Effects of MOx modification (M = Mn, Ce, and Fe) on the SCR catalytic properties of the CrOx-WOx mixed oxide catalysts

In this study, a series of MOx-modified (M = Mn, Fe, and Ce) CrOx-WOx mixed oxides were synthesized via the sol-gel technique for the selective catalytic reduction of NOx with NH3. Given the addition of MnOx or CeOx, the availability of the catalyst surface acid sites tended to decline, which negatively affected the proceeding of the deNO(x) process. Moreover, the retention of oxidative ability by introducing MnOx also favored the over-oxidation of NH3, which accelerated the additional formation of NOx and created a crucial barrier for the increment in the higher-temperature deNO(x) activity. Apparently, <80 % of the NOx could be effectively eliminated from the working gas within the whole temperature range for the CrCeW and CrMnW samples. By contrast, doping FeOx was able to introduce ample acid sites onto the catalyst surfaces, which was beneficial for the adsorption of NH3 and subsequently the facilitation of the progression of the deNO(x) process. Furthermore, the weakened oxidizability suppressed the over-oxidation of NH3. Consequently, a broad operating temperature window was obtained for the FeOx-doped catalyst; >90 % NOx conversion efficiency was achieved in the temperature range of 230-450 degrees C. During the deNO(x) process, the Eley-Rideal mechanism dominated over the four investigated samples.