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

Abstract

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 N₂ selectivity of 80.2% at 300 °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.