Composite Oxide Catalysts For Soot Combustion And NO_x Storage-Reduction

After-treatment technology of exhaust is the most effective ways for eliminating the pollution of both soot and NOx exhausted from diesel engine. Highly active catalyst is the key to the technology.In this paper, YBa(Co1-xMx)4O7+δ catalysts were prepared by the improved sol-gel method and used for the on-going soot elimination. XRD results showed that the pure YBa Co4O7 phase was obtained after doping with Ga and Al ions. The stability of the YBa(Co1-xMx)4O7+δcatalysts was improved by the dopants. O2-TPO and O2-TPD results suggested that the YBa(Co1-xMx)4O7+δ catalysts possessed the storage oxygen property at 200-400 oC and the temperature of oxygen release was decreased, which facilitates the catalytic combustion of soot at low temperatures. Hence, the dopants have enhanced the catalytic activity and CO2 selectivity for soot combustion. Steady-state isothermal reactions exhibited that the activation energy of soot combustion on YBa(Co1-xMx)4O7+δ catalysts was significantly reduced.Carbon-TPR proposed that the active oxygen in soot combustion at low temperatures was derived from the stored oxygen.18 O isotopic isothermal reactions showed that the gaseous oxygen was transformed into active oxygen species by activation of the catalyst. The active oxygen reacts with the adjacent free soot sites to form COx, which is subsequently released from the catalysts. The contact condition between soot and catalyst is a key factor for soot combustion.In this paper, Pd and K were supported on MgAl O composite oxide to obtain Pd-K/MgAlO catalysts by impregnation method and used for on-going NOx elimination. NOx conversion was enhanced by coupling NOx storage-reduction(NSR) with CO adsorption-oxidation(CAO), which was observed in NSR lean-rich cycle tests with CO as a reductant on catalysts of Mg-Al mixed oxides supported Pd(Pd/MgAl O) and Pd-K(Pd-K/MgAlO). CO was adsorbed on Pd sites in the rich condition and then oxidized by gaseous NOx via Eley–Rideal mechanism during the transition from the rich condition to the lean condition, which results in an enhanced NOx conversion. This is confirmed by different configuration experiments of Pd-K/MgAlO and Pd/MgAlO, acting as NSR and CAO catalysts, respectively. The intimate mixture of Pd-K/MgAlO and Pd/MgAlO showed muchhigher activity due to the resultant coupling effect of NSR with CAO in comparison with a zone-arranged catalyst system no matter whether Pd-K/MgAlO or Pd/MgAlO was in the front. The coupling also worked in the presence of H2 O and CO2 despite that the efficiency were spoiled. This strategy is ease to be implemented and thereby is potential for the practical after-treatment technology for lean-burn and diesel engines.