Influence of the nature of the noble metal on the lean C3H6-assisted decomposition of NO on Ce0.68Zr0.32O2-supported catalysts

The Selective Catalytic Reduction (SCR) of NOx assisted by C3H6 is investigated on Ce0.68Zr0.32O2 (CZ)-supported Platinum Group Metals (PGMs: Pd, Rh, Pt) catalysts. This study shows that the order of reactivity of the PGMs supported on CZ is: Pd >> Pt > Rh. The performances of the most active CZ-supported catalysts are comparable to those reported for SiO2- or Al2O3-supported PGMs catalysts in terms of N-2 production. In contrast, the CZ-supported catalysts are much more selective to N-2 than those supported on SiO2 or Al2O3, which makes them of particular interest. This difference of selectivity to N2 of the CZ-supported catalysts suggests that the mechanism of the SCR of No, assisted by C3H6 proposed for Pd/CZ catalysts [C. Thomas, O. Gorce, C. Fontaine, J.-M. Krafft, F Villain, G. Djega-Mariadassou, Appl. Catal. B: Environ. 63 (2006) 201] is also valid for Pt or Rh/CZ catalysts. In this mechanism, ad-NO2 species react with C3H6 to form ad-RNOx compounds that further decompose to NO and oxygenates (CxHyOz). The role of these oxygenates is to reduce the support to provide the sites responsible for NO decomposition to N-2 (Ce3+ surface cations). The much higher activity of the Pd-based catalysts in the SCR of NOx assisted by C3H6 might be attributed to the greater ability of the PdOx phase to adsorb NO2. This property might be assigned to the lower interaction of the PdOx phase with CZ compared with that of the PtOx or Rho(x) phases. (c) 2006 Elsevier B.V. All rights reserved.