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 depende d upon the kind of support. The change of activity was accompanied wit h sintering of palladium metal. The stabilized activity of the palladi um was ordered in the sequence; on SiO2 > on Al2O3 > on SiO2-Al2O3. Th e turn-over frequency of methane oxidation was about 50 times greater than that of platinum supported catalysts, and the activity sequence o f support was opposite to that of platinum. The effect of support on t he activity of palladium was smaller than on platinum from the viewpoi nt of activation energy as well as the turn-over frequency. The pallad ium dispersed on the support was less active, bur the large particle w hich was not interacted strongly with the support was active; the beha vior may be related to the small support effect on the palladium activ ity, Higher activity of the loaded palladium oxide than that of platin um oxide was caused by the higher reducibility of Pd-O chemical bonds, as confirmed by the temperature-programmed reduction. Silica deposite d alumina, prepared by a method of chemical vapor deposition, was desi gned to create new active sites for the loading of silica-rimmed palla dium; the sintering of palladium was suppressed to obtain the durable activity.