Catalytic dehydration of ethanol over post-treated ZSM-5 zeolites

Microporous ZSM-5 zeolite was post-treated by desilication with sodium hydroxide, dealumination with oxalic acid, or both of them in a sequential way to finely tune the zeolite catalysts with hierarchically porous structure and varying acidity. In the catalytic dehydration of ethanol, diethyl ether and ethylene were two main products competitively formed at 200 °C and atmospheric pressure. The post-treated ZSM-5 catalysts could display stable ethanol conversion and ethylene selectivity within time-on-stream of around 12 h. The correlation between the steady-state ethylene selectivity and the amount of weak acid sites from ammonia temperature-programmed desorption (NH3-TPD) indicated that the weak acid sites facilitated the ethylene production during ethanol transformation under present reaction conditions. The reaction pathways for diethyl ether and ethylene formations from ethanol were investigated by theoretical calculation. Both the activation energies and natural charges of the transition states strongly supported that the selectivity for the diethyl ether tended to deteriorate with decreasing catalytic Brønsted acidity.