The Research On The Synthesis And Catalytic Properties Of Pd/Co₃O₄/supporting For Methane Combustion

In recent years,more and more attention has been paid on the problem of environmental pollution caused by the use of traditional fossil resources.The efficient use of clean energy is considered to be an effective means to solve the problem.At present,natural gas is mainly used for natural gas vehicles and gas power plants,and how to remove the unburning methane exhausted by gas engines and gas-fired boiler attracted people’s attention.The chemical propertie of methane is very stable,for its four C-H bonds,and its traditional combustion requires really high temperature.But the presence of the catalyst can significantly reduce the combustion temperature of methane,with no NO_x and other toxic gases caused at high temperature.In this paper,we obtained Pd/Co₃O₄/supporting composites by coprecipitation-liquid phase mixing method.We investigated the effects of different oxide supportings,the acidity of the oxide supportings and the loading of Pd or Co₃O₄ on the catalytic activity of methane combustion,to obtain the Pd/Co₃O₄/alkaline-Al₂O₃ composites with low Pd content,good catalytic activity and strong stability.The details are as follows:1.We prepared six Pd/Co₃O₄/supporting composites,using alkaline-Al₂O₃（al-Al₂O₃）、SiO₂、ZrO₂、CeO₂、acid-Al₂O₃（ac-Al₂O₃）and neutral-Al₂O₃（ne-Al₂O₃）as oxide supportings,to investigate the effects of different oxide supportings on the catalytic activity of methane combustion.By comparing their catalytic behaviors on methane combustion,Pd/Co₃O₄/al-Al₂O₃ gave rise to the highest catalytic activity among the six Pd/Co₃O₄/supporting composites catalysts,that is,methane could be initially ignited at 250 ^oC and completely converted at 400 ^oC at the gas hourly space velocity of 30 000 m L/（g·h）.The catalytic activity order for methane combustion of these six catalysts is Pd/Co₃O₄/al-Al₂O₃>Pd/Co₃O₄/CeO₂>Pd/Co₃O₄/ZrO₂>Pd/Co₃O₄/SiO₂ and Pd/Co₃O₄/al-Al₂O₃>Pd/Co₃O₄/ac-Al₂O₃≈Pd/Co₃O₄/ne-Al₂O₃,indicating that Al₂O₃ was the best supporting among these four dofferent oxides on methane combustion,and alkaline properties was more better on same supportings.Through CH₄-TPR,O₂-TPD and XPS characterization,we found that Pd/Co₃O₄/al-Al₂O₃ had higher low-temperature reducibility,more surface adsorption oxygen species and higher Co²⁺species content,which could lead Pd/Co₃O₄/al-Al₂O₃ have better catalytic activity than the others Pd/Co₃O₄/supporting composites catalysts.2.We investigated the effects of the loading of Pd or Co₃O₄ on the catalytic activity of methane combustion,finding that 0.6 wt.%Pd and 9.4 wt.%Co₃O₄composites had the best catalytic activity of methane combustion.Then,we found that 0.6Pd/9.4Co₃O₄/al-Al₂O₃ had strong loop stability,high temperature stability and water vapour stability,for one of the reason that the used catalyst had no structural change and no sinting compared to the fresh catalyst,which was verified by the TEM,HRTEM and Mapping characterization.Finally,we used0.6Pd/9.4Co₃O₄/al-Al₂O₃ to catalyse the methane conversion in the simulation of the car exhaust atmosphere,leading pretty good catalytic results.