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Homogeneous dispersions and small size of deposited high-content cobalt on alumina were achieved by the co-precipitation method and were well maintained on the cobalt-based binary alumina catalysts with Zn, Ag, Fe, Cu or Ni as modifiers. The component and concentration of deposited cobalt species were characterized by UV–vis, EDX and XPS spectra and found to be greatly related to the Co loading, calcination temperatures and the type of additive metals. The optimal Co loading of 8 wt% and calcination temperatures of 800 °C were demonstrated. With respect to the single cobalt-based alumina catalyst, the surface concentration of Co 2+ on the binary catalysts with addition of Fe, Cu, Ag or Ni was all reduced and accompanying with part conversion of Co 2+ to Co 3 O 4 on the Fe and Ni-modified catalysts. A slight enhanced surface Co 2+ concentration was only achieved on the Zn-promoted catalyst. It was also demonstrated that for the case of Cu and Fe the additive metals themselves participated in the activation of propene. The octahedral and tetrahedral Co 2+ ions were suggested as the common active sites. A maximum deNOx activity of 96% was observed on the 8Co4ZnA800 catalyst at the reaction temperatures of 450 °C, and the catalytic performance on the cobalt-based binary alumina catalysts can be described as fellows: CoZn > CoAg, CoNi > Co Cu > CoFe. Based on the in situ DRIFT spectra, different reaction intermediates R–ONO and –NCO besides –NO 2 were formed on the 8Co4ZnA800 and 8Co4FeA800 samples, respectively, demonstrating their dissimilar reaction mechanisms. |
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