Non-oxidative aromatization and ethylene formation over Ga/HZSM-5 catalysts using a mixed feed of methane and ethane

Abstract

The effects of the total number of acid site and gallium loading on Ga/HZSM-5 catalysts for non-oxidative aromatization and ethylene formation were investigated using a mixed feed of methane and ethane, analogous to shale gas. When the acid sites of the catalysts increased with the change in the Si/Al ratio, the total conversion of hydrocarbons and the total yield of BTX and ethylene increased, but the selectivity of ethylene tended to decrease. This suggests that the Brønsted acid sites of catalysts is responsible for the dispersion of gallium species and the aromatization of intermediate. On the other hand, when the gallium loading of HZSM-5(15) catalysts increased from 1.0 to 7.0 wt%, the ethylene yield increased, but the BTX yield decreased. The excessive gallium loading resulted in the drastic change of textural properties and the dealumination leading to the decrease of Brønsted acid sites, which caused the decrease of BTX selectivity and the increase of ethylene selectivity. In addition, with the increase of the gallium loading of the HZSM-5(15) catalysts, while the ethane conversion did not change, the methane conversion and ethylene yield gradually increased. This suggests that the dehydrogenative coupling of methane was promoted by the gallium species formed at high gallium loading catalysts such as gallyl ion. Characterizations by N2 adsorption/desorption, ICP-AES, XRD, XPS, TEM, NH3-TPD, pyridine FT-IR, H2-TPR, AAS, and 27Al NMR were used to investigate the relationship between the catalytic performance for aromatization and ethylene formation.