Effects of oxygen and hydrogen chloride on NO removal efficiency by Rh/Al2O3 and Rh–Na/Al2O3 catalysts

The influences of oxygen, hydrogen chloride, and sodium modification on the activity of the Rh/Al2O3 catalyst for NO removal were investigated in simulated waste incineration conditions. The characterizations of the catalysts were analyzed by SEM/EDS, XRD, and ESCA. Experimental results indicated that the Rh/Al2O3 catalyst has high stability and activity for NO removal over a range of 0–20% O2. The addition of Na promoted the activity and N2 selectivity of the Rh/Al2O3 catalyst, but an increase in NO2 selectivity was observed when oxygen concentration and reaction time increased. The Rh/Al2O3 catalyst gradually deactivated on both NO and CO conversions when HCl concentration increased to 500 ppm because of the formation of RhCl3. The Rh–Na/Al2O3 catalyst has a low activity for NO conversion, but 100% CO conversion still remained even though 500 ppm HCl was contained in the feed gas. The Na added to the Rh/Al2O3 catalyst can react with HCl to form NaCl, resulting in a suppressed deactivation for Rh active sites. Low HCl concentrations do not affect NO2 selectivity of the Rh/Al2O3 catalyst but do decrease that of the Rh–Na/Al2O3 catalyst.

The SEM-mapping images show that the observed Cl elements dispersed on the surface of the catalysts. The existence of Al, O, Rh, Na, and Cl elements was further checked and could be observed from the results of EDS patterns. The peak intensity of Cl in the Rh/Al2O3 catalyst was significantly higher than that in the Rh–Na/Al2O3 catalyst.Figure optionsDownload as PowerPoint slide