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Applied Catalysis B: Environmental, Vol.9, No.1-4, 251-266, 1996
Reactivity of Steam in Exhaust-Gas Catalysis .3. Steam and Oxygen/Steam Conversions of Propane on a Pd/Al2O3 Catalyst
A 1% Pd catalyst (38% dispersion) was prepared by impregnating a gamma-alumina with palladium acetylacetonate dissolved in acetone, The behaviour of this catalyst in oxidation and steam reforming (SR) of propane was investigated, Temperature-programmed reactions of C3H8 with O-2 or with O-2 + H2O were carried out with different stoichiometric ratios S (S = [O-2]/5 [C3H8]). The conversion profiles of C3H8 for the reaction carried out in substoichiometry of O-2 (S < 1) showed two discrete domains of conversion : oxidation at temperatures below 350 degrees C and SR at temperatures above 350 degrees C. The presence of steam in the inlet gases is not necessary for SR to occur : there is sufficient water produced in the oxidation to form H-2 and carbon oxides by this reaction, Contrary to what was observed with Pt an apparent deactivation between 310 and 385 degrees C could be observed with Pd in oxidation. This is due to a reduction of PdOx into Pd-0, which is much less active than the oxide in propane oxidation. Steam added to the reactants inhibits oxidation while it prevents the reduction of PdOx into Pd-0. Compared to Pt and to Rh, Pd has a higher thermal resistance : no deactivation occurred after treatment up to 700 degrees C and limited deactivation after treatment up to 900 degrees C, provided that the catalyst is maintained in an oxygen-rich atmosphere during the cooling.
Keywords:SUPPORTED PALLADIUM CATALYSTS;NOBLE-METAL CATALYSTS;ALUMINA CATALYSTS;METHANE OXIDATION;COMBUSTION;HYDROCARBONS;CHEMISTRY;PLATINUM;WATER