Mechanism study on the adsorption and reactions of NH3, NO, and O2 on the CaO surface in the SNCR deNOx process

CaO significantly influences the SNCR deNO(x) process. The adsorption and reaction mechanism of NH3 + NO + O-2 system on the CaO surface were studied in this work. Results showed that NH3 adsorbed onto the Lewis acid sites of CaO and the main ad-species were NH2 and OH. With increased temperature, NH2 dehydrogenation occurred and formed dinitride, which eventually desorbed as N2O; whereas OH reacted with H to form H2O. O-2 accelerated NH3 conversion to NH2 and oxidized dinitride. NO ad-species on the CaO surface were cis-dimer nitroso and monodentate nitrate. With increased temperature, cis-dimer nitroso decomposed and desorbed as NO, and monodentate nitrate eventually desorbed as N2O. O-2 had no influence on NO ad-species. When NH3 and NO coexisted, they simultaneously adsorbed onto the CaO surface and formed the similar ad-species with their single adsorption. NO was reduced to N-2 by NH2, and the reaction followed Langmuir-Hinshelwood mechanism. NH2 dissociation to dinitride simultaneously occurred with NO reduction in the NH3 + NO system. In the NH3 + NO + O-2 system, NH3 conversion to NH2 was determined by O-2. The majority of NH2 was oxidized by O-2, and the remainder reacted with NO. NH2 dissociation to dinitride was negligible in the presence of O-2. (C) 2015 Elsevier B.V. All rights reserved.