No abstract

The Selective Catalytic Reduction (SCR) of NO x assisted by propene is investigated on Pd/Ce 0.68 Zr 0.32 O catalysts (Pd/CZ), and is compared, under identical experimental conditions, with that found on a Pd/SiO 2 reference catalyst. Physico-chemical characterisation of the studied catalysts along with their catalytic properties indicate that Pd is not fully reduced to metallic Pd for the Pd/CZ catalysts. This study shows that the incorporation of Pd to CZ greatly promotes the reduction of NO in the presence of C 3 H 6. These catalysts display very stable deNO x activity even in the presence of 1.7% water, the addition of which induces a reversible deactivation of about 10%. The much higher N 2 selectivity obtained on Pd/CZ suggests that the lean deNO x mechanism occurring on these catalysts is different from that occurring on Pd 0 /SiO 2. A detailed mechanism is proposed for which CZ achieves both NO oxidation to NO 2 and NO decomposition to N 2 , whereas PdO x activates C 3 H 6 via ad-NO 2 species, intermediately producing R-NO x compounds that further decompose to NO and C x H y O z. The role of the latter oxygenates is to reduce CZ to provide the catalytic sites responsible for NO decomposition. The proposed C 3 H 6-assisted NO decomposition mechanism stresses the key role of NO 2 , R-NO x and C x H y O z as intermediates of the SCR of NO x by hydrocarbons.