Selective catalytic reduction of NO x over Ag/Al 2O 3 catalyst: from reaction mechanism to diesel engine test

Abstract

Our recent research works on the selective catalytic reduction (SCR) of diesel engine NO x by hydrocarbons over alumina-supported silver (Ag/Al 2O 3) were reviewed. The reaction mechanism of the SCR of NO x by C 2H 5OH over Ag/Al 2O 3 was studied using in situ DRIFTS and DFT calculations. A novel enolic species originating from the partial oxidation of C 2H 5OH and C 3H 6, was found on the surface of Ag/Al 2O 3 during the SCR of NO x by in situ DRIFTS, which was also supported by DFT calculations. Based on this, a mechanism of the NO x reduction was proposed, which can successfully explain the high efficiency of the NO x reduction by C 2H 5OH over Ag/Al 2O 3. A palladium promoted Ag/Al 2O 3 catalyst (denoted Ag–Pd/Al 2O 3) was developed for the SCR of NO x by C 3H 6. The Ag–Pd/Al 2O 3 showed a higher NO x conversion than Ag/Al 2O 3, especially at temperatures ranging from 300 to 450 °C. The engine bench tests showed that the average NO x conversion was greater than 80% in the diesel engine exhaust temperature range of 300–400 °C using our catalytic converter with C 2H 5OH as reductant, which represents a leap from the Euro II standard to the Euro III standard for NO x emission control in diesel engines.