Detailed product and kinetic analysis for the low-pressure selective oxidation of isobutane over phosphomolybdic acid

Kendell, Shane; Brown, Thomas J.

doi:10.1007/s11144-010-0156-4

Cited by 8 publications

(15 citation statements)

References 74 publications

(107 reference statements)

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“…Products observed from the reaction of isobutane with phosphomolybdic acid using this technique were methacrolein, 3-methyl-2-oxetanone (lactone), acetic acid, carbon dioxide and water; these selective oxidation products for isobutane over phosphomolybdic acid have been previously reported by Kendell et al [44,51]. For the metal substituted phosphomolybdates, methacrolein, lactone, carbon dioxide and water were also detected.…”

Section: Products Observed With Tprssupporting

confidence: 66%

“…Category 1 methacrolein kinetic parameters are listed in Table 5, where T range refers to the temperature span used in the modeling procedure. Errors associated with the kinetic values are expressed as parenthetic terms in Table 5 The Arrhenius parameters for isobutane selective oxidation over phosphomolybdic acid have been reported previously [51]. This work showed that the activation energy for category 1 methacrolein formation varied from 56.9 ± 1.5 to 149 ± 4 kJ mol -1 .…”

Section: Category 1 Methacrolein Parameterssupporting

confidence: 54%

“…Therefore, the Keggin structure of phosphomolybdic acid is likely destroyed by the TPRS experiments. This disintegration of the Keggin structure resulted in the pure acid becoming progressively less active toward methacrolein formation with successive TPRS experiments, as performed by Kendell et al previously [51].…”

Section: Keggin Structure Confirmation Via Ir Spectroscopymentioning

confidence: 82%

“…A TPRS-exposed sample of phosphomolybdic acid was sourced from a recent published study by Kendell et al [51]. All IR measurements were performed on solid samples using a Varian 660-IR FT-IR spectrometer.…”

Section: Infrared (Ir) Spectroscopic Verification Of Keggin Structurementioning

confidence: 99%

“…Previous researchers have simulated temperature-programmed desorption using Gaussian curves and used these to determine thermodynamic parameters [66][67][68][69]. The mass spectral intensities in this work, I P , are a function of temperature, T. I P is simulated by the following Gaussian expression [51,70]: …”

Section: Resolution Of Category 2 Peaksmentioning

confidence: 99%

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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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Section: Products Observed With Tprssupporting

confidence: 66%

Section: Category 1 Methacrolein Parameterssupporting

confidence: 54%

Section: Keggin Structure Confirmation Via Ir Spectroscopymentioning

confidence: 82%

Section: Infrared (Ir) Spectroscopic Verification Of Keggin Structurementioning

confidence: 99%

Section: Resolution Of Category 2 Peaksmentioning

confidence: 99%

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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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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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Microkinetic simulation and fitting of the temperature programmed reaction of methanol on CeO2(111): H2 and H2O + V production

Savara

2020

Reac Kinet Mech Cat

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Detailed product and kinetic analysis for the low-pressure selective oxidation of isobutane over phosphomolybdic acid

Cited by 8 publications

References 74 publications

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

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

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

Microkinetic simulation and fitting of the temperature programmed reaction of methanol on CeO2(111): H2 and H2O + V production

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