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Stytsenko, V. D.; Lee, W. H.; Lee, J. W.

doi:10.1023/a:1010413301105

Cited by 21 publications

(15 citation statements)

References 2 publications

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“…Several attempts have been made to link the activity of a catalyst with the physical and chemical properties of the associated cations and these include: ionic radius [35], ionic potential [34], electronegativity [95][96][97][98][99][100][101], enthalpy of oxide formation [99,102,103], electronic polarisability [95,104,105] and optical basicity [106][107][108][109][110][111][112][113]. All of these parameters are listed in Table 9.…”

Section: Investigation Into Correlationsmentioning

confidence: 99%

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: Investigation Into Correlationsmentioning

confidence: 99%

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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“…In the primary structure, i.e., the heteropolyanion, such as [PMo 12 O 40 ] 3− , the central phosphorus atom is located at the center of a PO 4 tetrahedron, which is surrounded by twelve MoO 6 octahedra. The three-dimensional arrangement of heteropolyanions and counterions, perhaps also including water of crystallization and some additional molecules, is called the secondary structure.…”

Section: Introductionmentioning

confidence: 99%

“…There are important relationships between the catalytic function and the primary or the secondary structure of HPCs. It has been reported that V can partially substitute for Mo in the heteropolyanions and improve the catalytic property for selective oxidation reactions [12,13]. In particular, effective catalysts can be designed and prepared by controlling the distribution of vanadyl species in the primary or secondary structure [14].…”

Section: Introductionmentioning

confidence: 99%

“…Compared with the parent heteropolyacids, the formation of acidic salts with alkaline metals is effective on both the activity and stability of in water or other polar solvents, precipitate is generated in the heteropolyacids solution after the addition of these ions, and then the obtained slurry is usually evaporated to dryness to get the acidic cesium or ammonium salts. It was found that the mechanism of pore formation for (NH 4 ) x Cs y H 0.5 PW 12 O 40 exhibited a significant difference when it was synthesized through a precipitation/ion exchange process with a different addition order for each cation [20]. It was also found that the addition method of NH 4 + in the precursors for preparing Cu-and Fe-doped acidic cesium salts of molybdovanadophosphoric acid greatly affected the phase composition and catalytic property of the calcined catalysts in our previous work [16].…”

Section: Introductionmentioning

confidence: 99%

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Composition, Structural Evolution and the Related Property Variations in Preparation of Mixed Cesium/Ammonium Acidic Salts of Heteropolyacids

Zhang

Wang

et al. 2016

Catalysts

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Abstract:The composition, structural evolution and the related property variations of mixed cesium/ammonium acidic salts of heteropolyacids were investigated in detail by tracking and analyzing the initial precipitates, evaporation residues and the calcined products in their preparation process. Results show that V cannot completely enter the heteropolyanions in the initial precipitates when the Cs + added amount is low, and the increase in Cs + adding amount improves the substitution of V for Mo in the heteropolyanions. Both the initial precipitates and the evaporation residues are mixtures of cesium and ammonium salts of heteropolyacids before calcination. Thermal treatment causes the decomposition of the ammonium salts and the formation of single-phase solid solutions from mechanical mixtures. The calcined products of the initial precipitates and the evaporation residues vary greatly in textural properties. The determinants of the catalytic performance for the oxidation of methacrolein to methacrylic acid are acidity and specific surface area of the compounds. The increase in specific surface area mainly improves the conversion of methacrolein, but not the selectivity of methacrylic acid. Insufficient acidity caused by high Cs + content in the compounds is responsible for the low selectivity.

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“…The use of isobutyraldehyde [13] and isobutyric acid [14] as feedstocks rather than isobutane has also been explored, however the alkane is less expensive and hence preferred. Methacrolein is oxidized by heteropoly compounds to methacrylic acid [15][16][17][18][19][20], which in turn is readily esterified with methanol to yield methyl methacrylate [21].…”

Section: Introductionmentioning

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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Cited by 21 publications

References 2 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

Composition, Structural Evolution and the Related Property Variations in Preparation of Mixed Cesium/Ammonium Acidic Salts of Heteropolyacids

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

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