Bio-oil upgrading via vapor-phase ketonization over nanostructured FeO x and MnO x : catalytic performance and mechanistic insight

In this study, nanostructured FeO (x) and MnO (x) were prepared by two synthetic routes, nanocasting and hydrothermal, and evaluated for bio-oil upgrading via vapor-phase ketonization. Catalytic performance measurements in the ketonization of representative model compounds, acetic and propionic acid, at 335 A degrees C showed high activity for the hydrothermal MnO (x) and nanocast FeO (x) (conversion > 90%) with high selectivity to the respective ketones. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies followed by temperature-programmed thermogravimetric analysis (TGA) and MS showed that the reactive intermediates are bidentate acetate species that desorb as acetone over FeO (x) and unreacted acetic acid over MnO (x) (in contradiction to its associated catalysis). Powder X-ray diffraction and X-ray photoelectron spectroscopy analysis of used samples revealed that MnO2 was reduced to MnO during reaction. The relative surface concentrations of adsorbed acetate for the used MnO (x) catalysts (from DRIFTS) correlated with their corresponding acetic acid conversion (from ketonization studies), indicating that MnO is the active phase for acetic acid ketonization, with MnO2 a precursor which is reduced in situ at temperatures > 300 A degrees C. Vapor-phase ketonization of the aqueous phase of a real thermal bio-oil, produced from the fast pyrolysis of lignocellulosic biomass, was demonstrated successfully over MnO (x) prepared by the hydrothermal route, highlighting this as an attractive approach for the upgrading of pyrolysis bio-oils.