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Title: Relating adatom emission to improved durability of Pt-Pd diesel oxidation catalysts

Sintering of nanoparticles is an important contributor to loss of activity in heterogeneous catalysts, such as those used for controlling harmful emissions from automobiles. But mechanistic details, such as the rates of atom emission or the nature of the mobile species, remain poorly understood. Herein we report a novel approach that allows direct measurement of atom emission from nanoparticles. We use model catalyst samples and a novel reactor that allows the same region of the sample to be observed after short-term heat treatments (seconds) under conditions relevant to diesel oxidation catalysts (DOCs). Monometallic Pd is very stable and does not sinter when heated in air (T ≤ 800 °C). Pt sinters readily in air, and at high temperatures (≥800 °C) mobile Pt species emitted to the vapor phase cause the formation of large, faceted particles. In Pt–Pd nanoparticles, Pd slows the rate of emission of atoms to the vapor phase due to the formation of an alloy. However, the role of Pd in Pt DOCs in air is quite complex: at low temperatures, Pt enhances the rate of Pd sintering (which otherwise would be stable as an oxide), while at higher temperature Pd helps to slow the rate of Ptmore » sintering. DFT calculations show that the barrier for atom emission to the vapor phase is much greater than the barrier for emitting atoms to the support. Thus, vapor-phase transport becomes significant only at high temperatures while diffusion of adatoms on the support dominates at lower temperatures.« less
 [1] ;  [2] ;  [1] ;  [3] ;  [3] ;  [4] ;  [5] ;  [5] ;  [1]
  1. Univ. of New Mexico, Albuquerque, NM (United States)
  2. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
  3. Einhoven Univ. of Technology, Eindhoven (The Netherlands)
  4. New Mexico State Univ., Las Cruces, NM (United States)
  5. General Motors Global R&D, Warren, MI (United States)
Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 0021-9517; 594892
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of Catalysis
Additional Journal Information:
Journal Volume: 328; Journal Issue: C; Journal ID: ISSN 0021-9517
Research Org:
Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
54 ENVIRONMENTAL SCIENCES; 32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION adatom emission; Ostwald ripening; catalyst sintering; Pt–Pd; diesel oxidation; exhaust treatment