Selective Catalytic Reduction of Nitric Oxide with Propene and Diesel Fuel as Reducing Agents over Anodic Alumina Catalyst

Abstract

A novel metallic monolith anodic γ-alumina catalyst, prepared through anodization of aluminum, hot water treatment and active metal impregnation, was employed to investigate the selective catalytic reduction of NO under oxygen-rich conditions with propene and diesel fuel as reducing agents.
Using propene as a reducing agent, Pt/Al₂O₃/Al offered the best low-temperature SCR activity (about 573 K), and was resistant to SO₂ poisoning. However, a high undesired selectivity to N₂O and a narrow operating-temperature window were two major disadvantages. At a moderate temperature (about 673 K), Cu-Ce/Al₂O₃/Al showed a favorable de-NO_x activity comparable to Pt/Al₂O₃/Al, a higher N₂ selectivity and a wider operating-temperature window than Pt/Al₂O₃/Al. In particular, adding SO₂ into feedstream dramatically promoted the de-NO_x activity of Cu-Ce/Al₂O₃/Al, and this increase was unchanged with time-on-stream. Among the catalysts tested in this paper, the highest de-NO_x activity was obtained on the alumite support, but at a high temperature (about 773 K). Although the presence of SO₂ strongly inhibited the NO_x reduction of the alumite support, NO_x conversion of 80% could still be maintained in the coexisting SO₂ and H₂O.
When introducing diesel fuel instead of propene as a reducing agent, the over-oxidation of diesel fuel by oxygen remarkably decreased the NO_x reduction of Pt/Al₂O₃/Al and Cu-Ce/Al₂O₃/Al. The alumite support became a promising choice, due to the stable 67% of de-NO_x activity achieved under the same redox conditions. However, the presence of a high concentration of SO₂ substantially depressed the de-NO_x activity of the alumite support. On the contrary, a significant promotional effect of SO₂ on the de-NO_x activity was also observed over Cu-Ce/Al₂O₃/Al, when using diesel fuel as a reducing agent, as observed in the SCR-NO-C₃H₆.