Perovskite And Graphite Carbon Nitride Used For Catalytic Elimination Of Dyes Wastewater And Automobile Exhuast

In this work, perovskite oxides with ABO₃ structure and graphitic carbon nitride?g-C₃N₄? were synthesized and their catalytic performancs for oxidative degradation of organic dye in aqueous solution and oxidation/reduction removal of CO, soot and NO emitted from exhaust were investigated.For the oxidative degradation of organic dyes in aqueous solution, we used perovskite oxides as Fenton-like catalyst for investigation. In order to increase the surface area of perovskite oxides and improve the contact area between the catalyst and the organic dyes, we synthesized supported perovskite oxides by depositing them on high-surface-area mesoporous silica SBA-15. Screening tests showed that LaFeO₃/SBA-15 and La–Cu–O/SBA-15 were active for the reaction and thus were selected for investigation in the following study. Characterizations such as XRD, TEM and N2 physisorption isotherms indicate that the supported catalyst has typical perovskite structure, and the ordered mesoporous structure of SBA-15 remains unchanged after the perovskite formation. LaFeO₃/SBA-15 and La–Cu–O/SBA-15 have good catalytic performances, wide working pH ranges?from 2 to 10?, low H2O2 consumption, stable oxidation activity for the oxidation of RhB and considerable activity for other dyes such as reactive brilliant red X-3B, direct scarlet 4BS, methylene blue. Especially, RhB is completely mineralized into CO2 at reaction time of 3 h by La–Cu–O/SBA-15 in the present reaction conditions. This is the best perovskite-type catalyst reported in literature for RhB degradation using H2O2 as oxidant to the best of our knowledge. The excellent catalytic performances of LaFeO₃/SBA-15 and La–Cu–O/SBA-15 catalyst is suggested to be due to a synergistic effect between perovskite and SBA-15, in which perovskite is the active site of the reaction and SBA-15 acts as a gallery to adsorb and transport the organic dyes from solution to the surface of catalyst.Perovskite oxides also exhibit great prospect in the removal of exhaust pollutants including CO, NO and soot. In this study, porous LaFeO₃ and LaCoO₃ prepared using PMMA colloidal crystals as template, were investigated as catalysts for the oxidation of CO and soot powder, and in order to illuminate their advantages in the reactions, bulk and supported LaFeO₃ and LaCoO₃ were synthesized and compared. On the other hand, because LaFeO₃ has better thermal stability than LaCoO₃, it thus was selected for further studies regarding the effect of vapor on the catalytic activity of CO and soot oxidation.Porous-LaCoO₃ showed improved catalytic activity for CO oxidation than SBA-15 supported LaCoO₃ and bulk LaCoO₃. The catalytic performances of porous LaCoO₃ for CO oxidation are comparable to that prepared with 3DOM structure, indicating that the structure of pores is not crucial to the reaction as long as the pores were created. The excellent CO oxidation activity of porous LaCoO₃ is suggested to be due to its large amount of exposed metal sites, high surface Co3+/Co2+ ratio and numerous oxygen vacancy, and is also justified from the low activation energy?Ea?.Similarly, porous LaFeO₃ exhibits the best activity to CO and soot oxidation relative to the bulk and supported LaFeO₃, because of its large surface area, strong surface reducibility and rich active lattice oxygen. Further studies indicated that porous LaFeO₃ also has strong resistance to vapor poisoning in CO and soot oxidation. The CO conversion of porous LaFeO₃ maintained over 60% even up to 13.5% vapor in volume and the decreased activity can be recovered when the vapor is switched off. This provides directions for the preparation of high performance industrial perovskite catalysts.Polymeric graphitic carbon nitride?CNx? can be used as support and catalyst in heterogeneous catalysis. In this paper CNx was used both as support to disperse Au and Pt nanoparticles?NPs? and as metal-free catalyst for NO decomposition. In the preparation of Au and Pt NPs, CNx was first impregnated on SBA-15 to prepare CNx/SBA-15 composite and its role is to provide site for Au/Pt adsorption. By changing the condensation temperature, the degree of condensation and the loading of CNx can be controlled, thus leading to adjustable particle sizes for the Pt and Au NPs subsequently formed on its surface. The high stability and strong interaction with noble metals of CNx helps to stabilize Au and Pt NPs during the reaction. Catalytic studies demonstrated that Pt/CNx/SBA-15 shows far higher activity for CO oxidation than Au/CNx/SBA-15, which is partly attributed to the reason that Pt NPs on CNx are partially oxidized, whereas Au NPs exist exclusively as Au0, as identified from XPS results, leading to different behaviors for oxygen activation.In case of the application as a metal-free catalyst for NO decomposition reaction, g-C₃N₄ exhibited certain activity even at 300-500 ?C, and the activity can be significantly improved when metal ions are incorporated into the structure of porous g-C₃N₄ prepared by soft template. Among the metals investigated, Zn is found to be the best one, the addition of which can improve the NO conversion up to 80%, and the optimum Zn percentage is 12.4wt%.