Influence of Calcination Temperature over Vanadium-Molybdenum Catalysts for the Selective Catalytic Reduction of NOx with NH3

A coprecipitation approach was used to prepare vanadium-molybdenum composite oxide catalysts, which were then calcined at 300, 400, 500, 600, and 700 degrees C. The vanadium-molybdenum catalyst, under calcination at 500 degrees C, possesses abundant surface defects and acid species. As a result, it showed an outstanding active window, achieving over 90% NOx conversion efficiency within the temperature range of 220-340 degrees C. Compared with other catalysts, the vanadium-molybdenum catalyst with the calcination at 500 degrees C resulted in the formation of polymeric vanadate with the most active oxygen, which was conducive to the high catalytic efficiency for the NH3-SCR reaction. Based on our in-depth understanding gained from in situ DRIFTS experiments, we proposed that the NH3-SCR reaction occurred on the vanadium-molybdenum catalyst via an Eley-Rideal pathway. This mechanism involves the initial adsorption of ammonia on the catalytic surface, followed by its interaction with weakly adsorbed or gaseous NO to form an activated complex. Furthermore, the presence of molecular oxygen (O-2) serves to augment the adsorption and activation of nitric oxide over the catalytic surface. The augmentation arises from the generation of adsorbed NO2 species or nitrates, which possess pronounced oxidizing capabilities. Notably, the significant impact of NH3 and NO in the denitration reaction was elucidated, providing valuable insights that can guide the adjustment and optimization of practical operational conditions. This understanding is crucial for enhancing the efficiency and effectiveness of the denitration process, thereby contributing to improved environmental qualities.