Laurent Vanoye

Insights in the aerobic oxidation of aldehydes

The hydroformylation of olefins (oxo synthesis) is the most important process for the production of higher aldehydes (>C4). The liquid phase oxidation of the latter to carboxylic acids by molecular oxygen or air has been known for more than 150 years and is an industrially important process. However, in the recent literature, several different oxidizing reagents and catalytic processes have been reported for this oxidation but most of them have limitations as they use environmentally unacceptable reagents or unnecessarily sophisticated conditions. Herein, we re-evaluated the air oxidation of aldehydes. We show that under mild conditions (air or oxygen and non-optimized stirring), reactions are transfer limited and thus catalyst has no effect on reaction rate. Using efficient stirring (self-suction turbine), uncatalysed air oxidation of 0.8 M aldehyde is possible in 50 min at room temperature whereas less than 10 min was necessary with 10 ppm Mn(II). Thus, recommendations for avoiding common pitfalls that may rise during the evaluation of new catalysts are made.

Upgrading of biomass transformation residue: influence of gas flow composition on acetic acid ketonic condensation

Acetic acid, a common biomass transformation residue, can be converted into acetone by direct ketonization in the gas phase over γ-Fe2O3 (maghemite) pre-activated at 450 °C under air. This reaction was performed in a continuous flow reactor with varying temperature from 250 to 300 °C and different carrier gases. Using N2 as carrier gas, the activity of the iron based catalyst normally increased with increasing temperature and contact time and remained constant under stationary operating conditions. A slight decrease of activity was observed using a N2/CO2 mixture as carrier gas. A strong enhancement of the activity was observed when H2 was introduced in the carrier gas, as a N2/H2 or CO2/H2 mixture. This improvement could be attributed to the modification of the oxidation state of the iron catalyst used for which in situ characterisation is still to be performed.

Photocatalytic Degradation of Hexaethylene Glycol

Polyethylene glycol (PEG) photodegradation was studied in water under UV irradiation in the presence of catalytic amount of TiO2 using hexaethylene glycol as a model compound. Full conversion was achieved in 7 h with an average quantum yield around 1%. Formic acid was found to be the main intermediate and was slower to oxidize into CO2 (traces remains after 24 h). The other intermediates [lower PEG, oxidized PEG (formates, aldehydes and acids, acetic acid)] of the photodegradation have also been identified and quantified. A mechanism based on previous literature but also taking into account these new observations is proposed.Graphical Abstract