Study On Performance Of Pyrochlore-Type Composite Catalyst La₂Zr₂O₇ For Ventilation Air Methane Catalytic Combustion

In this paper,the pyrochlore-type La₂Zr₂O₇ catalyst was prepared by sol-gel method.The pyrochlore-type La₂Zr₂O₇/CeO₂,La₂Zr₂O₇/Co₃O₄ and La₂Zr₂O₇/CuO composite catalysts were further prepared by sol-gel symbiosis method and were applied to ventilation air methane combustion.The catalytic performance of these catalysts was tested by ventilation air methane catalytic combustion simulation system,and the phase,morphology and redox properties of the catalysts were characterized by XRD,BET,SEM,FT-IR,H₂-TPR,O₂-TPD and XPS,etc.1.The pyrochlore-type La₂Zr₂O₇ catalyst was prepared by four different complexing agents.Among them,the pyrochlore-type La₂Zr₂O₇ catalyst prepared by citric acid as a complexing agent in these four catalysts shows the most excellent catalytic performance in ventilation air methane catalytic combustion.The catalytic activity of the La₂Zr₂O₇ catalyst was T₁₀=485.7°C,T₅₀=588.8°C,and T₉₀=663.8°C.2.The La₂Zr₂O₇ was used as one of the main catalyst components and to introduce a promoter oxide with a mass fraction of 10%.The promoter oxides introduced are CeO₂,Co₃O₄,and CuO.And the composite pyrochlore-type catalysts La₂Zr₂O₇/10%B_x O_y?B=Ce,Co,Cu?were prepared by sol-gel symbiosis method.Thecatalyticactivityofthesefourcatalystsis La₂Zr₂O₇/10%Co₃O₄>La₂Zr₂O₇/10%CeO₂>La₂Zr₂O₇>La₂Zr₂O₇/10%CuO.Among them,the activity of La₂Zr₂O₇/10%Co₃O₄ catalyst has the optimal catalytical performance in this series of catalysts(T₁₀=396.3°C,T₅₀=533°C,T₉₀=622.4°C),which is 41.4°C lower than that of the complete conversion temperature of the pure phase La₂Zr₂O₇.3.The pyrochlore-type La₂Zr₂O₇/?X?Co₃O₄ series composite catalysts were mainly studied.Among them,the catalytic activity of ventilation air methane combustion of composite pyrochlore-type catalyst La₂Zr₂O₇/70%Co₃O₄ is significantly higher than that of the pure phase pyrochlore-type catalyst La₂Zr₂O₇.The catalyst had respectively T₁₀,T₅₀0 and T₉₀0 of 400.3°C,513.5°C and 597.4°C,and T₁₀0 and T₉₀0 decreased respectively by 139.8°C and 118.9°C relative to the pure phase La₂Zr₂O₇.The apparent activation energy of La₂Zr₂O₇/70%Co₃O₄ catalyst was calculated by kinetic fitting.The activation energy of the catalyst was 66.5KJ/mol,which was consistent with the activity sequence.And the optimum catalyst La₂Zr₂O₇/70%Co₃O₄also showed an excellent stability after certain stability experiments of cycling stability,hydrothermal stability and sulfur tolerance.What's more,X-ray photoelectron spectroscopy results show that there is a large amount of surface lattice oxygen on the surface of the pyrochlore-type composite catalyst La₂Zr₂O₇/70%Co₃O₄.This is the main reason why the pyrochlore-type composite catalyst La₂Zr₂O₇/70%Co₃O₄ has a good ventilation air methane catalytic combustion performance.4.The pyrochlore-type La₂Zr₂O₇/?X?CeO₂ series composite catalysts were studied.The results of XRD and SEDX showed that the target product was synthesized and no impurity phase was found.In this series of catalysts,the pyrochlore-type La₂Zr₂O₇/70%CeO₂ composite catalyst has the optimal catalytic combustion performance in the ventilation air methane.The T₁₀0 of the catalyst is442.2°C which is 43.5°C lower than that of the pure phase La₂Zr₂O₇ catalyst.The T₅₀0 is 515.2°C which is 73.6°C lower than that of the pure phase La₂Zr₂O₇ catalyst.The T₉₀0 is 590.8°C which is 73°C lower than that of the pure phase La₂Zr₂O₇catalyst.The proportion of the surface lattice oxygen content of the composite pyrochlore-type La₂Zr₂O₇/70%CeO₂ catalyst is 76.96%,while the surface lattice oxygen content of the pure phase pyrochlore-type La₂Zr₂O₇ catalyst is 62.07%,and the lattice oxygen content of the auxiliary CeO₂ surface is 54.97%.It shows that the introduction of proper proportion of additives can effectively improve the lattice oxygen content on the catalyst surface.