TOTAL COMBUSTION OF M-XYLENE OVER PALLADIUM CATALYSTS SUPPORTED BY STAINLESS-STEEL FLAKES

Total combustion of m-xylene over Pd/stainless steel flakes has been i nvestigated. Ignition temperature of the catalytic combustion of m-xyl ene mixtures over palladium catalysts is lowered by about 330 degrees C compared to that of thermal oxidation. Hysteresis in the conversion- temperature curves recorded in temperature programmed modes is control led not only by the operating conditions (the temperature ramp, concen tration of the reactants, contact time) but also by catalyst pretreatm ents. High and low activity states have been observed with typical ign ition temperatures of 200-250 degrees C and about 400 degrees C, respe ctively. In high activity state the combustion is likely initiated by the catalyst followed by a chain reaction which propagates into the ga s phase. This is strongly supported by the abrupt increase in the conv ersion profile. During the induction period preceding the combustion, active species are accumulated on the surface which are responsible fo r this process.