X-ray spectroscopic characterization of Cu2+-phenanthroline complexes intercalated in α-zirconium phosphate

X-ray photoelectron spectroscopy provides evidence that when [Cu(phen)₂]²⁺(phen = 1,10-phenanthroline) is diffused between the layers of -zirconium phosphate, the complex species does not remain intact after intercalation, but some Cu-N bonds are broken, replaced with Cu-O bonds and the released nitrogen atoms can now interact with the PO₃-OH groups of the host. XPS also provides evidence for coordination of the Cu²⁺ ions when they are diffused by ion exchange in the phenanthroline--zirconium phosphate intercalation compound. Although Cu²⁺ and phen are in a 1 : 1 molar ratio in the interlayer region of the host, so that a 1 : 1 coordination could be expected between the two species, the characteristic peaks of the uncoordinated phenanthroline, even though at a low intensity, are still present. The differences between the two Cu(II)-intercalation compounds are discussed.     

Intercalation of heterocyclic compounds in α-zirconium phosphate: Imidazole,benzimidazole, histamine and histidine

The intercalation of imidazole and some organic species containing the imidazole ring, between the layers of crystalline zirconium phosphate has been investigated. Fourteen new, well-ordered intercalation compounds are obtained with the batch procedure at r.t. and/or 60°C. A mechanism of formation of the various compounds is proposed on the basis of the interaction between the guest molecules (with their dimensions and geometries) and the free PO₃OH groups available between the layers of the host. The new phases have been characterized by TG and X-ray methods.     

Tg/dta,Xrd and NH3-TPD Characterization of Layered VOPO4·2H2O and its Fe3+-Substituted Compound

Iron(III)-substituted vanadyl phosphate, [Fe(H2O)]0.20VO0.80PO4·2.25H2O (FeVOP), has been prepared and characterized by XRD and TG/DTA analyses. The new compound is isomorphous with layered tetragonal VOPO4·2H2O (VOP), but it possesses a lower interlayer distance. Information on the reactivity and surface acidity of both VOP and FeVOP has been obtained by NH3-TPD experiments. The hydrated materials adsorb high amounts of NH3 (up to 2 mmol g-1). Different ammonia-containing phases are formed, characterized by lower interlayer distances in comparison with the NH3-free parent compounds. NH3 is intercalated between the layers without displacement of water. The materials dehydrated by heat treatment at 450°C retain the layered structure but adsorb NH3 only on the external surface. A wide variety of acid sites, from weak to strong, was observed. A mechanism is proposed for the NH3- acid sites interaction. SEM micrographs of VOP and FeVOP are shown. This revised version was published online in July 2006 with corrections to the Cover Date.     

Derivation of structural models for two intercalated compounds of α-zirconium phosphate

Reasonable structural models are proposed for two intercalated compounds of-Zr(HPO₄)₂·H₂O (-ZrP), one with 2,2-bipyridyl (A) and another one with 1,10-phenanthroline (B). The models are derived by considerations of the unit-cell geometry changes undergone by-ZrP upon insertion of the organic molecules and on a set of general criteria of structural analysis, already developed by us and called the comparison method. If it is assumed that the water molecules in A and B keep the positions they have in-ZrP, as fixed by their links to the phosphate-OH groups, the inserted molecules, while obeying the general conditions of optimum packing, establish interactions of the hydrogen-bonding type with the water molecules. This modeling gives for A and B a possible structural explanation to the maximum number of inserted molecules of the two species, as fixed by their stoichiometry.     

NH3 TPD study and thermal behaviour of vanadium-exchanged titanium phosphates as catalysts

The ion exchange technique was employed for the preparation of VO²⁺ modified titanium phosphates as catalysts for the selective reduction of NO with NH₃. The samples were prepared by contacting with a vanadyl sulphate solution different precursor materials, amorphous, crystalline or sodium half exchanged titanium phosphate. The vanadium contents of modified phosphates were in the range 0.08–2.3 wt%. XRD and thermal analysis TG/DTA showed that vanadium loading does not cause structural modification in hydrogen titanium phosphate. A vanadyl containing phase was obtained when half sodium titanium phosphate was employed. The NH₃ TPD measurements indicated the presence of a wide distribution of NH₃ adsorbing sites with medium-high strength. Catalytic activity measurements were performed under dilute conditions. It was found that the presence of vanadium even in low amounts strongly promote the catalytic activity.     

Studies on Water and Ammonia Programmed Thermodesorption of Mixed M(III)-vanadyl Phosphates

Hydrated M(III)-vanadyl phosphates (M (III)=Mn, Fe, Ga, Al) have been prepared and studied for water and ammonia adsorption properties by TG/DTA, NH₃ TPD, FTIR and XRD techniques. The compounds have the same tetragonal layered structure of VOPO₄ ⋅2H₂ O, but shorter interlayer distances. Ammonia adsorption leads to intercalation of large amounts (0.19–0.39 mol/mol) of base between the layers of the materials, without displacement of water. The ammoniated phases obtained from these compounds have interlayer distances shorter than that of the corresponding precursors. In this connection an interaction mechanism NH₃ -host is proposed. Treated at 450°C the materials adsorb ammonia only on the external surface because of the large decrease of the interlayer distance that prevents NH₃ from entering the interlayer space. All M(III)-vanadyl phosphates present a wide distribution of strength of ammonia adsorbing sites. This revised version was published online in July 2006 with corrections to the Cover Date.     

Diffraction and XPS studies of Cu complexes of intercalated compounds of α-zirconium phosphate. I: Derivation of structural models from powder diffraction data

Reasonable structural models are proposed for the Cu complexes of two intercalated compounds of -Zr(HPO₄)₂·H₂O (-ZrP): one with 1,10-phenanthroline (A) and the other with 2,2-bipyridyl (B). The models are derived from considerations of the unit-cell geometry changes undergone by -ZrP upon insertion of, first, the organic molecules and then copper, in accordance with a set of general criteria of structural analysis called the comparison method.     

Thermal, structural and acidic characterization of some vanadyl phosphate materials modified with trivalent metal cations

A set of new materials with general formula [M(H₂O)]_X(VO)_1–XPO₄·2H₂O (M ³⁺=Al, Cr, Ga, Mn), isomorphous with layered tetragonal VOPO₄·2H₂O and having potential catalytic properties, have been characterized by TG and DTA, X-ray diffraction and surface acid strength. During heating the compounds transform in the monohydrated and anhydrous phases, all maintaining a layered structure, with a proper interlayer spacing. Catalytic tests performed with 1-butene show that theM ³⁺-vanadyl phosphates greatly improve the conversion of the olefine with respect to pure vanadyl phosphate.This work was carried out in the framework of the Agreement for scientific cooperation between the National Research Council of Italy and the Academy of Sciences of the Czech Republic. V.Z. and L.B. wish to thank the Grant Agency of the Czech Republic for financial support (Grant no. 203/95/1321). Funds from Ministero dell'Universita e della Ricerca Scientifica (MURST) are also acknowledged by M.A.M.     

XPS studies on the host-guest interaction of 2,2′-Bipyridyl, 1,10-phenanthroline and 2,9-dimethyl-1,10-phenanthroline intercalated inα-zirconium phosphate

The host-guest interactions of 2,2-bipyridyl, 1,10-phenanthroline and 2,9-dimethyl-1,10-phenanthroline intercalated between the layers of crystalline-zirconium monohydrogen phosphate have been studied by X-ray photoelectron spectroscopy. Evidence that, on average, only one of the two nitrogen atoms of each aromatic diamine is protonated by the P-OH groups of the host is given. The acid-base interaction is strongly reduced on dehydration of the materials. The role of the cointercalated water is discussed, together with the probable disposition of the guests within the interlayer region.     

Spectrofluorimetric trace determination of terbium(III) with potassium oxalate

Potassium oxalate acts as a specific reagent in enhancing the fluorescence intensity of terbium in aqueous solutions. Maximum fluorescence intensity is obtained by irradiating (at 255 mμ) terbium(III) dissolved in 0.01 M potassium oxalate solution at pH 7.8. The enhancement and quenching phenomena caused by other lanthanides, errors in the determination, and various examples of spectrofluorimetric analysis of traces of terbium in mixtures with other lanthanides are described. The sensitivity of the method is 5·10^-2μg/ml of terbium.