Keggin-type heteropolyacids

Herve et al. (57) investigated the thermal changes of structures by means of XRD and TG-DTA for Keggin-type heteropolyacids and proposed Scheme 2. Infrared spectroscopy of H4PMo, VO40 showed the release of vanadium atoms to form H3PM012O40 and vanadium phosphate species (55). Exposure to water vapor induces the decomposition of the latter (indicated by the disappearance of a band at ca. 1037-1030 cm -1) (58). 

Figure 23 shows a correlation between the catalytic activity and the Hammett acidity function (H0) of Keggin-type heteropolyacids in CH3CN. The catalytic activity increases with the acid strength (63). 

Figure 3.11 FTIR skeletal spectra of a-Zr(HPOi)2 H2O, CdMo04 (scheelite type) and the Keggin-type heteropolyacid salt K3PM012O40.

The acid strength of Keggin-type heteropolyacids is stronger than such conventional solid acids such as Si02-Al203 and H-Y zeolites. The acid strength of crystalline heteropolyacids decreases in the series. ... 

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]. 

Izumi, Y., Ogawa, M., and Urabe, K. 1995. Alkali metal salts and ammonium salts of Keggin-type heteropolyacids as solid acid catalysts for liquid-phase Friedel-Crafts reactions. Appl. Catal. A Gen. 132 127-140. 

Figure 2 a,b 1-butene conversion and selectivity towards cis 2-butene for the Dawson-type heteropolyacid. C,d 1-butene conversion and selectivity towards cis 2-butene for the Keggin-type heteropolyacid. Total flow 10ml min , 20% 1-butene in Helium, 0.3ml catalyst. 

Mukai and co-workers [105] used Keggin-type heteropolyacids immobilized in the network structure of resorcinol-formaldehyde carbon gels as catalysts for the synthesis of methyl tert-butyl ether from methyl alcohol and tert-butyl alcohol. Large amounts of 12-tungstophosphoric and 12-molybdophosphoric acids were immobilized into the support by two methods, pore shrinkage and the ship-in-the-bottle method, which are essentially impregnation methods. The authors reported that these catalysts showed activity in the reaction studied and could be of practical utility as solid acid catalysts in various reactions. 

Here the active component in the catalyst has a finite vapor pressure and is carried out of the reactor. Examples are the loss of M0O3 from Keggin-type heteropolyacids (vanadomolybdatophosphates) and the loss of HgClj as the catalytically active species in the production of vinyl chloride from ethylene and HCl. A possible countermeasure is saturation of the feed with the active component. 

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. 

Molybdenum nitride containing phosphorous was prepared by a TPRe of 12-molybdophosphoric acid—a Keggin-type heteropolyacid— with CH4/4 H2 (46). 

M. M. Heravi, F. Derikvand, F. F. Bamoharram, J. Mol. Catal. A Chem. 2007, 263, 112-114. Highly efficient, four-component one-pot synthesis of tetrasubstituted imidazoles using Keggin-type heteropolyacids as green and reusable catalysts. 

Electroactive anions can also be used to prepare polypyrrole films, leading to new ways of applications, especially in the field of electrocatalysis [150]. For example, the phtalocyanine tetrasulfonate anion has been incorporated into a polypyrrole film during generation in aqueous solution [151]. Keggin-type heteropolyacids, such as (SiWi204o) ... 

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. 

Finally, it is interesting to address that both VPO and Mo-based MMO catalysts show low yields in the partial oxidation of isobutane. In addition, methacrolein rather than methacrylic acid is formed as the main partial oxidation product. " Moreover, the highest yields to methacrylic acid can be achieved during isobutane oxidation over Keggin-type heteropolyacid based catalysts. ... 

With respect to the catalysts, i.e. mixed-metal oxides and/or heteropolyacids, those presenting well-known structures — as is the case for vanadyl pyrophosphate, orthorhombic bronzes, or Keggin-type heteropolyacids — have been developed in well-known catal5dic processes. However, the roles of amorphous and/or quasicrystalline phases present in the more active and selective catalysts are still unclear and therefore should also be considered. 

A microwave-assisted method has been developed by Ighilahriz et al. (2008) for the synthesis of 4(3H)-quinazolinones by condensation of anthranilic acid, orthoesters (or formic acid) and substituted anilines, using Keggin-type heteropolyacids upw p p3Up, H SiMOjP o-nnp or... 

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