(Received : April 25, 1997 ; Accepted for publication : August 25, 1997 ; Published on Web : September 24, 1997)
The interactions of ethanol with a Brested acid site (a hydroxy group) and with a Lewis acid site (a metal ion) on surfaces of seven metal oxides (SiO2-Al2O3, SiO2, TiO2, ZnO, MgO, MnO and CdO) have been investigated using the DV-Xa method. The oxides were selected from a series of catalysts, whose selectivities for the dehydration and the dehydrogenation of ethanol had been experimentally determined by P. Sabatier and A. Mailhe.
By comparing the results of the DV-Xa calculations from several models of ethanol interacting with the Brested or Lewis acid sites with the experimental selectivities, it was concluded that a proton shift from the Brested site to the ethanol oxygen occurs when ethanol strongly interacts with the site and that this shift changed the electronic state of ethanol for the dehydration to be favorable. These results indicate that the dehydration of ethanol on oxide catalysts proceeds by the E1 mechanism.
Keywords: DV-Xa method, Ethanol, Dehydration, Dehydrogenation, Broensted acid site, Lewis acid site
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