Novel doubly-promoted catalysts for the lean NOx reduction by H2+CO:: Pd(K)/Al2O3-(TiO2)

The reduction of NO by CO + H-2 in the presence of excess O-2 has been studied on dispersed, low loading 0.5 wt.% Pd-based catalysts. Two different methods of promotion were imposed separately and together, in order to investigate the feasibility of their synergy to enhance de-NO, efficiency of the catalytic system. Therefore, the Pd-catalysed NO + CO + H-2 + O-2 reaction was gradually studied over: (i) Pd/Al2O3-(TiO2) catalysts (support-mediated promotion by modifying the Al2O3 support with TiO2), (ii) K-dosed Pd(K)/Al2O3 catalysts (surface-induced promotion by modifying the Pd surface with the addition of K), and (iii) doubly-promoted Pd(K)/Al2O3-(TiO2) catalysts. Both (i) and (ii) methods of promotion were found to significantly promote the system, when acting individually. However, the de-NO2 efficiency and N-2-selectivity of the doubly-promoted Pd(K)/Al2O3-(TiO2) catalysts were found to be better than both of the other two cases, indicating a synergy during the simultaneous imposition of the two methods of promotion. The resulted benefits with the optimal doubly-promoted catalyst were very high, similar to 85%, NOx conversion in a very wide temperature range (100-400 degrees C), accompanied by very good N-2-selectivities of similar to 85%, i.e., 15-30 additional percentage units in comparison to the selectivity of the original un-promoted Pd/Al2O3 catalyst. (c) 2006 Elsevier B.V. All rights reserved.