Studies On Methane Aromatization Over Mo/HZSM-5 Catalysts Modified By Some Rare Earth Elements

The main purpose of this research is to convert methane into benzene by direct aromatization on RE-modified Mo/HZSM-5 catalysts in the absence of oxygen. The experimental results have show that the addition of some rare earth elements (RE=Y,La,Er,Eu,Yb) can improve the activity and stability of the catalyst remarkably. The conversion of methane and selectivity to benzene were 19.3%, and 97.5% respectively at 1023K on the catalyst modified by Eu(Eu/Mo molar ratio was 0.04) which was prepared by co-impregnation. Compared with the non-RE-modified Mo/HZSM-5 catalyst elevation value of methane conversion was 5.6% and the enhanced degree was 40.8%. The modern physical and chemical characterization methods, such as XRD, XPS, TPD, IR, TG. DTA, SEM-EDX, isopropyl alcohol decomposition, ammonia-extraction, plus-CS₂ poisoning test, were applied to study the composition, surface structure and reaction performance of Mo-RE/HZSM-5. The informations about of the interaction of rare earth and molybdenum species, the molybdenum species states and the acidity of support were obtained. The results have revealed that rare earth elements can increase acidity of support, change coordination environment around molybdenum species, increase binding energy of Mo(3d) and enrich molybdenum on the surface layer. The variations of catalysts after reaction and the deposited carbon over the catalysts were analyzed and characterized by XPS, TEM and TG-DTG etc.. The results have show that deposited carbon, which can be removed by hydrogenation at reaction temperature, leaded to the catalyst deactivation. It was found that the catalyst was inactive when the total amount of deposited coke...