MnNiO spinel catalyst for high-efficiency selective catalytic reduction of nitrogen oxides with good resistance to HO and SO at low temperature.

Mn-Ni oxides with different compositions were prepared using standard co-precipitation (CP) and urea hydrolysis-precipitation (UH) methods and optimized for the selective catalytic reduction of nitrogen oxides (NO) by NH at low temperature. MnNiO-CP and MnNiO-UH (with Mn:Ni molar ratio of 2:1) catalysts showed almost identical selective catalytic reduction (SCR) catalytic activity, with about 96% NO conversion at 75°C and ~99% in the temperature range from 100 to 250°C. X-ray diffraction (XRD) results showed that MnNiO-CP and MnNiO-UH catalysts crystallized in the form of MnNiO and MnO-MnNiO spinel, respectively. The latter gave relatively good selectivity to N, which might be due to the presence of the MnO phase and high metal-O binding energy, resulting in low dehydrogenation ability. According to the results of various characterization methods, it was found that a high density of surface chemisorbed oxygen species and efficient electron transfer between Mn and Ni in the crystal structure of MnNiO spinel played important roles in the high-efficiency SCR activity of these catalysts. MnNiO catalysts presented good resistance to HO or/and SO with stable activity, which benefited from the MnNiO spinel structure and Eley-Rideal mechanism, with only slight effects from SO.