Mechanism study on the adsorption and reactions of NH3, NO, and O-2 on the CaO surface in the SNCR deNO(x) process

摘要

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.