Pulse reaction studies on variations of initial activity selectivity of O-2 and H-2 pretreated Ga-modified ZSM-5 type zeolite catalysts in propane aromatization

Influence of O-2 and H-2 pretreatments (at 600 degrees C for 10 h) on the initial activity and product selectivity and their variation with time on stream (0-180 min) of H-gallosilicate (H-GaMFI), H-galloaluminosilicate (H-GaAlMFI), and Ga/H-ZSM-5 catalysts (with bulk Si/(Al + Ga) = 34.5 +/- 2.5) in the propane aromatization (at 600 degrees C) has been investigated, using a microreactor operated in both the pulse and continuous reaction modes. The catalysts have been characterized for their acidity (measured in terms of pyridine chemisorbed at 400 degrees C), framework and nonframework Ga and Al, and surface Si/Ga ratio. The initial propane conversion/aromatization activity and aromatics selectivity of the H-GaMFI are decreased but that of the H-GaAlMFI and Ga/H-ZSM-5 are increased significantly due to the H-2 pretreatment for all the Ga-modified zeolite catalysts. The variation of the activity and product selectivity of all the three catalysts with the time on stream is found to be strongly dependent upon the pretreatment. Among the catalysts, H-GaAlMFI shows superior performance in the propane aromatization. (C) 1996 Academic Press, Inc.