| Nitrogen oxide (NOx) as one of the major pollutants in the atmosphere, not only destroys the ecological environment, but also endangers human health. Therefore, how to effectively eliminate NOx from both mobile and stationary sources has become a hot topic in the world. Recently, it was found that H2-SCR offers a solution to this problem since H2 efficiently reduces NOx at relatively low temperature in this process. Therefore, the H2-SCR method has attracted more and more attention in the wide world.Lots of the investigation results in the literature reveal that Pt-based catalysts are more active than the other catalysts for the H2-SCR reaction at low temperature. In the present study, ZrO2 being doped with Nb2O5 was used as support of Pt by wet impregnation method, and the resulting catalyst was investigated for catalyzing the reaction. The influence on the textural structure and surface property of the support, on the chemical states of Pt in the catalyst, as well as on the surface species over the catalyst due to the addition of Nb2O5 into ZrO2 were investigated. In addition, the property of the catalyst resisting H2O/SO2 was also studied.It was found that both of the NOx conversion and the N2 selectivity were greatly increased for the catalyst of 0.5 wt.% Pt loading on the composite support than that on pure ZrO2 under the same reaction conditions. Furthermore, working reaction temperature window was also shifted to the lower for the former comparing with the latter. For the Pt/nNb2O5-mZrO2 (n/m= 1:20,1:6,1:4,1:2,1:1) catalysts tested in the reaction, the NOx conversion changed in a "volcano" shape with the ratio of n/m, and the maximum NOx conversion appeared over the 0.5 wt.% Pt/Nb2O5-2ZrO2 catalyst. Textural structure and surface property of the the composite support, as well as the activity of the catalyst were studied with powder XRD, pyridine adsorption FTIR and CO adsorption FTIR. It was found that the appropriated amount of Nb2O5 adding to ZrO2 accelerated the crystal transformation of the ZrO2 from the monoclinic to the tetragonal, increased the acid sites in population, in particular that with stronger acidity, suppressed the NOx adsorption on the support. At the same time, it suppressed the NOx adsorption on Pt as well, which made Pt remained its more metallic property, so that the Pt could adsorb more H2 molecules for activating them. All of the factor changes caused by the Nb2O5 addition were favorable for increasing the activity of the 0.5 wt.% Pt/Nb2O5-2ZrO2 catalyst.The activity of the 0.5 wt.%Pt/Nb2O5-2ZrO2 catalyst rapidly decreased upon 20 ppm SO2 was introduced into the feed gas at 100?. However, the activity recovered to a level that was very closed to the original level when the SO2 was cut off from the feed gas. On the other hand, the Pt/Nb2O5-ZrO2 catalyst exhibited a better resistance to H2O (5 vol.%) and H2-SCR activity. |
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