Selective Catalytic Reduction Of NO_x By H₂Over Pt Based Catalyst

Pt was carried on γ-Al2O3by using equal volume impregnation method. Pt/Al2O3was pretreated by calcinations, H2reduction, O2oxidation after H2reduction respectively. The results showed that the reduction-oxidation pretreatment was the best method. The performance of catalyst was enhanced after the addition of transition metals Co, Fe, Ni, Cu, in which Pt/Co/Al2O3had the best performance, besides the best Co content was2wt%and Pt was0.5wt%. Loading Pt after loading Co was better than loading Pt and Co at the same time. Adding Na or K had no good effect on Pt/Al2O3. When the reaction gas contained water, both of the NOx conversion of0.5PtH2-o2and0.5Pt2COH2-o2decreased, however the latter had much better performance against H2O than the former.XRD patterns proved that Pt and Co had high dispersion over γ-Al2O3. H2-TPR results showed that reduction-oxiditon pretreatment decreased the PtO2reduction temperature, besides this pretreatment formed the PtCo alloy after adding Co, which greatly enhanced the H2-SCR performance of catalysts. NO-TPD patterns showed that the NO absorption capacity of catalysts was greatly enhanced after the reduction-oxiditon pretreatment. Transient and steady state in situ DRITFS experiments confirmed that NO3-was formed from NO on the catalyst surface only after introduced O2to the reaction gas. In fact, H2reacted with NO3-to produce N2and N2O during the H2-SCR. H2reduction pretreatment could greatly increase the amount and stability of NO3-. Bidentate nitrate, bridging nitrate and chelating nitrite could transform into monodentate nitrate and nitrite, in addition the former three were active nitrogen intermediates.