Cerium oxide catalysts (CeOx) supported on gamma-Al2O3 for high temperature (T > 200 degrees C) selective catalytic reduction (SCR) of nitrogen oxides (NOx) with NH3 in the presence of excess O-2 were prepared by a facile sol-gel method. Firstly, alumina was prepared by a precipitation technique. Field Emission Scanning Electron Microscope (FESEM) image of the support showed a spherical and uniform morphology with nano-metric particles. X-ray diffraction (XRD) pattern revealed that gamma alumina phase was formed. The effects of reaction temperature (T = 200-400 degrees C) and CeOx loading (4-19 wt%) were investigated on NOx conversion and selectivity to N-2 as a desired product. XRD and Brunauer, Emmett & Teller (BET) surface area analyzes showed that increasing the CeOx loading enhanced peak intensity and crystallite size of CeOx and declined the total surface area, respectively. H-2-temperature programmed reduction (TPR) results showed the presence of cerium oxide in form of CeO2 with a maximum normalized H-2 consumption of 4.18 mmol g(-1) catalyst for 14 wt% CeOx. Under the reaction conditions of 300 degrees C, 1 bar, NO=NH3 = 900 ppm, O-2 = 5 vol%, GHSV = 30,000 h(-1) and 14 wt% CeOx, NOx conversion and N-2 selectivity were 97% and 99%, respectively. It can be concluded that proper crystallite size, surface area, number of active sites and good redox ability might be effective for the excellent performance of 14 wt% CeOx. (C) 2017 Elsevier Ltd. All rights reserved.