Mechanistic causes of the hydrocarbon effect on the activity of Ag–Al2O3 catalyst for the selective reduction of NO
Ag–Al2O3 
 catalyst prepared by the sol–gel method was studied for the selective catalytic reduction 
 (SCR) of NO by various hydrocarbons (HC-SCR). The rates of NO reduction and hydrocarbon conversion depend strongly 
 on the type of hydrocarbon reductant; the rates were higher for the higher normal alkanes, higher 
 for alkene than alkane, and higher for normal alkane than branched alkane. The formation and reaction of 
 hydrocarbon-derived species adsorbed on the surface were investigated by in situ FTIR spectroscopy. The 
 apparent rate of acetate formation in the hydrocarbon + O2 reaction and the rate of nitrate reaction in hydrocarbon + O2 
 also depend on the nature of the hydrocarbon with a similar activity pattern to that for the SCR 
 reaction. For the various hydrocarbons used, the rate of nitrate reaction in hydrocarbon + O2 
 was close to the steady-state 
 rate of NO reduction, indicating that the nitrate is a possible intermediate in this reaction. The reaction 
 of nitrates with oxygenated hydrocarbon species, possibly the acetate, was proposed to be a crucial step in HC-SCR. A proposed mechanism explains the hydrocarbon effect on the de-NOx activity: the NO reduction 
 activity depends on the reactivity of the hydrocarbon molecule, which affects the rate of hydrocarbon oxidation 
 to oxygenates 
 and hence the rate 
 of nitrate reaction with oxygenated hydrocarbons.