Automotive Exhaust Emission Control Using Perovskite Catalysts Prepared By Mechanochemical Synthesis

Abstract

One of the main sources of air pollution in large cities is automotive exhaust gas emissions which contain pollutants like CO, HC, NOX and particulate matter. These pollutants have negative impact on air quality, environment and human health that leads in stringent norms of pollutant emission. These regulations require the need for more active and durable emission control system. Highly efficient durable emission control system is Three Way Catalytic Converter with noble (Platinum Group – Pt, Pd and Rh) metals for treatment of pollutants such as CO, HC and NOX . Noble metals pose problems due to limited resources, expensive as it is noble metals, it vaporize and metal lost at high operating temperature of exhaust, so it is necessary for a researcher to search for new catalytic material that reduce or replace the noble metals for auto exhaust applications. Perovskite oxides of general formula ABO3 (where A and B are usually rare earth and transition metal cations respectively) is promising alternatives to supported noble metals for treatment of pollutants such as CO, HC and NOX from auto exhaust because of their low cost, good thermal and mechanical stability at high temperatures and excellent redox properties. During synthesis of perovskite, high calcination temperature (around 800 °C) is require to form crystalline phase which sintered the perovskite catalyst and limits their practical application due to low specific surface area. To overcome the limitation of low specific surface area, perovskite phase synthesized on alumina or other support reported by many researchers. Large particle size due to sintering react with alumina support at high temperature and form undesirable phases like mullite and metal aluminates which also limits their application. To overcome above limitations, small amount of noble metals substitute into perovskite structure which can prevent their sintering, reduce losses due to volatilization at high operating temperatures and avoid reactions with the support that lead to catalyst deactivation and remarkably enhances the catalytic activity. Perovskites are mainly prepared by ceramic and wet chemical methods. These methods produce low specific surface area perovskite, they are complicated and relatively expensive to put into practice. To overcome the limitations of above conventional methods used for preparation of perovskites an improved high energy planetary ball mill has been adopted for reactive grinding. The reactive grinding method using improved planetary ball mill produces perovskites in an efficient, simpler and economical manner. Various parameters such as direction and revolution speed of sunwheel and jar, ball to powder ratio, milling time, extent of jar filling has been varied for synthesis of perovskites by reactive grinding method. In preparation of perovskites by reactive grinding method additives plays significant role by means of increasing specific surface area to enhance catalytic activity. Higher the specific surface area, results in low catalyst loading in catalytic converter. This project also includes kinetic study and time-on-stream activity over selected catalyst synthesized by reactive grinding method; Washcoating, fabrication and test run over catalytic converter.