Selective catalytic reduction (SCR) employs AdBlue, a reducing agent over a catalytic surface to reduce the oxides of nitrogen (NO x ) emission in diesel engines. SCR's inherent problem is its poor cold start performance at exhaust temperatures below 150 C. In the current work, the researcher has discussed the investigation of two techniques to enhance low-temperature NO x conversion and combined them to achieve the best results. First, AdBlue injection was replaced by gaseous ammonia injection. The gaseous ammonia was generated by heating solid ammonia precursor materials such as solid urea and ammonium carbonate. Second, to improve the catalytic performance, MnCeZrO x catalysts were introduced instead of conventional CuZ catalysts. MnCeZrO x were prepared in the laboratory using its component materials.The prepared catalyst was tested through SEM and EDAX analysis. The newly developed SCR system was tested and compared with a conventional Adblue-CuZ SCR.The results revealed with diesel fuel at exhaust temperatures below 150 C the ammonia-MnCeZrO x SCR system gave a 90% increase in NO x reduction compared to the conventional system. With biodiesel blend jatropha B20 the conversion was greater than 80% from 100 to 150 C. A maximum NO x conversion of 95% was obtained for diesel and 93% for jatropha Biodiesel blend B20.