Performance of Au/HZSM-5 catalysts for the isomerization reaction of n-butane

The activity and selectivity to isomerization of pure n-butane and mixed butane (with different proportions of iso-butane) of Au/HZSM-5 catalysts were evaluated using a micro-scale pulse reactor. Results showed that the conversion of pure n-butane was above 7.0% and the selectivity to iso-butane could be as high as 80% on Au/HZSM-5 catalysts with 1.31% Au loading at 300℃. By contrast, the conversion of n-butane and the selectivity to iso-butane was only 0.55% and 11.67% on the HZSM-5 supporter. The conversion of n-butane increased firstly and then decreased with the increase of Au loading at a range of 0.12%~1.91%. The selectivity to iso-butane increased with increase of Au loading apparently when Au loading was at a low level. When reaction temperature was lower than 400℃, the main reaction on Au/HZSM-5 catalyst was isomerization of pure n-butane. When the temperature was higher than 400℃, the main reactions were dissociation and aromatization. 400℃ was the watershed of dissociation and aromatization under the reaction conditions of micro-scale pulse reaction. Additionally, the composition of mixed butane had certainly influence on the isomerization reaction of n-butane. But the products in the isomerization reaction of n-butane were very rare at proper reaction temperature, showing a metal-acid bifunctional catalytic character. The species of Au⁺ possibly played an important role in the dehydrogenation and hydrogenation reactions.