Abstract
CeO2-based catalysts are widely investigated for selective catalytic reduction (SCR) of NO with NH3. Interaction of NO/O2 with CeO2 generally produces two surface species, i.e., nitrates and nitrites. However, the explicit quantification of these two species is still unresolved. Herein, we reported that spectrophotometry characterization was effective in determining surface adsorbed NOx species on CeO2 by measuring the corresponding ions (NO2– and NO3–) dissolved in aqueous solution. Experimental results show that both nitrate (–NO3) and nitrite (–NO2) species can be quantitatively evaluated and the accuracy is verified by calibrating with NOx-TPD result. Exclusive transfer of adsorbed NOx from catalyst surface to aqueous solution is confirmed and the dissolution process can be accelerated by ultrasonic treatment. Moreover, useful information related to evolution of surface NOx species under various conditions (O2 treatment, different adsorption temperature and duration) and over different catalysts (Fe2O3, MnO2 and MnOx–CeO2) are provided. The result of present study demonstrates the potential of spectrophotometry for quantitative discrimination of surface NOx species on CeO2 and other oxide-based materials, which is conducive to mechanism analysis of SCR reaction.
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