INVESTIGADORES
COSTILLA Ignacio Oscar
congresos y reuniones científicas
Título:
Influence of the preparation procedure in the activity of Pd supported catalysts used in CO2 reforming of CH4
Autor/es:
IGNACIO O. COSTILLA; CARLOS E. GIGOLA; MIGUEL D. SÁNCHEZ
Lugar:
Karlsruhe
Reunión:
Conferencia; 1st International Conference on Materials for Energy; 2010
Resumen:
In spite of
the high reaction temperature (> 650oC) required to obtain a reasonable
level of conversion, CO2 reforming of CH4 is a promising reaction to be used in
the production of synthesis gas from CH4/CO2 mixtures coming directly from
natural gas wells.
The
literature shows that Pt/ZrO2 and Rh supported on Al2O3 and MgO are highly
active and stable catalysts for the reforming reaction. Catalytic activity and
selectivity of Pd catalysts for dry reforming have not been extensively studied
despite the lower cost of Pd as compared with Pt or Rh.
In this
work we have studied the effect of the preparation method on the catalytic
activity of Pd catalysts with low metallic loading (< 0.5%) supported on a
commerciala-Al2O3. The catalysts were prepared by a recharging method
consisting of several impregnation steps with a solution of Pd(AcAc)2 in benzene (2 x 10-3 g Pd(AcAc)2 /ml) followed by
washing and calcination at 500oC. Catalysts with different metal loading and
dispersion were prepared by adjusting the number of washings steps.
The samples
were characterized by H2 chemisorption, FTIR and XPS. For H2 chemisorption,
sorption and back sorption isotherms were measured in a volumetric glass
adsorption apparatus. FTIR studies of adsorbed CO (1 Torr) were carried out at
room temperature using a NICOLET 20 DXB instrument at 4 cm-1 resolution. XPS
measurements were made in a PHI 548 spectrometer equipped with a preparation
chamber for heat treatment in hydrogen up to 700oC. The catalytic activity was
determined in a flow reactor operated at 650 °C temperature using a feed mixture of
CH4/CO2/Ar (25/25/50).
The
characterization by FTIR and H2 chemisorption demonstrates that catalysts with
a metallic dispersion above 30% and a low metal content (0.37%) are obtained
when several washing steps after impregnation are used. The XPS spectra
indicate the presence of a small fraction of Pd(4+) after an hour reduction
treatment at 700°C,
due to the presence of small particles with high substrate interaction. The
catalytic test showed that the catalyst with high metal dispersion undergoes a
slow activation during 24 hours of reaction time that correlates with a
particle-size increase and a diminution of the fraction of Pd(4+) species. On
the other hand, samples with low metal dispersion (< 0.25%) exhibit a steady
deactivation due to carbon deposition and sintering . The formation of
palladium particles with a (100) surface structure that favours the adsorption
and dissociation of CH4, seems to be a necessary condition to obtain a high
activity for the reforming reaction.