Precipitable silver compound catalysts for the selective catalytic reduction of NOx by ethanol

Abstract

The Ag/Al 2O 3, Ag 3PO 4/Al 2O 3, Ag 2SO 4/Al 2O 3 and AgCl/Al 2O 3 catalysts showed high activities for the selective catalytic reduction (SCR) of NOx by ethanol. AgCl was highly crystalloid on Al 2O 3, however, AgCl/Al 2O 3 gave the highest catalytic turnover frequency (TOF) for NOx reduction among the four catalysts. Calculated Mulliken charges of Ag compounds support the TOF results. The activity test and characterization results confirm that Ag + is the active silver species for NOx reduction. The in situ FT-IR results of Ag 3PO 4/Al 2O 3, Ag 2SO 4/Al 2O 3 and AgCl/Al 2O 3 for NOx reduction further reveal a positive correlation between the high dispersion of Ag + and the formation of active intermediates (the enolic and –NCO species), indicating a similar reaction pathway to that of the ethanol-SCR over Ag/Al 2O 3. Using the precipitable silver compounds greatly facilitates the preparation of monolith Ag/Al 2O 3 catalyst for practical usage. In fact, the high performance of the AgCl/Al 2O 3 honeycomb catalyst was confirmed by heavy duty diesel engine bench tests.