INVESTIGADORES
COSTILLA Ignacio Oscar
congresos y reuniones científicas
Título:
Characterization of Pd-CeOx Interaction on α-Al2O3 Support
Autor/es:
CARLOS E. GIGOLA; M. SERGIO MORENO; IGNACIO O. COSTILLA; MIGUEL D. SÁNCHEZ
Lugar:
Bariloche
Reunión:
Conferencia; 13th Internatinal Conference on Solid Films and Surfaces; 2006
Resumen:
The addition of small
quantities of CeO2 (0.3-0.5%) to a Pd(1%)/α-Al2O3,
as catalyst promoter, was investigated by X-ray photoelectron spectroscopy
(XPS), X-ray diffraction (XRD), infrared spectroscopy (FTIR), and transmission
electron microscopy (TEM and HRTEM). The activity and selectivity of this
catalyst, used in the reforming of CH4 with CO2 [1],
were in good agreement with that of other supported metal catalysts (Ni, Pt)
modified with different promoters [2].
Previous studies [3] have
shown the beneficial effect of 20 wt% of CeOx in the
activity and stability of a Pd(2 wt%)/γ-Al2O3 catalyst,
demonstrating a remarkable reduction of carbonaceous deposits. On the basis of
this study we have recently shown [4] that the aggregate of a 2.5 wt% of Ce to
a Pd(1wt%)/α-Al2O3 catalyst also eliminates the deposition of
carbon, with a slight increase in the CO/H2 ratio.
The XPS results showed
that CeOx promotes the partial oxidation of Pd to PdO even after in-situ
reduction treatment at 773K in H2. Both, XRD and HRTEM, indicate
that the CeOx forms small crystallites around the Pd particles. FTIR
spectra of adsorbed CO demonstrate that Ce is not deposited on the Pd particles.
The Pd/Al XPS intensity
ratios vs. the Pd average particle size, determined by TEM, show an excellent
correlation for fresh and used catalyst. These results give evidence that
the diminution of the Pd/Al ratios was due to Pd sintering. Consequently the
small amounts of CeOx species do not cover the Pd particle, in
agreement with the HRTEM and XRD results.
The crystallographic
analysis realized from HRTEM images show that Ce presents different oxidations
states between Ce+4 and Ce+3 in correspondence with the results obtained from
XPS spectra of the Ce 3d region.
From a catalytic point of
view, the overall results stand for a redox promoter mechanism of CeOx
during the reforming of CH4 with CO2.