Effect of formaldehyde on selective catalytic reduction of nitrogen oxides by ammonia on V2O5 WO3 TiO2 catalysts This dissertation studies on the effect of HCHO a side product from the uncompleted combustion of fuel to the selective catalytic reduction of NOx by ammonia. HCHO prefers to react with NH3 to form HCN as the main product leads to the decrease of NOx conversion and N2 selectivity. In situ FTIR reveals that the high surface acidity of catalyst will create a large enough of NH3 adsorbents for the reaction of HCHO to form HCONH2. In addition in situ EPR experiments indicate that the high redox property of catalyst also facilitates the rate of HCONH2 formation.<eng>