Heteropolyacids, supported

Cesium salts of 12-tungstophosphoric acid have been compared to the pure acid and to a sulfated zirconia sample for isobutane/1-butene alkylation at room temperature. The salt was found to be much more active than either the acid or sulfated zirconia (201). Heteropolyacids have also been supported on sulfated zirconia catalysts. The combination was found to be superior to heteropolyacid supported on pure zirconia and on zirconia and other supports that had been treated with a variety of mineral acids (202). Solutions of heteropolyacids (containing phosphorus or silicon) in acetic acid were tested as alkylation catalysts at 323 K by Zhao et al. (203). The system was sensitive to the heteropoly acid/acetic acid ratio and the amount of crystalline water. As observed in the alkylation with conventional liquid acids, a polymer was formed, which enhanced the catalytic activity. 

Rh- or Ir-exchanged heteropolyacids supported on Si02 catalyze vapor-phase carbonylation of methanol or dimethyl ether to give methyl acetate at 498 K and 1 atm (370). As shown in Table XXXIII, with RhPWi2O40/SiO2, the yield of methyl acetate is 44%. At this temperature, the yield of methyl acetate dropped rapidly to < 1 % during 6 h of reaction time accompanied by increases in the yields of dimethyl ether, methanol, and hydrocarbons. 

Dupont P., Vedrine J. C., Paumard E., et al.. Heteropolyacids supported on activated carbon as catalysts for the esterification of acrylic acid by butanol. Appl. Catal. A-Gen 129 (1995) pp. 217-227. 

J. N. Beltramini, Catalytic Properties of heteropolyacids Supported on MCM-41 Mesoporous Silica for Hydrocarbon Cracking Reactions, Stud. Surf. Sci. Catal, 146, 653-656 (2003). 

Yadav GD, Bhagat RD (2004) Synthesis of methyl phenyl glyoxylate via clean oxidation of methyl mandelate over a nanocatalyst based on heteropolyacid supported on clay. Org Process Res Dev 8 879... 

Shikata, S., Nakata, S., Okuhara, T., Misono, M. 1997. Catalysis by heteropoly compounds. 32. Synthesis of methyl tert-butyl ether catalyzed by heteropolyacids supported on silica. Journal of Catalysis 166(2) 263-271. 

Heteropolyacids supported on activate carbon as catalysts for the esterification of acrylic add by butanol. Appi Catal A Gen... 

Preyssler Heteropolyacid Supported on Nano-SiO, Hj pSlaPjWjjOjjJ/SiOj ... 

Preyssler Heteropolyacid Supported on Nano-Si02, Hj fNaPgWjQOjjJ/SiOj a Green and Reusable Catalyst in the Synthesis of Polysubstituted Quinolines... 

Polyolefin supported sulfonic acid. Heteropolyacid supported on activated carbon. Solid acids of metal oxide promoted with S04, H3PO4 supported on silica gel, Solid super acid of Zr(OH)4 exposing with H2SO4 by calcinations, Solid acid having salts of H3PW12O40CS2.5PW12O40... 

Alcaiiiz-Monge, J., Trautwein, G., Marco-Lozar, J.P., 2013. Biodiesel production by acid catalysis with heteropolyacids supported on activated carbon fibers. Applied Catalysis A General 468, 432—441. Available at http //www.sciencedirect.com/science/article/pii/ S0926860X13005486 (accessed 11.05.15.). 

Preparation, characterization, and catalytic activity of H3PW12O40 heteropolyacid catalyst supported on mesoporous Y-AI2O3... 

Finally, the abatement of NO pollution by using sorbing catalytic materials [59,60] must also be cited. Several solid sorbents for NO removal (metal oxides, spinels, perovskites, double-layered cuprates, zeolites, carbonaceous materials, heteropolyacids and supported heteropolyacids) have been tested. The results are interesting, but not competitive to actual technologies. To mention that the use of sorbing materials allows... 

Other materials that have been investigated include sulfated zirconia, Br0nsted and Lewis acids promoted on various supports, heteropolyacids, and organic resins, both supported and unsupported. On the whole, these materials also deactivate rapidly, and some of them also exhibit environmental and health hazards. 

Heterogenous reactions, Sh/Nu ratio, 27 64 Heteroligand complex, 32 260-262 Heteropolyacids defined, 41 117 heteroatoms, 41 118, 120, 121 Prins reaction, 41 156 supported, 41 149-150 Heteropolyanions, 41 113, 117, 119-121 Heteropoly blues, 41 191 Heteropoly compounds absorption, 41 179-180, 190-191 acid-catalyzed reactions heterogeneous, 41 161-178 liquid phase, 41 150-161 acidic properties in solid state, 41 141-150 in solution, 41 139—14] catalysis, 41 114, 116-117, 190-191 as catalyst, 41 113-116, 117, 223-232... 

They present strong acidities (the pH values of aqueous solutious of heteropolyacids indicate that they are strong acids) both in solid and in liquid solution (Figure 13.2). In addition, they can be prepared in an wide range of surface areas (partially salified heteropolyoxometalates permit the modification of the surface areas of these materials) or be supported in metal oxides. 

Thus, if the incorporation of some metal oxides indicated a notable improvement in the catalytic activity (permitting it to operate at lower reaction temperatures),the incorporation of metals, especially Pt and working in the presence of H2, has prolonged the hfe of the catalysts. However, new catalyst formulations have recently increased the resistance of these catalysts to such poisons as water or sulfur during the isomerization of n-C5 and n-C6 paraffins. Nevertheless, the use of other anions, by supporting WO3 or MoOf or heteropolyacids,which have higher thermal stability, can also be interesting alternative routes to develop new catalytic systems. 

It can be seen that the catal5dic activity strongly depends on the number and t) pe of the incorporated countercation, which determines the number and strength of acid sites. In addition to this, the existence of mesoporosity (which also depends on the countercation) is also a key factor in the catalytic behavior of these catalysts.In this way, Si02- or MCM-41-supported heteropolyacids also have been studied in order to increase catalytic activity, apparendy without modifying the acid strength. ... 

The first examples of an electrostatie attachment of POMs on solid supports are dated to the mid 1980. Baba et al. reported immobilization of heteropolyacids on the anion-exchange resin Amberlist-15 [68]. Later on, this type of the support was successfully used by Jacob s group to immobilize the Venturello complex P04[W0(02)2]4, well known as highly selective homogeneous catalyst for H202-based epoxidation of alkenes... 

In this context, much effort has also been invested in controlling the nuclearity of the catalyst ensemble through the selection of its precursor. One area in which considerable progress has been made involves the adsorption of polynuclear clusters onto supports [33]. Examples involving the immobilization of small, preformed polynuclear clusters on supports are the reactions of carbonyl clusters of the late metals [16, 34], the binding of polyoxometalates (POMs) and their neutral alkoxy analogues [35] and heteropolyacids such as the Keggin cluster [36, 37]. 

Scheme 3 Acrolein can be obtained by dehydration of glycerol. The reaction was reported many years ago using powdered KHSO4/K2SO4 as catalyst. Recently, the use of silica-supported heteropolyacids has also been described, notably with silicotungstic acid as catalyst.

The strength and the number of acid centers as well as related properties of heteropolyacids can be controlled by the structure and composition of heteropolyanions, the extent of hydration, the type of support, the thermal pretreatment, etc. 

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