In 2O 3/Al 2O 3 Catalysts for NO x Reduction in Lean Condition

The lean NO x performance and catalytic properties of In 2O 3/Al 2O 3 catalysts were investigated. High lean NO x activity was observed when propene was used as a reductant in the presence of 9% O 2 and 7% H 2O at a space velocity of 30,000 h −1. The optimum lean NO x activity of In 2O 3/Al 2O 3 catalysts was observed at a loading of 2.5 wt% indium on γ-Al 2O 3 which was prepared by a sol–gel technique (230 m 2/g). When propane was used as a reductant, the In 2O 3/Al 2O 3 catalyst did not promote NO x reduction compared to the alumina substrate. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and temperature-programmed reduction (TPR) have been used to characterize a series of In 2O 3/Al 2O 3 catalysts to increase understanding of the surface structure of indium oxide species on the alumina support. The XRD data indicated that crystalline In 2O 3 was present at In 2O 3 loadings >5 wt% and the quantity of the crystalline phase increased as a function of indium loading. XPS results suggested that indium oxide existed as a well-dispersed phase up to 10 wt% indium. The well-dispersed or reducible indium oxide species below 400°C in TPR experiments were assigned as the sites which activate propene to oxygenated hydrocarbons such as acetaldehyde and acrolein. Alumina sites readily utilize the oxygenated hydrocarbons to reduce NO x . A bifunction mechanism was proposed to explain high NO x reduction over In 2O 3/Al 2O 3 catalysts.