Research Support For Cobalt-based Catalytic Partial Oxidation Of Methane To Syngas

Partial oxidation of methane （POM） to syngas is a mild exothermic reaction. The ratio ofH₂to CO is2, which is very suitable for methanol and fuel liquid synthesis. Therefore, it is oneof the most important application routs of nature gas. This dissertation focuses on thecobalt-based catalysts for POM. The effects of the supports on the performance of methane par-tial oxidation had been studied by the combination of thermodynamic analysis andexperimentation. This work is of importance in developing novel catalysts for POM process.Thermodynamic analysis was carried out for studying POM, as well as the preparation,reduction and utilization of catalysts. It concludes that the carbon deposition couldn’t beavoided between700and800°C. Cobalt is prone to reacting with alumina or titanium speciesto form CoAl₂O₄and CoTiO₃, respectively. There is more Co₃O₄in the calcined Co/Ce-Ti-Zrcatalyst, which is the weak interaction between cobalt and ternary support. The metallic cobaltspecies can maintain under the O2flow in catalytic reaction, which is essential to generate thecatalytic active sites.Based on the thermodynamic analysis, the catalysts’ preparation and utilization conditionswere preliminary established. Then experiments were carried out. The results show that there isquite poor catalytic activity in the cobalt-based catalyst prepared with pure commercial alumina.However, the catalytic performance is improved remarkably by the strontium promoter. Stron-tium can weaken the interaction between active component and support. But the non-catalyticphase of CoAl₂O₄could be found under the high-temperature condition because of the limitedeffect of the strontium promoter. Although the mixed oxide of Al2TiO5in the Co/Al-Ti-1cata-lyst prepared by citric acid method could form, which could both restrain CoTiO₃and CoAl₂O₄;the catalytic performance of Co/Al-Ti-1is still lower than that of2Sr-Co/Al.There is high activity for Co/TiO₂and Co/ZrO₂on the initial stage of POM reaction. Butthe performance decreases under time on stream. The non-catalytic phase of CoTiO₃in Co/TiO₂,the coke and phase transition in Co/ZrO₂, are observed apparently. In comparison, Co/CeO₂isquite stable, but the low conversion of methane. Ce-Ti-O solid solution and mixed oxide ofCeTi2O6could form in the binary support of Co/Ce-Ti catalysts. But attribute to their poor ther-mal stability, the Co/Ce-Ti is not an optional candidate for POM. There is no solid solution inthe binary support of Co/Ti-Zr catalysts. Nevertheless, the mixed oxide of ZrTiO₄occurs inthese catalysts. The addition of zirconium could restrain the formation of CoTiO₃. Besides, inthe catalysts’ preparation process, the influence of chelates is investigated for POM. Amongthem, the catalyst used polyvinyl alcohol （PVA） shows the worst performance, which attributesto the low dispersion of cobalt. Ceria-zirconia solid solution could be found in the ternary sup- port of Co/Ce-Ti-Zr catalyst. Excellent catalytic performance and stability are obtained by thelattice defects of ceria-zirconia solid solution. But the obtained Co-Zr alloy decreases theperformance of Co/Ce-Ti-Zr calcined at900°C. While, there’s no CoTiO₃in this sample. Itseems the addition of ceria-zirconia can restrain the generation of CoTiO₃.The commercial alumina and Al-Ti composite support shows some acidity. While Ce-Ti,Ti-Zr and Ce-Ti-Zr exhibits very little acidity, or close to basicity. Owing to its high activityand stability, Co/Ce-Ti-Zr is an optimal catalyst for partial oxidation of methane.