Selective reduction of NO with methane over alumina-supported palladium catalysts

Selective reduction of NO with methane in the presence of oxygen using meta l oxide-supported palladium catalysts was explored. Effect of various metal oxides and the conditions for catalysts preparation on the catalytic activ ity was investigated. Alumina-supported palladium exhibited especially high est catalytic activity for the selective reduction of NO among the other al umina-supported metal catalysts; alumina was found to be most effective as the support among several metal oxides. Although most of preparation condit ions did not affect the activity of Pd/Al2O3, reduction at high temperature resulted in the decrease of deNO(x) activity. Result for catalyst characte rization indicated that alumina support had strong solid-acidity and that t he Pd dispersion for Pd/Al2O3 having high deNO(x) activity was high. The re duction at high temperature led to low dispersion of palladium supported on the same alumina. These results indicate that the solid acidity of the sup port and the dispersion of palladium are essential for the high catalytic a ctivity. Concerning the reaction pathway, it was presumed that methane was first oxidized on palladium particles to partially oxidized compounds, whic h then reacted with NO, on alumina support to give N-2, COx and H2O.