Promotion effect and mechanism of the addition of Mo on the enhanced low temperature SCR of NOx by NH3 over MnOx/γ-Al2O3 catalysts

A series of Mn/gamma-Al2O3 and MnxMn/gamma-Al2O3 catalysts were prepared by using Incipient Wetness Impregnation (IWI) method. The catalytic performance tests showed that the Mn3MnxMn/gamma-Al2O3 demonstrated a higher SCR performance (NO conversion of around 96%) at a broad low temperature range (150-300 degrees C). The characterization showed that the addition of Mo to the Mn/gamma-Al2O3 catalysts promoted the dispersion of MnO, on the surface of gamma-Al2O3. The adsorption of NO could form two different species, i.e., nitrites and nitrates, on the surface of the catalyst. The presence of nitrites is beneficial to low temperature SCR. It is found that the existence of Mo in the catalyst favours the formation of Mn-3, which plays a critical role in the adsorption of NH3 and therefore improves NH3 adsorption capacity of the Mn/gamma-Al2O3 catalysts. The low temperature SCR of the Mn3MnxMn/gamma-Al2O3 catalyst was found to mainly follow L-H mechanism, but E-R mechanism also plays a role to some extent. Moreover, it is found that the addition of Mo not only mitigates the deactivation of the catalysts, but also broadens the effective temperature range of the SCR catalysts.