Terephthalate-pillared hydrotalcite

Synthesis of Terenhthalate/Vanadate-Pillared Hvdrotalcite. To a 1350-g portion of a terephthalate-pillared hydrotalcite was added a solution consisting of 14.0 g NaVOg in 100 mL deionized water. (The amount of vanadate added corresponds to 25% of that needed for stoichiometric exchange of terephthalate with V10O28 .)... 

In neutral or basic media, terephthalate-pillared hydrotalcite is stable indefinitely. Acidification with dilute HCl or HNO3 results in the formation of the corresponding chloride- or nitrate-... 

Synthesis and Characterization of Isopolymetalate-Pillared Hvdrotalcites. Exchange of terephthalate-pillared hydrotalcite with the appropriate metalate under mildly acidic conditions (pH =4.5) proceeds smoothly to yield the corresponding isopolymetalate-pillared hydrotalcite, as indicated by X-ray diffraction and elemental analysis. The d-spacings of the products confirm that the shortest dimension of the isopolymetalate is perpendicular to the metal hydroxide layers. 

Table I. Exchange Reactions of Terephthalate-Pillared Hydrotalcite Clays with Decavanadate...

Figure 4. Vanadium-51 solid state MAS-NMR of terephthalate-pillared hydrotalcites partially exchanged with decavanadate (a) 39% exch. (b) 60% exch. (c) 91% exch.

This paper summarizes work done on the synthesis and characterization of terephthalate-, isopol3rmetalate-, and terephthalate/isopolymetalate-pillared hydrotalcites. Several test... 

Figure 1. Schematic representation of terephthalate exchange with heptamolybdate and decavanadate in hydrotalcite. Pillared hydrotalcite d-spacings were calculated from models.

Figure 4 shows the MAS-NMR spectra of several terephthalate/decavanadate-pillared hydrotalcites. These spectra are consistent with that previously published for (NH4)gVio028 (23). The changes which occur to the decavanadate pillars upon calcination of the pillared hydrotalcite are currently being investigated. It is known, however, that in the case of pillared materials containing as little as 25-30% polyoxometalate pillars the overall layered structure is maintained up to 500°C (Figure 5). 

Figure 5. TEM micrograph of a terephthalate/decavanadate-pillared hydrotalcite (39% decavanadate exchanged) after calcination at 500 .

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