Design And Preparation Of High Performance Catalyst For Methane Combustion

At present,the number of natural gas vehicles?NGVs?is increasing rapidly due to the ad,vanced shale gas and methane hydrate production technology and the advantages of low gas pollution.However,Methane has over 22 times greater greenhouse gas potential than that of CO2,so the unburned methane in the exhaust gas of natural gas can cause a serious greenhouse effect.The methane catalytic combustion process can effectively reduce the emission of methane,reducing the greenhouse effect while decreasing the energy loss.It is of great significance for the protection of the environment and the efficient use of energy.The catalytic methane combustion reaction can effectively reduce methane emission and energy loss,and prevent the global warming at the same time,which is essential to protect our environment.The CH₄ combustion reaction will reach high temperatures about 1300 ?.N₂ and O₂ will react to generate pollutant NOx,under this temperature.So it is obvious that the activity of the catalyst in low temperature region?300 ??500 ??is very important.In this research,we adopted three different methods to prepare varies Pd-based catalysts.Firstly,the Pd/MaMgbAlc-LTHs catalysts with different metal layers were prepared by adding different metal precursors.Secondly,commercial a-SiC was carbonized and N-doped by using CCl₄ and NH₃ as extractant.And then we obtained surface-modified Pd/C-SiC and Pd/N-C-SiC catalysts.Finally,an ordered mesoporous Pd/Al₂O₃ catalysts was synthesized by evaporation-induced self-assembly?EISA?method.Besides,the structure of these catalysts was analyzed by N₂ adsorption-desorption,X-ray diffraction?XRD?,transmission electron microscopy?TEM?,and hydrogen temperature-programmed reduction?H₂-TPR?.Also,the reasons that Pd based catalysts performed excellent activity in catalytic combustion of methane were studied in this research.The main conclusions were listed as follows:1.Pd/Co₂Mg₁Al₁-LTHs?Pd/Ni₂Mg₁Al₁-LTHs and Pd/Fe2Mg1Al1-LTHs catalysts were prepared through precipitation with 1 wt%Pd and calcined at 400 ?.And then the performance of these catalysts in methane combustion was investigated.The results showed that the Pd/Co₂MglAll-LTHs catalyst exhibited excellent activity and stability.N₂ adsorption and TEM showed that Pd/Co₂Mg₁Al₁-LTHs catalyst had the largest specific surface area,and there was strong interaction strength between Pd and Co-Mg-Al support,which increased the dispersion of Pd particles.At the same time,CO₂-TPD showed that the basicity of Pd/Co₂Mg₁Al₁-LTHs was stronger than those of Pd/Ni₂Mg₁Al₁-LTHs and Pd/Fe₂Mg₁Al₁-LTHs catalysts,which caused better activity of this catalyst.2.The specific surface area of C-SiC and N-C-SiC were increased by modifying the commercial a-SiC.The activity rank for these catalysts was Pd/N-C-SiC>Pd/C-SiC>Pd/SiC.Through analysis and comparison,it was found that the Pd/N-C-SiC which carbonized and N doping for 1 h respectively performed the best activity in methane combustion reaction.N₂ adsorption,XRD and TEM results showed that the promotion of activity was due to the better dispersion of Pd on C-SiC and N-C-SiC supports.But it was not determined by the specific surface area of the support entirely.3.The ordered mesoporous Al₂O₃ support was prepared by the EISA with 1 wt%Pd and 800 ? calcination temperature.The active component Pd was added and Pd/Al₂O₃-O and Pd/Al₂O₃-I were prepared by one-pot sythesis and impregnation method respectively.In addition,the activities of these catalysts were compared in methane combustion.The results showed that the activity rank for the catalysts was Pd/Al₂O₃-I>Pd/Al₂O₃-0>Pd/Al₂O₃-C.Moreover,the 10 h stability test showed that Pd/Al₂O₃-I had excellent stability.The results of N2 adsorption,XRD and H₂-TPR indicated that Al₂O₃ had a regular pore structure,Pd particles were uniformly dispersed on the surface of the support and interacted with the Al₂O₃ support strongly.