Authors:S. Casenave, H. Martinez, C. Guimon, A. Auroux, V. Hulea, and E. Dumitriu
MgCuAl layered double hydroxides (LDHs) with a hydrotalcite like structure containing different proportions of Mg2+ and Cu2+ cations have been prepared. Thermogravimetry and X-ray diffraction data indicated that the transformation of LDH into mixed
oxides is effective after calcination at 723 K, irrespective of the composition. The acid-base properties of these mixed oxides
have been investigated using adsorption microcalorimetry and X-ray photoelectron spectroscopy with NH3 (for acidity) and SO2 (for basicity) as probe molecules. Their catalytic behaviour for the conversion of cyclohexanol has been tested. The acid-base
properties and the selectivity of catalysts has been related to their composition.
Authors:Wincenty Turek, Joanna Strzezik, and Agnieszka Krowiak
oxidation reaction were correlated with their oxidation–reduction and acid–baseproperties.
Experimentals and methods
Preparation of catalysts
Catalysts NiCo 2 O 4 and NiFe 2 O 4 were prepared using the
The acid-base character of vanadium pentoxide, V2O5/SiO2 and V2O5/γ-Al2O3 catalysts has been investigated by adsorption of ammonia and sulphur dioxide using microcalorimetry. By depositing vanadium
oxide on silica; new surface sites are formed which present more acid strength than bulk vanadium pentoxide and pure silica.
Alumina-supported vanadium catalysts can be regarded as acidic monolayers VOx. Sulphur dioxide was found to be selective for uncovered alumina.
Distribution coefficients, pH dependence, isotherms, kinetics and breakthrough curves of Sr binding have been measured on
several types of adsorbents (carbons modified with titanium silicate, crystalline titanium silicate, mixed titanium-manganese
oxide, and synthetic zeolites A4 and P) from different water solutions. It is concluded that acid-base properties of the adsorbent
is very important for Sr binding. Titanium silicate based adsorbents had reduced chemical stability in an artificial food
fluid below pH 2, the mixed titanium manganese oxide below pH 6, zeolite A4 below pH 5 and zeolite P below pH 7. Consideration
is given to the feasibility of the adsorbents for food decontamination.
Authors:Sergei N. Shtykov, Elena G. Sumina, Varsenia Z. Uglanova, and Victor G. Berezkin
A comparison of the chromatographic behavior of benzoic acids on normal (silica gel), reversed (RP-18), and polyamide-11 plates using thin-layer chromatography (TLC) with controlled gas phase inside the chamber has been performed. This variant of TLC is based on the use of a gas phase moving over the TLC plate for regulation of the stationary and mobile phases as well as the acid—base properties of analytes during the separation process. The feasibility of such an approach is illustrated by the separation of benzoic acid derivatives using carbon dioxide, ammonia, and acetic acid vapor. It was shown that a gradual change of mobile phase acidity makes it possible to enhance separation efficiency and selectivity, this effect being dependent on the type of the stationary phase. The most considerable change in the retention of benzoic acid derivatives was observed for normal-phase plates with silica gel or silica sol, or starch binders used as the stationary phase. An alteration of surface acidity for polyamide and RP-18 plates is not so pronounced as for silica gel ones so that a smaller change in chromatographic parameters of benzoic acid derivatives was observed.
Authors:A. Kaddouri, C. Mazzocchia, E. Tempesti, and R. Anouchinsky
Zirconia samples with different structures (monoclinic, tetragonal or a mixture of the two) was prepared by different methodologies,
including a novel procedure involving the precipitation of an oxalate precursor and the formation of pure tetragonal ZrO2.
The different precursors obtained by varying the preparative procedure (ex oxychloride, ex oxalate, and ex gel) were studied
by means of differential thermal analysis and thermogravimetric analysis under air and under N2, while the final oxides were
characterized by BET, porosimetry and XRD analysis. The surface acid-base properties of the different oxides were assessed
via the catalytic decomposition isopropanol. A prevalence of acid sites found for the ex-oxalate ZrO2 seems to justify the
different mechanism of chain growth observed in the carbonylation of methanol with CO/H2 mixtures in the presence of Rh.
The interactions of the alumina-electrolyte in the presence of inorganic ions (copper, selenium) and/or organic acids (benzoic acid, glutamic acid, phenol) have been studied. The acid-based properties of-alumina have been determined in NaCl media (pzc=8.5±0.3). Three types of hydroxy groups with different acidity constants have been found. The adsorption of copper and selenium have been described by the formation of the surface complexes: (=Al1–OH, CuCl) and (=Al1, SeO3)–. The interaction of copper with the surface oxygen atoms is strong and so is the interaction of selenium with the surface aluminium atoms, which involves a shift of the iep of alumina. For the three organic acids studied (HX), the adsorption equilibrium is:=Ali–OH+HX(=Ali, X)+H2O. The interaction of the X– group and the aluminium atoms is strong following the order: glutamic acid > benzoic acid > phenol. The uptake of selenium is uninfluenced by the presence of organic acids with carboxylic, amino-acidic and phenolic groups. The uptake of copper is highly increased by the presence of organic acids but it is not influenced by the presence of the phenolic groups. Both of these behaviours can be extrapolated to inorganic ions of the same chemical structure.
Authors:G. Ingo, C. Riccucci, G. Bultrini, and G. Chiozzini
By means of the combined use of scanning electron microscopy+energy dispersive spectrometry(SEM+EDS), X-ray photoelectron
spectroscopy (XPS), X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetry (TG), the thermal decomposition
of gypsum and gypsum bonded investment used for casting jewellery products has been studied in order to gain a further insight
into the origin of the gas porosity in gold-based alloys produced via lost wax casting. The occurrence of the defect is related
to the thermal decomposition of CaSO4 that constitutes with silica the investment material and the decomposition of which takes place at a temperature very close
to the casting temperature of some typical gold alloys. The decrease of the thermal decomposition temperature of gypsum is
induced by the presence of silica and is related to the surface acid-base interaction between SiO2 and CaSO4. On the base of these results, the solid state thermal decomposition of calcium sulphate in the presence of other metal oxides
characterised by different acid-base nature has been investigated and a correlation between the surface acid-base properties
measured as isoelectric point of the solid surface (IEPS) and via XPS analysis and the temperature of CaSO4 thermal decomposition is observed.
Authors:D. Meloni, M. F. Sini, M. G. Cutrufello, R. Monaci, E. Rombi, and I. Ferino
, the acid–baseproperties of the ex-hydrotalcite oxides, as well as their redox properties, may be tailored, with the aim of obtaining bifunctional catalysts with a unique combination of such properties [ 5 ]. The basic character of ex