Heteropolyacids functionalized

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

Polymers have served roles in PEM fuel cell cathodes such as modifiers to macrocycle-based electrodes to improve conductivity and stability,165 composite materials with heteropolyacids,166 and as precursors to pyrolyzed catalysts.38,112,132,133 However, as discussed in the previous section, the activity of nitrogen-containing carbon raises the possibility of non-metal electrodes functioning in a cathode environment. Likewise, researchers have noted ORR activity for various conducting polymers containing nitrogen, and recently studies on their potential use in PEM fuel cell cathodes have been reported. 

Scheme 5 Xylose can be dehydrated to produce furfural. The reaction has been reported using several different catalysts including zeolites, sulfonic acid functionalized MCM-41 and immobilized heteropolyacids. The best selectivity towards furfural was achieved using zeolite H-mordenite, although at low conversion of xylose.Overall, the best yield of furfural was obtained using sulfonic acid functionalized MCM-41.

Fig. 17. Differential heat of NH3 absorption as a function of the ammonia uptake for heteropolyacids. (From Ref. 132.)...

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). 

In this section, these influences will be described. Besides the acidic properties, the absorption properties of solid heteropolyacids for polar molecules are often critical in determining the catalytic function in pseudoliquid phase behavior. This is a new concept in heterogeneous catalysis by inorganic materials and is described separately in Section VI. With this behavior, reactions catalyzed by solid heteropoly compounds can be classified into three types surface type, bulk type I, and bulk type II (Sections VII and IX). Softness of the heteropolyanion is important for high catalytic activity, although the concept has not yet been sufficiently clarified. 

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... 

This is an attractive method since it does not require the functionalization of the ligand. Augustine et al. [57] developed heteropolyacids (HPA), notably phos-photungstates, as a magic glue to attach cationic Rh and Ru complexes to various surfaces. The interaction of the heteropolyacid is thought to occur directly... 

Figure 2.25 Examples of solid acid catalysts (a) zeolite MFI (ZSM-5) (b) functionalized ordered mesoporous silica (MCM-41) (c) pillared clay (d) a heteropolyacid (H3PMoi204o)-...

Functionalized SiMCM-41 as support for heteropolyacid based catalysts... 

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]. 

Montmorillonite, silicate, aluminosilicate, titanosilicate, calcium phosphate, zirconium phosphate, metal oxides, and heteropolyacids composites with Nation exhibit in general a modest barrier effect to methanol permeation (F, > 0.1), with a couple of exceptions aCloisite lOA composite [62] with 0.013 < F, < 0.065, and a chitosan-functionalized montmorillonite composite [71] with 0.028 < F < 0.050, in both cases for clay contents between 1 and 10 wt%. 

Solvent-free synthesis of functionalized pyridine derivatives using WeUs-Dawson heteropolyacid as catalyst. 

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