Hamdy M. Ismail

Ceria on silica and alumina catalysts: dispersion and surface acid-base properties as probed by X-ray diffractometry, UV-Vis diffuse reflectance and in situ IR absorption studies

Abstract X-ray diffractometry and UV-Vis diffuse reflectance spectroscopy revealed that fluorite-structured CeO 2 crystallites (mean size 22.3 nm) are dispersed on silica surfaces (CeSi) into microcrystallites (11.2-8.1 nm) and dispersed further on alumina surfaces (CeAl) into nanocrystallites ( x monolayers. Consequently, IR spectroscopy of adsorbed pyridine found Lewis acid sites to be far more strengthened on CeAl. Bronsted acid sites (proton-donors) were probed exclusively on CeAl. On the other hand, IR spectroscopy of adsorbed deuterated chloroform (CDCl 3 ) showed the originally moderate Lewis base sites (low-coordinated OH − and O 2− ) to be weakened on CeSi, but markedly strengthened on CeAl. Lewis base sites exposed on ceria surfaces assume a strong nucleophilic reactivity.

Thermal and chemical events in the decomposition course of manganese compounds

Abstract Thermogravimetry and differential thermal analysis, infrared spectroscopy (solid phase and gas phase), and X-ray diffraction were used to characterize the pathways of the decomposition of the hydrated acetate, oxalate and nitrate of manganese in air. The non-isothermal activation energy ( ΔE , kJ mol −1 ) was determined for the thermal processes monitored throughout the decomposition course. The results showed that Mn ( CH 3 COO ) 2 ·4 H 2 O dehydrates in three steps up to 130 °C, and then decomposes to a mixture of manganese oxides Mn 3 O 4 (major) and Mn 2 O 3 (minor) through the intermediates Mn(OH)CH 3 COO and/or MnOCH 3 COO and MnCO 3 . MnC 2 O 4 ·2 H 2 O dehydrates in one step at 150 °C, and then decomposes via MnCO 3 into Mn 3 O 4 (hausmannite structure) at 350 °C. Mn ( NO 3 ) 2 ·4 H 2 O undergoes stepwise dehydration up to 175 °C, and decomposes above 200 °C via an unstable oxynitrate intermediate yielding MnO 2 ; this decomposes at about 550 °C to the α-Mn 2 O 3 phase.

A thermoanalytic study of metal acetylacetonates

Abstract The thermal decomposition reactions of iron(III) and zinc(II) acetylacetonates, in dry nitrogen were thoroughly studied. Thermal events occurring throughout the decomposition range (room temperature to 1000° C) were monitored by means of thermogravimetry and differential thermal analysis. These events were characterized on the basis of solid and gas product analyses, using X-ray diffractometry and infrared spectroscopy. Non-isothermal kinetic parameters (A, k and ΔE) were determined. The results showed Zn(C5H7O2)2·2H2O dehydrates at ⩽110° C, and, then, decomposes similarly to Fe(C5H7O2)3 via a complex pathway. The ultimate products at ⩾ 600° C were ZnO and Fe2O3. The metal acetates and mixed metal carbonate-oxide phases were observed as intermediate solid products. Gas phase products included propyne, acetone, isobutene, methane and carbon oxides. Some of these were initial decomposition products, whereas others resulted from interfacial reaction involving the initial products.

Characterization of lanthanum oxide formed as a final decomposition product of lanthanum acetylacetonate: thermoanalytical, spectroscopic and microscopic studies

Abstract The porous and high surface area of lanthanum oxide was obtained as a final decomposition product of lanthanum acetylacetonate tetrahydrate. The decomposition course in dry nitrogen was thoroughly studied. Thermal processes occurring throughout the decomposition range (100–800 °C) were monitored by thermogravity; differential thermal analysis and infrared spectroscopy gaseous products. These processes were characterized on the basis of the solid products analyses, using X-ray diffractometry and IR-spectrometry. The results showed La(C5H7O2)3 completely decomposed to La2O3 at 730 °C, through amorphous and unstable intermediates La(CH3COO)(C5H7O2)2 at 190 °C, La(CH3COO)2(C5H7O2) at 225 °C, La(CH3COO)3 at 285 °C, La2(CO3)3 at 390 °C and crystalline and stable La2O2(CO3) at 430 °C. Gas phase decomposition products included propyne, acetone, carbon oxides, methane and isobutene. Methane and isobutene resulted from interfacial reactions involving the initial product (acetone). The ultimate products, La2O3 at 700 °C and 800 °C, are crystalline porous solids and having a surface area of 21 and 45 m2/g respectively.

Texture properties of yttrium oxides generated from different inorganic precursors

Abstract The texture properties of four samples of Y 2 O 3 (cubic structure) generated from different inorganic precursors (hydrated Yttrium acetate, Y(CH 3 COO) 3 ·4H 2 O; nitrate, Y(NO 3 ) 3 ·5H 2 O and oxalate, Y 2 (C 2 O 4 ) 3 ·8H 2 O) at different temperatures have been studied using BET, pore size distribution, cumulative surface area, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that samples obtained from both acetate at 700°C (55 m 2 /gm) and nitrate at 500°C (58 m 2 /gm) are very similar in surface area and pore structure (a wider spectrum of mesoporosity); i.e., good precursors for catalyst and catalyst support. The third sample obtained from oxalate at 700°C exhibits a lower surface area (12 m 2 /gm) and different in pore structure, i.e., a good precursors for ceramics and superconductor manufacture. For Y 2 O 3 generated from nitrate, the increase in calcination temperature from 500 to 700 °C caused a decrease in the surface area from 58 to 20 m 2 /g, and in the microporosity development. The SEM and particle size calculations have been used to assess the surface properties of Y 2 O 3 samples.

Characterization of the decomposition products of zirconium acetylacetonate: nitrogen adsorption and spectrothermal investigation

Abstract The thermal decomposition reactions of zirconium acetylacetonate in dry nitrogen were thoroughly studied. Thermal processes occurring throughout the decomposition range (100–800 °C) were monitored by means of thermogravimetry, differential thermal analysis and IR spectroscopic analysis of the gaseous products. These processes were characterized on the basis of the solid products analyses using X-ray diffractometry and IR spectroscopy. The results showed that the square antiprism Zr(C 5 H 7 O 2 ) 4 had completely decomposed to tetragonal ZrO 2 at 800 °C, through intermediates Zr(CH 3 COO) 2 (C 5 H 7 O 2 ) 2 at 190 °C, ZrO(CH 3 COO) 2 at 340 °C and ZrOCO 3 at 450 °C. The latter decomposed immediately to give ZrO 2 at 800 °C. Gas-phase products included propyne, acetone, carbon oxides, methane and isobutene. Methane and isobutene resulted from interfacial reaction involving the initial product (acetone). The texture analyses of the thermal decomposition products obtained at different temperatures (300–800 °C) were assessed by the analysis of nitrogen isotherms, using a number of widely accepted methods. The results of nitrogen adsorption, scanning electron microscopy and X-ray diffractometry showed that the final product ZrO 2 developed micro- and mesoporous texture and a growing crystallinity.

Thermal genesis course of iron oxide pigmentary powders from steel-pickling chemical waste

Abstract The thermal genesis course of Fe 2 O 3 pigmentary powders from steel-pickling chemical waste was thoroughly explored. Thermal analysis in oxidizing and inert atmospheres provided a means of monitoring weight-variant and invariant processes involved. These were physicochemically characterized on the basis of solid and gas product analyses using X-ray diffraction and infrared absorption techniques. The kinetic parameters (A,k andΔ E and reversibility were also determined. The results obtained indicated a strong influence of the atmosphere on the reaction pathways and products. Thus, a dominant topochemical character was revealed for the thermal recovery course of Fe 2 O 3

Chromia on Silica and Alumina Catalysts: Chromia Dispersion as Determined by N2-Adsorption Measurements

Silicaand alumina-supported chromia catalysts at loadings varying between 0.5 and 10 mole % Cr203 were prepared from different parent compounds and characterized by N2-adsorption at 77 K. The adsorption isotherms were evaluated on the basis of the BETand as-methods. The results suggest that the chromia exists on the surface of silica with rather low dispersion probably in the form of small Cr203 crystallites which lead to pore blocking. In contrast, on alumina narrowing of pores is observed, this being suggestive of formation of a highly dispersed chromia layer. These conclusions can be rationalized on the basis of the different surface chemical properties of the oxide supports, and they are consistent with previously reported spectroscopic characterizations of the same materials. It is inferred that in fact N2-adsorption data do provide valuable qualitative information on the dispersion of supported oxide materials.

Structure analysis of phosphated zirconia catalysts using XRD and nitrogen adsorption methods

Abstract Phosphated zirconia catalysts were prepared by impregnating two different precursors (zirconium hydroxide and crystalline ZrO2) with an aqueous solution of diammonium hydrogen phosphate. X-ray powder diffractograms and nitrogen adsorption isotherms at −196°C on pure and phosphated zirconia catalysts were investigated. The pore volume was calculated from the adsorption branch to explore the modification of porosity for pure and phosphated zirconia. Pore structure analysis shows that phosphated zirconia, resulted from calcination of zirconium hydroxide at low temperature, exhibited high surface area and accessible porosity. Whereas for those calcined at higher temperatures, inaccessible porosity is shown to predominate. Phosphation of crystalline zirconia did not modify either surface area or the porosity, as compared to pure zirconia. The influence of phosphation on the structure of zirconium hydroxide and zirconia during the calcination course was studied.

Texture assessment of thoria as a final decomposition product of hydrated thorium nitrate and oxycarbonate

Abstract Th(NO 3 ) 4 ·5H 2 O and ThO(CO 3 )·0.5H 2 O were used as parent compounds for the formation of ThO 2 . Thermal processes involved during the course of decomposition up to 500°C in air were monitored by thermogravimetry, differential thermal analysis and infrared (IR) gas phase analysis. Intermediate and final solid products were characterized by IR spectroscopy and X-ray diffractometry. The results showed that Th(NO 3 ) 4 ·5H 2 O is completely decomposed to ThO 2 at 300°C via three unstable intermediates: Th(OH)(NO 3 ) 3 at 165°C; ThO(NO 3 ) 2 at 210°C and ThO 1.75 (NO 3 ) 0.5 at 250°C. Similarly, ThOCO 3 ·0.5H 2 O is completely decomposed to ThO 2 at 300°C via the unstable intermediate ThO 1.5 (CO 3 ) 0.5 at 160°C. Surface texture measurements and scanning electron microscopy showed that ThO 2 , the final decomposition product at 500°C of both Th(NO 3 ) 4 ·5H 2 O and ThO(CO 3 )·0.5H 2 O is crystalline and has surface areas of 32 m 2 g −1 and 56 m 2 g −1 , respectively. ThO 2 formed from the nitrate is mainly microporous. However, ThO 2 obtained from the oxycarbonate contains different types of porosities.