Aromatization of n-pentane over Zn/ZSM-5 catalysts: effect of Si/Al ratio and reaction pathway

The metal modified ZSM-5 catalysts has been widely used in the aromatization of light alkanes. To investigate the effect of Si/Al ratio of ZSM-5 zeolites, a series of Zn/ZSM-5 catalysts with different Si/Al ratios have been prepared by wet impregnation and tested for n-pentane aromatization. The results indicated that, the introduced Zn species consumed the strong Brønsted acid sites and inhibited the undesired cracking reactions effectively. With the increase of Si/Al ratio of ZSM-5 zeolites, the n-pentane conversion decreased obviously due to the reduced acid content and strength, while the selectivity to BTX remained almost unchanged. Attributed to the weakened cracking and hydrogen-transfer reactions with increasing Si/Al ratio, the selectivity to light alkanes decreased, while that to olefins increased remarkably. Further, the possible reaction pathways have been proposed to better elucidate the changing product distribution with the Si/Al ratios.