Room temperature removal of NO by activated carbon fibres loaded with urea and La2O3

Abstract

In this paper, catalytic samples of 10, 20, 30, 40 and 50% (w/w) urea/activated carbon fibre (AFC), 10% urea–5% La2O3/ACF, 10% urea–10% La2O3/ACF, 10% urea–15% La2O3/ACF, 20% urea–5% La2O3/ACF, 20% urea–10% La2O3/ACF, and 20% urea–15% La2O3/ACF were prepared and used for removal of NO under the condition of: NO, 500 ppm; O2, 21%; N2, balance, gas space velocity=10000 m3·h−1·m−3, total gas flow = 266.7 mL min−1, temperature = 30°C, relative humidity=0%. The physical and chemical properties of the prepared catalysts were characterized by surface area measurements (BET) and scanning electron microscopy studies. Furthermore, the catalytic stability of 10% urea–5% La2O3/ACF under different concentrations of NO and O2 were also studied. The results showed that, among the prepared urea/ACF samples, 20% urea/ACF yielded the highest NO conversion at room temperature. Meanwhile, among the prepared urea–La2O3/ACF catalysts, 10% urea–5% La2O3/ACF yielded the highest NO conversion. Both 20% urea/ACF and 10% urea–5% La2O3/ACF could yield over 95% NO conversion at ambient temperature. However, 10% urea–5% La2O3/ACF had a more stable activity than that of 20% urea/ACF. The catalytic and characterization experimental results, including BET, thermogravimetric analysis and Fourier transform infrared analysis, showed that the NO selective catalytic reduction mechanism of urea–La2O3/ACF was different from that of ACF and urea/ACF. The NO was purified by ACF mainly by adsorption, whereas there was mainly a reduction reaction when NO was purified by urea/ACF or urea–La2O3/ACF. ACF-C was not only the catalyst but also the reducing agent for urea/ACF, whereas, for urea–La2O3/ACF, the catalytic centre was La2O3, and ACF was mainly the carrier. These differences resulted in the higher and more stable NO removal by 10% urea–5% La2O3/ACF.