Study On Catalytic Oxidation Of Methane From Coal Mining Ventilation Air Over Modified Pd/Al₂O₃ Honeycomb Ceramics

Methane makes the second largest contribution to global warming after carbon dioxide and the methane emitted to atmosphere from coal mining is also a great waste of energy.About 70%of all mining-related methane emissions is ventilation air methane?VAM?and it has the characteristics of large volume,low methane concentration and unstable conditions.Owing to the lower reaction temperature and methane concentration requried by catalytic reaction,the catalytic combustion of VAM has obvious advantages.The monolithic catalyst has high mechanical strength and specific surface area.From the above,in this paper,the catalytic oxidation performance of Pd/Al₂O₃ modified by different metal oxides were studied using cordierite honeycomb ceramics.Pd/Al₂O₃ catalysts were prepared and tested for catalytic oxidation of ventilation air methane by addition of different metal?M=Ce,Ni,Ba,Mg,Fe,La and Mn?oxides,then the catalysts were characterized by XRD,SEM and other methods.The deactivation characteristics of the catalysts under humid environment and sulfur-containing atmosphere were studied as well.The results showed that:The catalysts modified by Ni and Mg react with Al₂O₃ at high temperature,forming NiAl₂O₄ and MgAl₂O₄ spinel;The change of the crystal phase of the supporter Al₂O₃ can reflect the sintering phenomenon on the catalyst surface.The catalysts modified by Ni and Mg have the distinct characteristic peak of?-Al₂O₃,while the catalysts modified by Fe and Mn showed that Al₂O₃ has changed to a more stable?state;the deactivation of the catalyst caused by water vapor is reversible;in the sulfur-containing atmosphere,the sintering of the surface and the accumulation of Pd particles are the main reasons for the reduction of catalytic activity.Secondly,the influence of modification on catalytic activity and thermal stability was studied.The temperature profile of the reaction zone during startup and shutdown was tested using a special honeycomb ceramic reaction device.The results showed that the catalytic reaction started at the outlet of the combustor and the high-temperature reaction peak moves from the outlet to the inlet over time;Pd/Al₂O₃ modified by Ni and Mg require a preheating temperature not lower than 340°C during startup.At temperatures below this value,the catalytic efficiency cannot increase with the reaction;there is a hysteresis loop of about 40°C during the startup and shutdown process;the production of CO in the reaction is almost negligible.Finally,the thermodynamic calculation software was used to simulate the catalytic oxidation process in honeycomb ceramics.The influence of the change of experimental parameters on the catalytic oxidation process was also analyzed.The results showed that the presence of catalyst can significantly reduce the temperature required for the oxidation of methane;the increase of methane concentration as well as wall temperature can improve the conversion of methane;at the preheating temperature of 350°C,the catalytic reaction begins at the outlet and after the preheating temperature reaches 450°C,the reaction starts at the inlet.