Hydrogen applications in selective catalytic reduction of NOx emissions from diesel engines

Diesel engines have been considered as a major source in nitrogen oxide (NO_x) formation worldwide. The widespread use of diesel engines in consequence of their low fuel consumption, high durability and efficiency increases NO_x emissions day by day. NO_x emissions from diesel engines cause unavoidable damage on environment and people health. Although so many technologies such as exhaust gas recirculation (EGR), lean burn combustion, electronic controlling fuel injection systems, etc. have been developed to control NO_x emissions from diesel engines, they couldn't meet the desired reduction in NO_x emissions. In any case, Selective Catalytic Reduction (SCR) as one of the most promising aftertreatment-emission control technologies is an effective solution in restriction of NO_x emissions. The use of SCR systems especially in heavy-duty diesel powered vehicles has been increasing nowadays. In these systems, to use of hydrogen (H₂) as a reductant or promoter have been improved the conversion efficiency especially at low exhaust temperatures. Many researchers have been focused on the use of H₂ in SCR systems for controlling NO_x emissions.In this study, the applications of H₂ in SCR of NO_x have been discussed. The studies on use of H₂ in SCR of NO_x emissions were examined and the effects on NO_x conversions were determined. Consequently, it is confirmed that H₂ is a promising and alternative reductant in SCR of NO_x and it has been kept as an attracting subject for many researchers.