Samih A. Halawy

Non-isothermal decomposition of nickel acetate tetrahydrate

Abstract Non-isothermal decomposition of nickel acetate tetrahydrate was studied by means of thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) from ambient temperature up to 500°C. The parent salt was found to commence dehydration near 80°C giving the anhydrous nickel acetate, which on further heating produced basic nickel acetate. Decomposition took place above 250°C with the formation of nickel carbide (Ni3C), which, together with the basic acetate, decomposed to a mixture of NiO and nickel metal. Kinetic parameters (ΔE and ln A) and thermodynamic parameters (ΔH and Cp) are given for the dehydration and decomposition processes. Infrared spectroscopy and X-ray powder diffractometry were used to identify the solid decomposition products while gas chromatography was employed to identify the volatile decomposition products (acetic acid, acetone, CO2, and trace amounts of CO, ethyl acetate and propionic acid). The distribution of these volatile products was found to be influenced by the prevailing atmosphere (N2 or O2).

The non-isothermal decomposition of cobalt acetate tetrahydrate

The non-isothermal decomposition of cobalt acetate tetrahydrate was studied up to 500°C by means of TG, DTG, DTA and DSC techniques in different atmospheres of N2, H2 and in air. The complete course of the decomposition is described on the basis of six thermal events. Two intermediate compounds (i.e. acetyl cobalt acetate and cobalt acetate hydroxide) were found to participate in the decomposition reaction.IR spectroscopy, mass spectrometry and X-ray diffraction analysis were used to identify the solid products of calcination at different temperatures and in different atmospheres. CoO was identified as the final solid product in N2, and Co3O4 was produced in air. A hydrogen atmosphere, on the other hand, produces cobalt metal. Scanning electron microscopy was used to investigate the solid decomposition products at different stages of the reaction. Identification of the volatile gaseous products (in nitrogen and in oxygen) was performed using gas chromatography. The main products were: acetone, acetic acid, CO2 and acetaldehyde. The proportions of these products varied with the decomposition temperature and the prevailing atmosphere.Kinetic parameters (e.g.E and lnA) together with thermodynamic functions (e.g. °H, Cp and °S) were calculated for the different decomposition steps.ZusammenfassungIn verschiedenen Atmosphären aus N2, H2 und in Luft wurde mittels TG, DTG, DTA und DSC bis zu 500°C die nichtisotherme Zersetzung von Kobaltacetat-Tetrahydrat untersucht. Der gesamte Umsetzungsprozeß wird auf der Grundlage von sechs thermischen Ereignissen beschrieben. Man fand, daß zwei Zwischenprodukte (Acetylkobaltacetat und Kobalt-acetathydroxid) an den Zersetzungsreaktionen beteiligt sind.Die Bestimmung der Feststoffprodukte der kalzinierung bei verschiedenen Temperaturen und in verschiedenen Atmosphären erfolgte mittels IR-Spektroskopie, Massenspektrometrie und Röntgendiffraktion. In Stickstoff entsteht als festes Endprodukt CoO, in Luft hingegen Co3O4. In Wasserstoffatmosphäre kommt es jedoch zur Bildung von metallischem Kobalt. Mittels Scanning-Elektronenmikroskopie wurden die festen Zersetzungsprodukte zu verschiedenen Reaktionsstadien untersucht. Die Bestimmung flüchtiger gasförmiger Produkte (in Stickstoff und in Sauerstoff) erfolgte mittels Gaschromatographie. Die Hauptprodukte waren: Aceton, Essigsärue, CO2 und Acetaldehyd, deren relative Menge von der Zersetzungstemperatur und der vorherrschenden Temperatur abhängt.

Non-isothermal kinetic and thermodynamic study of the decomposition of lead acetate trihydrate

Abstract The non-isothermal decomposition of lead acetate trihydrate was studied up to 450°C by means of TG, DTG, DTA and DSC measurements in a dynamic atmosphere of N2 (or dry air). The parent salt was found to undergo melting concurrently with the dehydration process, which takes place in two steps between 30 and 110°C. The anhydrous salt melts at 204°C and later forms two intermediate basic lead acetate salts, namely Pb(CH3COO)2 · PbO (between 230 and 270°C) and Pb(CH3COO)2 · 2PbO (between 275 and 325°C) respectively. The latter basic salt decomposes, between 325 and 380°C in N2 atmosphere, to produce a mixture of PbO and a small amount of metallic Pb. In air, however, the decomposition produces solid PbO only. X-ray powder diffraction and IR transmission spectroscopy were used to identify the solid intermediates and products of the reaction. Gas chromatography was used to identify the volatile products of the decomposition in N2 and in O2. Scanning electron microscopy was also used to investigate the structure changes and possible occurrence of melting during the decomposition. Values of the kinetic (ΔE and ln A) and thermodynamic (ΔH, Cp and ΔS) parameters were calculated for the dehydration and decomposition processes.

Surface composition, charge and texture of active alumina powders recovered from aluminum dross tailings chemical waste

Three different methods were successfully applied to recover alumina (Al2O3) powders from aluminum dross tailings chemical waste (ADT) and Bauxite (BUX) ore. The six powder samples thus obtained were examined by X-ray diffractometry and photoelectron spectroscopy, f-potential measurement, N2 sorptometry and transmission electron microscopy (TEM). The results obtained revealed that alumina powders recovered from the chemical waste also assume catalytic-grade properties; viz., g-structured bulk, pure surfaces having a net zero charge at pH=8.3–9.2 and apparently uniform mesopores with apparent pore diameters in the range 60–70 Au . Thus, the present investigation presents an adequate utilization of the aluminum dross tailings chemical waste, which is, to date, neither adequately utilized nor properly dispensed in developing countries. D 2003 Elsevier Science B.V. All rights reserved.

Kinetic and thermodynamic studies of the non-isothermal decompositions of nickel malonate dihydrate and nickel hydrogen malonate dihydrate

Abstract Non-isothermal decompositions (including TG, DTG, DTA and DSC) of nickel malonate dihydrate and of nickel hydrogen malonate dihydrate were studied in different dynamic atmospheres of N 2 , H 2 or air. The reaction of the hydrogen malonate salt commences at a lower temperature than the corresponding nickel malonate salt. IR spectroscopy showed that nickel acetate was formed as a reaction intermediate during the decompositions of both reactants. X-ray diffraction showed that nickel metal was the predominant product from reactions in N 2 or H 2 atmospheres while nickel oxide, together with some nickel metal, was formed during reaction in air. Gas chromatography identified CO 2 , CO, acetic acid ethyl alcohol together with appreciable amounts of methyl formate and ethyl formate as the volatile decomposition products. Kinetic and thermodynamic parameters of the decomposition of the two reactant salts were calculated.

Unsupported MoO3Fe2O3 catalysts: characterization and activity during 2-propanol decomposition

Abstract The catalytic decomposition of 2-propanol (2-PrOH) was studied as probe reaction, in the gas phase, over unsupported MoO3Fe2O3 mixed catalysts. The samples were prepared by mixing MoO3 (as ammonium heptamolybdate) with different x mol% Fe2O3 (as ferric nitrate) and calcined at 500°C in air for 5 h. All catalysts were characterized by TPR, IR, XRD and XPS analyses. The surface area of these samples were determined using the BET method. Also, the acidity and the basicity of all catalysts were estimated thermogravimetrically using the adsorption of pyridine and formic acid as probe molecules. The catalytic decomposition of 2-PrOH was studied over the catalysts in the temperature range of 150–260°C. A correlation between the catalytic activity and the acidity or the basicity of these catalysts has been made. The activation energies for both propene and acetone formation, over MoO3Fe2O3 catalysts, were calculated.

Recovery of high surface area alumina from aluminium dross tailings

Aluminium dross tailings (ADT), a chemical waste from a factory producing aluminium in Egypt, was used for the recovery of the aluminium content in the form of alumina (Al 2 O 3 ). Extraction of the aluminium was carried out via atmospheric- and high-pressure leaching with caustic soda. Then, it was separated from the sodium aluminate solutions thus obtained, using six different precipitation methods (via H 2 O 2 , via carbonation, via ammonium carbonate, via ammonium bicarbonate, via ammonium aluminium sulfate, via addition of active seeds). The precipitates were filtered, washed, dried and calcined at 600°C to produce the test aluminas. The precipitates and the calcination products were analysed for their chemical and crystalline phase compositions. The calcination products (aluminas) were subjected to sorpometry for surface area determination, and to particle sizing. The results indicated that highly pure (SiO 2 200 m 2 /g) and uniform small crystallite sizes (60-70A) could be efficiently recovered from ADT. Optimal recovery conditions were examined and determined.

The effect of different ZnO precursors on the catalytic decomposition of ethanol

Abstract Three different samples of ZnO were prepared from the thermal decomposition, at 500°C in N2, of three precursors, i.e. Zn(CH3CO2)2 · 2H2O, Zn3(C6H5O7)2 · 2H2O and Zn(NO3)2 · 6H2O. These oxide samples were characterized by XRD and IR spectroscopy and their surface area were calculated using the BET method. The excess surface oxygen for each oxide was determined using the hydrazine method. Also, the basicity of such oxides were estimated thermogravimetrically using formic acid adsorption method. The catalytic decomposition of ethanol, as a test reaction, was studied over ZnO samples in a flow system. Ethylene and acetaldehyde were identified as the reaction products using gas chromatography. The activation energy for the decomposition process of ethanol over ZnO samples was calculated as ≈ 43 kJ mol−1. Reaction mechanisms for the formation of ethylene and acetaldehyde as the decomposition products of ethanol are given.

Thermal and spectroscopic studies of chromium chromate hexahydrate – a likely composition for redox surfaces of calcined chromia catalysts

Abstract Invoked by the possibility that chromium chromate species might constitute the surface composition of calcined chromia catalysts, a commercial Cr 2 (CrO 4 ) 3 ·6H 2 O compound was examined by thermogravimetry and differential scanning calorimetry in different reactive gas atmospheres. The principle goal was a proper assessment of its thermal and chemical stabilities with the hope of making an objective judgment on current environmental reservations about industrial applications of calcined chromia catalysts, owing to volatility of Cr IV –O species. On the basis of the thermal analysis results, the chromate compound was calcined at some selected temperatures in the range from 150°C to 1000°C. The solid products were, then, subjected to X-ray powder diffractometry and spectroscopies of infrared absorption and UV–Vis diffuse reflectance. The results have shown the parent bulk chromate to dehydrate completely near 300°C and to decompose into chromate-covered α-Cr 2 O 3 particles at 450–1000°C, encompassing formation of noncrystalline polychromate (Cr 1+ x O 2− 4+3 x ) and nonstoichiometric γ-Cr 2 O 3+ x bulk phases. In the presence of hydrogen atmosphere, the dehydration is intercepted by an immediate reduction, however the eventual product (α-chromia) remained chromate covered to 1000°C. The high-temperature thermal and chemical stabilities thus revealed for the dispersed chromates are attributed to electronic interactions with nearby Cr III –O species dwelled in a crystalline lattice.

Kinetic and Thermodynamic Parameters of the Decomposition of Chromium Chromate in Different Gas Atmospheres

Non-isothermal decomposition of chromium chromate hexahydrate, Cr2(CrO4)3−6H2O, was studied on heating up to 600°C in different dynamic atmospheres of N2, O2 and H2, using thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). The results obtained at various heating rates (2–20°C min−1) were used to derive kinetic (Ea and lnA) and thermodynamic (ΔH, Cpand ΔS parameters.It has been found that the activation energies of the dehydration and decomposition steps in N2 are generally larger than in H2 atmosphere, and the reverse is true for the enthalpy change of the decomposition. Thus, it has been concluded that the reductive decomposition (in H2) is easier than the thermal decomposition (in N2 or O2) of the chromate. Irrespective of the gas atmosphere applied, the eventual decomposition product was a mixture of α-Cr2O3 and non-crystalline chromate species, γ-Cr2O3+x. Above 400°C in H2 atmosphere, more deoxygenation of the non-crystalline chromate takes place at high rates of heating to give α-Cr2O3.