Influence of the activation temperature on the metal accessibility in model three-way catalysts

• Published in: Catalysis today Vol. 29; no. 1; pp. 83 - 87
• Main Authors: Rogemond, E., Essayem, N., Fréty, R., Perrichon, V., Primet, M., Chevrier, M., Gauthier, C., Mathis, F.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 31-05-1996; Elsevier Science; Elsevier
• Subjects: Catalysis; Catalysts: preparations and properties; Chemical Sciences; Chemistry; Exact sciences and technology; General and physical chemistry; Pt catalysts; Rh catalysts; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Pt catalysts; Rh catalysts; Cerium Oxides; Aluminium Oxides; Rhodium; Hydrogen; Platinum; Three way catalyst; Cerium; Catalyst activity; Alumina
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/0920-5861(95)00272-3

The influence of the reduction temperature on the accessibility of the metallic surface was studied on model ceria-alumina supported platinum or rhodium catalysts. For a 0.5% Pt-Ce/Al solid, the
H
M
values, deduced from hydrogen irreversible chemisorption, decrease deeply with T
r, the reduction temperature, from 60% at
T
r = 300°C to 19% at
T
r = 500°C. This can be attributed to strong interactions between ceria and platinum, since, the initial H
2 chemisorption could be restored after reoxidation. The presence of BaSO
4 in the support accelerates the loss of metallic area, because of sulfur poisoning of the platinum surface. For
T
r = 300°C, the dispersion values were in agreement with those deduced from FTIR spectroscopy of adsorbed CO. In the case of rhodium, a 37% H/M dispersion was obtained, which did not change when T
r was increased from 300 to 500°C. For two industrial Pt-Rh three-way catalysts, the behaviour was found similar to that of platinum, the amount of chemisorbed hydrogen decreasing for T
r > 350°C. Thus, in the three-way catalysts characterization, the maximum metal accessibility is obtained after a reduction at 300°C.