Review of Ag/Al₂O₃-Reductant System in the Selective Catalytic Reduction of NO _x

Ag/Al2O3 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/Al2O3 catalyst are reviewed, including the efficiencies and sulfur tolerances of different Ag/Al2O3-reductant systems for the SCR of NO (x) ; the low-temperature activity improvement of H-2-assisted HC-SCR of NO (x) over Ag/Al2O3; and the application of a Ag/Al2O3-ethanol SCR system with a heavy-duty diesel engine. The discussions are focused on the reaction mechanisms of different Ag/Al2O3-reductant systems and H-2-assisted HC-SCR of NO (x) over Ag/Al2O3. A SO2-resistant surface structure in situ synthesized on Ag/Al2O3 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/Al2O3-ethanol system is promising for catalytic cleaning of NO (x) in diesel exhaust.