INVESTIGADORES
SANCHEZ Miguel Dario
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; First Internacional Conference on Materials for Energy; 2010
Institución organizadora:
Gesellschaft für Chemische Technik und Biotechnologie e.V.
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
[1-3] are highly active and stable catalysts for reforming reaction. Catalytic
activity and selectivity of Pd catalysts for dry reforming have not been
extensively studied despite the lower cost of Pd 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 commercial a-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 washing 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 performing several washing
steps after impregnation. The
XPS spectra indicate the presence of a small fraction of Pd(4+)
after 1 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%) exhibits a steady deactivation due to carbon deposition and sintering [4]. 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 higher activity for the reforming reaction.
References
1. J.H. Bitter, K. Seshan, J.A. Lercher, J. Catal. 1997, 171,
279.
2. A. Erdöhelyi, J. Cserényi, F. Solymosi, J. Catal. 1993,
141, 287.
3. H.Y. Wang, E. Ruckenstein, Appl. Catal. A 2000, 204, 143.
4. P. G. Schulz, M.G.
Gonzalez, C.E. Quincoces, C.E. Gigola, Ind. Eng. Chem. Res. 2005,
44, 9020.