Preparation of alumina-supported palladium catalysts for complete oxidation of methane

Alumina-supported palladium catalysts (Pd/Al2O3) have been prepared by incipient wetness (IW), grafting (G) and microemulsion techniques (ME). Two slightly different microemulsion methods have been used (ME1) and (ME2). The catalysts have been calcined at 1000 degreesC for 4 h. The catalysts have then been examined with respect to their activity for the combustion of methane, during heating and cooling ramps. Pd/Al2O3-IW and Pd/Al2O3-ME2 exhibit the highest activity whereas Pd/Al2O3-ME1 and Pd/Al2O3-G are the less active. There is not much of a difference in activity between Pd/Al2O3-IW and Pd/Al2O3-ME2, despite strong differences in palladium particle size observed by TEM analysis. TPO experiments show that Pd/Al2O3-IW and Pd/Al2O3-ME2 present a higher PdO/Pd ratio than the other samples exhibit. The preparation technique affects the reoxidation ability of palladium during cooling, hence the combustion activity of the fresh catalyst, as PdO is more active than Pd for the complete oxidation of methane under lean conditions. (C) 2003 Elsevier B.V. All rights reserved.