NH3-SCR Of NOx Research Articles

In situ DRIFTS and temperature-programmed technology study on NH3-SCR of NOx over Cu-SSZ-13 and Cu-SAPO-34 catalysts

In situ diffuse reflectance infrared Fourier transform spectroscopy (In situ DRIFTS), temperature-programmed desorption (TPD), and temperature-programmed surface reactions (TPSR) were employed to investigate the adsorption and reactive properties of Cu-SSZ-13 and Cu-SAPO-34 zeolite catalysts; these fully formulated washcoat cordierite monoliths were hydrothermally treated at 750°C in the simulated feed gases. The intrinsic mechanism and reasons for the differences in NH3-SCR activity were proposed based on the characterization results. The in situ DRIFTS and TPD results showed that ammonia could adsorb on both the Lewis and Brönsted acidic sites on these two catalysts; the ammonia on the Brönsted acidic sites might be active in the NH3-SCR reaction. For the different NOx adsorption processes, the total NOx desorption levels followed the following sequence: NO<NO+O2<NO2=NO2+O2. The results confirm that the reaction pathways are totally different in the low and high temperature ranges on the Cu-SSZ-13 and Cu-SAPO-34 catalysts. In the low temperature range, the ammonium nitrates from the reaction between surface ammonia and nitrates are the key intermediates and are further reduced to form N2 and H2O by the NO gas. In the high temperature range, the gas-phase NO2 gradually become more important in the NH3-SCR reaction. The activity tests indicated that the Cu-SAPO-34 catalyst had a relatively higher DeNOx performance than the Cu-SSZ-13 catalyst across the entire reaction temperature range, showing a double peak shapes with a dip point at approximately 390°C. Cu-SAPO-34 might retain many surface nitrate species and did not produce much more NO2 gas than Cu-SSZ-13; this species hindered the SCR reaction at 390°C.

Changes in the chemical composition of V2O5-loaded CVC-TiO2 materials with calcination temperatures for NH3-SCR of NOx

In this study, the aim was to evaluate the effect of calcinations temperature on the catalytic activity and chemical composition of V2O5/TiO2. We prepared V2O5-loaded CVC-TiO2 catalysts by a combination of chemical vapor condensation (CVC) and impregnation method at different calcination temperatures. These catalysts were analyzed for their ability to catalyze NH3-based selective catalytic reduction of NOx. Compared with V2O5 loaded P25-TiO2 (commercial). V2O5/CVC-TiO2 catalysts calcined above 200 °C exhibited better performance towards NOx conversion than that by a commercial catalyst prepared using P25-TiO2 (calcined at 500 °C). In addition, the NOx conversion rate obtained with the sample calcined at 500 °C gave the best result (90 %) at a reaction temperature of 200 °C. From the XPS results, we observed that the V4+/5+ ratio was well balanced when the V2O5 loaded CVC-TiO2 sample was calcined at 500 oC.