No Reduction Over Activated Carbon Honeycomb Supported Mno_x And CeO₂at Low Temperature

Nitrogen oxide (NOx) is one of the most important source of atmospheric pollution that must be removed before emission. Among various controlling technologies, selective catalytic reduction (SCR) of NO with NH3is the most effective for NOx removal. Although V2O5-WO3(MoO3)/TiO2catalyst has been commercialized, it has great harm to the environment and can only be kept better activity at high temperatures. Therefore, developing a kind catalyst which is environmental, nontoxic and has high NO conversion at low temperature has become the problem that needs to be solved urgently.This work is on the basis of the early stage of MnOx supported activated carbon honeycomb (MnOx/ACH) catalyst denitration behavior research, by adding CeO2to the MnOx/ACH catalyst, aiming to overcome the shortage of the lower sulfur resistance and further improve the catalytic activity by using the MnOx-CeO2synergistic catalytic function. The amount of Ce doping, temperature, the SCR reaction mechanism and the effect of SO2were studied systematically. To further improve the sulfur resistance of the catalysts, a series of Fe, Sn modified MnOx-CeO2/ACH catalysts were prepared and used for low temperatures SCR of NO with NH3. In the process of the above research, this work deeply analyzed the related mechanism of resistance to sulfur and got the following main results or conclusions:(1) NO conversion could be improved by doping Ce in temperature range of80～200℃The MnOx-CeO2/ACH catalyst with a molar ratio of Ce/Mn=1showed the best performance of NO removal, with a NO conversion nearer to100%at the temperature of160℃. This activity improvement may be contributed to the improvement of the distribution for manganese and cerium oxide on ACH after CeO2doping. Furthermore, the addition of CeO2increased the chemisorbed oxygen concentration.(2) Transient experiments were used to elucidate the reaction mechanism of the SCR of NO by ammonia over the MnOx-CeO2/ACH catalyst. The results indicated that the SCR reaction occurs between the adsorbed NH3and the gas phase NO or weakly adsorbed NO, following the Eley-Rideal model.(3) The addition of Ce to the MnOx/ACH enhanced its resistance to SO2poisoning but the deactivation of MnOx-CeO2/ACH poisoned by SO2still occurred. The characterization results showed that the catalyst deposited on the surface ammonium sulfites and ammonium sulfates were the main reason leading to deactivation. Furthermore, competitive adsorption of SO2and NH3on the catalysts also could reduce catalytic activity.(4) The capacity of removing NO was not improved over the Fe、Sn modified catalysts(FeOx-MnOx-CeO2/ACH, SnOx-MnOx-CeO2/ACH), but the resistance to SO2was enhanced slightly over FeOx-MnOx-CeO2/ACH catalysts at the temperature of160℃, also can be enhanced significantly over SnOx-MnOx-CeO2/ACH catalysts at the temperature of250℃.