Selective catalytic reduction of nitric oxide with propene and diesel fuel as reducing agents over anodic alumina catalyst

A novel metallic monolith anodic gamma-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-NOx activity comparable to Pt/Al2O3/Al, a higher N-2 selectivity and a wider operating-temperature window than Pt/Al2O3/Al. In particular, adding SO2 into feedstream dramatically promoted the de-NOx 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-NOx activity was obtained on the alumite support, but at a high temperature (about 773 K). Although the presence of SO2 strongly inhibited the NOx reduction of the alumite support, NOx 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 NOx reduction of Pt/Al2O3/Al and Cu-Ce/Al2O3/Al. The alumite support became a promising choice, due to the stable 67% of de-NOx activity achieved under the same redox conditions. However, the presence of a high concentration of SO2 substantially depressed the de-NOx activity of the alumite support. On the contrary, a significant promotional effect of SO2 on the de-NOx activity was also observed over Cu-Ce/Al2O3/Al, when using diesel fuel as a reducing agent, as observed in the SCR-NO-C3H6.