The enhanced performance of Ti doped MnOx for the removal of NO with NH3

Abstract

• Ti doped MnO x show an excellent SCR activity below 200 °C and above 300 °C. • Ti doping yields amorphous oxides, developed pore structure and more Mn 4+ . • Ti doped to MnO x brings more acid sites with proper acid strength. • Mn 1 Ti 1 O x forms more nitrites and shows a better low-temperature SCR activity. • Nitrates and strong NH 3 adsorption over Mn 1 Ti 2 O x delay the deactivation. Ti doped MnO x catalysts for the removal of NO with NH 3 (NH 3 ‒SCR) were prepared by coprecipitation method. The results showed that pure MnO x is composed of dominant Mn 3 O 4 with (101) plane and small amorphous MnO 2 , while TiO x only forms anatase TiO 2 . When Ti is doped into MnO x , as-prepared samples can form amorphous phase, and Mn 1 Ti 2 O x samples achieve 446 m 2 /g of specific surface area and 0.65 cm 3 /g of total pore volume. NH 3 can be adsorbed on MnO x and TiO 2 surface, but the former is weak and the latter is strong. Ti doping changes the acid site distribution and surface adsorbed oxygen of MnO x . Mn 1 Ti 1 O x has more available oxygen vacancies to produce NO 2 and achieves a good deNO x activity below 200 °C. With the increase of reaction temperature, more O 2 can be dissociated into O ‒ , causing that Mn‒containing catalysts show a complete NO removal at 200‒300 °C. When the temperature is higher than 300 °C, adsorption and activation of NH 3 become the rate‒determining step with the strong supply of NO 2 . TiO x can achieve 30% NO removal efficiency while MnO x is 100% at 200‒300 °C. Mn 1 Ti 1 O x samples have 95% of NO removal efficiency at 100 °C and maintain 100% in the range of 150‒320 °C. Nearly 100% N 2 selectivity is attained for all samples in the range of 80–160 °C, but the N 2 selectivity gradually decreases when the temperature is higher than 200 °C.