Effect of the addition of Na to Pt /Al_2O_3 catalysts for the reduction of NO by C_3h_8 and C_3H_6 under lean-burn conditions

摘要

A series of pt/gamma-Al_2O_3 catalysts promoted by various concentrations of Na were prepared and tested for the SCR of NO by propene and propane under lean-burn conditiosn The addition of Na markedly modifies the Pt catalytic behaviors Under a C_3H_8/NO/O_2 atmosphere the presence of Naa leads to a drastic decreased of the C_3H_8 and NO conversions In contrast under C_3H_6/NO/O_2 Na promotion improves the Pt catalytic performance For high Na loadings (5 wt%) we observed and enhancement of the selectivity to N_2 and a widening of the operating temperature window The promotional phenomena observed have been explained in terms of modification of the adsorption strengths of the various reactants on the metal surface The Na effects shouls be to strengthen the pt-electron-acceptor (O and NO) bonds and to weaken the Pt-electron-donor (C_3H_8 and C_3H_6) bonds The opposite effects observed by using propane or propene have been attributed to their different mechanisms of adsorption on Pt.