Structural Analysis of Rh-Pd/CeO2 Catalysts Under Reductive Conditions: An X-ray Investigation

M. S. Scott, G. I.N. Waterhouse, K. Kato, S. L.Y. Chang, H. Idriss, T. Söhnel

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) were used to probe the electronic and geometric structures of Rh-Pd/CeO2 catalysts before and after ethanol steam reforming (ESR) at 400 °C, as well as after heating in CO atmospheres as a function of time and temperatures. The O/Ce ratio determined by XPS for the as-prepared Rh-Pd/CeO2 catalysts (individual metal loadings of 0.5 or 2 wt%) were close to 2, with the Rh and Pd present primarily in oxidized form (as oxide and chloride surface species). After ESR at 400 °C the ceria support was heavily reduced to CeO2-x (x = 0.3-0.4), with Rh0 (64 % of total Rh) and Pd0 (67 % of total Pd) being the dominant species. Heating the as-prepared Rh-Pd/CeO2 catalysts under a CO atmosphere at 200-400 °C while monitoring the Pd and Rh K edges by XAS was also conducted. XAS of the K edge of Pd and Rh indicated, as expected, reduction of Pd before that of Rh from 200 °C onward. The FCC order of Pd is however perturbed at 400 °C. On the contrary, Rh once reduced maintained a well ordered (FCC) structure. This observation is rationalised by the greater reduction effect of Pd on CeO2 compared to Rh and therefore at the interface Pd structure may be altered at high temperatures.

Original languageEnglish (US)
Pages (from-to)123-133
Number of pages11
JournalTopics in Catalysis
Volume58
Issue number2-3
DOIs
StatePublished - Feb 27 2015
Externally publishedYes

Keywords

  • Bimetallic catalysts
  • CeO HRTEM
  • Ethanol steam reforming (ESR)
  • In-situ CO reduction
  • Rh and Pd XANES
  • Rh and Pd XPS

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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