Investigation of propene oxidation to acrolein by the method of ultralow conversion: A new mechanism of the reaction

• Published in: Journal of catalysis 2018-12, Vol.368, p.315-323
• Main Authors: Panov, Gennady I., Parfenov, Mikhail V., Starokon, Eugeny V., Kharitonov, Alexandr S.
• Format: Article
• Language: English
• Subjects: Acrolein; Allyl alcohol; Allyl hydroxylation mechanism; Allyl radical; Intermediate products; Method of ultralow conversion; Multicomponent catalysts; Propene oxidation
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2018.09.033

[Display omitted] •The ultralow conversion method for identifying reaction intermediates is described.•Allyl alcohol is identified as a key intermediate product of the title reaction.•A reaction mechanism proceeding through allyl hydroxylation rout is suggested.•The new mechanism explains all the reaction features inexplicable by the allyl radical concept. Investigation of reaction mechanisms by identifying the intermediates released into the gas phase is most effective at low conversion of reactants, ideally approaching zero. However, conversions below 0.5–1% are rarely used, due to the difficulty of analysis of low-concentration products. The mechanism of the title reaction is a subject of long-term discussion. We studied the mechanism using an original ultralow conversion (ULC) method. The idea is to perform the analysis of products after their preliminary accumulation in a suitable absorbent at the reactor outlet. This allows decreasing conversion by 2–3 orders of magnitude. The ULC experiments were conducted with a Bi–Mo catalyst at 100–250 °C and with propene conversion down to 0.001%. A new so-called allyl hydroxylation mechanism was revealed. A key step is the hydroxylation of the CH3 group to form an allyl alcohol intermediate, which is further oxidized to acrolein. The mechanism explains all reaction features and was confirmed by experiments at 350 °C.