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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.

The dehydration reaction was studied using pure and palladium doped Keggin type heteropoly compounds (H3PW12O40 and Cs2.5H0.5PW12O40) in the temperature range from 433 to 573 K. The structure and texture of catalysts were characterized by thermal analysis, FTIR, XRD, BET and SEM–EDS methods. Pd doped samples exhibit a deviation of Pd concentration value from the stoichiometric ones, while parent samples have concentration values similar to the stoichiometric ones. The catalytic activity of the compounds was tested by continuous flow reactor technique at different temperatures. The favorable effect of Pd doped on the catalysts for dehydration reaction to ethylene results from the examination of apparent activation energies Ea and reaction rate values. Evidence of a decreasing Ea was obtained for ethylene formation in the case of PdCs2.5PW (83.4 kJ/mol) comparatively with pure Cs2.5PW (160.7 kJ/mol). For all reaction temperatures, the reaction rates of ethylene formation are higher for palladium-doped samples than undoped ones.

Thermogravimetric analysis (TGA) was used to evaluate the thermal stability and the amount of coke deposition resulting from the deactivation of catalysts during ethanol dehydration reaction in a fixed bed continuous flow reactor. In this study, a series of catalysts containing 30% of Pd doped and pure 12-tungstophosphoric acid and its insoluble Cs2.5H0.5PW12O40 salt supported on SBA-15 were prepared. The catalytic efficiency of ethanol dehydration reaction was also evaluated. Two types of coke are identified from the TPO (Temperature programmed oxidation) profiles and assigned to the coke precursor and hard coke, respectively. The results indicate that cesium salts reduced the formation of hard coke. The amount of total coke formed was significantly reduced by supporting the catalysts on mesoporous SBA-15 molecular sieves.

In this study, the preparation by grafting of amino-functionalized SBA-15 molecular sieves was carried out. Amino-functionalized molecular sieves were synthesized using a silane coupling agent and different types of amination reagents which react with modified SBA-15. These composites were characterized by FT-IR spectroscopy, X-ray diffraction at low angles, nitrogen physisorption at 77 K, and evaluated by the adsorption of CO2 and its temperature-programmed desorption—TPD. Thermal stability was investigated by TGA and DTA methods. In the view of a possible use of these amino-functionalized molecular sieves as sorbents for CO2 removal, their adsorption–desorption properties towards CO2 were also investigated by the TPD method. The mass loss of amino-functionalized molecular sieves above 215 °C was due to the oxidation and decomposition of amino propyl functional groups. This means that these composites could be used for adsorption of CO2 at temperatures below 215 °C. The adsorption of CO2 and its temperature programmed desorption using thermogravimetry were studied for amino-functionalized molecular sieves at 60 °C. The evolved gases during the adsorption–desorption of CO2 on amino-functionalized molecular sieves were identified by online mass spectrometry coupled with thermogravimetry. CO2 adsorption isotherms of functionalized samples at 60 °C showed that both the adsorption capacity (mg CO2/g adsorbent) and the efficiency of amino groups (mol CO2/mol NH2) depend on the type of amination reagents and the amount of organic compound used.

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.

Some heteropoly salts–mesoporous silica composites were prepared from Co salt of molybdophosphoric acid CoHPMo12O40 (CoHPM) by supporting on mesoporous silica in different concentrations (20–40 mass% CoHPM) of active phase. The structure and texture of these CoHPM/silica composites were studied by powder X-ray diffraction, Fourier transformed infra-red (FT-IR) and micro-Raman spectroscopy, nitrogen physisorption at 77 K and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS). Thermal stability was investigated by thermogravimetric analysis, differential thermal analysis and differential scanning calorimetry. FT-IR and Raman studies showed that heteropoly anions preserved their Keggin structure after impregnation on mesoporous silica support. From SEM–EDS analysis, it observed that for low loading of active phase, the average content of chemical elements (Mo, P and Co) is close to the stoichiometric values, while for higher loadings, the samples exhibit some deviation of concentration values from the stoichiometric ones. The mesoporous silica–HPA composites are thermally more stable than the parent acids, due to the strong anion-support interaction.

A series of heteropolyacids (HPA)–silica composites were prepared from H3PMo12O40 (HPM) and H4PVMo11O40 (HPVM) by chemically anchoring to the amine-functionalized mesoporous MCM-41 and SBA-15. These composites were characterized by FT-IR, XRD, N2 adsorption, SEM, and TEM for their structural integrity and physicochemical properties. The effect of the support on thermal stability was investigated by TG–DTG and DTA. The evolved gases during the thermal analysis of prepared composites were identified by online mass spectrometry coupled with TG technique. It was evidenced that HPAs species were finely dispersed on amine-functionalized molecular sieves via chemical immobilization and the structure of the HPAs is preserved over mesoporous materials. From thermal analysis of HPA–silica composites was observed an important mass loss above 553 K which is due to the decomposition of amino propyl functional group. For this reason prepared composites can be utilized as dispersed catalysts for the reactions performed below 553 K. Catalytic properties of these composites were studied by using ethanol conversion at different temperatures. The HPA supported on molecular sieves exhibited an enhanced oxidation catalytic activity (formation of acetaldehyde) and a lower acid catalytic activity (formation of ethylene and diethyl ether) compared to the parent catalysts. The favorable effect of HPAs deposition on silica supports for oxidehydrogenation pathway to acetaldehyde results from the examination of and reaction rate values. For all reaction temperatures, the reaction rates of acetaldehyde formation are higher for supported samples than unsupported ones.

The calculation of thermal endurance and the estimation of lifetime at certain temperatures based on thermogravimetric data for the tungstophosphoric acid, H3[PW12O40]·H2O (H3PW) and its Cs acidic salts, pure or doped with Pd, were done. The calculation of catalyst’s lifetime with high degree of confidence needs reliable values for activation energy. For this reason, the activation energy values were calculated with ASTM E 1641-04 “Standard Test Method for Decomposition Kinetics by Thermogravimetry” based on Flynn–Wall isoconversional method and with Friedman isoconversional method (differential model-free) for checking, because the last provides accurate values of activation energies compared with the integral model-free methods. The thermal decomposition of the H3PW and some of its acidic Cs salts, pure or doped with Pd, occurs through the constitutional water release [the water formed of the protons and the oxygen from the [PW12O40]3−] having as result the loss of acid sites (protons) and its catalytic activity diminution at the same time. The activation energies are reliable values for the conversion range of 5 ≤ α ≤ 20, but the value for α = 10 % is recommended for the calculation of the lifetime. The estimation of lifetimes was done with ASTM E 1877-00 “Standard Practice for Calculating Thermal Endurance of Materials from Thermogravimetric Data” method. The estimated thermal life of the H3PW and some of its acidic Cs salts pointed out a very good thermal endurance at temperatures below 573 K. The Pd doping decreases drastically the thermal endurance in all cases.

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.

A series of heteropolyacids–mesoporous silica composites were prepared from nickel salt of molybdophosphoric acid Ni1HPMo12O40 (NiHPM) by supporting on SBA-15 mesoporous silica in different concentrations of active phase. The structure and texture of these NiHPM/SBA-15 composites were studied by XRD, FT-IR and micro-Raman spectroscopy, nitrogen physisorption at 77 K, UV–Vis–DRS and SEM–EDX. The effect of the support on thermal stability was investigated by TG-DTG, DTA and DSC methods. By impregnation of Ni salt on mesoporous silica the thermal stability of the Keggin structure increases in comparison with its parent bulk heteropolyacid. From XRD at small angles could be observed that NiHPM/SBA-15 composites with low surface coverage preserve the mesopore structure of silica, with well dispersed NiHPM on the surface of the pore walls for SBA-15. The adsorption of ammonia and its temperature programmed desorption using thermogravimetry were studied for acidity evaluation. The total acidity of the weak and strong acidic sites of NiHPM/SBA-15 composites is obviously increases in comparison with bulk Ni salt. The main products observed in the evolved gases during desorption of NH3 were NH3, CO2 and NO/NO2.

A series of heteropolyacid (HPA)—silica composites were prepared from H3PMo12O40 (HPM) and H4PVMo11O40 (HPVM) by supporting on two types silica supports: Aerosil–Degussa and Romsil–Ramnicu Valcea with different active phase concentrations. The structure and texture of these HPA/silica composites were studied by XRD, FT-IR spectroscopy and nitrogen physisorption at 77 K. The effect of the support on the thermal stability was investigated by TG-DTG and DTA. By the deposition of heteropolyacids on silica type supports, an important decrease of thermal stability was observed on Romsil types and a small decrease on Aerosil types. By comparing with initial supports, the specific surface areas of HPAs deposited on all supports decreased with the active phase concentration. The catalytic properties of the prepared samples were studied by using a reactant pulse method at different temperatures. The ethanol conversion proceeds by two main pathways: an oxide hydrogenation reaction on redox catalytic centers with acetaldehyde formation, and a dehydration reaction on acidic centers with ethylene and diethyl ether formation. The reaction rates of ethanol conversion and acetaldehyde formation increased on supported HPA compared to bulk HPA. The favorable effect of HPAs deposition on silica supports for the oxidehydrogenation pathway to acetaldehyde results from the examination of apparent activation energies Ea and reaction rate values. Evidence of decreasing Ea was obtained for acetaldehyde formation in the case of silica Romsil-supported HPM (39.6 kJ/mol) comparatively with bulk HPM (56.6 kJ/mol). For all reaction temperatures, the reaction rates of acetaldehyde formation are higher for supported samples than unsupported ones.

The method for acidity measurement through temperature programmed desorption (TPD) of ammonia was adapted for simultaneous TG/DTG–DTA analysis of the H3[PMo12O40] and its Cs acid salts, in bulk and supported on SBA-15 support. The desorption of NH3 consists of the NH3 and H2O release in steps as a result of temperature increase. The last step corresponds to expelling of NH3 by decomposition of species strong bonded like the ammonium cation, simultaneously with constitutive water, within the 300–600 °C range. The MS analysis showed that the oxidation of ammonia to N2O and NO during desorption had occurred simultaneously with reduction of Mo6+. The reoxidation of samples with air in all cases was done finally. In order to separate the water release (water formed by condensation of hydroxyl groups belonging to SBA-15) from the ammonia desorption for supported samples, a TPD of H2O was done for every sample. In the case of pure compounds, the mass loss corresponding to the last stage of desorption (after correction with the mass loss as a result of reduction, equal with the mass increase owing to the reoxidation) gives the amounts of NH3 and constitutive water, which correspond stoichiometrically with the Bronsted acidity. The subtraction of mass loss for TPD of water from the corrected mass loss for TPD of ammonia and water (because of the mass loss as a result of the reduction) gives the amount of NH3 corresponding stoichiometrically with the Bronsted acidity. The acidic strength was estimated on the basis of the temperatures for the DTG peaks.

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 reduction kinetics with CO of the 12-molybdophosphoric—HPMo, 1-vanado-11-molybdophosphoric—HPVMo acids and their salts with NH4 +, K+ and Cs+ cations were studied for reduction/reoxidation cycles with mixtures of CO:Ar and O2:Ar, by means of “in situ” UV–Vis–DRS measurements. The reflectivity versus time curves registered during the reduction/reoxidation processes for the HPMo and HPVMo and its salts with NH4 +, K+ and Cs+ cations, at the constant wavelength of 620 nm and different reaction temperatures between 523 and 623 K, were processed as the Kubelka–Munk function versus time. The linear shape of Kubelka–Munk function versus time curves for the reduction process suggests apparent zeroth order kinetics and it was used for the calculation of apparent activation energy. The kinetic compensation effect between the apparent activation energy and the pre-exponential factor was observed. The Kubelka–Munk function versus time curves for the reoxidation process consist of two steps, the first with a very fast reaction rate and the second with a slow reaction rate. An explanation for their shape is proposed. The heteropoly oxomolybdates reach a degree of reoxidation higher than heteropoly compounds containing vanadium together with molybdenum.

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 heterometallic complexes [Cu(VO)2(CSN2H4)3Cl(OH)4]·H2O, [Cu2(VO)2(CSN2H4)2(C2H3O2)2·(OH)4], and [Cu2(VO)3(CSN2H4)4(C2H3O2)4(OH)4] were prepared and characterized in terms of their molecular electrical conductivity, electronic and IR spectra, and thermal behavior. A polymeric structure is proposed in which a thiourea ligand is bonded via a sulfur atom to the tetracoordinated copper(I) and via amino groups to the oxovanadium(IV) ion. The polymeric nature of the complexes is due to bridging via the OH, thiourea, and/or acetate moieties between oxovanadium(IV) coordination centers.

New mixed-ligand complexes, [M2(BAMP)(bipy)2][MCl4]2, M=Co+2(1), Cu+2(2), [M2(TAMEN)(bipy)2][MCl4]2, M=Fe+2(3), Co2+(4), and [Fe2(TAMEN)(bipy)2][FeCl6]2 (5), where BAMP and TAMEN stand for the Mannich bases N,N′-bis(antipyryl-4-methylene)-piperazine and N,N′-tetra(antipyryl-4-methylene)-1,2-ethane-diamine, respectively, have been obtained and characterized by elemental analyses, conductometric and magnetic susceptibility measurements at room temperature, mass spectrometry, UV-Vis, infrared, and mass spectroscopy, and 1H NMR spectra for the ligands.

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.

The aim of this study is to investigate the influence of some monovalent counter-ions (NH4 +, K+ and Cs+) on thermal behavior of polyoxometalates derived from H3PMo12O40 (HPM) and H4PVMo11O40 (HPVM) by replacing the protons. The IR and UV-VIS-DRS spectra of some acid and neutral NH4 +, K+, Cs+ salts, which derived from HPM and HPVM, confirmed the preservation of Keggin units (KU) structure. The X-ray diffraction spectra clearly showed the presence of a cubic structure. The non-isothermal decomposition of studied polyoxometalates proceeds by a series of processes: the loss of crystallization water; the loss of O2 accompanying with a reduction of V5+→V4+ and Mo6+→Mo5+; the loss of constitution water started at 360°C for HPVM salts and 420°C for HPM salts; the decomposition of ammonium ion over 420°C with NH3, N2 and H2O elimination and simultaneous processes of reduction (V5+→ V4+ and Mo6+→ Mo5+ or Mo4+) associating with endothermic effects; reoxidation of Mo5+, Mo4+ and V4+with a strong exothermic effect; destruction of KU to the oxides: P2O5, MoO3 and V2O5 and the crystallization of MoO3.

Homopolynuclear complexes of Cu(II) respectively Cr(III) with the glyoxylate dianion, C2H2O42-, have been studied in non-isothermal regime in air and nitrogen. The results of the non-isothermal analysis performed for the synthesised complexes, Cu(C2H2O4)·0.5H2O, respectively [Cr2(OH)2(C2H2O4)2(OH2)4]·2H2O, correlated with the results of the IR and TG analysis of the compounds obtained by thermal treatment from the initial complexes and the results of the GLC and XR analysis have led to the establishment of the thermal decomposition mechanisms for the two studied complexes. The decomposition mechanisms confirm the stoichiometric and structural formulae proposed for the two synthesised homopolynuclear complexes.

Two new Schiff base ligands 1 and 2 (where 1 = 4-(2-hydroxybenzilidenamino)-phenyl-4-(decyloxy)-2-(pent-4-enyloxy)benzoate, 2 = 4-(4-(decyloxy)-2-hydroxybenziliden amino)-phenyl-4-(decyloxy)-2-(pent-4-enyloxy)benzoate) and their copper (Cu)(II) complexes have been synthesised and characterised. The derivatives were fully characterised structurally, and their mesomorphic behaviour was investigated by polarised optical microscopyand differential scanning calorimetry. The structure of Cu(II) complex having 1 as ligand (3) was determined by X-ray diffraction. The Schiff base ligands exhibit enantiotropic nematic phases, the Cu(II) complex 4 shows monotropic nematic phase behaviour, while compound 3 does not show mesomorphism.

Changes in AC electrical conductance G of vanadium substituted 12-molybdophosphoric acid and of its (mono)-acid and neutral cesium salts were studied. Depending on the environment, the electrical conductivity is a combination of protonic and electronic conduction, the protonic one dominating at low temperature.

Complexes of Cr(III):Cu(II) with the glyoxylate dianion as ligand were synthesized in the range of cation atomic ratios (0.01–8):1.0. The results of non-isothermal analysis of the synthesized compounds correlated with the results of IR and UV-VIS spectroscopy, and gas chromatography of the volatile products of the decomposition allowed the formulation of a mechanism for the decomposition of the complex with Cr(III):Cu(II)=2:1 and the assumption that the other complexes are mixtures of this with the homopolynuclear complexes of Cr(III) and Cu(II), depending on the ratio of the cations Cr(III):Cu(II). The thermal conversion of the complexes takes place at relatively low temperatures, with partial transformation of the ligand into oxalate and of the oxide mixture into CuCrO4.

This paper reports a comparative study of the non-isothermal decompositions of the heteropolyacids HPM and HPVM, with structures consisting of Keggin units (KUs). Non-isothermal analysis at low heating rates demonstrated the existence of 4 crystal hydrate species, depending on the temperature. The stability domains of the anhydrous forms of HPM and HPVM were found to be 150–380°C, respectively. Processing of the TG curves obtained at different heating rates by the Ozawa method revealed that the decomposition of anhydrous HPM takes place according to a unitary mechanism, whilst for anhydrous HPVM two mechanisms are observed. Thus, the first part of the constitution water is lost simultaneously with the departure of vanadium from the KU as VO2+, while the second part is lost at higher temperatures as in the case HPM.

The band gap energy (absorption edge energies) of the pure H3[PMo12O40]·13H2O and H4[PVMo11O40]·13H2O, respectively, supported on SiO2 and SiC and some of its NH4+ and Cs+ salts were determined by different methods. The influence of the counter-cations and the temperature on band gap energy was studied. In this purpose, the diffuse reflectance spectra of above mentioned compounds were registered at different temperatures, and it were transposed in the curves of the Kubelka-Munk function vs. wavelength. The band gap energies were determined by processing of low field energy of the ligand-metal charge transfer band (O2− → Mo6+ and O2− → V5+) usually observed between 200 and 400 nm on these curves. In this aim, the Tauc's relation was adapted for Kubelka-Munk function use and it was plotted for n = 1/2 (direct transition) and 2 (indirect transition) vs. wave energy (photon energy). The intersection of the curves’ tangent drawn to their point of inflection with horizontal axis gives the band gap energy. The o...