- Title
- Structural and activity investigation into Al3+, La3+ and Ce3+ addition to the phosphomolybdate heteropolyanion for isobutane selective oxidation
- Creator
- Kendell, Shane M.; Alston, Amy-Sue; Ballam, Nick J.; Brown, Trevor C.; Burns, Robert C.
- Relation
- Catalysis Letters Vol. 141, Issue 3, p. 374-390
- Publisher Link
- http://dx.doi.org/10.1007/s10562-010-0514-x
- Publisher
- Springer
- Resource Type
- journal article
- Date
- 2011
- Description
- Twelve phosphomolybdate compounds were synthesized via cationic exchange and were of the form: MxH3–3x[PMo12O40] (M = Al, La or Ce; 0 ≤ x ≤ 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 Al3+ 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-1to[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.
- Subject
- selective; oxidation; heteropoly; isobutane; kinetics
- Identifier
- http://hdl.handle.net/1959.13/936805
- Identifier
- uon:12410
- Identifier
- ISSN:1011-372X
- Language
- eng
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