The selective non-catalytic reduction (SNCR) deNO(x) process was influenced by high-concentration CaO particles in the pre-calciners when applied to cement industry. The influence of CaO on the SNCR deNO(x) process was investigated using a fixed bed reactor at temperature that ranges from 873 K to 1373 K and the mechanism of the process was analyzed. The experimental results demonstrated that CaO has catalytic effects on NH3 decomposition, NO reduction by NH3, and NH3 oxidation. It inhibits the SNCR deNO(x) process mainly via catalyzing NH3 oxidation to NO. The catalytic effect of CaO can be ignored at temperatures higher than 1273 K. NH3 was found that first adsorbed onto the CaO surface and then dissociated to NH2 by Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The mechanism analysis of CaO catalysis during the SNCR deNO(x) process showed that NH3 dissociation on the CaO surface is the rate-controlling step, and the intermediate substance, NH2, reacts with O-2 or NO to produce NO or N-2. The competition of the two reactions determines the product selectivity. A kinetic model including CaO-catalyzed NH3 conversion and gas phase SNCR deNO(x) reaction was developed, which well predicted the CaO-involved SNCR deNO(x) process. (C) 2014 Elsevier B.V. All rights reserved.