Study On Efficient CaO-beta Adsorbent For NOx At Room Temperature

With the advantages of high efficiency, recycling useful components, simple equipment, simple operation and easy to automate, the approach of low temperature adsorption-high temperature (or decompression) desorption-decomposition (reduction) is usually adopted to deal with large space velocity and low concentrations of NOx gases to eliminate NOx. In this study, various support materials and active components for adsorbing NOx were studied, and the effects of textural properties, surface acidity of the absorbents on NOx adsorption were characterized by XRD, low temperature N2adsorption, TPD-MS, CO2-TPD, and in-situ FT-IR. The CaO-beta zeolites adsorbent was prepared to use as an efficient adsorbent for NOx, and the effects of preparation factors and operation conditions on the adsorption capacity of the CaO-Beta adsorbent were investigated and the mechanism for adsorbing NOx was discussed.Beta zeolites exhibit high adsorption capacity for NOx in the presence of oxygen or without, because it has high surface area, large pore volume, and its micopore size is2-6times than NO molecular diameter. Using H-beta zeolites as the supporter and Ca(NO3)2-4H2O as the precursor, the CaO-Beta adsorbent was prepared by an incipient wetness impregnation and two-step calcination. In the space velocity was24000h-1, the NOx adsorption capacity of the10wt.%CaO-Beta adsorbent can reach753μmol/g. The used adsorbent can be used repeatedly after calcination in airNOx adsorption on CaO-Beta is depended on two ways. One is related to the physical adsorption which has a better correlation with the structure of H-beta, BET surface area, micropore volume and experiment condition and so on. The second one is very important and that the selective adsorption sites (CaO) react with NOx to form nitrate and nitrite.Increasing the concentration of O2in the feed gas can promote the oxidation of NO to NO2, which is easily adsorbed on the CaO-Beta adsorbent, resulting in an obvious improvement of its adsorption capacity. When the concentration of O2is increased from1%to20%, the penetration time is prolonged from51min to61min, and the time when NOx concentration in outlet reachs C/Co≥0.5is enhanced from102min to152min. The presence of water vapor in feed gas would partially in hibit the adsorption property of the CaO-Beta adsorbent.