Pasquale Patrono

Oxidative carbonylation of aniline catalyzed by Pd(II)-2,2'-bipyridyl complex intercalated in α-zirconium-phosphate

Abstract Palladium(II) and palladium(II)-copper(II) complexes (with N-donor ligands intercalated between the layers of α-zirconium phosphate) have been employed in the oxidative carbonylation of aniline. The catalytic activity of the materials has been studied together with the properties of α-zirconium phosphate as a supporting agent. Their very low activity observed in an initial induction period slowly increases to more marked levels in mild working conditions (80 °C, atmospheric pressure); in more drastic conditions diphenylurea and methyl carbamate are produced in a non-selective way due to a concomitant oxidation of aniline. By pre-heating the materials at 130 °C under CO or CO/O2, an increase of the catalytic activity is obtained, and the treated systems are able to catalyze selectively the carbonylation of aniline in mild conditions. By submitting the pretreated systems to a series of catalytic cycles and by re-employing the same catalyst in each cycle, a decrease in activity is observed until complete deactivation of the catalyst, when Pd is almost completely eliminated by the solid. On the basis of the analysis of the pretreated sample before and after deactivation, this behaviour is ascribed to migration of the Pd from the inner layers to the surface of the solid matrix and to its subsequent solubilization in the reaction medium.

Coordination of Co2+, Ni2+ and Cu2+ to 2,9 - dimethyl - 1,10 phenanthroline intercalated in α-zirconium phosphate: Evidence for dimers

2,9-Dimethyl-1,10-phenanthroline (dmp) intercalates into α-Zr(HPO4)2. (2EtOH) to form α-Zr(HPO4)2 (dmp)0.50. 2.5H2O at maximum uptake, at 25°C. This lamellar composite has an interlayer distance of 14.60(5) A, which changes little - to 13.58(5) A - when the pseudo-zeolitic water is lost. An almost vertical orientation of the dmp between the phosphate layers is proposed, as was found previously for the unsubstituted phenanthroline analogue. When the material is exchanged with Co2+, Ni2+, and Cu2+, under conditions such that [M] : [L] = 1:1 there is partial elution of the dmp, giving rise to materials of formulation α-ZrH1.3M(OH2)0.35(dmp)0.35(PO4)2·nH2O, with no change in interlayer distance. Spectroscopic evidence for the formation of dimers to the intercalated dmp is described.

XPS characterisation of iron-modified vanadyl phosphate catalysts

Iron-modified vanadyl phosphate is an interesting material with potential applications in catalysis due to the oxidising and dehydrogenating properties of the trivalent metal. Alumina-supported samples have been characterised by X-ray photoelectron spectroscopy (XPS) and compared with respect to the temperature of calcination and their catalytic behaviour in the oxidative dehydrogenation of ethane. XPS has been used to analyse the surface chemical composition of the samples and the modifications induced by different temperatures of calcination and catalysis. The oxidation state, amount, distribution and evolution of vanadium species have been investigated both after calcination at T=450 and 550°C and after catalytic tests at T=450, 550 and 650°C. Quantitative XPS analysis has been used to determine the surface concentration of different vanadium species.

Pillaring of layers in α-zirconium phosphate by 1,10-phenanthroline and bis(1,10-phenanthroline)copper(II): formation of complex pillars in situ

The complex [Cu(phen)2]2+(phen = 1,10-phenanthroline) can be diffused between the layers of α-zirconium phosphate only if the layers are first pre-swelled by preparing the diethanol intercalate, α-Zr(HPO4)2(EtOH)2. At maximum uptake a material of formula α-ZrH1.6[Cu(phen)2]0.20(PO4)2·3H2O is obtained and no further complex can be intercalated. X-Ray and spectroscopic evidence show that the [Cu(phen)2]2+ remains intact after intercalation, and probably has a tetragonal-octahedral geometry. A ‘complex pillared’ layer structure is still present after the zeolitic water has been removed. However, the geometry adopted by the [Cu(phen)2]2+ is now square-based pyramidal, and it is bonded asymmetrically between the phosphate layers. Further ions (Cu2+, Pd2+, or Ag+) can be exchanged into the pillared cavities, to form solid solutions. 1,10-Phenanthroline itself diffuses into α-Zr(HPO4)2(EtOH)2 to form the ‘intercalated ligand’ phase α-Zr(HPO4)2(phen)0.50·2H2O at maximum uptake. This is a pure, well ordered Stage I phase with an interlayer distance of 13.58 A, and it is suggested that the phen is ordered throughout the layers in a ‘slanted’ fashion. This phase exchanges Co2+, Ni2+, and Cu2+(in the order Cu2+ Co2+ > Ni2+) much more slowly than does the 2,2′-bipyridyl analogue, due to the steric hindrance caused by the bulkier ligand backbone and higher pillar density. Only in the case of Cu2+ does subsequent co-ordination to the phen proceed to complete formation of α-ZrH [Cu(phen)]0.50(PO4)2·3H2O. In the cobalt and nickel analogues there is competition between phen-co-ordinated and cavity-co-ordinated metal ion. Spectroscopic evidence (u.v.–visible, e.s.r.) is presented which shows that these complex pillars formed in situ have very distorted geometries, caused by the steric constraints imposed by the interlayer region.

Intercalation compounds of α-zirconium hydrogen phosphate with RhIII ions and RhIII-diamine complexes. Part 1.—Preparation, thermal behaviour and X-ray photoelectron spectroscopy investigation

Rhodium(III) can be exchanged between the layers of α-zirconium phosphate by employing the pre-swelled diethanol intercalate, α-Zr(HPO4)2(ethanol)2. During the Rh3+/H+ exchange, four rhodium-containing phases are formed with different interlayer distances. However, only the fully Rh-exchanged compound, α-ZrRh0.66(PO4)2.4H2O, is obtained as a pure phase. Rhodium(III) can also be exchanged into the layered intercalation compounds α-Zr(HPO4)2(bipy)0.251.5H2O (bipy = 2,2′-bipyridyl), α-Zr(HPO4)2(phen)0.52H2O (phen = 1,10-phenanthroline) and aZr(HPO4)2(dmp)0.5·2.5H2O (dmp = 2,9-α-dimethyl-1,10-phenanthroline). Exchange is accompanied by a partial elution of the diamine for the phen and dmp derivatives. Various materials are obtained and their thermal properties discussed. X-Ray photoelectron spectroscopy (XPS) gives evidence that RhIII-diamine complex species mixed N- and O-coordinated RhIII are formed in the interlayer region of the three intercalation compounds.

In situ coordination of Fe2+ to aromatic diamines intercalated into γ-zirconium and γ-titanium phosphates : evidence from Mössbauer spectroscopy and thermal studies

Iron(ii) can be exchanged into layered γ-Zr(H 2 PO 4 )(PO 4 )–diamine and γ-Ti(H 2 PO 4 )(PO 4 )–diamine composites (diamine=2,2′-bipyridyl, 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline). Mossbauer spectroscopy indicates that an in situ iron–amine coordination occurs in the case of iron–bipyridyl– and iron–phenanthroline–γ-zirconium phosphate: Fe 2+ low-spin trischelates [Fe(bipy) 3 ] 2+ and [Fe(phen) 3 ] 2+ are formed between the layers of the host; high-spin Fe 2+ also forms complexes in the interlayer region and the chromophores could be any of the possibilities provided by the formulation [FeN x O 6-x ] (x=1–4). Iron(ii) partially transforms into iron(iii) when the former is not stabilized by the formation of strong complex species. The thermal behaviour of the exchanged compounds has been investigated and correlated with the composition of the materials. X-Ray patterns of some of the new materials are also reported.

ZIRCONIUM PHOSPHATES AS PHOTOCATALYSTS

Abstract The photo-oxidation of several alkylbenzenes in mild conditions has been achieved using zirconium phosphate prepared by different methods. By irradiating solutions of 1,2-dimethylbenzene, 1,4-dimethylbenzene or 1,2,4,5-tetramethylbenzene in a polar solvent with light of λ greater then 280 nm, in the presence of zirconiun phosphate or its derived phases in a stream of air, we have observed only oxidation of the side chain. The degree of crystallinity and the chemical composition of the inorganic sensitizer, and the polarity of the solvent, influence the conversion rate of the substrate. Moreover, different oxidation products are obtained, depending on the different reaction conditions. The results of these test reactions lead to a hypothesis for their mechanism; fundamental knowledge for any further utilization of this effective photocatalytic system.

Pillar chemistry. Part 4. Palladium(II)–2,2′-bipyridyl, –1,10-phenanthroline, and –2,9-dimethyl-1,10-phenanthroline complex pillars in α-zirconium phosphate

Palladium(II) can be exchanged into the layered composites α-Zr(HPO4)2(bipy)0.25·1.5H2O (bipy = 2,2′-bipyridyl), α-Zr(HPO4)2(phen)0.50·2H2O (phen = 1,10-phenanthroline), and α-Zr(HPO4)2(dmphen)0.50·2.5H2O (dmphen = 2,9-dimethyl-1,10-phenanthroline) to give new palladium(II) amine complex–pillared materials. In all three cases, both 1 :2 and 1 :1 PdII:amine complexes are formed between the layers. Pillared materials with an interlayer distance as high as 17.3 A can be obtained. Thus, using such in situ preparation methods, it is possible to prepare pillared materials with pore dimensions approaching those found in zeolite Y. Electronic spectral evidence for the presence of different geometries for the pillars is described (square planar for bipy and phen, but five-co-ordinate for both 1 :2 and 1 :1 dmphen pillared materials). All the materials exchange further metal ions, Co2+, Ni2+, and Cu2+, to high loading levels, a demonstration that they are indeed pillared. Evidence is presented which shows that uptake of Cu2+ occurs at different rates for the 1 :1 and 1 :2 complex–pillared materials, i.e. the cavities have different sizes and therefore different accessibilities. In addition, spectroscopic probing (visible–near u.v. and e.s.r.) of these cavity-exchanged ions clearly demonstrates that the new cavities formed have geometries different from those present in the parent α-Zr(HPO4)2·H2O.

On the synthesis and characterization of layered antimony(III) phosphate and its interaction with moist ammonia and amines

Samples of antimony(III) phosphate, a layered material, were prepared at room temperature, using the two allotropic forms of Sb2O3, layered valentinite and cubic senarmontite. The compounds were characterized by infrared spectroscopy, X-ray diffraction, and thermogravimetric–differential thermal analysis. Solids exposed to ammonia, ethylenediamine, or hydrazine vapors also were studied. The interaction between SbPO4 and the bases always led to the formation of stoichiometric amounts of Sb2O3 and hydrogen phosphate(–2) salts of the bases. With ammonia, the SbPO4 raw materials gave rise to valentinite or senarmontite, depending on which Sb2O3 allotropic form was used to prepare antimony phosphate. This effect was modified when the SbPO4 preparations were preheated at 600°C, in which case, a mixture of both forms was obtained. With ethylenediamine and hydrazine, SbPO4 of whatever origin always gave rise to senarmontite. No evidence of intercalation in the interlayer region of SbPO4 was obtained.

Ge-Zr phosphate system: the advantages of thermal methods in the investigation of phase mixtures or solid solutions

Abstract Several Ge and Zr phosphates, coprecipitated with different methods have been characterized by TG-DTA and X-ray techniques; from the data obtained it has been possible to evidentiate when solid solutions or mixed phases are formed. A possible mechanism of their formation is put forward.