Hybrid catalysts containing zeolite ZSM-5 and supported gallium oxide in the aromatization of n-butane

It is shown that in the aromatization of n-butane, hybrid catalysts containing irreducible oxides (silica and alumina) as co-catalysts provide aromatic yields which are almost twice that obtained with ''pure'' zeolite ZSM-5 zeolite. The interpretation of these results is based on the hydrogen back spillover concept. The addition of Ga2O5 to these co-catalysts enhances further the aromatizing performance of the hybrid catalysts. It is believed that such an additional improvement is due to the gallium species located in the interface between the two types of particles, and the Ga containing regions of the zeolite crystallites near the pore openings. This contamination results from the transfer of some partially reduced gallium oxide from the co-catalyst surface to the zeolite pores. In such a case, it is probable that the reaction is governed by the conventional bifunctional catalysis mechanism. These gallium oxide sites appear more active than the normal ones because of their location near the zeolite pore openings which enables them to react with both inward- and outward-diffusing molecules.