AN IN-SITU ELECTRICAL-CONDUCTIVITY STUDY OF A CEO2 AEROGEL SUPPORTED PALLADIUM CATALYST IN CORRELATION WITH THE TOTAL OXIDATION OF PROPANE

The electrical conductivity of a Pd/CeO2 aerogel catalyst has been mea sured in situ during the reduction of the catalyst in H-2 and during t he oxidation of propane, both carried out during programmed heating. T he results can be rationalized on the basis of (i) the formation of an ionic vacancies in ceria upon reduction, (ii) the subsequent electron transfer from reduced ceria to Pd, a transfer which persists during th e catalytic reaction, (iii) the partial reoxidation of the surface of ceria in the presence of the reaction mixture at temperatures <523 K, and (iv) the reduction of CeO2 at the Pd-CeO2 interface by H atoms abs tracted from propane chemisorbed on Pd at temperatures >523 K, this ab straction being thereby favored by the support. Attempts have been mad e to correlate the various conduction activation energies with corresp onding surface reactions. (C) 1996 Academic Press, Inc.