Synergetic effect of Pd addition on catalytic behavior of monolithic platinum–manganese–alumina catalysts for diesel vehicle emission control

Abstract The advanced diesel emission control catalyst Pt–Pd–MnO x –Al 2 O 3 has been developed on the basis of the synergetic effect of Pt with Pd and manganese oxides observed in hydrocarbon and carbon monoxide oxidation reactions. This effect allows a decrease in the total loadings of Pt and Pd down to 0.52 g/L in the monolithic catalyst, providing high activity in low temperature oxidation of light hydrocarbons and high thermal stability. The catalytic activity of Pt–Pd–MnO x –Al 2 O 3 monolithic catalysts in butane oxidation and DIESEL tests depends on the Pt and Pd precursors, their individual loadings and their ratio (Pt/Pd). For a selected Pt precursor at its content 0.17 g/L, the catalytic performance of Pt–Pd–MnO x –Al 2 O 3 catalyst improves with an increase in Pd loading from 0 to 0.35 g/L and is nearly constant at a higher Pd loading (0.70 g/L). The most active monolithic Pt–Pd–MnO x –Al 2 O 3 catalyst is prepared by using platinum-dinitrodiamine and palladium nitrate solutions as noble metal precursors. The catalytic activity in light hydrocarbon oxidation is shown to correlate with the RedO x properties of PdPt–MnO x –Al 2 O 3 catalysts and the Pt–Pd particle size. The non-additive increase in the catalytic activity of bimetallic catalyst is suggested to connect with a formation of nanoscale PdO–PtO x particles on the surface of Mn 3 O 4 and a modification of alumina structure by Mn 3+ and PtPd clusters.