Zirconium pillars

Zirconium Pillared Montmorillonite Reduced Charge of the Clay... 

Non-aggressive way using zirconium acetate for preparation of zirconium pillared clay developing high sulfur thermal stability over 830 °C... 

ZIRCONIUM PILLARED CLAYS. INFLUENCE OF BASIC POLYMERIZATION OF THE PRECURSOR ON THEIR STRUCTURE AND STABILITY E.M. Faifan-Tortes, O. Dedeycker, P. Grange... 

Organic phosphonates represent another class of anchoring agents, which react with zirconium hydroxide to form pillared structures. These are also referred to as molecularly engineered layered structures (MELS). Layered compounds of organic phosphonates of zirconium with the formula of Zr(RP03)2 have been rec-... 

Fig. 9 Schematic representation of pillared a-zirconium phosphite-4,4 -(3,3 5,5 -tetram-ethylbiphenylene)bis(phosphonate) [64, 65]...

Brindley and Sempels (1), Vaughan et al. (2) and Shabtai (3) have shown that the experimental conditions of Al intercalation influences the physicochemical properties of the clay. The nature, amount and spacial distribution of the pillars change the thermal stability, texture and acidity of the pillared clays. For example, Rausch and Bale (4) have reported that the OH/Al ratio modifies the structure of the Al complex and that monomeric [Al(0H)x(H20)6-x] " or polymeric [A1i304(0H)24(H20)i2] species can be obtained. Clearfield (5) demonstrated that the polymerisation state of Zr species depends on the temperature, concentration and pH of the solutions. In any case, the height of pillars is largely controlled by the polymerisation state of the intercalated complexes. However, in order to maintain the accessibility of the inner surface, the density or spacial distribution of the pillars has to be controlled. This parameter has been studied by Flee et al (5), and Shabtai et al (7) for Al pillared clays and Farfan-Torres et al (8) for zirconium. 

Many other inorganic pillars have been incorporated into clays for instance, calcining after ion exchange with zirconium oxychloride can create zirconia pillars. 

More recently, crown ether pillared and functionalized a-zirconium phosphonates have been synthesized [34], Incorporation of crown ethers was achieved by first converting them to their respective phosphonic acids. X-ray diffraction studies showed that the interlamellar spacing was about 15 A when a biphospho-nic acid was used. Both a- and y-type zirconium phosphonates could be synthesized using this methodology. Preliminary results showed that these layered materials have good selectivity toward binding transition metal ions and that the interlamellar fluoride ions could be replaced by anion exchange. 

Zhang B. and Clearfield A., Crown ether pillared and functionalized layered zirconium phosphonates a new strategy to synthesize novel ion selective materials, J. Am. Chem. Soc. 119(1997) pp. 2751-2752. 

The acidity of pillared clays has been characterized by both microcalorimetric measurements of the adsorphon of aromatic molecules and pyridine and the catalytic ethylbenzene test reaction [111]. The aromatic probe molecules used were a reactant and a product of the catalytic reaction ethylbenzene and m-diethylben-zene, respectively. In this way, only the strongest of the accessible acid sites were htrated. The heats of adsorphon of these molecules indicate that a zirconium oxide pillared clay had stronger acidity than an aluminum oxide pillared clay, whereas the pyridine results were equal for both samples. 

Many other materials, including synthetic aluminas, aluminum carbonates, aluminum silicates, magnesium silicates, various forms of attapulgite and sepiolite (81-83), alumina-pillared acid-activated montmorillonite (84), synthetic mica mont-morillonite, HY-zeolite, zirconium phosphate (85), mica, kaolin, and synthetic hectorite (86), have been evaluated for their ability to purify virgin fats and oils, but none were as good as acid-activated bentonite. 

Advancements in the preparation of new PLS s nearly parallels that of the zeolite and zeolite-like phases. Initially the pillared smectite clays were investigated but the quest for new materials with new properties led to e qiloring the pillaring of other layered phases. These include, most notably, the layered zirconium phosphates, double hydroxides (hydrotalcites), sihcas and metal oxides. The parallel paths of discovery in new material compositions for the layered phases and the microporous (zeoUte) phases are summarized in Table 1. A conq>arison between the pore architectures of the zeohtes and the two dimensional PLS is shown in Table 2. 

Zirconium phosphate derivatives have been investigated for a number of applications. Thio-phosphate derivatives,542 as well as [PhNH3]2[Zr(P04)3],545 have been employed as ion-exchange media. Similarly, a variety of materials derived from pillared Zr phosphates offered promise as selective ion-exchange materials.546-549... 

We have prepared other mixed composition pillared compounds irtiich have as their non-pillaring group the hydroxyl moiety, and thus are simply relatives of zirconium phosphate in which the layers are spread at a fixed distance apart. These products behave as expected in titration and ion-exchange experiments, and will not be further discussed here. 

G. Alberti, U. Costantiono, F. Marmottoni, R. Vivani, and P. Zappelli, Preparation of a Covalently Pillared a-Zirconium Phosphite-diphosphonate with a High Degree of Interlayer Porosity. Microporous Mesoporous Mater., 1998, 21, 297-304. 

Al, - Novel alumina-pillared y-zirconium phosphate materials have... 

Pillared zirconium clay modified by sulfate constitutes a new class of materials. Nevertheless, the classical procedure consisting of impregnating these solids with sulfate solutions presents some disadvantages such as low surface area and a poor sulfur thermal stability. In a previous work, we have developed a new in situ sulfation preparation method using zirconyl chloride as zirconium precursor. However, the use of this salt gives an intercalation solution with a very low pH which can affect the clay layers. Furthermore, the addition of sulfate ions to the ZrOz solution is limited by Hauser salt or polymeric phase precipitation. 

In this work, zirconium acetate solution was used in order to increase the pH of the pillaring solution and the content of sulfate ions introduced. Different preparation parameters and their effect on the structural and textural properties have been investigated. The resulting materials present a best zirconium-sulfate intercalation with higher sulfate rate and develop very high thermal stability of sulfur even at about 830 °C. 

Some attempts eonsisting of adding ammonium sulfate to the pillared montmorillonite suspension have been reported [4,5], These preparation methods show that adding sulfate ions decreases considerably the basal spacing without developing high acidity. Other studies attempted to prepare zirconium sulfate pillared clays by adding in situ sulfate. However, the solids obtained have a low surface area, low thermal stability [6] and low sulfate to zirconium ratios [7], Earlier, we have prepared a zirconium sulfate pillared clay by in situ... 

Na-montmorillonite suspension was added dropwise to the fresh pillaring solution with different clay to zirconium ratios. The mixture was magnetically stirred for different times at 15 °C. The dispersed montmorillonite was separated by centrifugation and washed by dialysis. The resulting clay was dried overnight in oven at 120 °C. 

The diffraction patterns of dried zirconium sulfate pillared clay obtained after different intercalation times are presented in Fig. 2. These samples were prepared using a 0.1 mol/L zirconium acetate solution with an S04 Zr ratio = 0.5. The clay concentration was 10 g/L, with Clay Zr =10 g/mol, at pH = 4.00. The intercalation was performed at 15 °C. 

All samples were prepared using 0.1 mol/L zirconium acetate solution at 15 °C with 42 hours intercalation reaction. The clay suspension pH was fixed at the same value as that of the intercalation solution. The X-ray diffraction patterns of zirconium sulfate pillared clays prepared with different sulfate to zirconium ratios are shown in Fig. 4. This figure shows a shoulder at about 19.5 A for the sample prepared using a S04 Zr ratio equal to 0.125. The 19.5 A spacing corresponds to the intercalation of non sulfated zirconium polycations [13]. Non-drastic loss in surface area is observed when the sulfate to zirconium ratio increases. But the use of zirconyl chloride solution shows a drastic loss of surface area when the SOarZr ratio increases (more than 50 %) [13]. 

The XRD patterns of zirconium sulfate pillared clays obtained after 90 hours of intercalation with different zirconium acetate concentrations using 0.5 as sulfate to Zr ratio and the same clay concentration as used earlier are presented in Fig. 5. The diffraction data show the appearance of two first order reflections. The first one is at 23.4 A for the lowest zirconium concentration and appears as a shoulder at the same distance for 0.05 mol/L concentration. The second reflection is observed at approximately 12.3 A for the lowest concentration and at 13.7 A for 0.1 mol/L zirconium acetate. The first one results from the intercalation of sulfated zirconium species. Those species are more voluminous than the non sulfated one which gives a distance spacing at only 19.6 A. The better intercalation of sulfated zirconium species at low Zr concentration is probably due to the slow progress of polycondensation reactions. This process reduces the number of different zirconium species and gives a better cristallinity of the solid. Table 2 summarizes the textural properties of samples prepared with different zirconium concentrations. The decrease of the surface area with the decrease of the Zr concentration is probably due to the increase of the sodium clay layers by comparison with the intercalated layers. The microporous volume increases when the Zr concentration decreases. The higher microporosity is due to the important basal distance of this sample. 

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