Partial oxidation of ethanol on supported Rh catalysts: Effect of the oxide support

• The highest conversion was obtained on ceria supported Rh.
• Rh is in partially oxidized states on alumina, titania and ceria during reaction.
• Acetaldehyde is oxidized to acetate species on Rh/Al2O3 and on Rh/CeO2.
• Acetaldehyde is dehydrogenated to acetyl species on Rh/Al2O3 and on Rh/CeO2.
• On Rh/TiO2 the one of intermediate is HCOOH/HCOO(a) formed via aldehyde oxidation.

In this work, the effect of the nature of oxide support on the reaction mechanism of the partial oxidation of ethanol on Rh catalyst was studied by diffuse reflectance infrared (DRIFTS) and X-ray photoelectron spectroscopy (XPS). The conversion of ethanol and the product distribution were analysed by gas chromatography. The highest ethanol conversion was measured on Rh/CeO2 catalyst. The results showed that the nature of the oxide support affected the reaction mechanism. On supported Rh catalysts ethanol adsorption gives rise to ethoxide species, which can be decomposed to CO2, CO and CH4 and dehydrogenated, forming acetaldehyde. The latter species are oxidized to acetate or dehydrogenated to acetyl species on Rh/Al2O3 and on Rh/CeO2. On Rh/TiO2 the acetaldehyde can also be oxidized in a parallel process to HCOOH/HCOO(a) which forms CO2 and water. Furthermore, the acetate species previously formed can be decomposed to CH4, CO and/or oxidized to CO2 via carbonate species at higher temperature depending on the oxide support. On silica support acetaldehyde was the dominant intermediate and it desorbed or directly decomposed with or without oxygen to CO2 and methane. The partial oxidation of ethanol proceeds on partially oxidized Rh sites on Rh/Al2O3, Rh/TiO2 and on Rh/CeO2. In spite of the presence of O2, ceria is not fully oxidized during the partial oxidation of ethanol.

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