(671c) Elucidating the Roles of Lattice and Molecular Oxygen during the Oxidative Scission of Methyl Ketones over Supported Vanadium Oxides
AIChE Annual Meeting
Tuesday, November 17, 2020 - 8:30am to 8:45am
The role of molecular oxygen was investigated by conducting TPSR experiments over Î³-Al2O3 under both anaerobic (He) and oxidizing conditions (15% O2 in He). Our results indicate that Î³-Al2O3 is a non- reducible material. Interestingly, despite its non-reducible lattice, oxidative ketone scission does occur over Î³-Al2O3 under aerobic environments. This indicates direct participation of molecular O2 in the oxidative scission mechanism.
We additionally examined the role of lattice oxygen by performing analogous TPSR experiments over VOx/Î³-Al2O3 under both anaerobic and aerobic conditions. Results indicate that lattice oxygen from reducible VOx can also initiate oxidative scission.
A final contrast between oxidative scission over Î³-Al2O3 and VOx/Î³-Al2O3 is that, although we observe evidence of oxidative scission of 3-methyl-2-butanone on Î³-Al2O3 under aerobic conditions, we only observe production of the acetone fragment. Co-production of acetic acid is only observed over VOx/Î³-Al2O3. These results suggests that molecular oxygen initiates the scission reaction to form acyl and carboxylate surface species; the former will desorb as acetone without requiring further reduction of the lattice, whereas the latter can only desorb upon reduction of a V-O-X bond. We therefore conclude that both molecular and lattice oxygen participate directly in the oxidative scission of methyl ketones, indicating a mechanism that combines both Langmuir-Rideal and Mars-van-Krevelen pathways.