Complete oxidation of methane on supported palladium catalyst: Support effect

A palladium loaded catalyst was examined in order to reveal the effect of the support on the activity of oxidation of methane. The activity was declined or enhanced with time on stream, and its behavior depended upon the kind of support. The change of activity was accompanied with sintering of palladium metal. The stabilized activity of the palladium was ordered in the sequence; on SiO2 > on Al2O3 > on SiO2-Al2O3. The turn-over frequency of methane oxidation was about 50 times greater than that of platinum supported catalysts, and the activity sequence of support was opposite to that of platinum. The effect of support on the activity of palladium was smaller than on platinum from the viewpoint of activation energy as well as the turn-over frequency. The palladium dispersed on the support was less active, bur the large particle which was not interacted strongly with the support was active; the behavior may be related to the small support effect on the palladium activity, Higher activity of the loaded palladium oxide than that of platinum oxide was caused by the higher reducibility of Pd-O chemical bonds, as confirmed by the temperature-programmed reduction. Silica deposited alumina, prepared by a method of chemical vapor deposition, was designed to create new active sites for the loading of silica-rimmed palladium; the sintering of palladium was suppressed to obtain the durable activity.