C. Ferragina

Preparation and ion-exchange properties of a new phase of the crystalline titanium phosphate, Ti(HPO4)2·2H2O

The preparation of a new inorganic ion-exchanger with the formula Ti(HPO4)2·2H2O and its ion-exchange properties towards sodium and strontium ions, are reported and discussed. This exchanger is shown to be very stable to hydrolysis and to have high exchange capacity in strongly acid medium. Comparison with the corresponding zirconium phosphate dihydrated phase (γ-ZP), suggests that Ti(HPO4)2·2H2O possesses a different lattice structure from that reported for the monohydrated exchanger.

Catalytic activity of zirconium phosphate and some derived phases in the dehydration of alcohols and isomerization of butenes

Abstract The catalytic activity of α-Zr(HPO 4 ) 2 · H 2 O prepared by different methods and of phases derived from it by heating between 200 and 1100 °C or by ion exchange with Na + , Cs + , or Ag + , has been investigated by means of different acid-catalyzed test reactions, namely, isopropanol, 1- or 2-butanol dehydration, and 1-butene isomerization. The active centers of both Zr(HPO 4 ) 2 and ZrP 2 O 7 phases are mainly the surface Bronsted sites, as indicated by the strong decrease or annihilation of their catalytic activity after surface Cs + poisoning. An explanation of the low residual activity detected for some samples is given. As deduced from the products of 1-butene isomerization, the acidic sites are generally of medium strength. However, on heating between 350 and 700 °C, when partial or total condensation of hydrogen phosphate to P-O-P groups occurs (with progressive formation of the layered pyrophosphate phase) they transform into sites of medium-high Strength.

X-ray photoelectron spectroscopic evidence of interlayer complex formation between Co(II) and N-heterocycles in α-Zr(hpo4)2 · H2O

Abstract Evidence from XPS Spectroscopy for coordination of the Co(II) in zirconium phosphate-phen composite is described. Analysis of the shape of the Co2 p photoelectron peak indicates that high-spin N-coordinated Co(II) is present mixed with O-coordinated Co(II). Comparison of the N1 s peak with those in parent α-Zr(HPO 4 ) 2 (phen) 0.5 · 2H 2 O confirms that Co(II) is indeed N-coordinated, but that some phenanthroline molecules anchored to the host are also present.

TPD study of NH3 adsorbed by different phases of zirconium phosphate

Abstract Thermodesorption of NH 3 has been used to measure the acidity of α-zirconium hydrogen phosphate and different phases obtained from this material by thermal treatments. It was found that samples treated at temperatures lower than 300 °C, consisting of hydrated or anhydrous α-phases, adsorbed an amount of ammonia corresponding almost to neutralization of all acidic -POH groups and formation of a well-characterized diammonium phase. Samples treated at t ≥ 400 °C, in which partial or total condensation of interlayer -POH groups occurred, showed a strongly reduced capacity for adsorption of NH 3 , because of the formation of P-O-P bridges between layers which hindered diffusion of NH 3 . After pretreatment of Zr hydrogen phosphate at 600 °C, the TPD spectrum of ammonia adsorbed at room temperature showed only the signal of NH 3 adsorbed by surface -POH sites, indicating that its interaction with internal sites was now precluded. From the shape of the TPD curves from these samples information on the strength of surface acidic sites was deduced.

Ag-zirconium phosphate system: Characterization of the phases obtained at different temperatures

Abstract The products obtained by ion exchange of zirconium phosphate loaded with Ag + (from 13% to 96% of conversion) have been characterized by thermal and X-ray methods. The materials maintain a layered structure until around 550–600°C, with a d 002 of about 7,6–7,8 A. At low Ag conversion solid solutions can be obtained. For all samples, above 600°C the layered structure disappears and the phase AgZr 2 (PO 4 ) 3 is produced. Other phases, ZrP 2 O 7 , Ag 4 P 2 O 7 or Ag 3 PO 4 (depending on the initial composition) are formed together with AgZr 2 (PO 4 ) 3 . The conditions of formation and possible transformation of some of these phases are discussed.

Synthesis and chemical-physical characterization of palladium and rhodium new materials derived from octadecyltrimethylammonium cationic surfactant intercalated into zirconium and titanium dihydrogen phosphate

Abstract The intercalation of octadecyltrimethylammonium ion into group IV phosphates α- and γ-zirconium and γ-titanium has been investigated. These host matrices exchange cationic surfactant to give organo-inorganic composite materials. The obtained materials have an interlayer distance d notably increased with respect to the precursors, and are stable up to 200°C. These intercalated materials can, in turn, exchange transition metal ions, as Pd (II) and Rh (III) to give composite materials that can be used in heterogeneous catalysis. After metal exchange, partial surfactant elution does not remarkably modify the XRPD. The IR spectra confirm insertion of metals: competition of the metal with the amine for the P—OH bonding is evident.

Intercalation compounds of α-zirconium hydrogen phosphate with Rh3+ ions and Rh3+-diamine complexes. Part II. Their behaviour towards CO, CO2 and H2 and their use in the CO catalytic oxidation

The reactivity of Rh3+ ions and Rh3+-diamine α-Zr(HPO4)2·H2O complexes intercalated in α-zirconium hydrogen phosphate towards small molecules (CO, O2, H2) was studied. The compounds only containing Rh3+ ions, of composition ZrHxRhy(PO4)2·4H2O (x = 2 – 3y; 0 < y ≤ 0.66) react with CO at atmospheric pressure and temperatures ranging from 80 to 100°C, and undergo selective reduction of Rh3+ to Rh1+. The resulting materials containing Rh1+ are reoxidized to Rh3+ by molecular dioxygen under the same pressure and temperature conditions. The simultaneous action of a COO2 mixture determines the catalytic oxidation of the CO to CO2 and the system acts as a stable catalyst of this reaction. At higher temperatures, the reduction of Rh3+ is no longer selective and in these conditions Rh0 is formed, which escapes from the support and causes its deactivation. Similar behaviour is found in systems containing Rh3+-diamine complexes, which react with CO at temperatures higher than 120°C and undergo an irreversible reduction of Rh3+ to Rh0. The reaction with H2 (70 < T < 100°C) also causes a non selective reduction of the Rh3+ to Rh1+ and Rh0. The progress over time of the catalytic activity of some compounds with different contents of Rh3+ in converting CO to CO2 has shown not only that these materials maintain a constant catalytic activity, indicating the stability of the systems to the loss of metal during working cycles, but also that Rh3+ supported in these matrixes is more active and selective in this type of reaction than Rh3+ in solution.

Incorporation of Cadmium Ions and Cadmium Sulfide Particles into Sol-gel Zirconium Phosphate. Synthesis, thermal behavior and X-ray characterization

The inorganic ion-exchanger α-zirconium phosphate was synthesized by the sol-gel method and its properties relating to the exchange of Cd2+ and the intercalation of CdS particles were studied. The Cd2+-exchange process is a fast process and the material obtained exhibits an increased interlayer distance d with respect to its precursor (9.56 vs. 7.56 Å). The resulting Cd-containing material was exposed to aH2S gas flow to give CdS particles in the exchanger. The zirconium phosphate containing CdS particles still possesses a layered structure, with a pattern almost identical to that of the initial ion-exchanger precursor. Moreover, the material may exchange further Cd2+ and hence lead to a higher CdS particle content. The thermal behavior of this ion-exchangers containing Cd2+ or CdS particles was studied.

γ-Zirconium Phosphate Rhodium Intercalation Compounds: Preparation, Chemical and Thermal Characterization

Rh{sup 3+}/H{sup +} ion exchange in {gamma}-zirconium phosphate and in its intercalation compounds with organic diamine (2,2{prime}9bipyridyl, 1,10-phenanthroline, and 2,9-dimethyl-1,10-phenanthroline) has been investigated. Fully exchanged rhodium-zirconium phosphate has the composition {gamma}-Zr(PO{sub 4}) (H{sub 0.86}Rh{sub 0.38}PO{sub 4}) {center_dot} 2.3 H{sub 2}O and an interlayer distance of 15.2 {angstrom}. The exchange of Rh{sup 3+} in intercalation compounds leads to phases in which the molar ratio Rh{sup 3+}/diamine within the layers is about one. In some cases, a partial leaching of organic ligand during the Rh{sup 3+}/H{sup +} exchange has been observed. All the materials produced were characterized by their chemical compositions, X-ray powder diffraction patterns, and coupled TG/DTA analysis. In the presence of Rh{sup 3+} ions, the temperature of thermal deintercalation of diamine is lower than that observed in the pure intercalation compounds.

Zinc ions and zinc sulfide particles in sol–gel zirconium phosphate synthesis, thermal behavior and X-ray characterization

Abstract Zinc ions can be exchanged in sol–gel zirconium phosphate by using the batch or hydrothermal method. The zinc materials obtained that undergo thermal treatment after complete dehydration, can rehydrate fully or partially depending on whether half or all the zinc ions are exchanged. At high temperature syntherization is evident. By flowing sulfide acid over the zinc forms, zinc sulfide particles are formed and their amount depends on the length of time of the gas flow and on the state of hydration of the original material. This is not the case in the half exchanged zinc zirconium phosphate material. The decomposition temperature of the ZnS particles depends on their position in the exchanger: whether on the surface or between the layers of the host matrix. The XRD patterns of the materials obtained are similar to those of the sol–gel zirconium phosphate. The presence of ZnS particles is evident.