Aromatization activity of gallium containing MFI and TON zeolite catalysts in n-butane conversion: Effects of gallium and reaction conditions

Abstract

A kinetic study of n -butane conversion over acidic and gallium (Ga) containing MFI and TON zeolites has revealed that Ga active sites create a new pathway for aromatics formation via dehydrogenation reaction steps. This pathway does not involve bulky bimolecular hydrogen transfer steps of the aromatization process over acidic zeolites, and, as a consequence, leads to considerably higher enhancement of the aromatization activity of the one-dimensional TON catalyst when compared to the three-dimensional MFI catalyst. This finding highlights fundamentally different spatial requirements for alkane aromatization over acidic and Ga containing zeolites and indicates that the zeolites with severe spatial constraints could become very selective catalysts for alkane aromatization after their modification with Ga. It is anticipated that these results will initiate the search for new, highly selective aromatization catalysts based on zeolites with different structures. The second important finding of this work is the evolution of the aromatization activity of GaH-TON and GaH-MFI catalysts during n -butane reaction that is likely associated with formation of catalytically active Ga + ions. In our study, this process was completed in about 15 min, i.e. much faster then similar processes that were reported earlier in the literature for the GaH-MFI catalysts. To the best of our knowledge, no data on the evolution of the aromatization activity was reported up to day for the one-dimensional GaH-TON catalysts. This paper highlights fundamentally different spatial requirements for alkane aromatization over acidic and gallium containing zeolites and indicates that the zeolites with severe spatial constraints could become very selective catalysts for alkane aromatization after their modification with gallium. It is anticipated that our results will initiate the search for new, highly selective aromatization catalysts based on zeolites with different structures.