 2015. 328: p. 151-164. 4. C. Carrillo, et al. Journal of Physical Chemistry Letters, 2014. 5(12): p. 2089-2093.

Emission and trapping of adatoms during Ostwald ripening

251st National Meeting (2016)

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