A Review on Selective Catalytic Reduction of NOx by NH3 over Mn-Based Catalysts at Low Temperatures: Catalysts, Mechanisms, Kinetics and DFT Calculations

It is a major challenge to develop the low-temperature catalysts (LTC, < 250 degrees C) with excellent efficiency and stability for selective catalytic reduction (SCR) of NOx by NH3 from stationary sources. Mn-based LTC have been widely investigated due to its various valence states and excellent redox performance, while the poisoning by H2O or/and SO2 is one of the severe weaknesses. This paper reviews the latest research progress on Mn-based catalysts that are expected to break through the resistance, such as modified MnOx-CeO2, multi-metal oxides with special crystal or/and shape structures, modified TiO2 supporter, and novel carbon supporter (ACF, CNTs, GE), etc. The SCR mechanisms and promoting effects of redox cycle are described in detail. The reaction kinetics will be a benefit for the quantitative study of Eley-Rideal (ER) and Langmuir-Hinshelwood (LH) mechanisms. This paper also introduces the applications of quantum-chemical calculation using density functional theory to analyze the physic-chemical properties, explicates the reaction and poisoning mechanisms, and directs the design of functional catalysts on molecule levels. The intensive study of H2O/SO2 inhibition effects is by means of the combination analysis of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT), and the amplification of tolerance mechanisms will be helpful to design an excellent SCR catalyst.