Significance of Oxygen Storage Capacity of Catalytic Materials in Emission Control Application

Abstract

The fossil fuel run engines emit hazardous pollutants like CO, unburnt hydrocarbons, NOx, etc., due to partial burn of the fuel. These pollutants are converted to nontoxic elements like CO₂, H₂O and N₂ by the catalytic convertor before releasing in the atmosphere. To carry out the redox conversion of the pollutants in the fluctuating O₂ atmosphere of the real engine exhaust, CeO₂-ZrO₂ is used as an oxygen storage/release component of the catalytic convertor. High oxygen storage capacity (OSC) of the catalytic material usually ensures high conversion. The rare earth metal oxide CeO₂ exhibits OSC property by virtue of its reversible redox capability. The redox conversion is carried out by the participation of the lattice oxygen and adsorbed active oxygen species present on the CeO₂ surface. During the redox process, oxygen vacancies are generated on the catalyst surface, which consequently acts as the active centre for the next cycle of the catalytic reaction. Thus, the ease of oxygen vacancy formation along with other factors like the preparation/post-preparation treatment of the catalysts, presence of dopants, thermal treatment/ageing conditions, etc., strongly influences the OSC of CeO₂. In the present article, these factors have been discussed in brief. Hopefully, this compendium will be helpful to gain a preliminary idea on this topic, especially for the student community.