The role of steam in selective oxidation of methacrolein over H3PMo12O40

Selective Oxidation of Methacrolein over Crystalline Mo3VOx Catalysts and Comparison of Their Catalytic Properties with Heteropoly Acid Catalysts

“…The MCR conversion and MAA selectivity were not suddenly dropped after stopping the water feed, possibly due to the replenishment of H 3 O + on the surface by the diffusion of water from the bulk. 37 The MCR conversion and MAA selectivity gradually increased with the reaction time by the refeed of water and were restored by 12 h. The gradual increase in the MCR conversion and MAA selectivity suggests surface reconstruction under the reaction condition in the presence of water. The MCR conversion and MAA selectivity changed in a similar manner in the following water switching experiments.…”

“…region was similar to that reported over the conventional HPA catalysts. 17,37 The activation energy, on the other hand, significantly changed when the temperature was decreased. Kamiya et al reported that the rate-determining step changes in the presence or absence of steam in the reaction gas when MCR is oxidized over the HPA catalyst.…”

“…Kamiya et al reported that the rate-determining step changes in the presence or absence of steam in the reaction gas when MCR is oxidized over the HPA catalyst. 37 Andrushkevich et al recently pointed out that the effect of water on oxidation reactions changes depending on the reaction temperature. 40 Based on these reports, it was proposed that the ratedetermining step over HPA-2 changes from (3) to ( 2) or (5) when the reaction temperature decreases, meaning that the reaction rate is determined by the rate of insertion or regeneration of H 3 O + .…”

“…Recently, Kamiya et al proposed a reaction mechanism for MCR oxidation over the HPA catalyst at ca. 300 °C: (1) adsorption and activation of MCR via the hydroxyl group of a hydrated proton (H 3 O + ) on the catalyst surface, (2) insertion of the hydrated proton (H 3 O + ) into MCR to form a diol, (3) abstraction of a diol C–H by the lattice oxygen, (4) desorption of MAA and a water molecule from the catalyst surface with a leaving hydroxyl group, and (5) reoxidation of the consumed lattice oxygen by molecular oxygen with regeneration of H 3 O + through the diffusion of a water molecule from the bulk or the direct activation of a gas-phase water molecule . A similar reaction mechanism was also proposed by Misono et al ,, HPA-2 is thought to follow this reaction mechanism.…”

Production of Methacrylic Acid and Metacrylates

“…The Japanese authors of [15] showed that adding water vapor to the initial mixture of methacrolein and air allows us to increase the rate of the process (at 300°C) by 500%, and the selectivity toward methacrolein by 200%. This is due to a 20000% increase in the pre-exponential factor in the production of methacrolein.…”