(175h) Vapor Phase Ethanol Selective Oxidation to Acetaldehyde and Acetic Acid on Gold Catalysts | AIChE

(175h) Vapor Phase Ethanol Selective Oxidation to Acetaldehyde and Acetic Acid on Gold Catalysts


Bravo-Suárez, J. J. - Presenter, The University of Kansas
Srinivasan, P. D., The University of Kansas
Zhu, H., The University of Kansas
Alzahrani, H. A., The University of Kansas
The selective oxidation of ethanol to acetaldehyde and acetic acid on gold nanoparticles supported on a metal oxide (Au/TiO2) was examined via in situ UV-Vis and FTIR spectroscopies and kinetic studies. In situ UV-Vis spectroscopy via a gold plasmon surface resonance sensing technique provided evidence for O2 adsorption at the Au-TiO2 metal-support perimeter interface. Additionally, in situ Modulation Excitation-Phase Sensitive Detection-UV-Vis and FTIR spectroscopies performed during O2 modulation at reaction conditions also showed the presence of charge transfer events likely occurring during the spillover of hydrogen arising from ethanol dissociative adsorption at the Au-TiO2 metal-support perimeter. Moreover, kinetic results over a wide range of conditions (473-533 K, 0.1-20 kPa O2, 0.1-5 kPa ethanol, 0-8 kPa water) showed that ethanol oxidized selectively in vapor phase to mainly acetaldehyde (~50-95%) and acetic acid (~2-30%) with respective apparent activation energies of 47 and 70 kJ/mol. It was also found that acetic acid selectivity was favored at increasing O2/ethanol partial pressure ratios. Although water presence in the reaction mixture has been implied to promote oxidations on gold catalysts in gas phase and acetic acid formation in ethanol liquid phase oxidation, the present results indicated that in the vapor phase acetaldehyde and acetic acid production rates were mostly insensitive to co-fed water. Average apparent reaction rate orders of O2, ethanol, and water for acetaldehyde production were ~0.2, ~0.5, and ~0.1, whereas for acetic acid production they were ~0.5, ~0.3, and ~0, respectively. A kinetic model involving ethanol dehydrogenation to acetaldehyde, oxygen adsorption and activation, and acetaldehyde oxidation to acetic acid on a two-site ensemble at the Au-TiO2 metal-support perimeter comprised of Au-O vacancy-Ti-O was found to adequately explain the spectroscopic and kinetic experimental findings. Overall, this study highlights a metal-support synergy which can be explored to further guide the development of new selective oxidation catalysts.