Display omitted •Additive manufactured catalytic converter to reduce emissions from gasohol fuels.•A novel substrate design of catalytic converter is proposed for better conversion efficiency.•The substrate of catalytic converter is fabricated using additive manufacturing technique.•The catalytic converter is insulated with phase change material to reduce cold-start emissions.•The cold start emissions are reduced by 75% compared to a conventional catalytic converter. In recent years, there have been many investigations carried on the regulated emissions in SI engines using gasohol fuels. However, there has been a lack of research on unregulated emissions, the technique required to reduce unregulated emissions, and cold start emissions at gasohol fuels. In this research work, a unique design for substrate in the catalytic converter is proposed to increase the conversion efficiency and reduce both regulated and unregulated emissions. The Computational Fluid Dynamics (CFD) results show that unique design has 10.4% greater surface area, 1.29 times higher cell density, with the more uniform flow, greater pressure drop, and lesser exit velocity than conventionally shaped substrate. The novel design of substrate is fabricated using an additive manufacturing (AM) process with Stainless Steel (SS) 316L material to have high mechanical and thermal strength. The AM substrate and conventional shaped substrate are coated with non – Platinum Group Metal (PGM) catalysts such as cobalt oxide and vanadium pentoxide as catalysts using sol–gel dip-coating technique. Both the catalytic converters are tested with gasoline, E10, and E20 blends in SI engine. The emission results show 17.39% higher conversion efficiency than conventional shaped Three-way catalytic converter (TWC). The catalytic converter with the novel shaped substrate is insulated with Phase Change Material (PCM) to reduce cold-start emissions. From the cold start study, it was concluded that the PCM-KOH insulated catalytic converter is found to be the most efficient way to resolve the cold start emissions with 75% higher conversion efficiency than a conventional TWC.