Study On Pd/Al₂O₃ Catalyst Modified By Additives For Catalytic Combustion Of Methane In High Concentration CO₂ Atmosphere

For the waste gas pollution control,catalytic combustion method has been considered as one of the most widely used control technologies.The waste gas from rectisol process is organic waste gas with huge emissions in the coal chemical industry.Because of high concentrations of CO₂contained in the waste gas from rectisol process,it is difficult to effectively burn organic pollutants contained.Therefore,it is of great significance to develop a catalyst for efficiently burning organic pollutants in a high concentration CO₂atmosphere for the environmental management of the coal chemical industry.This study aims to achieve efficient catalytic conversion of low-concentration organic pollutants.Focusing on the precious metal Pd/Al₂O₃catalyst and selecting CH₄as the model compound,this thesis study on the effects of the types of additives and preparation conditions such as doping methods,additive doping amount,modified support calcination temperature on catalytic performance of the low concentration CH₄combustion over catalyst in high concentration CO₂atmosphere in order to develop a catalyst with excellent catalytic oxidation performance in a high-concentration CO₂environment,and to reveal the reason for the improved performance of the catalyst.The main conclusions are as follows:（1）The Pd/Al₂O₃catalyst was modified by doping Ni,Mg,Co,Cr,Ba,Fe by using the impregnation method,and catalytic performance of methane combustion over Pd/MAl catalysts in high concentration CO₂atmosphere was investigated.Through various characterization tests,it was found that catalytic activity of Pd/Al₂O₃catalyst was enhanced after doping Ni,Mg,Co,respectively,and catalytic activity of Pd/Al₂O₃catalyst was decreased after doping Cr,Ba,Fe,respectively;The Pd/NiAl catalyst showed the best methane catalytic activity in high concentration CO₂atmosphere.The main reason is that the doping of Ni,Co and Mg increases the content of Pd²⁺species and active adsorbed oxygen species of catalyst,and reduces the acidity of the support.In addition,the spinel phase produced by the interaction with the Al₂O₃support is beneficial to stabilize the active component Pd O and improve the dispersion of the active component Pd O.（2）The effects of impregnation method,sol-gel method,co-precipitation method and hydrothermal method on the catalytic performance of methane combustion over Pd/NiAl catalyst were comparatively studied.The test found that the Pd/NiAl catalyst synthesized respectively by the impregnation method and the sol-gel method showed the best catalytic activity of methane combustion under high concentration CO₂atmosphere,followed by the co-precipitation method,and the hydrothermal method was the worst.（3）The effect of Ni doping on the catalytic performance of methane combustion over Pd catalyst was studied,and Pd catalyst with 10Ni/Al₂O₃as support was developed for methane combustion.Through characterization analysis,the result shows that the high concentration of Pd²⁺species and adsorbed oxygen species in the Pd/10NiAl-SG catalyst jointly promote the methane catalytic combustion reaction;meanwhile,the interaction between the Pd O and NiAl₂O₄spinel phases in the Pd/10NiAl-SG catalyst is effectively improves dispersion of the active component Pd O on the support and reduces the size of Pd particles.Too much NiAl₂O₄spinel will make the active component-support interaction too strong,which is not conducive to methane combustion catalytic reaction.（4）The effect of the calcination temperature of the support on the catalytic performance of methane combustion over Pd catalyst was investigated.When the calcination temperature range is 450-800℃,increasing the calcination temperature can improve catalytic activity of methane combustion.Above800℃,the catalytic activity of methane combustion can not be further improved.The analysis shows that within a certain temperature range,increasing the calcination temperature will increase the content of the spinel phase of NiAl₂O₄,thereby improving catalytic activity of methane combustion.