Methanol-to-aromatics conversion over H-Gallosilicate (MFI): influence of Si/Ga ratio, degree of H⁺ exchange, pretreatment conditions, and poisoning of strong acid sites

Abstract

The conversion of methanol to aromatics over H-gallosilicate (H-GaMFI) zeolite with different Si/Ga ratios and degrees of H⁺ exchange, calcined at different temperatures (600-1,100°C), and pretreated hydrothermally at different temperatures and partial pressures of steam, has been investigated in a pulse microreactor at 400°C. The aromatization activity and product distribution in the methanol-to-aromatics conversion are found to be influenced strongly by the above zeolite factors and calcination/pretreatment parameters. The aromatization activity of the zeolite shows a close relationship with its strong acidity (measured in terms of pyridine chemisorbed at 400°C). H-GaMFI and H-ZSM-5 zeolites (having almost the same Si/(Ga or Al) ratio and degree of H⁺ exchange and pretreated under similar conditions) have been compared for their catalytic activity/selectivity in the methanol-to-aromatics conversion and also for the poisoning of their strong acid sites by pyridine chemisorption at 400°C. H-GaMFI shows much higher aromatization activity. Unlike H-ZSM-5, H-GaMFI shows appreciable aromatization activity even after the poisoning of its strong acid sites or in the presence of only weak acid sites because of its higher dehydrogenation activity.