Mechanistic Investigation into the Rearrangement of Lactone into Methacrylic Acid over Phosphomolybdic Acid Catalyst

Nguyen, Ngoc Ha; Kendell, Shane; Minh, Cam Le; Brown, Thomas J.

doi:10.1007/s10562-010-0321-4

Cited by 9 publications

(10 citation statements)

References 49 publications

(72 reference statements)

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“…This intimates that lactone is a precursor to methacrylic acid formation. Nguyen et al have shown that the lactone rearranges into methacrylic acid via catalysis by water and acid [38]. It is proposed that lactone rearranges to methacrylic acid under normal reaction conditions of high pressures but is instead isolated in this work due to the molecular flow regime.…”

Section: Discussionmentioning

confidence: 88%

“…However propene forms over some of the Group 1 salts (but not over Group 2 compounds) and methacrylic acid is also seen over a single Group 2 phosphomolybdate: BaH[PMo 12 O 40 ]. It has been shown that lactone is a precursor to methacrylic acid, and the lactone is prevented from rearranging into methacrylic acid due to the unique low-pressure, steady-state, molecular flow conditions used in TPRS [38]. Interestingly, the cesium series of phosphomolybdates were the compounds that did not produce any lactone or acetic acid, and only minimal CO 2 , but were very active toward methacrolein formation.…”

Section: Products From Tprsmentioning

confidence: 99%

“…It is not clear why a single barium substitution facilitates methacrylic acid formation, or why the acid forms in conjunction with the second lactone desorption site only. However, since it has been shown by Nguyen et al [38] that water and acid catalyze the rearrangement of the lactone into the acid, it may be inferred that the particular site responsible for this rearrangement has water and acid in close proximity.…”

Section: Detection Of Methacrylic Acidmentioning

confidence: 99%

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Comprehensive Study of Isobutane Selective Oxidation Over Group I and II Phosphomolybdates: Structural and Kinetic Factors

Kendel

Brown

2011

Catal Lett

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Various phosphomolybdates were synthesized using cations from Groups 1 and 2 of the periodic table. These compounds were of the form M x H 3-xn [PMo 12 O 40 ], with n being the cationic charge (?1 or ?2). XRD analysis shows pure phosphomolybdic acid has a triclinic structure. A body centered cubic (BCC) structure gradually develops with addition of Group 1 cations, and the triclinic phase is completely replaced by the BCC phase once metal cations occupy a volume greater than 9-11 Å 3 per phosphomolybdate anion. The Group 2 compounds do not form a cubic phase, however the triclinic phase distorts once cationic volume is greater about 5 or 6 Å 3 and appears to become somewhat amorphous. Isobutane selective oxidation over the compounds yielded methacrolein (primary product), 3-methyl-2-oxetanone (lactone), acetic acid, propene, methacrylic acid, carbon dioxide and water as products. Propene was formed over the Group 1 compounds exclusively and methacrylic acid formation was observed with BaH[PMo 12 O 40 ] only. Products form via two distinct processes: Category 1 product has an exponential profile and coverage is consistent with a Langmuir model, Category 2 formations are consistent with desorptions from within the bulk of the substrates. Methacrolein forms via both Category 1 and 2 processes, whilst all other products are formed by Category 2 exclusively. A rigorous kinetic analysis yielded accurate activation parameters. Category 1 methacrolein formation apparent activation energies ranged from 34.7 ± 1.3 to 119 ± 4 kJ mol -1 . Category 2 formations ranged from 34.3 ± 0.4 to 726 ± 172 kJ mol -1 . No relationship between activity and composition or structure could be ascertained, despite investigation into correlations using several different models.

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Section: Discussionmentioning

confidence: 88%

Section: Products From Tprsmentioning

confidence: 99%

Section: Detection Of Methacrylic Acidmentioning

confidence: 99%

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Comprehensive Study of Isobutane Selective Oxidation Over Group I and II Phosphomolybdates: Structural and Kinetic Factors

Kendel

Brown

2011

Catal Lett

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“…This corresponds to declining methacrolein pressures within the Knudsen cell as temperature increases. Negative activation energies may indicate competing reactions (e.g., formation of β-lactone [29]), secondary methacrolein reactions on the catalyst surface (e.g., dimerization), or the formation of metastable states. Activation energy distributions in the high-temperature region, for all catalysts are investigated in this paper, and have been the focus of previous analyses [2,10].…”

Section: High-temperature Average Rate-parameters For Methacrolein Fmentioning

confidence: 99%

Time- and Temperature-Varying Activation Energies: Isobutane Selective Oxidation to Methacrolein over Phosphomolybdic Acid and Copper(II) Phosphomolybdates

et al. 2016

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Abstract:The selective oxidation energetics of isobutane to methacrolein over phosphomolybdic acid and copper(II) phosphomolybdates have been investigated using low-pressure, pseudo-steady-state and temperature-programming techniques. Time-varying flexible least squares methods were used to determine variations in oxidation activation energies as the temperature increases at 5 • C·min −1 . Catalyst activity stabilizes by the fourth consecutive temperature-programmed run. Rate parameters increase linearly with temperature in two sinusoidal, oscillating wave packets. For H 3 PMo 12 O 40 , three distinct reaction pathways are apparent in the fourth run with activation energies 76 ± 3, 93 ± 7 and 130 ± 3 kJ·mol −1 , and under these experimental conditions are observed at the optimum temperatures 704 ± 7 K, 667 ± 25 K and 745 ± 7 K, respectively. Over the copper-containing catalysts, two pathways are apparent: 76 ± 3 kJ·mol −1 at 665 ± 9 K and 130 ± 3 kJ·mol −1 at 706 ± 9 K. The three activation energies indicate either different reaction pathways leading to methacrolein or distinct active sites on the catalyst surface. The intermediate activation energy, 93 kJ·mol −1 , only observed over phosphomolybdic acid, may be linked to hydrogen bonding. Differences in optimum temperatures for the same activation energies for H 3 PMO 12 O 40 and for the copper catalysts indicate that compensating entropy changes are smaller over H 3 PMo 12 O 40 . The inclusion of copper enhances catalyst stability and activity.

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“…Methacrylic acid is commonly reported from isobutane oxidation, but is not observed. It has been shown that lactone is a precursor to methacrylic acid, and the lactone is prevented from rearranging into methacrylic acid due to the unique low-pressure, steady-state, molecular flow conditions used in TPRS [65].…”

Section: Products Observed With Tprsmentioning

confidence: 99%

Structural and Activity Investigation into Al3+, La3+ and Ce3+ Addition to the Phosphomolybdate Heteropolyanion for Isobutane Selective Oxidation

et al. 2010

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Twelve phosphomolybdate compounds were synthesized via cationic exchange and were of the form: M x H 3-3x [PMo 12 O 40 ] (M = Al, La or Ce; 0 B x B 1). These compounds were analyzed by XRD and adsorption isotherm. Aluminum addition causes a primitive cubic phase, while lanthanum and cerium yield body-centered structures. La and Ce addition reduces surface area of phosphomolybdate structure. Temperature-programmed experiments for the selective oxidation of isobutane yielded methacrolein, 3-methyl-2-oxetanone (lactone), acetic acid (not with aluminous compounds), propene (only with aluminous compounds), carbon dioxide and water. The preference for propene rather than acetic acid formation with Al 3? may be due to the smaller cation size, or primitive cubic structure. These products form via two distinct reaction processes, labeled categories 1 and 2. Category 1 formation is associated with isobutane forming products on the surface, but reaction rate determined by bulk migration of charged particles. Category 2 formation is concerned with isobutane penetrating deep within the bulk of the substrate and forming products which subsequently desorb in a series of bell-shaped humps. Methacrolein forms via both category 1 and 2, whilst all other products form via category 2 exclusively. Kinetic analysis showed apparent activation barriers for category 1 methacrolein formation range from 67 ± 2 kJ mol -1 to [350 kJ mol -1 , and occur in groups with small, medium and large activation barriers. The addition of ?3 metal cations to the phosphomolybdate anion increase thermal stability, significantly decreasing deactivation; IR spectroscopy shows that the Keggin structure remains intact during temperature-programmed experiments with the Al, La and Ce salts.

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Mechanistic Investigation into the Rearrangement of Lactone into Methacrylic Acid over Phosphomolybdic Acid Catalyst

Cited by 9 publications

References 49 publications

Comprehensive Study of Isobutane Selective Oxidation Over Group I and II Phosphomolybdates: Structural and Kinetic Factors

Comprehensive Study of Isobutane Selective Oxidation Over Group I and II Phosphomolybdates: Structural and Kinetic Factors

Time- and Temperature-Varying Activation Energies: Isobutane Selective Oxidation to Methacrolein over Phosphomolybdic Acid and Copper(II) Phosphomolybdates

Structural and Activity Investigation into Al3+, La3+ and Ce3+ Addition to the Phosphomolybdate Heteropolyanion for Isobutane Selective Oxidation

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