Synthesis and characterization of H-ZSM-22, Zn-H-ZSM-22 and Ga-H-ZSM-22 zeolite catalysts and their catalytic activity in the aromatization of n-butane Original Research Article

K-ZSM-22 zeolites with a Si/Al ratio of 53 have been synthesized by means of the hydrothermal synthesis method using 1,6-diaminohexane as the templating agent. The H-ZSM-22, Ga and Zn modified ZSM-22 zeolite catalysts have been prepared and characterised by X-ray powder diffraction (Philips pw 1830), scanning electron microscopy (Leica Cambridge Stereoscan 360), nitrogen adsorption (Carlo Erba Instruments), X-ray fluorescence (Outokumpu-8000) and temperature programmed desorption of ammonia. The synthesised ZSM-22 zeolite was highly crystalline and free of amorphous material. The TPD of ammonia profiles revealed that the H-ZSM-22, Ga and Zn modified ZSM-22 were acidic and consisted of Brønsted and Lewis acid sites. The catalytic activity were investigated for the conversion of n-butane to aromatic hydrocarbons over H-ZSM-22, Ga-H-ZSM-22 and Zn-H-ZSM-22 catalysts. Further, the effect of temperature and the space velocity on the conversion of n-butane and the selectivity to aromatic hydrocarbons were studied. The selectivity to aromatics was higher for Ga and Zn modified ZSM-22 than for H-ZSM-22. The effect of time on stream on n-butane conversion and the selectivity to aromatics was studied at 803 K for 4.5 h.