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The pure and palladium doped 12-tungstophosphoric acid - H3PW12O40 (HPW) and its cesium salts CsxH3-xPW12O40 (x = 1, 2, 2.25 and 2.5) were prepared and characterized by thermal analysis, FTIR, XRD, BET and XPS methods. In this paper were determined the optimal reaction temperature and the effect of palladium on the coke content during the dehydration of ethanol in the temperature range of 200−350 °C. Above 300 °C, a strong deactivation of the catalysts was caused by coke formation. The catalytic tests demonstrate that by supporting the HPW and PdyPW (y = 0.15, 0.2 and 0.25) on mesoporous molecular sieve SBA-15 the catalytic activity in ethanol dehydration reaction was improved. Palladium doping of HPW/SBA-15 significantly decreases the formation of coke deposit. The formation of coke during the ethanol dehydration does not affect the Keggin structure which led us to conclude that such catalysts can be regenerated in air and regain their catalytic activity for a short time.

New heteroleptic complexes having the general formula (N^N)MQCl, where N^N = 2,2′-bipyridine or 1,10-phenanthroline, M = Cu(II) or Zn(II) and Q = quercetin were synthesized and characterized by analytical and spectroscopic methods. The complexes are more sensitive to air oxygen in solution or solid state than their flavonoid ligand. The increased sensitivity towards oxidation of the metal complexes was evidenced in the solid state by TGA-DTA measurements and in solution by UV–Vis absorption. The Zn(II) heteroleptic derivatives are luminescent in solution, their emission maxima being red-shifted with respect to quercetin precursor. The free radical scavenging activity of the complexes was evaluated using the stable DPPH radical. Cu(II) heteroleptic complexes have higher antioxidant activity than the Zn(II) complexes. Different oxidative mechanisms were evidenced for the Cu(II) and Zn(II) heteroleptic complexes.

Some heteropoly salts – mesoporous silica composites were prepared from Co salt of molybdophosphoric acid CoHPMo 12 O 40 (CoHPM) by supporting on mesoporous silica in different concentrations (20–40 wt% CoHPM) of active phase. The acidity of composites was studied by the adsorption of ammonia and its temperature programmed desorption – TPD using thermogravimetry. The evolved gases during the adsorption–desorption of ammonia on CoPM-silica composites were identified by online mass spectrometry coupled with thermal gravimetry technique. The elemental concentrations based on the relative area of XPS spectra components for Co 2p, Mo 3d, Si 2p and O 1s were obtained for the surface of CoHPM/silica. The dehydration of ethanol was used to probe the catalytic properties of the CoHPM samples incorporated on the silica matrix. The main reaction products obtained on acid (dehydration) catalytic centres were ethylene and diethyl ether, besides acetaldehyde which was obtained on redox (dehydrogenation) catalytic centres. It is shown that silica – supported catalysts, appeared to be more active than bulk CoHPM catalyst in dehydration and dehydrogenation reactions. The higher values of dehydration and reaction products formation are obtained with the lowest loading (20 wt% CoHPM) and as a consequence the highest dispersion of active phase. The ethanol conversion and the carbon selectivity to the primary compounds were investigated during time on stream in order to study the stability and regenerability of supported catalysts.

The influence of the counterions on the geometry of Cu(I) and Cu(II) unsubstituted phen-based (phen = 1,10-phenanthroline) complexes was investigated. The synthetic strategy used afforded the synthesis of both the tetracoordinated Cu(I) and pentacoordinated Cu(II) species with general formula [(phen)2Cu]+Y− (Y− = ClO4−, I−, SCN− and BF4−) and [(phen)2CuX]+Y− (X = Cl−, I−, NCS−, and Y− = ClO4−, I−, SCN− and BF4−), respectively. The firstly isolated Cu(I) complexes were characterized by IR, 1H NMR and UV-Vis spectroscopies, their proposed structures being confirmed by elemental analysis, atomic absorption spectroscopy (AAS) and thermogravimetric analysis (TGA). The molecular structure of Cu(II) complexes was determined by single crystal X-ray diffraction analysis. While for Cu(I) complexes, the coordinating nature of the counterions seems to have a strong influence (observed in the solid state and concentrated solution) on the flattening distortion (D2d → D2) of the geometry about the Cu(I) ion, in the Cu(II) derivatives, the size, shape, number and type of intermolecular interactions established by the counterions, drive not only the overall cations supramolecular organization, but also the molecular stereochemistry around the Cu(II) ion.

The thermal decomposition in dynamic oxidative atmosphere of the new homopolynuclear coordination compound [Fe(C 2 O 4 )(OH)(OH 2 )] n ·0.3 n H 2 O was investigated by simultaneously using TG, DTG and DTA techniques. Solid-state decomposition products formed during heating at different temperatures (350 °C, 800 °C and 1000 °C) were analyzed by physical-chemical methods, including electronic spectroscopy (diffuse reflectance technique), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD analysis data show that the final decomposition product, namely hematite (α-Fe 2 O 3 ), is relatively well crystallized, while SEM images reveal that the particles exhibit irregular forms, their size being widely distributed between 6 nm and 4 μm.

The current study reports the synthesis and characterization of tungstophosphoric acid and its acid silver salt supported on mesoporous molecular sieve SBA-15 and TiO2. Because silver salts are partially insoluble, the SBA-15 and TiO2 supported silver acid salts were prepared by two step sequential impregnations. The synthesized catalysts were characterized by various physicochemical methods such as Fourier transform infrared and Raman spectroscopy, differential thermal analysis, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy and nitrogen physisorption at -196 degrees C. It is observed that both active phases keep their Keggin-type structure after being supported on the supports while their specific surface area is considerably increased by deposition on mesoporous substrates. The results also indicated that the synthesized catalysts retained the morphology specific for each of the supports, while their thermal stability is increased in comparison with their active phases. The catalytic activity of the prepared catalysts was probed for the vapor phase dehydration of ethanol at 300 degrees C. Results revealed that all the catalysts show considerably improved catalytic activity in comparison to the bulk active phases.

The Cs salts of molybdophosphoric acid Cs1H2PMo12O40 (Cs1PM) and Cs3PMo12O40 (Cs3PM), were supported on SBA-15 in the concentration of 20, 30 and 40 wt.% loadings. Because Cs salts are insoluble, the SBA-15 supported Cs-acid salts were prepared by two-step sequential impregnation and in situ reaction on the support. The structure and texture of these CsPM/SBA-15 composites were studied by XRD, SEM-EDS, FT-IR and micro-Raman spectroscopy, UV–vis-DRS and N2 adsorption. Thermal stability was investigated by thermo gravimetric analysis (TGA), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The acidity of composites was studied by the adsorption of ammonia and its temperature programmed desorption – TPD using thermogravimetry. The evolved gases during the adsorption–desorption of ammonia on CsPM/SBA-15 composites were identified by online mass spectrometry coupled with thermal gravimetry technique. FT-IR and Raman studies demonstrated that CsPM maintained its Keggin structure after deposition on mesoporous SBA-15, regardless of the active phase concentration. For both Cs1H2PMo12O40 and Cs3PMo12O40-SBA-15 composites could be observed an important increase of band gap energy in comparison with pure salts. The values of specific surface area of pure CsPM were increased by deposition on mesoporous silica support. The immobilization of CsPM on mesoporous SBA-15 obviously increases the thermal stability and the total acidity of the strong acidic sites of the Keggin structures in comparison with their parent bulk Cs salts.

The salts of the H 3 PW 12 O 40 (H 3 PW) with Cs counter cation were prepared and characterized by thermal analysis, IR, XRD, BET, XPS LEIS and SEM methods. The samples are denoted as Cs x H 3 − x PW 12 O 40 ( x = 1, 2, 2.25, 2.5 and 3). The catalytic activity of the compounds prepared with various cesium/Keggin unit ratios was tested in ethanol conversion by pulse reaction technique. The change of catalytic activity vs. pulse number was explained by formation of strong adsorbed species on catalysts. A microstructure model of the Cs x H 3 − x PW 12 O 40 containing spherical aggregates, which consist of Cs 3 PW 12 O 40 crystallites core coated with H 3 PW 12 O 40 layers, was proposed on the basis of the structural–textural properties and their catalytic performances in ethanol conversion. The model explains the abrupt increase of the specific surface area for x > 2 and also the highest selectivity for C 4 hydrocarbons on Cs 2.5 H 0.5 PW 12 O 40 due to its special microstructure: a H 3 PW monolayer embedding a core of Cs 3 PW. The Cs concentrations on the Cs x H 3 − x PW 12 O 40 surface were determined by XPS and were found less than expected based on their chemical composition, but which correspond to the proposed model of microstructure.

The Cs salt of molybdophosphoric acid Cs 2.5 H 0.5 PMo 12 O 40 (CsHPM) was supported on SBA-15 in the concentration of 20, 30 and 40 wt.% loadings. Because Cs acid salts are insoluble, the SBA-15 supported Cs-acid salts were prepared by two-step sequential impregnation and in situ reaction on the support. The structure and texture of these CsHPM/SBA-15 composites were studied by XRD, SEM-EDS, FT-IR and micro-Raman spectroscopy and N 2 adsorption. Thermal stability was investigated by thermogravimetric analysis (TGA), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The dehydration of ethanol was used to probe the catalytic properties of the CsHPM samples incorporated on the silica matrix. FT-IR and Raman studies demonstrated that CsHPM maintained its Keggin structure after deposition on mesoporous SBA-15, regardless of the active phase concentration. The values of specific surface area of pure CsHPM were increased by deposition on mesoporous silica support. The immobilization of CsHPM on mesoporous SBA-15 obviously increases the thermal stability of the Keggin structures in comparison with their parent bulk Cs salts. The main reaction products obtained on acid (dehydration) catalytic centres were ethylene and diethyl ether, and respectively acetaldehyde which was obtained on redox (dehydrogenation) catalytic centres.

The synthesis of heteropolyacids–mesoporous silica composites was carried out in acidic media by impregnation and/or by direct incorporation of active phase. The effect of incorporation of heteropolyacids (HPAs) species into organized mesoporous silica was studied by using non-ionic and cationic surfactants. A comparison between direct incorporation of HPAs into mesoporous silica and impregnation of HPAs on mesoporous silica was done. The structure and texture of H3PMo12O40 and H4PVMo11O40 included on mesoporous silica were studied by XRD, SEM–EDS, FT-IR and Raman spectroscopies and BET and pore size distribution. Thermal stability was determined by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). FT-IR and Raman studies showed that HPAs anions preserved their Keggin structure after incorporation or impregnation on mesoporous silica support.

The method for Bronsted acidity measurement based on TPD of alkyl amines desorption by gas-chromatography or thermogravimetry was adapted for simultaneous TG/DTG–DTA analysis. The acidity measurements were focused on the 12-tungstophosphoric acid (H3PW12O40) and its salts, especially with Cesium since these posses the highest Bronsted acidity and they are among the most interesting catalysts. The n-butyl amine (NBA) desorption takes place in three steps for CsxH3−xPW12O40, x = 0–2, and four steps for the Cs2.5H0.5PW12O40. The steps of desorption correspond to the release of NBA molecules in stages, as NBA or butene molecules resulted from the Hofmann elimination reaction and NH3 + H2O formed by decomposition of ammonium salt. The quantities of desorption products, C4H8 and NH3 + H2O, corresponding to the stages with the maximum desorption rates at 400–420 °C, respectively 560–600 °C, are in the stoichiometric ratio with the Bronsted acidity.

Heteropolyacids (HPAs) which are included in mesoporous silica, H3PMo12O40/SiO2 and H4PMo11VO40/SiO2 have been synthesized by a sol–gel technique that involves hydrolysis of ethyl orthosilicate. The effect of incorporation of heteropolyacids species on silica matrix was studied by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Raman spectroscopy, thermo gravimetric analysis (TGA) and differential thermal analysis (DTA), N2 adsorption–desorption, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). X-ray powder patterns prove that heteropolyacids are uniformly dispersed in the silica network. IR and Raman spectra have show that the HPAs anions preserved their Keggin structure on the surface of silica–HPA composites. SEM images and BET adsorption–desorption isotherms confirm the presence of nanometer particles and mesoporous structures. SEM micrographs of silica–HPAs composites show that silica–HPAs composites are composed of spherical particles with an average diameter of approximately 20–30 μm. The silica-included heteropolyacids were thermally more stable than the parent ones.

Keggin type heteropolyacids (HPAs) have been used in acid-catalysed reactions as well as oxidation reactions both in the heterogeneous and homogeneous systems. In order to be more effective for catalytic reactions, HPAs are usually impregnated on different porous materials with high surface area. The structure and texture of H 3 PMo 12 O 40 and H 4 PVMo 11 O 40 supported on Al-MCM41 and Fe-MCM41 were studied by XRD, low-temperature nitrogen adsorption and thermal analysis. Catalytic properties of prepared samples were studied by using a reactant pulse method at different temperatures. The ethanol conversion proceeds by two main pathways: an oxidehydrogenation reaction on redox catalytic centers, and a dehydration reaction on acidic centers, respectively. The favourable effect of HPAs deposition on Al-MCM41 and Fe-MCM41 supports for oxidehydrogenation pathway to acetaldehyde results from the examination of apparent activation energies E a and reaction rate values. An evidenced decreasing of E a was obtained for acetaldehyde formation in the case of Fe-MCM41-supported HPM (25 kJ/mole) comparatively with pure HPM (56.6 kJ/mole). For all reaction temperatures, the reaction rates of acetaldehyde formation are with one order of magnitude higher for supported samples than unsupported ones.