1 research outputs found
Understanding the Role of Oxygen Vacancies in the Water Gas Shift Reaction on Ceria-Supported Platinum Catalysts
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/CeO<sub>2</sub> 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 (CO<sub>2</sub><sup>δ−</sup>)
species, which suggests the prevalence of a carboxyl (HOCO) mechanism
activated at the oxide–metal interface of the catalyst