Molecular design of solid acid catalysts. Isomerization of n-butane catalyzed by acidic cesium salts of 12-tungstophosphoric acid combined with platinum1Catalysis by Heteropoly Compounds, part 29. Part 28: K.Y. Lee, S. Oishi, H. Igarashi and M. Misono, Catal. Today, in press. Communication presented at the First Francqui Colloquium, Brussels, 19–20 February 1996.1

Na, Kyutae; Iizaki, Takeshi; Okuhara, Toshio; Misono, Makoto

doi:10.1016/s1381-1169(96)00350-0

Cited by 42 publications

(13 citation statements)

References 11 publications

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“…Therefore, it is urgent to develop a solid acid catalyst without chloride for the industrial process of n -butane hydro-isomerization. Heteropolyacids [18,19,20,21,22,23], solid superacids (SO 4 /ZrO 2 , WO x /TiO 2 , etc. ) [24,25,26,27,28,29,30,31,32], and acidic zeolites (H-ZSM-5, H-Beta, etc. )…”

Section: Introductionmentioning

confidence: 99%

Hydroisomerization of n-Butane over Platinum-Promoted Cesium Hydrogen Salt of 12-Tungstophosphoric Acid

Liu

Misono

2009

Materials

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The hydroisomerization of n-butane was carried out in a fixed-bed gas-flow reactor over Pt-promoted Cs2.5H0.5PW12O40 (denoted as Cs2.5). Two kinds of catalysts, a direct impregnation of Pt on Cs2.5 (denoted as Pt/Cs2.5), as well as a mechanical mixture of Pt/Al2O3 and Cs2.5 (denoted as Pt/Al2O3+Cs2.5), were used for the hydroisomerization. Pt/Al2O3+Cs2.5 showed a higher stationary activity than Pt/Cs2.5 because the Pt particles supported on Al2O3 were much smaller than those supported on Cs2.5. The initial activity decreased with increasing H2 pressure over Pt/Al2O3+Cs2.5. This indicates that the hydroisomerization of n-butane over Pt/Al2O3+Cs2.5 proceeded through a bifunctional mechanism, in which n-butane was hydrogenated/dehydrogenated on Pt sites and was isomerized on acid sites of Cs2.5. For the hydroisomerization of n-butane over Pt/Al2O3+Cs2.5 the hydrogenation/dehydrogenation on Pt sites is a limiting step at a low Pt loading and the isomerization on solid acid sites is a limiting step at a high Pt loading. During the reaction, hydrogen molecules were dissociated to active hydrogen atoms on Pt sites, and then the formed active hydrogen atoms moved to the solid acid sites of Cs2.5 (spillover effect) to eliminate the carbonaceous deposits and suppress the catalyst deactivation. Because Cs2.5 has suitably strong and uniformly-distributed solid acid sites, Pt/Al2O3+Cs2.5 showed a higher stationary activity than Pt/Al2O3+H-ZSM-5 and Pt/Al2O3+SO4/ZrO2 for the hydroisomerization of n-butane at a low H2 pressure.

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Section: Introductionmentioning

confidence: 99%

Hydroisomerization of n-Butane over Platinum-Promoted Cesium Hydrogen Salt of 12-Tungstophosphoric Acid

Liu

Misono

2009

Materials

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“…This decrease has been related to the formation of ultrafine precipitate of particles (probably Cs 3 PW 12 O 40 , 8 -10 nm) which are thickly covered by H 3 PW 12 O 40 , being deposited upon evaporation of water, and form large aggregates, whereby the hydrogen form is possibly acting as cement substrate. After heat treatment they are converted to particles having a similar size as before heat treatment and nearly uniform composition, but with small specific surface area [38,39]; 3) Supporting Cs 1 PW and K 1 PW on silica resulted in increasing the catalytic activity due to an effective increase of the S BET from 9.9 to 296 m 2 /g for Cs 1 PW and from 11.6 to 268 m 2 /g for K 1 PW. This significant increase in the specific surface area is expected to be accompanied by a corresponding increase in the concentration of active sites involved in the catalytic conversion process; 4) Figure 4 shows that the % alcohol conversion over un- supported K x and Cs x salts of tungstophosphoric acid (x = 2, 2.5) decreased by supporting on silica surface.…”

Section: Catalytic Properties Of Different Solidsmentioning

confidence: 99%

Catalytic Activity and Selectivity of Unsupported Dodecatungstophosphoric Acid, and Its Cesium and Potassium Salts Supported on Silica

Ibrahim

2013

MRC

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Potassium and cesium salts of tungstophosphoric acid were prepared by precipitation method. For sake of comparison HPW, potassium and cesium tungstophosphates were supported on silica (20 wt%) by wet impregnation method. The catalysts were characterized by XRD, nitrogen adsorption-desorption measurements at 77 K, and the catalytic activity has been studied by using the catalytic conversion of tert-butanol at temperatures between 323 and 423 K. The results revealed that all of the catalysts were active and selective towards dehydration of tert-butanol yielding isobutene with low amount of isooctene as result of oligomerization process. Substitution of one proton of HPW by cesium or potassium cation exerted no measurable effect on the catalytic activity. The conversion over unsupported catalysts increased by increasing the cation content per Keggin unit of x ≥ 2. Supporting the previous salts on SiO 2 resulted in a significant decrease in the catalytic activity upon increasing cation content. Activation energy was calculated for different solids.

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“…These reactions are the ones involving nonpolar molecules such as hydrocarbons (butene isomerization, butane cracking, propene oligomerization, n-butane isomerization, cracking of C 6 -C 8 alkenes and aromatics alkylation [13]) which are unable to penetrate the bulk of a heteropoly compounds. It implies that the reaction occurs mostly on the surface acids of the heteropoly compounds [13,38]. In these reactions the activity of acidic salts of HPA does not correlate with the total proton content of the catalyst, but with the ''surface acidity''.…”

Section: K-salts Of H 3 Pw 12 O 40mentioning

confidence: 99%

“…accessing to all the protons. The reactions may proceed in the bulk of heteropoly compounds at the state called the ''pseudoliquid phase'' [38]. For example, the activity of K-salts of HPW in dehydratation of ethanol and hydration of ethylene decreases stepwise when the number of K ?…”

Section: K-salts Of H 3 Pw 12 O 40mentioning

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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Cited by 42 publications

References 11 publications

Hydroisomerization of n-Butane over Platinum-Promoted Cesium Hydrogen Salt of 12-Tungstophosphoric Acid

Hydroisomerization of n-Butane over Platinum-Promoted Cesium Hydrogen Salt of 12-Tungstophosphoric Acid

Catalytic Activity and Selectivity of Unsupported Dodecatungstophosphoric Acid, and Its Cesium and Potassium Salts Supported on Silica

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

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