Influence of O_2 and H_2 pretreatments on acidity/acid strength distribution and acid functions of Ga/H-ZSM-5, H-GaMFI and H-GaAl MFI zeolites

摘要

H-gallosilicate (H-GaMFI), H-galloaluminosilicate (H-GaAlMFI) and Ga, impregnated H-ZSM-5 (Ga/H-ZSM-5) zeolites pretreated with O_2 and H_2 (at 600°C for 10 h) have been characterized for their acidity/acid strength distribution (by chemisorption andstepwise thermal desorption of pyridine from 100°-400°C) and also for their acid functions by acid catalysed reactions [viz. isooctane cracking (at 400°C) (for characterizing external acid sites) and toluene disproportionation (at 500°C) and methanol-to-aromatics conversion (400°C)] using a pulse microreactor. The catalysts were also characterized by XPS, ~(29)Si,~(27)Al and ~(71)Ga MAS NMR. The acidity/acid strength distribution, activity in the acid catalyzed reactions, framework Si/Ga ratio andsurface Ga/Si ratio of the zeolites are significantly affected by their pretreatment by O_2 or H_2.