Mixed Catalyst SmMnO/Cu-SAPO34 for NH-Selective Catalytic Oxidation.

Low-temperature selective catalytic oxidation (SCO) is crucial for removing the NH slip from the upstream of NH-selective catalytic reduction (NH-SCR). Herein, combining zeolite Cu-SAPO34 and the active oxidant mullite SmMnO, we developed mixed-phase catalysts SmMnO/Cu-SAPO34 by grinding powder mixtures to achieve a low-temperature activity and a reasonable N selectivity. The physicochemical properties of the catalysts were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) measurement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The evaluation of NH oxidation activity showed that for 30 wt % SmMnO/Cu-SAPO34, 90% NH conversion was at a temperature of 215 °C in the presence of 500 ppm NH and 21% O balanced with N. The in situ DRIFTS spectra reveal the internal SCR mechanism (i-SCR), i.e., NH oxidizing to NO on mullite and NO subsequently to proceed with SCR reactions, leading to higher conversion and selectivity over the mixed catalysts. This work provides a strategy to design the compound catalyst to achieve low-temperature NH oxidation via synergistic utilization of the advantages of each individual catalyst.