Zirconium phosphate crystalline

Addition of a soluble Zr(IV) salt to phosphoric acid results in the precipitation of a gelatinous amorphous solid. The stoichiometric crystalline zirconium phosphate can be prepared by refluxing zirconium phosphate-gel in concentrated phosphoric acid [5]. The procedures for synthesis of zirconium phosphate have been described in detail elsewhere [6]. 

Another preparative method in which the rate of precipitation is slow involves slow decomposition of zirconium fluoro complexes [14], These are first prepared by adding an appropriate amount of hydrofluoric acid (HF) to the zirconyl salt and these complexes are decomposed in the presence of phosphoric acid, with a slow stream of nitrogen or water vapor passing through the system. The rate of precipitation of zirconium phosphate is controlled by the rate of removal of HF from the system, and when this is very slow, a highly crystalline a-ZrP is obtained. The gamma form of the metal phosphate differs significantly from the alpha and current discussion will be concerned with the latter phase. 

Slade, R.C.T., Forano, C.R.M., Peraio, A. and Alberti, G. (1993) A JH NMR relaxation-time study of dynamic processes in zirconium phosphates of differing crystallinities and in related compounds. Solid State Ionics, 6, 23-31. 

We discuss crystalline inorganic ion exchangers, such as [97,98,104,134-146] zeolites, hydrotal-cites, alkali metal titanates, titanium silicates, and zirconium phosphates, and also organic ionic exchangers such as the ion-exchange resins. However, details are given only in the case of the archetypal crystalline ionic exchangers, that is, aluminosilicate zeolites [97,98,104,134]. 

About 40 years ago, Clearfield and coworkers started a fertile activity in the synthesis and characterization of crystalline zirconium phosphates [136,140,148], After the initial findings, an enormous research effort directed toward the syntheses and characterization and investigation of the properties of the many phases of crystalline zirconium phosphate have been carried out [140], In this regard, it has been shown that, in general, all of the zirconium phosphate phases have excellent ion-exchange properties. 

This section describes the applications of some important crystalline inorganic ion exchangers, such as the hydrotalcites, titanates, and zirconium phosphates [3,87-111],... 

Appreciable ionic conductivity is found in open framework or layered materials containing mobile cations (see Ionic Conductors). Several phosphates have been found to be good ionic conductors and are described above NASICON (Section 5.2.1), a-zirconium phosphates (Section 5.3.1), HUP (Section 5.3.3), and phosphate glasses (Section 5.4). Current interest in lithium ion-conducting electrolytes for battery apphcations has led to many lithium-containing phosphate glasses and crystalline solids such as NASICON type titanium phosphate being studied. ... 

The following laboratory method was used for the introduction of zirconium phosphate into ceramic porous strucmres. The method is based on impregnation of the porous materials with crystalline sol of zirconium dioxide. 

There are several forms of metal(IV) phosphates, including amorphous, crystalline, and pellicular. However, here only the preparation of amorphous zirconium phosphate is described. Phosphoric acid (10 % w/w. 162 ml) was added to zirconyl chloride octahydrate (14.4 g in 112 ml of demineralized water), and stirred at room temperature for 4 h. The resulting gel was washed repeatedly with demineralized water (3 x 500 ml) and centrifuged each time. 

Alluli et al. [119] demonstrated, the effective use of synthetic inorganic adsorbents in gas chromatography. Clear separations of hydrocarbons and mercaptans on crystalline zirconium phosphate were obtained. 

In general, the crystalline form does not hydrolyze to the extent that the amorphous form does (19,123, 237), although ion exchange which is accompanied by an increase in distance between the layers makes the crystalline form more susceptible to hydrolysis (23). Since the j8 and y forms of zirconium phosphate are more open, exchange of cations such as Cs+ and Ba +, which are excluded in the a form, can occur in these forms. Since one hydrogen is opposed to the other, the theoretical capacity of 7.06 meq/gm is not achieved. 

The ion exchange behavior of various substituted ammonium ions on crystalline zirconium phosphate has also been investigated 448). A nearly complete separation of various substituted ammonium ions was achieved. As measured in units of meq/ml of bed, the breakthrough capacities were octylammonium, 0.10 ethylammonium, 0.16 methyl-ammonium, 0.30 and ethylenediammonium 0.37. The separation of triethanolammonium, 0.18 ethanolammonium, 0.20 and ammonium ions was only partially successful. Decreasing temperature increased the breakthrough capacities. 

Inorganic ion exchangers fall roughly into two groups crystalline, such as the ammonium salts of the 12-heteropolyacids, and amorphous, such as zirconium phosphate. One example from each group will be described. 

A large number of inorganic layer crystals such as micas, sodium silicates, niobate, uranate, vanadate, titanate, zirconium phosphate, graphitic acids, crystalline silicic acids, vanadium oxyhydrate, calcium phosphoric acid esters, and titanium disulfide develop alkyl crystals between their rigid crystal layers by ion exchange with, for example, alkyl ammonium salts and by intercalation inorganic... 

Crystalline zirconium phosphate was prepared by the method described by Clearfield and Thakur. Thermal activation was carried out at 100, 200, 300, 400 C. A portion of the amorphous material used to make the crystalline zirconium phosphates was retained for evaluation. Catalysts were characterised using titrimetric methods to measure acidity and x-ray diffraction to examine crystallinity. Thermogravimetric analysis (TGA) was used to determine phase changes on heat treatment. 

X-ray diffraction analysis of the catalyst samples would tend to show that a chemical change takes place about 100 C. The crystalline sample has a very distinct diffraction pattern (Figure 4). However the sample heated to 400°C is pure zirconium pyrophosphate (Figure 5). At intermediate temperatures the samples are shown to be mixtures of zirconium phosphate and pyrophosphate. This contradicts Segaura s findings. 

Five catalysts were assessed for activity in phenol hydroxylation. These were amorphous zirconium phosphate and the four crystalline samples heated at 100, 200, 300 and 400°C. The best catalyst in terms of conversion of phenol to catechol and hydroquinione was the crystalline sample heated at 100°C. This gave typically >90% selectivity to dihyroxybenzenes at 12% conversion of phenol and 2 1 mole ratio of phenol to Reactivity decreased with high activation temperatures. 

The existing method for preparing crystalline zirconium phosphate is firstly to precipitate the amorphous form from a mixture of phosphonic acid and zirconyl chloride and secondly to reflux the amorphous form in 12M phosphoric acid for several days after washing the amorphous form free of chloride. This gives the a-form. Not only is this a time consuming process, but the amorphous form is difficult to filter. We aimed to develop a one step process to the crystalline material by using crystal habit modifiers. 

Nonetheless these materials were found to be effective phenol hydroxylation catalysts (Table 5) showing similar conversions and selectivities to a crystalline zirconium phosphate heated at 100°C. 

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