Pore structures of the monovalent salts of the heteropoly compounds, 12-tungstophosphoric and 12-molybdophosphoric acid

McMonagle, J.B.; Moffat, J.B.

doi:10.1016/0021-9797(84)90060-2

Cited by 138 publications

(41 citation statements)

References 22 publications

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“…The NLDFT surface areas ranged from 0.387 to 28 [27,36,98], although work by Okuhara et al supports our finding [41]. The surface area also decreases with respect to increased cation size, which also contrasts with established findings [25,30,37,38,64]. The aluminum salts have a greater number of lower width pores than the pure acid and the lanthanum and cerium phosphomolybdates.…”

Section: Discussioncontrasting

confidence: 45%

“…Distinguishing between the primary and secondary structures is vital to understanding catalytic processes [26]. Many X-ray diffraction studies have been conducted and several phases have been identified with heteropoly compounds, including triclinic, and primitive and body-centered cubic [27][28][29][30][31][32][33][34][35]. The unit cell dimensions of heteropoly compounds are heavily dependent upon the degree of hydration, whereby complete phase changes can occur [36].…”

Section: Introductionmentioning

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: Discussioncontrasting

confidence: 45%

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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“…The small pores of heteropoly compounds generally result in low surface areas [4,5]. XRD studies have identified several phases, including triclinic, primitive and body-centered cubic [6][7][8][9][10][11][12][13][14]. The degree of hydration heavily influences unit cell dimensions, whereby complete phase changes can occur [15].…”

Section: Introductionmentioning

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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“…which are insoluble in water can be used. By combining various proportions of cations and heteropolyacid, a range of insoluble, microporous solid catalysts of different acidity, surface area and crystallinity can be obtained [16][17][18][19][20][21] [26]. Quite recently, cesium salts Cs x H 3-x PW 12 O 40 of various Cs content (x = 0.9-3) were successfully tested as the solid catalysts in methanolysis of tributyrin, a model compound of natural triglycerides [27].…”

Section: Introductionmentioning

confidence: 99%

Methanolysis of Castor Oil Catalysed by Solid Potassium and Cesium Salts of 12-Tungstophosphoric Acid

et al. 2008

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Methanolysis of castor oil to methyl esters, a key step in Biodiesel production, was studied with the use of KOH, H 2 SO 4 and 12-tungstophosphoric acid (H 3 PW 12 O 40 , HPW) as the homogeneous catalysts. Reaction was also performed in the presence of solid salts of HPW, namely M x H 3-x PW 12 O 40, where M = K or Cs and x = 2, 2.5 and 3 (abbreviated as K2, K2.5, K3 and Cs2, Cs2.5, Cs3, respectively). The HPW salts were precipitated by K 2 CO 3 and Cs 2 CO 3 or CsCl. Their properties were characterized by BET, electron microscopy (SEM, EDS) and colloidal particles size distribution (laser diffraction technique). The potassium doped HPW samples, K2 and K2.5, prove to be much more active catalysts (ca. 3 times) than their Cs-containing analogues. Among the K, Cs salts, K2 salt was the most active catalyst. The activity of catalysts was found to depend on preparation stages such as the temperature of drying or annealing and aging of the samples. Microscopic studies evidenced colloidal form of Cs and K salts particles under the catalytic reaction. The size of colloidal particles was found to depend upon the type of cation, Cs ? or K ? , as well as the ''history'' of catalysts preparation (temperature of drying). Based on the results obtained in this work, we concluded that activity was determined by the accessibility of the reactants to acid sites which is facilitated by the high surface area and open structure of the colloidal form. This may lead to better utilization of acid sites and higher activity of samples with lower content of K ? or Cs ? cations in the HPW.

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Pore structures of the monovalent salts of the heteropoly compounds, 12-tungstophosphoric and 12-molybdophosphoric acid

Cited by 138 publications

References 22 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

Methanolysis of Castor Oil Catalysed by Solid Potassium and Cesium Salts of 12-Tungstophosphoric Acid

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