(544db) Investigating the Effect of Addition of Potassium to the Mo/HZSM-5 during the Non-Oxidative Conversion of Methane to Aromatics

Mo/HZSM-5 catalysts with different Mo loadings (2,5 and 10 wt%) were prepared by incipient wetness impregnation method and their activity for non-oxidative methane conversion was studied using a recirculating batch reactor. K-Mo/HZSM-5 catalysts were prepared by sequential impregnation method where Mo is first impregnated. Three different set of catalysts with K loading of 0.5%, 0.8% and 1.2% were prepared with Mo weight percentage of 2,5 and 10. All the catalysts were characterized using Brunauer-Emmett-Teller (BET) surface area analysis, X-ray Diffraction (XRD), Scanning Electron Microscopic analysis (SEM), n-propylamine Temperature Programmed Desorption (TPD), Temperature Programmed Reduction (TPR) and Temperature Programmed Oxidation (TPO) to understand the physicochemical properties of the catalysts. In case of Mo/HZSM-5 the coking was high when compared to K-Mo/HZSM-5 catalyst. The n-propylamine TPD showed that with addition of K to the Mo/HZSM-5, there was a decrease in total acid sites present in the zeolite supported catalyst. These acid sites highly enhance the oligomerization reaction and results in coke formation. When potassium was loaded to the catalyst few of the strong acid sites were replaced by this potassium species. Thus, the acidity of the support decreased and the coking was reduced. The TPO results also showed that weight loss in a K-Mo/HZSM-5 catalyst was lower when compared to the weight loss in Mo/HZSM-5 catalyst. This confirmed that coke formed on the catalyst was reduced on addition of potassium. But as the potassium loading increased, the yield of aromatics decreased. Therefore, to improve the selectivity of aromatics and reduce coking, lower loading of potassium is required.