Keggin-type heteropolyacid HPA

MOFs. An exceptional feature of HKUST-1 is its controlled dimensionality and high porosity with potential applications in gas storage, catalysis and drug delivery. Sun et al. [31] have reported the incorporation of Keggin-type heteropolyacids (HPA) into the HKUST-1 pores by hydrothermal synthesis with the objective of using this hybrid material in acid catalysis. 

Song, I. and Barteau, M. (2004). Redox Properties of Keggin-type Heteropolyacid (HPA) Catalysts Effect of Counter-cation, Heteroatom, and Polyatom Substimtion, J. Mol. Catal. A Chem., 212, pp. 229-236. 

The Keggin-type heteropolyacid (hereafter abbreviated HPA) is a unique catalyst material because it has the dual catalytic functions of strong acidity and high oxidizing capacity [1-5]. HPA has been applied commercially as an efficient catalyst in several petrochemical processes, including the direct hydration of propene (1972) [6,7], isobutene (1984) [8] and n-butenes (1989) [9], the oxidation of metha-crolein to methacrylic acid (1982) [10], the oligomerization of tetrahydrofuran to polymeric diols (1985) [11], and the oxidation of ethene to acetic acid (1997) [12]. 

Keggin-type heteropoly compounds have attractive and important characteristics in terms of catalysis. They consist of heteropolyanions and counter-cations such as H, Cs or NHT When the counter-cations are protons, they are called heteropolyacids (HPA). An important characteristic of HPAs, such as 12-tungstophos-phoric acid (H3PW12O40), is the presence of very strong Bronsted acid sites. But the characteristics of HPAs strongly depend on temperature and relative humidity. When they are used in heterogeneous catalysis, it is often necessary to support them on high-surface-area oxides or activated carbons, in order to increase the surface contact with the reactants. 

The development of catalysts obtained by means of heteropolyacids (HPA) and related compounds is a very important growing field. Since HPA are less corrosive and produce lower amount of wastes than conventional acid catalysts, they can be used as replacement in ecofriendly processes. Within the HPA, there is a special interest in those which present a Keggin type structure. 

Immobilization of Keggin-type and Dawson-type heteropolyanions (HPA) PMoi204o> SiWi204o and P2W18O62 in PMT is performed by electropolymerization of 3-methylthiophene in aqueous and nonaqueous solution in the presence of corresponding heteropolyacids and salts. It is possible to obtain electrodes modified with HPA molecules. These are stable in acidic solutions [696-699]. 

---