Conversion of n-Butane to iso-Butene on Gallium/HZSM-5 Catalysts

Abstract

-The conversion of n -butane to iso-butene on gallium/HZSM-5 catalysts at 350 º C and WHSV=2.5h8 -1 was studied. The catalysts were prepared by ion exchange from a Ga(NO3) 2 solution and further submitted to calcination in air at 530 º C. TEM analysis with an EDAX detector and TPR-H 2 data showed that after calcination the Ga species were present mainly as Ga 2 O 3 , which are reduced to Ga 2 O at temperatures near 610 º C. The specific acid activity (SAA) of the catalysts increased with the increase in aluminum content in the zeolite, and for a fixed Si/Al ratio, the SAA increased with Ga content. Values for specific hydro/dehydrogenation activity (SH/DHA) were significantly higher than those for SAA, indicating that the catalytic process is controlled by the kinetics on acid sites. Moreover, the production of iso-butene with a selectivity higher than 25% was a evidence that in gallium/HZSM-5-based catalysts the rate of the hydrogenation reaction is lower than that of the dehydrogenation reaction; this behavior confirmed the dehydrogenation nature of gallium species, thereby showing great promise for iso-butene production.