Dynamic behavior of adsorbed NO and CO under transient conditions on Pd/Al{sub 2}O{sub 3}
- Univ. of Akron, OH (United States). Dept. of Chemical Engineering
The dynamic behavior of adsorbed NO and CO under transient NO-CO reaction conditions on Pd/Al{sub 2}O{sub 3} has been studied by in situ infrared (IR) spectroscopy coupled with TPR and pulse reaction techniques in the 303--673 K range. Below the light-off temperature (i.e., 561 K), Pd{sup 0}-NO and Pd{sup 0}-CO are the dominant adsorbates on the Pd surface. Pd{sup 0}-NO competes favorably over Pd{sup 0}-CO for the same reduced Pd{sup 0} site when the temperature is increased. Pulse reaction studies at 473 K suggest that Pd{sup 0}-NO dissociates to form adsorbed nitrogen and adsorbed oxygen. Adsorbed oxygen further reacts with Pd{sup 0}-CO to produce CO{sub 2}. Concentration profiles of CO{sub 2} and Pd{sup 0}-CO during the pulse reaction studies indicate that removal of adsorbed oxygen from the Pd surface to produce CO{sub 2} is the rate-limiting step. Prolonged exposure of the catalyst to the NO flow at 473 K results in oxidation of Pd{sup 0} to Pd{sup +} and produces Pd-NO{sup +}; the presence of gaseous CO reduces Pd{sup +} to Pd{sup 0} and increases the surface coverage of Pd{sup 0}-NO. Above the light-off temperature, Pd-NO{sup +}, Al-NCO, nitrate, and carbonate species are the dominant adsorbates. The presence of Pd-NO{sup +} indicates that the process for Pd{sup 0} oxidation to Pd{sup +} by NO is faster than that of Pd{sup +} reduction to Pd{sup 0} by CO. This study demonstrates that careful selection of transient IR techniques allows (1) determination of the modes of adsorbed NO and CO participating in the reaction and (2) development of a comprehensive mechanism for the NO-CO reaction on Pd/Al{sub 2}O{sub 3} catalyst.
- OSTI ID:
- 354387
- Journal Information:
- Journal of Catalysis, Vol. 184, Issue 1; Other Information: PBD: 15 May 1999
- Country of Publication:
- United States
- Language:
- English
Similar Records
In situ infrared study of catalytic decomposition of NO. Semiannually technical progress report, August 1, 1995--February 1, 1996
Reduction of Stored NOx on Pt/Al2O3 Catalysts with H2 and CO