Heteropoly compounds liquid phase

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... 

Early attempts to use heteropoly compounds as catalysts are summarized in reviews published in 1952 (//) and 1978 (7). The first industrial process using a heteropoly catalyst was started up in 1972 for the hydration of propylene in the liquid phase. The essential role of the Keggin structure in a solid heteropoly catalyst was explicitly shown in 1975 in a patent concerning catalytic oxidation of methacrolein. Systematic research in heterogeneous catalysis with these materials started in the mid-1970s and led to the recognition of quantitative relationships between the acid or redox properties and catalytic performance... 

Typical examples of liquid-phase oxidation with molecular oxygen catalyzed by heteropoly compounds are listed in Table XXVI. Introduction of Vs + or... 

Liquid-Phase Oxidation Reactions with Molecular Oxygen Catalyzed by Heteropoly Compounds Reaction Catalyst Temp. (K) Ref. 

The use of platinum, heteropoly compounds, and metal-containing heteropoly compounds in the aerobic oxidation of cyclohexane, cyclohexene, and a-pinene in the liquid phase has been reviewed. The catalysts serve to control free radical processes. The role of peroxide intermediate in determining the final products is discussed.251... 

As mentioned above, H3PW12O40 (HTP) is very active solid acid for various reactions. It is also known that polar molecules are absorbed in the solid bulk phase and the polar reactants undergo chemical transformations in the solid bulk as well as on the surface. This behaviour of heteropoly compounds is called a pseudo liquid phase phenomenon. 

Zhang, F.M., Wang, J., Yuan, C.S., Ren, X.Q. 2005. A pronounced catalytic activity of heteropoly compounds supported on dealuminated USY for liquid-phase esterification of acetic acid with n-butanol. Catalysis Letters 102(3-4) 171-174. 

Activated carbons are also adequate supports for HPA since the acidity of the heteropoly compounds is preserved [P3j. In the case of microporous carbons the HPA will be deposited on the external surface. However, in any support, if liquid phase processes are used, leaching of the supported HPA can be a serious problem [37]. Conjugated polymers such as polyacetylene, polypyrrole and polyaniline have been used as HPA supports. In the case of polyacetylene the HPA can be introduced on the surface of the polymer, while retaining its acidity [38]. However, unless a very special behaviour could be achieved, this will nor be able to compete with other less expensive inorganic supports. 

Owing to the flexible nature of the secondary structure of the acid forms and group A salts, polar molecules such as alcohols and amines are readily absorbed into the solid bulk by substituting water mol ciiles and/or by expanding the interdistance between polyanions. Heteropoly acids which have absorbed a significant amount of polar molecules resemble in a sense a concentrated solution and are in a state between solid and solution. Therefore, this state is called the pseudo-liquid phase . Some reactions proceed mainly in this bulk phase. The tendency to form a pseudoliquid phase depends on the kind of heteropoly compound and the molecules to be absorbed and on the reaction conditions. 

---