How the interaction between In2O3-ZrO2 promotes the isobutene synthesis from ethanol?

A physical mixture comprising In2O3 and ZrO2 and its components were employed as catalysts in the generation of isobutene from ethanol. These solids were characterized by means of several techniques such as EPR, HRTEM, XPS, XRD, N-2 physical adsorption, isopropanol-TPD, CO2-TPD, ethanol-TPD and pyridine adsorption. The addition of 7% of In2O3 to ZrO2 employing the physical mixture procedure generates a catalyst which shows physicochemical and catalytic properties which are not a linear combination of its components properties. This catalyst is not only much more active compared with In2O3 and ZrO2, but it also generates isobutene at high selectivity. The interaction between In2O3 and ZrO2 changes the quantity and strength of the acidic and basic sites. However, these modifications do not correlate with the catalytic behavior. The HRTEM data suggest that the epitaxy alignment occurs between these two oxides which might cause stresses in the In2O3 lattice. The XRD and XPS analysis have identified distortions in the In2O3 lattice provoked by ZrO2, which facilitate the generation of O vacancies and consequently increases the concentration of these species during the reaction. This phenomenon promotes the acetone and acetaldehyde syntheses which are very relevant intermediate of this cascade reaction. Thus, it can be suggested that the catalytic behavior of the modified physical mixture is associated with the In2O3 lattice distortions promoted by ZrO2.