A mixed catalyst prepared by mechanically milling VW/TiO2 and low content of Pt/Al2O3 for SCO of high-concentration NH3

It is believed that high-concentration NH3 in exhaust gas needs to be removed for the application of marine NH3-fuel engines in the near future. Herein, a novel mixed catalyst with VW/TiO2 as the main component mixed with a small quantity of Pt/Al2O3 (denoted Pt-x@VW) was prepared by a facile mechanical milling method. Activity tests showed that the mixed catalyst exhibited superior low-temperature NH3-SCO performance compared to VW/TiO2 or Pt/Al2O3 catalysts. The results indicated that there was an obvious synergistic effect between VW/TiO2 and trace Pt/Al2O3, resulting in efficient NH3 oxidation by trace Pt/Al2O3 and selective catalytic reduction by VW/TiO2. In particular, when the mass ratio of Pt/Al2O3 to VW/TiO2 was 0.01, the corresponding mixed catalyst obtained complete NH3 conversion and a high N-2 selectivity of 80.2% at 300 degrees C. This was mainly ascribed to its excellent low-temperature redox property and enhanced NH3 oxidative ability. In situ DRIFTS results indicated that NH3-SCO reactions over a Pt@VW mixed catalyst followed both internal selective catalytic reduction (i-SCR) and hydrazine mechanisms at the same time. The active species on the surface of the Pt@VW mixed catalyst, including coordinated NH3 species, chemisorbed oxygen species and lattice oxygen species, participated in the NH3-SCO reactions.