Adsorption/desorption of NOx on MnO₂/ZrO₂ oxides prepared in reverse microemulsions

A series of MnO₂/ZrO₂ mixed oxides were prepared in reverse microemulsions for NOx adsorption and abatement. The results show that the amount of NOx adsorbed was increased with increasing MnO₂ content in various MnO₂/ZrO₂ samples. The maximum uptake value of NOx was 27.66 mg NOx/g adsorbent on the 40% Mn-Zr sample at 200 °C with NOx initial adsorption rate as 2.63 mg/(g adsorbent min). TPD results show that the complete desorption of NOx was easily obtained by heating the sample to 450 °C, and the temperature for the complete desorption can be further decreased to 210 °C by adding carbon monoxide into the argon desorption streams. Furthermore, water vapor was found to reduce NOx adsorption capacity because of its stronger competitive adsorption with NOx species. It is noteworthy that a small amount of sulfur dioxide could significantly increase the initial rate of NOx adsorption although it slightly decreased the NOx adsorption capacity.