Heteropolyacid catalysts, supported

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

NEW OXIDATIONS OF ORGANIC SUBSTRATES USING PEROXIDE AND SUPPORTED HETEROPOLYACID CATALYSTS... 

Cui, Z., Li, C.M. Jiang, S.P. PtRu catalysts supported on heteropolyacid and chitosan functionalized carbon nanotubes for methanol oxidation reaction of fuel-cells. Phys. Chem. Chem. Phys. 13 (2011), pp. 16,349-16,357. 

Several studies have reported the catalytic conversion of cellulose into sorbitol. Among the metal catalysts used, Ru and Ft promoted both hydrolysis and hydrogenation steps (Dhepe et al., 2008). A catalytic system containing molecular acids such as H2SO4, HCl, or heteropolyacids combined with supported metal catalysts like Ft, Pd, and Ru could efficiently catalyze the conversion of cellulose to sorbitol (Anand et al., 2012 Palkovits, 2010,2011 Geboers et al., 2010 Dhepe et al., 2008). The highest yield of sugar alcohols (81%) could be achieved by the combination of heteropolyacids with supported mthenium catalysts (Palkovits et al., 2011). 

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. 

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... 

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.

It was confirmed that the reaction did not proceed in the liquid phase. A rapid decline in catalytic activity was observed. The deactivation is probably caused by strong adsorption of the product benzophenone on the catalyst the acylation was retarded when the reaction was started in the presence of benzophenone. The reaction also proceeded with H3PMo 2O40/SiO2 as the catalyst, but the H3PMO 204o decomposed during the reaction. It was presumed that the catalyti-cally active species was not the heteropolyacid on the support, but was probably Mo chloride instead (213). 

The influence of bulk-type behavior also exists in supported heteropoly catalysts. Changes in the activity as a function of the loading of heteropolyacids depend on the reaction type (151). At low loadings, the rates of both the bulk and the surface reactions increase as the loading increases because the... 

Selective oxidation materials fall into two broad categories supported systems and bulk systems. The latter are of more practical relevance although one intermediary system, namely vanadia on titania [92,199-201], is of substantial technical relevance. This system is intermediary as titania may not be considered an inert support but rather as a co-catalysts [202] capable of, for example, delivering lattice oxygen to the surface. The bulk systems [100, 121, 135, 203] all consist of structurally complex oxides such as vanadyl phosphates, molybdates with main group components (BiMo), molybdo-vanadates, molybdo-ferrates and heteropolyacids based on Mo and W (sometimes with a broad variation of chemical composition). The reviews mentioned in Table 1.1 deal with many of these material classes. 

In this paper factors controlling the catalytic activity in the hydrodesulfurization reaction (HDS) are discussed. The SiOa-supported phosphormolybdenum heteropolyacid (HPMo) is used as a model catalyst. Two types of the catalyst deactivation have been shown. The reversible deactivation effect is related with changes in the molybdenum valence, its 0- and 0,S-surrounding and adsorbtion of the S-containing reaction products. The HDS activity is irreversibly changed when the transformation of the catalyst phase composition is carried out ... 

In this paper deactivation of the hydrodesulfurization (HDS) catalysts is examined using the results obtained for the thiophene conversion on the supported phosphormolybdenum heteropolyacid as a model catalyst. 

Noble metal salts of heteropolyacids function in novel ways as catalysts. Pd. sPW12O40 supported on... 

Friedel-Crafts alkylation processes were traditionally operated at 65-70°C with AICI3 and at 40-60°C with HF. A variety of solid acid catalysts have been developed at the laboratory level, mainly based on zeolites, heteropolyacids or sulfated zirconia (zirconia treated with sulfuric acid). The most recent industrial achievement is the Detal process (UOP-CEPSA) which is based on silica-alumina impregnated with HF. The selectivity towards linear alkylbenzenes exceeds 95%. The cymene processes use AICI3 in the liquid phase or supported phosphoric acid as catalysts. 

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. 

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