Property of Pd-supported catalysts for catalytic combustion

The catalytic properties of Pd/Sr(0.8)La(0.2)XAl(11)O(19) (X = Al and Mn) and Pd/Al2O3-MO(x) (M = Co, Cr, Cu, Fe, Mn and Ni) catalysts were investigated for use in catalytic combustion. The activity of Pd/Sr0.8La0.2Al12O19 initially increased with rise in temperature, but decreased at high temperatures (ca. 700 degrees C). The drop in catalytic activity was steep when the supported Pd particles were sintered after calcination above 1000 degrees C. The activity drop accompanied dissociation of PdO into metallic Pd. Such significant drop in catalytic activity can be avoided by the use of Mn-substituted hexaaluminate (X = Mn) as a catalyst support, due to its activity for combustion. The drop could be also avoided by use of Pd/Al2O3-NiO catalysts calcined at low temperatures. Although the surface area decreased with increasing NiO content, the catalytic activity increased. Pd particle size is an important factor in determining catalytic activity.