Molybdenum oxide modified HZSM-5 catalyst: Surface acidity and catalytic performance for the dehydration of aqueous ethanol

The catalytic dehydration of ethanol into ethylene was studied over 5 wt% Mo/HZSM-5 prepared by impregnation. The effect of calcination temperature on the structure, acidity and catalytic performance of the catalysts was investigated by XRD, N₂ adsorption, NH₃-TPD and TG. A correlation between the catalytic performance of Mo modified catalysts and the amount of weak and medium acidity was observed. It was found that 5 wt% Mo/HZSM-5 catalyst calcined at 500 °C exhibited the highest weak and medium acidity and much better catalytic performance in ethanol dehydration reaction compared with HZSM-5. TPR characterization showed that the Mo species on the external surface of HZSM-5 was easier to be reduced during the reaction. Combining quantitative analyses of NH₃-TPD and H₂-TPR profiles of fresh and used catalysts revealed that the decrease of weak and medium acidity could be correlated with the reduction of Mo species. It is proposed that reduction of Mo species caused the decrease of weak and medium acidity, which contributed to activity drop at the initial reaction stage.