Effect of Sulfated CaO on NO Reduction by NH₃ in the Presence of Excess Oxygen

Abstract

The effect of sulfated CaO on NO reduction by NH3 in the presence of excess oxygen was investigated to evaluate the potential of simultaneous SO2 and NO removal at the temperature range of 700−850 °C. The physical and chemical properties of the CaO sulfation products were analyzed to investigate the NO reduction mechanism. Experimental results showed that sulfated CaO had a catalytic effect on NO reduction by NH3 in the presence of excess O2 after the sulfation reaction entered the transition control stage. With the increase of CaO sulfation extent in this stage, the activity for NO reduction first increased and then decreased, and the selectivity of NH3 for NO reduction to N2 increased. The byproduct (NO2 and N2O) formation during NO reduction experiments was negligible. X-ray photoelectron spectroscopy (XPS) analysis showed that neither CaSO3 nor CaS was detected, indicating that the catalytic activity of NO reduction by NH3 in the presence of excess O2 over sulfated CaO was originated from the CaSO4 product. These results revealed that simultaneous SO2 and NO x control by injecting NH3 into the dry flue gas desulfurization process for NO reduction might be achieved.

Effects of water vapor, CO2 and SO2 on the NO reduction by NH3 over sulfated CaO

“…Finally, the SO 2 was switched off, and the NO conversion increased to 13.5% immediately, which verified the restraining effect of SO 2 again. However, the little difference between the NO conversion of 13.5% (at last, without SO 2 ) and 15.1% (at first, without SO 2 ) was caused by the long term introducing of SO 2 over CaO sulfation products making the sulfation extent change, and the reason that the NO conversion decreased as the CaO sulfation increased after a certain CaO conversion has been described and analyzed in detail in our previous work [1,2]. Besides, the increase of the No conversion to 13.5% at last time when SO 2 was 0 ppm also verified the gas restraining effect of SO 2 on the catalytic activity when SO 2 was added during the experiments, without considering the CaO sulfation effect.…”

“…The CaO sulfation extent (X Ca ) was calculated from the mass increase of the solid sample defined as (1): (1) where n S was the molar of sulfur element in the sulfated CaO, and n Ca was the molar of calcium element in the sulfated CaO. The catalytic activity of the sulfated CaO in the presence/absence of H 2 O, SO 2 and CO 2 was mainly measured over 4.0 g sulfated CaO.…”

“…The nitric oxide (NO) reduction by ammonia (NH 3 ) over sulfated CaO has been investigated extensively because of its potential application in the simultaneous removal of SO 2 and NO x in circulating fluidized bed by flue gas desulphurization technique (CFB-FGD) [1][2][3]. Previous pilot-scale CFB-FGD results have indicated that the SO 2 removal efficiency could be as high as 85-95% at the Ca/S molar ratio of 2 in the temperature range of 700-800 o C [4].…”

“…For NO x removal, the previous investigation indicated that sulfated CaO has a catalytic effect on NO reduction by NH 3 [1][2]5] in NH 3 + NO+O 2 +N 2 atmosphere. However, little investigation has been done on the effects of flue gas components, such as CO 2 , SO 2 , and H 2 O, which may have significant influences on the catalyst activity [6][7][8][9][10].…”

DRIFTS Study of Ammonia Activation over CaO and Sulfated CaO for NO Reduction by NH3

“…while CaO sulfation products have a positive effect on the SCR reaction (4,5,8). In the reaction system of 500 ppm NH 3 + 500 ppm NO + 5% O 2 + N 2 , the conversions of NO and NH 3 at 800°C over 5.5 g of CaO and different sulfation products of the initial 5.5 g of CaO, shown in Figure 1 (5), indicate the NO conversion changing with the CaO sulfation extent.…”