Do observations on surface coverage-reactivity correlations always describe the true catalytic process? A case study on ceria

Ramzi Farra, Maik Eichelbaum, Robert Schlögl, L. Szentmiklósi, Timm Schmidt, Amol P. Amrute, Cecilia Mondelli, Javier Pérez-Ramírez, Detre Teschner

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

In situ (operando) investigations aim at establishing structure-function and/or coverage-reactivity correlations. Herein, we investigated the gas-phase HCl oxidation (4HCl + O2 → 2Cl2 + 2H2O) over ceria. Despite its remarkable performance, under low oxygen over-stoichiometry, this oxide is prone to a certain extent to subsurface/bulk chlorination, which leads to deactivation. In situ Prompt Gamma Activation Analysis (PGAA) studies evidenced that the chlorination rate is independent of the pre-chlorination degree but increases at lower oxygen over-stoichiometry, while dechlorination is effective in oxygen-rich feeds, and its rate is higher for a more extensively pre-chlorinated ceria. Even bulk CeCl3 could be transformed into CeO2 under oxygen excess. Electron Paramagnetic Resonance experiments strongly suggested that oxygen activation is inhibited by a high surface chlorination degree. The coverages of most abundant surface intermediates, OH and Cl, were monitored by in situ infrared spectroscopy and PGAA under various conditions. Higher temperature and p(O2) led to enhanced OH coverage, reduced Cl coverage, and increased reactivity. Variation of p(HCl) gave rise to opposite correlations, while raising p(Cl2) did not induce any measurable increase in the Cl coverage, despite the strong inhibition of the reaction rate. The results indicate that only a small fraction of surface sites is actively involved in the reaction, and most of the surface species probed in the in situ observation are spectators. Therefore, when performing in situ steady-state experiments, a large set of variables should be considered to obtain accurate conclusions.

Original languageEnglish
Pages (from-to)119-127
Number of pages9
JournalJournal of Catalysis
Volume297
DOIs
Publication statusPublished - Jan 2013

Fingerprint

Cerium compounds
chlorination
Chlorination
reactivity
Oxygen
activation analysis
Activation analysis
oxygen
Stoichiometry
stoichiometry
Dechlorination
deactivation
Oxides
Reaction rates
Paramagnetic resonance
Infrared spectroscopy
electron paramagnetic resonance
reaction kinetics
Gases
Experiments

Keywords

  • CeO
  • EPR
  • HCl oxidation
  • In situ FTIR
  • In situ PGAA
  • Surface coverage

ASJC Scopus subject areas

  • Catalysis
  • Physical and Theoretical Chemistry

Cite this

Do observations on surface coverage-reactivity correlations always describe the true catalytic process? A case study on ceria. / Farra, Ramzi; Eichelbaum, Maik; Schlögl, Robert; Szentmiklósi, L.; Schmidt, Timm; Amrute, Amol P.; Mondelli, Cecilia; Pérez-Ramírez, Javier; Teschner, Detre.

In: Journal of Catalysis, Vol. 297, 01.2013, p. 119-127.

Research output: Contribution to journalArticle

Farra, R, Eichelbaum, M, Schlögl, R, Szentmiklósi, L, Schmidt, T, Amrute, AP, Mondelli, C, Pérez-Ramírez, J & Teschner, D 2013, 'Do observations on surface coverage-reactivity correlations always describe the true catalytic process? A case study on ceria', Journal of Catalysis, vol. 297, pp. 119-127. https://doi.org/10.1016/j.jcat.2012.09.024
Farra, Ramzi ; Eichelbaum, Maik ; Schlögl, Robert ; Szentmiklósi, L. ; Schmidt, Timm ; Amrute, Amol P. ; Mondelli, Cecilia ; Pérez-Ramírez, Javier ; Teschner, Detre. / Do observations on surface coverage-reactivity correlations always describe the true catalytic process? A case study on ceria. In: Journal of Catalysis. 2013 ; Vol. 297. pp. 119-127.
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