Study Of Low-concentration NO Removal By Adsorption

Nitrogen oxides(NOx)remain to be a major source for air pollution.They are known to be associated with several environmental problems and health hazards,including photochemical smog,acid rain and ozone depletion.In recent years,due to the increasingly stringent regulations on nitrogen oxides emissions,development of methods to remove NOx,especially NO from the flue gas efficiently has become an active research area.Currently,the selective catalytic reduction(SCR)technology has been widely used to remove NO.However,this method is not suitable for the removal of low concentration of NO as well as it may exist the drawbacks of ammonia slipping or catalytic deactivation caused by SO2 poisoning.Among various strategies,adsorption is a promising alternative for low-concentration NO removal since it is relatively simple and easy to control automatically,furthermore,it can efficiently trap low concentration of hazardous substances.In this paper,a series of Mn-based two or three components mixed metal oxides were prepared by a co-precipitation method and used for low-concentration NO removal at 25 oC in the presence of O2.The adsorbents were characterized by X-ray diffraction(XRD),N2 sorption,X-ray photoelectron spectroscopy(XPS)and scanning electron microscopy(SEM).The results showed that the mixed metal oxides were able to remove low-concentration NO in the presence of O2 efficiently.The addition of Al not only increased the surface area of MnOx greatly but also effectively enhanced the dispersion of Mn species in the adsorbent shown by BET and XRD,which were beneficial to improve the performance of NO removal.The addition of metal Ce and Fe enhanced the activities of NO oxidation and NO breakthrough capacity.Among them,the adsorbent 10Ce-Mn-Al-O exhibited the highest NO conversion reaching 56% and the highest breakthrough capacity of 22.5 mg g-1.The results of the experiment found that the adsorbents with high efficiency for NO removal all had large surface areas and high activities in NO oxidation to NO2.The influence of space velocity,adsorption temperature and O2 concentration on the removal of NO with the mixed metal oxides 10Ce-Mn-Al-O were investigated.Moreover,searching for the regeneration conditions of 10Ce-Mn-Al-O and investigating its performance of multiple regeneration cycles.It was found that a larger space velocity and higher adsorption temperature will inhibit the NO adsorption.The NO breakthrough capacity of 10Ce-Mn-Al-O increased with the O2 concentration rise.The regeneration experiment indicated that the used adsorbent 10Ce-Mn-Al-O could be regenerated completely by heating in N2 at 500 oC for 2 h.In addition,the NO breakthrough capacity of regenerative 10Ce-Mn-Al-O after seven regeneration cycles could reach more than 80% of fresh 10Ce-Mn-Al-O.The total NO breakthrough capacity of seven regeneration cycles was 167 mg g-1.Finally,the effects of CO2 on NO adsorption were investigated.The NO breakthrough capacity of all adsorbents decreased greatly with the addition of CO2,and 10Ce-Mn-Al-O decreased nearly 40 percent.CO2 inhibited the removal of NO on the sorbents significantly.