NOx storage and reduction over Cu/K2Ti2O5 in a wide temperature range : Activity, characterization, and mechanism

A novel NOx storage-reduction catalyst Cu/K2Ti2O5, which uses K2Ti2O5 rather than Ba and Al2O3 as NOx storage compound as well as support, has been synthesized and investigated. Activity tests including temperature-programmed ramping, isothermal storage, and lean-rich cycling reveal that Cu/K2Ti2O5 adsorbs NOx over a very wide temperature range (200-600 deg C), with two peak temperatures at 280 and 550 deg C, respectively. The NOx storage and reduction mechanism over Cu/K2Ti2O5 is studied in detail. We demonstrate that, at low temperature (200-400 deg C), NOx is adsorbed on the oxygen vacancy sites which are formed on K2Ti2O5 support during the lean-period; whereas at high temperature (500-600 deg C), the NOx storage and reduction is explained by a structure switching between K2Ti2O5 and K2Ti6O13 caused by NO2 adsorption and de-sorption. Our results also provide another option for synthesizing NSR catalysts with K2Ti2O5 or even with other potassium containing compounds.