INVESTIGADORES
BONIVARDI Adrian Lionel
artículos
Título:
Understanding the role of oxygen vacancies in the water gas shift reaction on ceria-supported platinum catalysts
Autor/es:
J. VECCHIETTI; A. BONIVARDI; W. XU; D. STACCHIOLA; J.J. DELGADO; M. CALATAYUD; S. COLLINS
Revista:
ACS Catalysis
Editorial:
American Chemical Society
Referencias:
Año: 2014 vol. 4 p. 2088 - 2096
ISSN:
2155-5435
Resumen:
Reducible oxides have been shown to greatly improve the activity of
water gas shift (WGS) catalysts. The precise mechanism for this effect
is a matter of intense debate, but the dissociation of water is
generally considered to be the key step in the reaction. We present here
a study of the water activation on oxygen vacancies at the support as
part of the mechanism of the WGS reaction on Pt supported on pure and
gallium-doped ceria. Doping the ceria with gallium allows tuning the
vacancies in the support while maintaining constant the metal
dispersion. An inverse relationship was found between the catalytic
activity to WGS and the amount of oxygen vacancies. In situ
time-resolved X-ray diffraction, mass spectrometry, and diffuse
reflectance infrared spectroscopy (DRIFT) showed that the oxygen vacancy
filling by water is always fast in either Pt/CeO2 or
Pt/CeGa. DFT calculation provides molecular insights to understand the
pathway of water reaction with vacancies at the metal?oxide interface
sites. Our results suggest that the activation of the water molecule in
the WGS mechanism is not the rate-limiting step in these systems.
Concentration-modulation spectroscopy in DRIFT mode under WGS reaction
conditions allows the selective detection of key reaction intermediates,
a monodentate formate (HCOO) and carboxylate (CO2δ−) species, which suggests the prevalence of a carboxyl (HOCO) mechanism activated at the oxide?metal interface of the catalyst.