Temperature Programmed Surface Reaction of the Oxidative Scission of Methyl Ketones over Gamma-alumina Supported Vanadium Oxides

Date of Award

August 2019

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biomedical and Chemical Engineering

Advisor(s)

Jesse Q. Bond

Keywords

Eley-Rideal, Langmuir–Hinshelwood, Mars-van-Krevelen, methyl ketone, oxidative cleavage, Temperature Programmed Surface Reaction

Subject Categories

Engineering

Abstract

In order to provide insight into the mechanism governing methyl ketone scission, Temperature Programmed Surface Reaction (TPSR) spectroscopy was employed to study the oxidative cleavage of methyl ketones over VOX/γ-Al2O3. Specifically, 2-butanone, acetone, and 3-methyl-2-butanone (3M2B) are applied as reactants in this thesis. Macroscopically, the cleavage of methyl ketones produces, as cleavage products, an aldehyde or ketone fragment and a carboxylic acid fragment. And the oxidative cleavage of methyl ketone should involve two fragments. The fragment with a carbonyl group forms carboxylic acid and the left alkane fragment forms aldehyde or acetone.

Profiles of the oxidative cleavage of 2-butanone (MEK) and acetone over the supported vanadium oxides and the pure support show that there is no oxidative cleavage reaction occurring under anaerobic conditions. Therefore, these data sets can be treated as Temperature Programmed Desorption (TPD) data. TPD data of MEK and acetone show that three distinguishable binding modes exist both over VOX/γ-Al2O3 and γ-Al2O3. Either gaseous oxygen or lattice oxygen may play a role in the oxidative cleavage reaction. TPSR for 3M2B over the pure support shows that gas-phase oxygen participated in the formation of acetone. As for TPSR for 3M2B over VOX/γ-Al2O3 under the aerobic condition, desorption temperatures of acetone were consistent with the case over the support in the presence of gaseous O2. So, the step of producing acetone from 3M2B should go through Langmuir–Hinshelwood or Eley-Rideal mechanism in the presence of gas-phase oxygen. And TPSR for 3M2B over VOX/γ-Al2O3 under the anaerobic condition demonstrated that acetone was generated via the Mars-van-Krevelen mechanism. When it comes to acetic acid, the other cleavage product, it could be concluded that acetic acid was not generated spontaneously with acetone and the oxidative cleavage of 3M2B produces acetic acid via the Mars-van-Krevelen mechanism. Thus, we suggest two possible pathways for the oxidative cleavage of methyl ketone: 1) the oxidative reactions occur via combining the Langmuir–Hinshelwood or Eley – Rideal mechanism and the Mars-van-Krevelen mechanism; 2) the oxidative reactions occur via two sequential MVK mechanisms.

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