Hydration, with heteropoly compounds

In addition to large-scale industrial applications, solid acids, such as amorphous silica-alumina, zeolites, heteropoly acids, and sulfated zirconia, are also versatile catalysts in various hydrocarbon transformations. Zeolites are useful catalysts in fine-chemical production (Friedel-Crafts reactions, heterosubstitution).165-168 Heteropoly compounds have already found industrial application in Japan, for example, in the manufacture of butanols through the hydration of butenes.169 These are water tolerant, versatile solid-phase catalysts and may be used in both acidic and oxidation processes, and operate as bifunctional catalysts in combination with noble metals.158,170-174 Sulfated zirconia and its modified versions are promising candidates for industrial processes if the problem of deactivation/reactivation is solved.175-178... 

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... 

Han et al (61) reported that the Al2(Mo04)3 phase on alumina is easily hydrated by moisture in air and transforms into amorphous M0O3, whereas AIPO4 only shghtly reacts with water. Further addition of phosphorus decreases the formation of Al2(Mo04)3 since competitive adsorption of phosphorus and molybdenum oxo-species occurs on the alumina surface. Phosphorus inhibits the formation of Al2(Mo04)3 in the presence of nickel (62). The number of deposited polymeric phosphorus-oxo compounds decreases in the presence of molybdenum, probably through the formation of dispersed Mo—P heteropoly compounds (63). 

Heteropoly-compounds of Molybdenum and Phosphorus.— Heteropoly-compounds include those acids and salts which contain acid anhydrides of one or more elements combined with a hydrate or salt of the acid of another element.- Compounds which contain the acid anhydride and the acid hydrate or salt of the same element—for example, polychromates, polytungstates, etc.—are distinguished as isopolycompounds. 

X-ray studies of crystalline compounds of a number of salts of isopoly and heteropoly anions have been made and will be discussed below. By using these structures as a guide, considerable headway has been made in the interpretation of solution s tudies, and, especially in recent work, reliable, internally consistent data have been obtained. It is to be noted, however, that the X-ray studies do not show positions of hydrogen atoms and that, while the basic units determined crystallographically often persist in solutions, hydration and protonation in solution depend on the conditions. Also the fact that a salt with a particular structure crystallizes from solution under certain conditions does not necessarily mean that the same anion is the major species... 

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