Exhaust after treatment systems have become a necessity to eliminate pollutant emissions as required by standard. Nowadays, DOC and SCR are widely used after treatment technologies in diesel vehicles. In this experimental study carried on DOC and SCR systems, two different catalysts as Al2O3-TiO2/Fe2O3 and Al2O3-Pt/Fe2O3 were produced with impregnation method. The catalysts were characterized by Field Emission-Scanning Electron Microscope (FE-SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF) and Brauner-Emmett-Teller (BET). Each catalyst was tested as DOC and SCR in real working state to see the effect of catalyst on pollutant emissions in diesel engine. Results showed that the use catalysts as DOC led to significant decrease in CO, HC, NO and smoke emissions. The exhaust temperature rose up to 50 degrees C after DOC. The use of catalysts in SCR system eliminated NOx emission by high rates. Furthermore; the use of catalysts in emission control systems led to an increase in specific fuel consumption and a decrease in excess air coefficient of engine. (C) 2017 Elsevier Ltd. All rights reserved.