Aluminum halides, Al2Cl6 and Al2Br6 in particular, are strong Lewis acids that are known for their applications in Friedel Crafts reactions including: alkylation and acylation. These can be supported on solid inorganic supports like SiO2, Al2O3, or even zeolites to avoid the separation problems associated with liquid catalysts. H-ZSM-5 is a well-known shape selective acid catalyst with strong Brønsted acid sites. Its activity in acid catalyzed reactions, including methane aromatization, is well documented. In the current study, Al2Br6 is anchored to the surface of H-ZSM5 using a vapor phase grafting technique, in which Al2Br6 vapor reacts with the surface hydroxyl groups of ZSM-5. The acidity of the zeolite is greatly enhanced by aluminum bromide, confirmed by NH3-TPD and pyridine-DRIFTS (Figure attached). Brønsted acid sites (~ 1540-1545 cm-1) were stable even at temperatures of 400 °C, although the concentration of Lewis acid sites (~ 1450 cm-1) showed less intense bands at elevated temperature. Also, DRIFTS measurements revealed a new Brønsted acid site peak at around 1540 cm-1. When AlBr3 was grafted on H-ZSM-5, the peaks in the NH3-TPD shifted to higher temperatures. This solid acid catalyst can find applications in variety of acid-catalyzed reactions such as alkylation, isomerization, and oligomerization. This catalyst was tested for oligomerization of methane at mild reaction temperatures (&lt; 500 °C). At these temperatures, methane was converted into C2-C8 products. Higher temperatures led to higher conversion, but there was little effect on selectivity. These higher temperatures also led to faster deactivation of the catalyst, which appears to be due to the formation of coke. Lower temperatures showed lower conversion, lower rates of coke formation and deactivation. The work described here tries to identify a new solid superacid system for the low temperature oligomerization of methane.

Effect of temperature in methane activation using AlBr3 supported H-ZSM-5 catalysts

255th National Meeting (2018)

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