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

The reduction of NO by CO + H2 in the presence of excess O2 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-NOx efficiency of the catalytic system. Therefore, the Pd-catalysed NO + CO + H2 + O2 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-NOx efficiency and N2-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, ∼85%, NOx conversion in a very wide temperature range (100–400 °C), accompanied by very good N2-selectivities of ∼85%, i.e., 15–30 additional percentage units in comparison to the selectivity of the original un-promoted Pd/Al2O3 catalyst.