M-PILCs

To examine the thermal stabilities of the M-PILCs, oriented thin films were prepared on quartz slides. Powder X-ray diffraction patterns of the slides were run from 4-22 20 employing a step width of 0.02 20, and a step scan time of 4 seconds. The absolute intensities of the dooi peaks of the three different M-PILC species were measured and compared at room temperature and after treatment at increasing temperatures. 

The formation of the M-PILCs involved the use of a suspension of <2pm STx-1 montmorillonite (Source Clay Minerals Repository, University of Missouri), which had been acid washed (2M HCl), neutralized and exchanged three times with 4M NaCl. This clay mineral has a cation exchange capacity of approximately 84 meq/l(X)g, and a surface area of about 83.3 m2/g (Van Olphen and Fripiat 1979). The hydrolyzed metal solutions were added dropwise to vigorously stirred suspensions (ca. 1% w/w) of the Na-STx-1 (or vice versa), to solution loadings of ca. 10 meq metal/g STx-1. The suspensions were then washed with distilled water by centrifugation until testing with silver nitrate revealed the supernatant fluid to be negative for chloride ions. 

Figure 2. Concentration profile of p-Coumaric acid (A) p-hydroxybenzoic acid ( ) and p-hydroxybenzaldehyde ( ). ([p-coumaric] = 500 ppm, pHi= 3.5, T=343 K, [H202] = 2xl0 2 M, 0.5g/l (Al-Fe)PILC).

The effect of thermal treatment was investigated on the samples of the lOTi series. The specific surface areas were measured according to the different temperatures. As shown in Fig. 1, the BET surface areas of sulfated Ti-PILC decreased with the increase of the thermal treatment temperature, while the surface areas for vanadia Ti-PILC increased. At 400 °C which is the calcination temperature for SCR reaction, all samples showed almost the same value of specific surface area (near 160 m /g). 

Jiang, Y.-X., X.-M. Chen, Y.-F. Mo Z.-F. Tong (2004) Preparation and properties of Al-PILC supported S042-/Ti02 superacid catalyst. Journal of Molecular Catalysis A Chemical, 213,231-234,ISSN 13811169. 

Procedures leading to preparation of vanadium-doped alumina- and/or titania-pillared montmorillonites are described and physicochemical characterization (chemical analysis, XRD, BET, ESR) of the products is provided. Results show that introduction of vanadium into the pillared montmorillonites leads to a rigid association of the dopant with pillars, irrespective of the method of preparation. The mode of vanadyl attachment in alumina-pillared samples does not depend on the mode of preparation, while in titania-pillared montmorillonite it does. Certain degree of delocalization of the unpaired electron into ligands and increased in-plane 7t-covalent bonding is observed for vanadyl ions present in the co-pillared (V-Ti)-PILC samples which also show particularly high activity in catalytic ammoxidation of m-xylene to nitrile product, as monitored by IR. A hypothesis is advanced that this effect is due to the unique character of vanadyl species present in these catalysts. 

This paper describes preparation, physicochemical characterization and catalytic properties of a series of vanadium-doped alumina- and titania-pillared montmorillonites obtained by various methods The aim of this work was to investigate the influence of the preparation procedure and pretreatment on location of vanadium dopant within the PILC structure and to correlate the physicochemical characteristics of tiie samples with their catalytic activity in ammoxidation of m-xylene. 

The direct intercalation of metal oxide sols (DIMOS) according to Pinnavaia is a good technique to achieve stable oxide pillars [31]. Aqueous oxide sols with uniform particle sizes of 20-80 A can be used to create mesoporous pillared clays. The materials are also called supergallery PILCs, a term covering all substrates with an interlayer distance substantially larger than the thickness of the host layers. Ti-sol prepared from Ti-alkoxides results in Ti-PILCs with interlayer free spacings of 13 A and surface areas of 300 m /g. 

FIGURE 16 Adsorption-desorption isotherms of p- and m-xylene on Al-PILC doped with various amounts of Na ions. The pH value of the dispersion for loading the Na into the PILC structure is given on top of the plots. (From Ref. 89.)... 

V-PILC = vanadium-pillared montmorillonite catalyst rhoudary. B.M. Valli, V.L.K. Prasad, A.D. J. Chem. Soc., Ghent. Commun., 1990, 721. 

Chromium pillared clays represent an interesting case it was possible to obtain products with 27 A interlayer spacings [52]. These PILCS were prepared from hot basic chromium nitrate solution for which OH/Cr = 2. Surface areas were between 353 and 433 m /g. Heating to 500 C reduced the interlayer spacing to 21 A. Pore size data, however, are lacking. 

After pillaring and calcination the C.E.C of the clay is lost due to the migration of H+ to the octahedral layer (8,9). A treatment of the PILCs calcined at 500°C using a 4.10-3 M solution of K COa at 80°C restores the C.E.C (10). Exchanges were further realized with 3.75.10-3 M solutions of MgCl. eH O, Ca(N03)2.4Ha0. ZnCl. CeCU.OHaO and LaCla.SHaO. After washing samples were dried at 60°C. 

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