Preparation Of Transition Metal Cr-based Catalysts And Its Catalytic Performance For Methane Combustion

Recently, much more attention has been paid to the utilization of natural gas due to the decrease of the petroleum reserves in the world. In this condition, developing an efficient and environmentally-friendly route for the use of natural gas is highly desired. The catalytic combustion, as a route of high combustion efficiency and high energy efficiency, has received extensive attention compared to the conventional flame combustion. In this study, we focused on the effect of supported catalysts on the catalytic combustion of methane, including the types of metal active components, supports, promoters and the preparation of catalysts. We comprehensively study on Cr-based catalyst and Co-based catalyst modified by Ce. The following results and conclusions were obtained:1. The metal active component played an important role in the catalytic methane combustion. Taking γ-Al2O3as the support, the activity of Cr, Mn, Co, Cu and Fe supported catalysts followed the Cr> Mn> Co≈Cu> Fe in the descending order at the same conditions. Among these catalysts, Cr/γ-Al2O3catalyst exhibited the best catalytic activity of methane combustion and the light-off temperature and completely combustion temperature of methane combustion on Cr/γ-Al2O3is359℃and486℃, respectively.2. The activity of Cr-based catalyst in the catalytic methane combustion can be improved by choosing appropriate precursors of metal, promoters and the loading of Cr. Taking chromium chloride as the precursor, the Cr-based catalyst with30wt%Cr loading was modified by the CeO2promoter. We found that the light-off temperature and completely combustion temperature of methane combustion on30Cr3Ce/Al2O3catalyst could be decreased to320℃and420℃, respectively. Besides, the stability of Cr-based catalyst in the high temperature was increased during the methane combustion. The reason is that the Cr species mainly exists as Cr6+in the form of tetrahedral chromate [CrO4]ads before CeO2addition. However, the activity of methane catalytic combustion depends on the transition of Cr species between Cr3+and Cr6+. Interestingly, the transient Cr5+was formed and the process of oxidation reduction was favored after CeO2addition. Besides, the modification of support by CeO2could also increase the combustion performance of methane by influencing the valence and increasing the lattice oxygen of catalyst.3. The catalytic performance has been decreased when amplification prepared with industrial scale. The catalytic activity improved by secondary dipping. The methane conversion of laboratory catalyst and amplification catalyst were27.3%and19%at350℃, after time on stream of80h, the methane conversion were26.5%and18.1%, respectively. 4. To further decrease the light-off temperature and completely combustion temperature of methane combustion on Cr-based catalyst, the Pd was used to modify the Cr-based catalyst by optimizing the progress of catalyst preparation. Results show that the light-off temperature and complete combustion temperature was obviously decreased to290℃and390℃. In addition, the addition of CeO2can restrain the sinteringγ-Al2O3, and relieve the decline of specific surface area and the catalyst activity.5. Supports have little influence on the Co catalysts modified by Ce. When nano-γ-Al2O3was used as the support and the mass ratio of Ce/Co is5:5, the light-off temperature and completely temperature of methane combustion on the5Co5Ce/Al2O3catalyst are398℃and560℃, respectively.