Details

Autor(en) / Beteiligte

• Ezekoye, O.K.
• Drews, A.R.
• Jen, H.-W.
• Kudla, R.J.
• McCabe, R.W.
• Sharma, M.
• Howe, J.Y.
• Allard, L.F.
• Graham, G.W.
• Pan, X.Q.

Titel

Characterization of alumina-supported Pt and Pt–Pd NO oxidation catalysts with advanced electron microscopy

Ist Teil von

• Journal of catalysis, 2011-05, Vol.280 (1), p.125-136

Ort / Verlag

Amsterdam: Elsevier Inc

Erscheinungsjahr

2011

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• High angle annular dark field imaging along with energy dispersive spectroscopy were used to study the evolution of metal particle size and composition in alumina-supported Pt-Pd NO oxidation catalysts made using two precursors, acetylacetonate (AcAc) and nitrate, aged under oxidizing conditions. In spite of distinctly different initial metal distributions, aging led to very similar characteristics for both precursors. [Display omitted] ► Pd inhibits growth of anomalously large Pt particles under lean-aging conditions. ► Pt-rich Pt–Pd alloy catalysts oxidize NO almost as well as pure Pt catalysts. ► Pt–Pd alloy formation readily occurs in situ below 500 °C. Alumina-supported Pt and Pt–Pd catalysts for NO oxidation were fabricated from two different precursors, acetylacetonate and nitrate. A variety of electron microscopy techniques, notably aberration-corrected scanning transmission electron microscopy, were used to investigate both sets of catalysts in the fresh state (air calcined at 300 °C, then reduced in 1% H 2 at 300 or 500 °C) and after oxygen-rich hydrothermal aging at 500 °C and 900 °C. Aberration-corrected microscopy and spectroscopic analysis revealed a significant difference in particle size and composition between the two fresh bimetallic catalysts, with the catalyst made from nitrate precursors containing relatively large (3–10 nm) Pd-rich particles in addition to smaller (1–2 nm) Pt-rich particles that were typical of the acetylacetonate precursors. Regardless of initial state, however, bimetallic particles underwent similar degrees of growth and homogenization (alloying) with aging. In particular, particle growth in the bimetallic catalysts from both precursors was limited relative to that in the pure Pt catalysts, where anomalously large (∼500 nm) particles formed at 900 °C, and the bimetallic catalysts from both precursors thus showed similar improvements in thermal stability, with little effect on measured NO reaction rates.