Review of Ag/Al2O3-Reductant System in the Selective Catalytic Reduction of NOx.

Ag/A1203 is a promising catalyst for the selective catalytic reduction (SCR) by hydrocarbons (HC) of NO_x in both laboratory and diesel engine bench tests. New developments of the HC-SCR of NO_x over a Ag/ A1₂O₃ catalyst are reviewed, including the efficiencies and sulfur tolerances of different Ag/ A1₂O₃-reductant systems for the SCR of NO_x; the low-temperature activity improvement of H₂-assisted HC-SCR of NO_x over Ag/ A1₂O₃; and the application of a Ag/ A1₂O₃-ethanol SCR system with a heavy-duty diesel engine. The discussions are focused on the reaction mechanisms of different Ag/ A1₂O₃-reductant systems and H₂-assisted HC-SCR of NO_x over Ag/ A1₂O₃. A SO₂-resistant surface structure in situ synthesized on Ag/ A1₂O₃ by using ethanol as a reductant is proposed based on the study of the sulfate formation. These results provide new insight into the design of a high-efficiency NO_x reduction system. The diesel engine bench test results showed that a Ag/ A1₂O₃-ethanol system is promising for catalytic cleaning of NO_x in diesel exhaust. [ABSTRACT FROM AUTHOR]