Selective catalytic reduction of NOx over Ag/Al2O3 catalyst: from reaction mechanism to diesel engine test

Our recent research works on the selective catalytic reduction (SCR) of diesel engine NOx by hydrocarbons over alumina-supported silver (Ag/Al2O3) were reviewed. The reaction mechanism of the SCR of NOx by C2H5OH over Ag/Al2O3 was studied using in situ DRIFTS and DFT calculations. A novel enolic species originating from the partial oxidation of C2H5OH and C3H6, was found on the surface of Ag/Al2O3 during the SCR of NOx by in situ DRIFTS, which was also supported by DFT calculations. Based on this, a mechanism of the NOx reduction was proposed, which can successfully explain the high efficiency of the NOx reduction by C2H5OH over Ag/Al2O3. A palladium promoted Ag/Al2O3 catalyst (denoted Ag–Pd/Al2O3) was developed for the SCR of NOx by C3H6. The Ag–Pd/Al2O3 showed a higher NOx conversion than Ag/Al2O3, especially at temperatures ranging from 300 to 450 °C. The engine bench tests showed that the average NOx conversion was greater than 80% in the diesel engine exhaust temperature range of 300–400 °C using our catalytic converter with C2H5OH as reductant, which represents a leap from the Euro II standard to the Euro III standard for NOx emission control in diesel engines.