Selective catalytic reduction (SCR) of nitric oxide (NO) with ammonia over vanadia-based and pillared interlayer clay-based catalysts



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Texas A&M University


The selective catalytic reduction (SCR) of nitric oxide (NO) with ammonia over vanadia-based (V2O5-WO3/TiO2) and pillared interlayer clay-based (V2O5/Ti-PILC) monolithic honeycomb catalysts using a laboratory laminar-flow reactor was investigated. The experiments used a number of gas compositions to simulate different combustion gases. A Fourier transform infrared (FTIR) spectrometer was used to determine the concentrations of the product species. The major products were nitric oxide (NO), ammonia (NH3), nitrous oxide (N2O), and nitrogen dioxide (NO2). The aim was to delineate the effect of various parameters including reaction temperature, oxygen concentration, NH3-to-NO ratio, space velocity, heating area, catalyst arrangement, and vanadium coating on the removal of nitric oxide. The investigation showed that the change of the parameters significantly affected the removals of NO and NH3 species, the residual NH3 concentration (or NH3 slip), the temperature of the maximum NO reduction, and the temperature of complete NH3 conversion. The reaction temperature was increased from the ambient temperature (25?C) to 450 ?C. For both catalysts, high NO and NH3 removals were obtained in the presence of a small amount of oxygen, but no significant influence was observed from 0.1 to 3.0% O2. An increase in NH3-to-NO ratio increased NO reduction but decreased NH3 conversions. For V2O5-WO3/TiO2, the decrease of space velocity increased NO and NH3 removals and broadened the active temperature window (based on NO > 88% and NH3 > 87%) about 50?C. An increase in heating area decreased the reaction temperature of the maximum NO reduction from 350 to 300?C, and caused the active reaction temperature window (between 250 and 400?C) to shift toward 50?C lower reaction temperatures (between 200 and 350?C). The change of catalyst arrangements resulted slight improvement for NO and NH3 removals, therefore, the change might contribute to more gas removals. The catalyst with extra vanadium coating showed higher NO reductions and NH3 conversions than the catalyst without the extra vanadium coating.