Preparation And Characterization Of Lam_1-xFe_xO₃（M=Ni And Co;0≤x≤1）Perovskite-type Catalysts For NO_x Removal

The perovskite-type oxides with a general formula of ABO3 have been widely used in various catalytic reactions because of their low price, good redox property, high stability and good sulfur tolerance. Moreover, their catalytic performances can be easily tuned through partial substitution of cations at A and/or B sites, resulting in generation of oxygen vacancies and modification of oxidation state. It is well known that the oxidation capability of perovskites mainly depends on cations at B sites, while A-metal site is responsible for stabilizing structure. Their synergetic interactions provide the probability of improving catalytic performance. Although a variety of La-based perovskite-type oxides have been reported through introducing other cations. In this dissertation, a series of LaM1-xF3xO3 (M=NL Co) were synthesized by sol-gel method and investigated in selective catalytic reduction (SCR). Moreover, SO2 resistance and regeneration performance of catalysts were also systemically investigated in NOX removal. The catalysts were well characterized by N2 physisorption, XRD, SEM, H2-TPR, O2-TPD, CO2-TPD, Raman and XPS. The main results were summarized as follows:(1) A series of LaNi1-xFexO3 (x=0,0.2,0.4,0.7, and 1.0) perovskites were synthesized and characterized. The perovskites were investigated for selective catalytic reduction of NOX by hydrogen (H2-SCR). It is shown that Fe addition into LaNiO3 leads to a promoted efficiency of NOX removal, as well as a high stability of perovskite structure. Moreover, easy reduction of Ni3+ to Ni2+ with the aid of appropriate Fe component mainly accounts for the enhanced activity.(2) LaNiO3 and LaNi0.6Fe0.4O3 were chosen to investigate sulfur resistance and regeneration. It is obtained that SO2 poisoning leads to an obvious decrease in NOx conversion for both catalysts. Nevertheless, sulfated samples can nearly recover to initial activities after 12 h of regeneration by H2. Moreover, it is obtained from XPS studies that sulfate species are not predominantly formed on active Ni component while doping of Fe partly involves in sulfation, resulting in an improved sulfur resistance.(3) The addition of 0.5 wt% Pt on the structure and performance of Pt/LaNi0.8Fe0.2O3 were synthesized and characterized. It was found that NOx conversion of in Pt/LaNi0.8Fe0.2O3 was higher than that of LaNi0.8Fe0.2O3. It can be attributed to Pt enhance the oxidation of NO to NO2, which is more facile than that of NO on the catalysts. Moreover, reduction properties and alkaline site were improved.(4) A series of perovskite-type LaCo1-xFexO3 (x= 0,0.5 and 1.0) were synthesized. The results demonstrate that SCR performances of Fe-substituted LaCo1-xFexO3 perovskite are higher than that of LaCoO3, and LaFeO3 possesses the best SCR properties with NOx. It may be due to reduction properties and desorption of surface oxygen species.