Potassium and antimony mixed oxides were obtained by calcination of the commercial potassium-antimony tartrate trihydrate K(SbO)C4H4O6.3H2O at temperatures ranging from 300 to 800 °C. The structure varied with temperature as revealed by XRD characterization. The modifications occurring during the calcination process were also studied by FT-IR and DRS spectroscopies, along with by thermal analysis (TG/DTG). The solids were tested in 2-propanol decomposition at 200 °C, used as probe reaction for the investigation of acid-basic and redox properties. The catalytic activity was function of the calcination temperature and the best 2-propanol conversion was achieved with the tartrate precursor calcined at 500 °C that crystallizes forming KSbO3 as main phase along with K0.51Sb2.67O6.26 as secondary phase. Under N2 the activity reached the maximum after 10 min, 80% of 2-propanol conversion was the highest value, over the sample calcined at 500 °C, but rapidly decreased with time on stream and almost declined after 1 h. In the presence of air in the reaction mixture, 85% of 2-propanol conversion was achieved at 200 °C, after 20 min under stream, with the most active sample. By increasing the calcination temperature above 500 °C, the conversion decreased, especially for the sample calcined at 800 °C showing the worse conversion, although the stability over time increased, likely due to the achievement of stable crystalline phases and crystallite sizes. In all cases, the 2-propanone selectivity was close to 100%. This behaviour confirmed the occurrence of a dehydrogenation reaction involving the basic sites typical of KSbxOy oxides along with the redox couple Sb(V)/Sb(III).

This paper involves the investigation of the calcined Ca-hydroxyzincate dehydrate (CHZ) as solid base catalysts for photocatalytic degradation of methylene blue. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG–DTA), and UV–Vis spectroscopy were carried out to characterize and evaluate the as-prepared samples. The calcined catalysts performances were promising compared to non-calcined material. All the photocatalysts prepared under different processing temperatures (200, 400 and 600 °C) displayed 100% methylene blue degradation compared to the non-calcined sample with 100% dye removal.

In the present study, a series of ferroelectrics Li1-xTa1-xWxO3 materials have been prepared by a solid-state process, characterized by using XRD, UV - vis spectroscopy and SEM, and then tested as new photocatalysts for the degradation of Methylene Blue (MB) in dye solution. The X-ray diffraction reveals a rhombohedra structure for all compositions from x = 0.00 to x = 0.25 which is the limit value. The photo-catalytic performance was evaluated through degradation of Methylene blue dye with ferroelectricmaterials. The best results in terms of photodegradation were obtained with x = 0.10, 0.20 and 0.25; more specifically, the initial degradation rate of methylene blue was four times higher than with the x = 0.00.

Moroccan waste fish oil was used as raw material to produce the biodiesel in this study. The biodiesel sample is achieved by a dual step esterification-transesterification acid-base to reduce the higher FFAs content of fish oil after a rapid method of purification. It is characterized by techniques such as Fourier Transform Infrared spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR) spectroscopy, and the Gas Chromatography–Mass Spectrometry (GC/MS). The experimental results showed that biodiesel produced from waste fish oil contained a significantly greater amount of methyl ester group in the biodiesel sample. The GC/MS results showed the presence of a good quantity of palmitic acid, oleic acid and linolenic acid which are essential biodiesel components. The biodiesel did not contain any trace of glycerol and it did meet international standards.

This work establishes a simple method for synthesising layered double hydroxides (LDHs) powders with coprecipitation. The characteristics of the samples were investigated y X-ray diffraction (XRD), scanning electron microscopy (SEM) and spectrophotometer UV–Vis (DRS). Non-uniform distribution was shown for LDHs samples by SEM. Photocatalytic efficiencies were tested using methylene blue (MB) dye as a model contaminant under UV irradiation. In particular, Zn–Al-Ti LDH exhibited an excellent performance towards MB degradation compared with commercial TiO 2 nanoparticles. Methylene blue removal percentage was reached at almost 100%, whereas commercial TiO 2 reached a removal rate of only 66% under the same conditions within 20 min. The aim of the current work is to prepare Zn-Al-Ti layered double hydroxides nanocomposite and to evaluate their photocatalytic activity in the removal of methylene blue under UV irradiation.

The corrosion behavior of brass in Simulated Drinking Water (SDW) without and with mineral compound (P) has been investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and optical microscope. The obtained results showed that the inhibitor addition significantly reduced the corrosion current density. The inhibition efficiency increased with concentration of inhibitor to reach a maximum of 84 % at 1000 ppm. Polarization studies showed that this inhibitor acted as cathodic type for brass in Simulated Drinking Water (SDW). The Appropriate electric equivalent circuit model was used to calculate the impedance parameters. The corrosion parameters obtained from polarization curves and from EIS spectra are in good concordance and point out the inhibitory action of mineral compound (P). Optical microscope observation after three days of immersion showed the formation of mixed products with inhibitor.

We have investigated, in aqueous solution, the exchange process of calcium by copper (Ca2+/Cu2+) and its effects on the chemical and structural stability of dicalcium phosphate dihydrate (CaHPO4 center dot 2H(2)O). The compounds obtained at different concentrations of Cu2+ and various pH were characterized by X-ray diffraction, spectroscopically, chemical analysis and SEM-EDS microscopy. The combined results of these methods, confirmed that copper ions incorporate partially the dicalcium phosphate dihydrate framework by the exchange of Ca2+ ions with copper favouring the formation of Ca1-xCuxHPO4 center dot 2H(2)O center dot 2H(2)O solid solution which is isomorphic to the pure dicalcium phosphate dihydrate. The upper limit of copper solubility in dicalcium phosphate dihydrate is observed at 25 %. Unlike calcium, Cu2+ ions prefer to be hosted by low symmetry sites in dicalcium phosphate dihydrate structure causing a slight compression of the unit cell. This exchange inhibits the nucleation of derived hydroxyapatite compounds frequently observed with many other divalent cations. The dehydration in air at 250 degrees C of dicalcium phosphate dihydrate - % Cu2+ can lead to the formation of stable anhydrous products Ca1-xCuxHPO4 center dot 2H(2)O (DCPA) with monetite structure.

Several samples of exchanged cobalt/calcium (Co 2+ /Ca 2+ ) hydroxyapatite were synthesized and characterised by XRD, IR and UV-visible spectroscopy. The level of Co 2+ /Ca 2+ exchanged was limited to 1.35 wt% of Co and the Co 2+ ions incorporated in the phosphate matrix were mainly hosted by octahedral sites. The catalytic activity of these materials was measured in the oxidative dehydrogenation of ethane into ethylene in the 450-550°C range. The global conversion and the ethylene yield increase with temperature and depend upon the cobalt content. They reached 35% and 22% at 550°C respectively for a Co wt% of about 1%.

Different compositions of calcium-cobalt phosphate Ca3-xCOx(PO4)(2) (0 <= x <= 3) were synthesized by the precipitation method. The X-ray diffraction patterns showed that in the range 0 <= x <= 0.3 the solid displays a whitlockite-type structure which belongs to rhombohedral symmetry with the space group R3c (Z = 6). U.V.-visible investigations showed that Co2+ ions occupy the M(5) sites of the phosphate. The same technique revealed that all cobalt cations exist under the +II oxidation state. Pure tricalcium phosphate beta-Ca-3(PO4)(2) was found inactive in the ODH reactions of ethane and propane. An increase of Co2+ concentration in the catalysts improved the performances.

The molybdenum-tungsten phosphate (W 2-x Mo x O 3 (PO 4 ) 2 ) was synthetised and characterised using several techniques. Its catalytic performances was studied in butan-2-ol conversion. The UV-visible investigations showed that the catalyst contains Mo(V) ions. This results was confirmed by the EPR spectra. Additional U.V. visible in-situ experimentss, in dynamic conditions revealed that butan-2-ol reduces Mo(VI) into Mo(V) ions. The active sites in the catalytic reaction appearto be built up arround the Mo(VI) ions.

Several compositions of palladium-loaded calcium hydroxyapatite Pd(x)/CaHAp were prepared and characterized by XRD, IR, and UV–visible spectroscopy and temperature-programmed reduction (TPR). The acid–base properties of the samples were studied with the use of butan-2-ol conversion and IR spectroscopy coupled with lutidine adsorption/desorption. Calcium hydroxyapatite bears Lewis acid sites of moderate strength and a limited number of Brønsted acid sites, which produce butenes by dehydration. The selectivity of the dehydrogenation reaction (formation of methyl ethyl ketone) is very limited in the absence of oxygen but indicates the existence on the surface of phosphate of basic sites that are as essential as the acid sites in the direct synthesis of methyl isobutyl ketone (MIBK) from acetone and H2. Dispersion of Pd on the hydroxyapatite introduces redox properties and the bifunctionality needed in the hydrogenation of mesityl oxide (MO). Temperature-programmed reduction (TPR) of Pd(x)/CaHAp catalysts shows a sharp peak of H2 consumption between 268 and 276 K, depending on palladium loading, followed by a negative peak at about 338 K, which is associated with the decomposition of β-PdH. Hydrogen chemisorption measurements carried out at 353 K allowed the determination of the size of palladium particles, which varies between 8 and 28 nm. The Pd(x)/CaHAp catalysts showed good performance in the low-pressure one-step synthesis of MIBK. They are stable under the experimental conditions, and they exhibit a MIBK and MIBC selectivity that reaches 92% for a conversion of 22% and an optimal Pd loading of 2 wt%. Other parameters of the reaction (such as temperature of reaction, residence time, H2/acetone ratio) were studied. They all play an important role in acetone conversion and product distribution. However, the reaction temperature has the most significant influence, since a maximum of the global conversion was observed at 423 K.

The molybdenum-tungsten phosphate (W2-xMoxO3(PO4)(2)) was synthetised and characterised using several techniques. Its catalytic performances was studied in butan-2-ol conversion. The UV-visible investigations showed that the catalyst contains Mo(V) ions. This results was confirmed by the EPR spectra. Additional UN. visible in-situ experimentss, in dynamic conditions revealed that butan-2-ol reduces Mo(VI) into Mo(V) ions. The active sites in the catalytic reaction appearto be built up arround the Mo(VI) ions.

A series of exchanged cobalt/calcium (Co2+/Ca2+) hydroxyapatite Ca10−xCox(PO4)6(OH)2 was synthesized and characterized by XRD, UV-visible-near-infrared (NIR) and IR spectroscopy, magnetic measurements (SQUID), and X-ray photoemission spectroscopy (XPS). The level of Co2+/Ca2+ exchange was limited to 1.35 wt% Co. After calcination in air at 550°C, cobalt was still present as Co2+ and all samples were paramagnetic, showing that the apatite matrix impedes the oxidation of Co2+ and that the Co2+ ions are isolated, whatever the Co content. Magnetic measurements and UV-visible diffuse reflectance spectra show that the exchanged Co2+ ions are hosted by two types of sites (with octahedral and trigonal prismatic symmetries). XPS confirmed the surface cobalt enrichment and did not reveal Co3+ ions. Dehydrogenation of 2-butanol leads almost exclusively to the formation of butanone. As the Co content increases, the ketone yield passes through a maximum. In the oxidative dehydrogenation of ethane, the ethylene yield also reaches a maximum (22 mol%) for 0.96 wt% Co at 550°C. These results are ascribed to (i) the partial compensation of the intrinsic dehydrogenating activity of cobalt by the decrease in basicity of apatite induced by the replacement of Ca2+ by Co2+, and (ii) the involvement of two types of sites.

Cobalt- and cobalt–boron-loaded TiO2 (anatase) catalysts were prepared and characterized before and after catalytic tests by XRD, HRTEM, IR, UV–visible, and laser Raman spectroscopy. Their activity was investigated in oxidative dehydrogenation (ODH) of ethane. In the absence of boron, the best performances were exhibited by the sample containing 7.6 wt% Co, which was selected for further investigations. At 550°C, it displayed a stationary state with a conversion of 22.2% and an ethylene selectivity around 60%. This catalyst also showed in the first 3 h on stream a 30% decay in activity that was attributed to a concomitant loss of specific surface area and the formation of CoTiO3 and Co2TiO4 phases. The addition of 0.25 wt% boron to this Co(7.6)/TiO2 sample improved the ethane conversion and the ethylene selectivity, which attained 28.4 and 67%, respectively. Boron concentrations superior to 0.25 wt% negatively affected the catalysts performances, probably because at high loadings it profoundly modified the acid–base properties of the surface. XRD and HRTEM analyses showed that at the same time the size of Co3O4 crystallites decreased. IR investigations confirmed the increase in acidity upon boron addition and the decrease in strength of the basic sites which were involved in the dehydrogenation processes. The catalytic behavior and the acid–base properties of Co(7.6)/TiO2 loaded with different amounts of boron were also studied using butan-2-ol conversion. Boron addition enhanced the dehydration and the dehydrogenation reactions. However, above 0.25 wt% it decreased the dehydrogenation activity, confirming the modifications of the properties of the acid–base centers revealed by the IR studies. For this optimal concentration of boron, the activity and the selectivity in butan-2-ol dehydrogenation exhibited a maximum that coincided with the one observed in the ethane ODH, which suggests that both reactions possibly involved the same type of active centers.

TiO2-supported Cobalt and cobalt–phosphorus catalysts prepared by impregnation are characterized by XRD, XPS, Laser Raman Spectroscopy (LRS), and Diffuse Reflectance Spectroscopy (DRS) and investigated in ethane oxidative dehydrogenation (ODH). At low cobalt loadings, the carrier is essentially covered by octahedral Co2+ ions, whereas at concentrations superior to 3.7 wt% formation of the Co3O4 spinel is observed. The best performance in ethane ODH is achieved at 550°C with the sample containing 7.6 wt% Co. The reaction begins with a conversion of 33% and a selectivity around 75%, then it decreases to reach after 150 min on stream a stationary state at 22% of conversion and 60% selectivity. This loss of 30% of the initial activity may be associated with a decrease of the specific surface area and the concomitant formation of CoTiO3 and Co2TiO4, as revealed by LRS, in situ DRS, and XPS analysis. The activity in ethane ODH seems to be mainly related to the presence of Co2+ ions octahedral sites. Addition of phosphorus to Co(7.6)/TiO2 catalysts results in the reduction of Co3+ ions and a growth of amorphous cobalt–phosphorus compounds which provoke a severe decrease of the catalyst performance.

The silver-hafnium phosphate (AgHf2(PO4)(3)), belonging to the Nasicon-type structure, was synthesized by a sol-gel method and characterized by several techniques. The Ag+ cations were found to be, as in zeolite frameworks, easy to reduce to metallic silver. This reduction was investigated by STEM/EDX which showed that, under an intense electron beam, the Ag+ ions diffuse toward the surface of the sample and form metallic particles of sizes varying from 3 to 15 nm, The X-ray diffraction patterns confirmed that the reduction does not damage the phosphate structure, The Ag+ ions were replaced in the structure by protons giving rise to (PO-H) acid groups.The catalytic behavior of AgHf2(PO4)(3) was studied in butan-2-ol conversion. In the absence of O-2, the reaction leads to an abrupt decrease of the dehydrogenation activity and a dehydration reaction that reaches a pseudo-stationary state. Concomittantly, the Ag+ cations are reduced to Ag-0. In the presence of O-2, the dehydrogenation reaction undergoes a complex transitory state which can be decomposed into two steps. During the first one, the activity decreases in concert with the reduction of Ag+ ions. Tn the second step it increases as the amount of oxidized silver species (AgxOy), which are the active sites for the alcohol dehydrogenation, increases.UV-VIS characterization of AgHf2(PO4)(3) in dynamic conditions similar to those used in the catalytic tests confirmed that butan-2-ol reduces Ag+ ions to metallic silver which, in the presence of O-2 in the reaction mixture, are oxidized to (AgxOy). (C) 2001 Elsevier Science B.V. All rights reserved.

Fresh (f-) and reduced (r-) Ca9Fe(PO4)7 whitlockite-like compounds were prepared and characterized by X-ray diffraction (XRD), IR, temperature programmed reduction and oxidation (TPR/TPO), UV-visible, electron paramagnetic resonance (EPR), and 57Fe Mössbauer spectroscopy. TPR/TPO, XRD, and IR investigations showed that cycles of reduction and oxidation reversibly affected the iron cations without noticeable modification of the structure. The reduction by H2 was accompanied by a protonation of the sample and a slight increase of the unit-cell parameters. It was observed that the reduction of Fe3+ to Fe2+ never exceeded 91%. The simulation of f-Ca9Fe(PO4)7 EPR spectra and the Mössbauer investigations confirmed that the Fe3+ cations are located in highly symmetrical sites. These techniques also revealed that in r-Ca9Fe(PO4)7 the residual ferric ions are in a rhombic symmetry and the Fe2+ ions are in octahedral sites slightly distorted by the Jahn-Teller effect.

Different compositions of calcium–copper Ca10.5−xCux(PO4)7 (0≤x≤1) and calcium–sodium–copper phosphates Ca10−x/2NaxCu0.5(PO4)7 (0≤x≤1) belonging to the whitlockite-type structure were synthesised and characterised. They crystallise in the rhombohedral space group R3c (Z=6) and are isostructural with the tricalcium phosphate β-Ca3(PO4)2. The catalytic behaviour of these series of phosphates was studied in butan-2-ol conversion. Pure tricalcium phosphate β-Ca3(PO4)2 was found to be inactive while the samples containing Cu2+ ions exhibited mainly a dehydrogenation activity producing methyl ethyl ketone. An increase in Cu2+ concentration in the catalysts improved the dehydrogenation activity. Structural characteristics of these Cu2+ ions were investigated by spectroscopic techniques and correlated to the catalytic behaviour. UV–VIS and EPR showed that the Cu2+ ions are distributed in the phosphate lattice between two different positions: the Ca(4) and the Ca(5) sites. Progressive substitution of Cu2+ located in the Ca(4) sites by sodium resulted in a decrease in the activity. The Ca9.5NaCu0.5(PO4)7 that contains cupric ions only in the Ca(5) sites is inactive. 31P MAS NMR investigations of Ca10.5(PO4)7 and Ca10Na(PO4)7 showed that the occupancy level of the Ca(4) sites does not modify notably the symmetry of the (PO4)3− groups. UV–VIS and XPS analysis performed on the samples after a catalytic test showed that the dehydrogenation reaction lowers the amount of Cu2+ ions in the phosphate by reducing them to Cu+. It was proven that the active sites are the Cu2+ ions hosted by the Ca(4) sites.

The present study deals with ethane dehydrogenation on V2O5/TiO2 modified by different amounts of P2O5. Catalysts containing P/V ratios ranging from 0 to 3.3 were prepared by impregnation in presence of oxalic acid. Their characterization by various spectroscopic techniques showed that in absence of phosphorus, the vanadium is essentially present in the sample as V5+. Addition of P2O5 favors the formation of supported vanadyl phosphate and isolated V4+ species. Catalytic measurements have showed that phosphorus improves the selectivity towards ethene. At 550 degrees C, the total conversion reaches 33% and the selectivity 50%. The activity of the sample investigated seems to be governed by the V5+/V4+ ratio. At higher concentration of V5+ like. in V2O5/TiO2 a good activity is achieved but the selectivity is poor. When the concentration of V4+ is increased by an addition of P2O5 the selectivity increases.

Dans l'étude qui sera présentée, nous avons examiné le système V2O5/TiO2 modifié par le phosphore à différents rapports molaires dans la réaction de déshydrogénation oxydante de l'éthane en éthylène. Une série de catalyseurs V2O5- P2O5/TiO2 contenant des rapports P/V compris entre 0 et 3,3 a été préparée par la méthode d’imprégnation en présence d’acide oxalique. La caractérisation de ces solides par différentes techniques spectroscopiques a montré qu’en absence de phosphore, le vanadium présent dans le catalyseur est essentiellement sous forme d’ions V5+. L’ajout de P2O5 favorise l'apparition du phosphate de vanadyle supporté et d’entités V4+ isolées.