Selective Catalytic Reduction Techniques for Postcombustion Control of Nitrogen Oxide Emissions From a Diesel Engine

Air pollution effects of nitrogen oxide emissions from diesel engines have now become a global crisis as the emissions greatly endanger environmental and human existence. The detrimental effects as a result of nitrogen oxide emissions include climate change, ozone layer depletion, skin cancer, respiratory and cardiovascular illnesses, and mortalities. Selective catalytic reduction is viewed as the most effective and feasible technique in the control of nitrogen oxide emissions. However, this after‐treatment method faces several setbacks that include poor cold start below 200°C, low catalytic activity due to poisoning effect, regulated reductants, and narrow operational temperature window. Therefore, in this review, we will consider discussing currently applied selective catalytic reduction catalysts that include noble metals, zeolites, manganese, copper, cerium, and iron. We will also highlight their benefits, limitations, and proposed potential future catalyst. Additionally, we will discuss various reducing agents including urea, ammonia, hydrocarbons, their potential for application, regulations imposed, merits, and demerits.