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Five and ten weight percent-alumina-containing chitosan-AlOx films were prepared via sol-gel processing. The films were AlOx-agglomerate-free. These organic-inorganic films were degraded by heating at 500 °C. The solid powder residues were found by means of thermogravimetry, X-ray diffractometry, infrared spectroscopy, and electron microscopy to consist of alumina (Al2O3) nanoparticles entraping volatile components, whose thermal removal encouraged ambient oxygen uptake. The surface microstructure and morphology of the recovered alumina nanoparticle were inspected by high-resolution transmission and scanning electron microscopy. Also, the surface chemistry and texture were evaluated by X-ray photoelectron spectroscopy and N2 sorptiometry. Coalescences of globular nanoparticles of γ-/η-Al2O3 were the dominant composition of the 800 °C calcination product of the recovered alumina, irrespective of the alumina-content of the film. Upon increasing the calcination temperature up to 1100 °C, an enhanced polymorphic transition into agglomerated nanoparticles of the seldom encountered Iota-(ι-)Al2O3 took place. The high thermal stability of the otherwise unstable transition aluminas (at ≥950 °C) may suggestively owe to its polymorphic interdependence and/or persistent nanoscopic nature (average particle size = ca. 3-4 nm; specific surface area = ca. 80-60 m2/g). The surface chemical composition for the recovered transition aluminas nanopowders promises versatile acid-base properties for catalysis applications. Accordingly, the highly abundant bio-waste, chitosan, was successfully utilized as a novel synthesis medium for catalytic-grade alumina nanoparticles.The highly abundant bio-waste material, chitosan, is successfully employed as a synthetic medium for catalytic-grade alumina nanoparticles. This novel sol-gel synthesis process resulted in nearly 100%-recovery of nanoparticle transition γ-/η- and ι-Al2O3 and may be utilized in fabricating other materials/metal oxides [ABSTRACT FROM AUTHOR]

New insight was gained into the acidity-reactivity relationships of sulfated zirconia (SZ) catalysts prepared via (NH4)2SO4 impregnation of Zr(OH)4 for propanoic acid esterification with methanol. A family of systematically related SZs was characterized by bulk and surface analyses including XRD, XPS, TGA-MS, N2 porosimetry, temperature-programmed propylamine decomposition, and FTIR of adsorbed pyridine, as well as methylbutynol (MBOH) as a reactive probe molecule. Increasing surface sulfation induces a transition from amphoteric character for the parent zirconia and low S loadings <1.7 wt %, evidenced by MBOH conversion to 3-hydroxy-3-methyl-2-butanone, methylbutyne and acetone, with higher S loadings resulting in strong Brønsted-Lewis acid pairs upon completion of the sulfate monolayer, which favored MBOH conversion to prenal. Catalytic activity for propanoic acid esterification directly correlated with acid strength determined from propylamine decomposition, coincident with the formation of Brønsted-Lewis acid pairs identified by MBOH reactive titration. Monodispersed bisulfate species are likely responsible for superacidity at intermediate sulfur loadings. [ABSTRACT FROM AUTHOR]

The thermal decomposition course of europium acetate tetrahydrate (Eu(CH3COO)3·4H2O) was probed on heating up to 1000 °C in a dynamic atmosphere of air by thermogravimetry and differential thermal analysis. The solid- and gas-phase decomposition products were identified by X-ray diffractometry, ex- and in situ infrared spectroscopy and mass spectrometry. Results obtained showed the acetate to dehydrate stepwise at 145–283 °C, and then decompose stepwise to yield eventually cubic-Eu2O3 at ≥663 °C encompassing the formation of intermediate oxycarbonate (Eu2O(CO3)2/Eu2O2(CO3) solid products (at 347–466 °C)) and H2O, (CH3)2CO and CO2 as primary gaseous products. A considerable enhancement of the production of the primary gas phase products at 400–450 °C and the emergence of (CH3)2C=CH2, CH4 and CO molecules in the gas phase are ascribed to reactions occurring at the gas/solid interface at the expense of some of the primary products. These interfacial activities impart application-worthy adsorptive and catalytic functions for the associated solid products. [ABSTRACT FROM AUTHOR]

Abstract: The issue of size-sensitivity of the surface properties of anatase TiO2 is addressed by examining three samples synthesized by aqueous sol–gel method having different particle sizes on the nanoscale (8–19nm). A number of characterization methods, namely, X-ray powder diffractometry, infrared spectroscopy, UV–vis diffuse reflectance spectroscopy, sorptiometry and electron microscopy are employed. The data obtained reveal interrelated dependencies of the surface area, porosity, nitrogen and pyridine adsorption capacity and strength, and catalytic methylbutynol decomposition activity on the size of titania nanoparticles. Pertinent size-dependent bulk properties are also revealed and used to account for the changes conceded by the surface properties. Accordingly, going from 19 to 8-nm sized titania particles has been found to stabilize the anatase structure, weaken the surface acidity, and blueshift the UV absorption edge of titania. [Copyright &y& Elsevier]

Abstract: A surfactant-stabilized microemulsion method was used to prepare nano-sized particles (<10 nm) of cubic-CeO2 exposing surfaces of not only highest specific areas (142–201 m2/g) ever reported for polycrystalline ceria, but also high thermal stability at 800 °C. Three different surfactants, a non-ionic, an anionic and a cationic, were used to form the microemulsions. Then, N2 sorptiometry and pore volume distribution calculations, were used to reveal microporous and mesoporous structures of these cerias as a function of surfactant type. Transmission electron microscopy was used to visualize consequent particle behaviors. Suggestions have been made as to the textural attributes of the high surface area and thermal stability. Accordingly, cationic surfactants, in the presence or absence of added non-ionic surfactant, are seen to assist in producing cerias of promising surface textural properties for the chemical makeup of combustion catalysts. [Copyright &y& Elsevier]

Mixed metal oxides are promising heterogeneous catalysts for biofuel production from lipids via alcoholysis, however, the impact of solid acidity and/or basicity on reactivity is comparatively poorly understood. Two systematically related families of MgO–ZrO2 mixed oxide catalysts were therefore prepared by different synthetic routes to elucidate the impact of surface acid-base properties on catalytic performance in the transesterification of tributyrin with methanol. The resulting materials were characterized by TGA-MS, ICP-OES, N2 porosimetry, XRD, TEM, XPS, DRIFTS, and CO2-temperature-programmed desorption (TPD). MgO–ZrO2 catalysts prepared by both non-aqueous impregnation and citric acid-mediated sol–gel routes exhibit excellent activity and stability. The citrate routes favor highly dispersed MgO and concomitant Lewis acid-base pair formation at the interface with zirconia. However, for both the citrate and impregnation routes, tributyrin transesterification occurs over a common, strongly basic MgO active site. [ABSTRACT FROM AUTHOR]

The need for highly concentrated hydrogen peroxide solutions to fuel spacecraft propulsion systems necessitates the development of new catalytic formulations mainly based on supported manganese oxides. In order to improve the preparation of such catalysts, the thermal decomposition and the hydrothermal reduction of different permanganate precursors were studied, as well as the effect of washing on the products. The test samples were characterized by X-ray power diffraction (XRD) and surface area determination, and compared for their catalytic activity towards H2O2 decomposition using a constant pressure reactor (for 1.71% H2O2) and a constant volume reactor (for 50% H2O2). The catalysts prepared by thermal decomposition of KMnO4 or NaMnO4·H2O have shown the intermediate formation of potassium (or sodium) manganate, and its partial dissolution during washing with water; higher catalytic activity and larger surface area were observed for the decomposition products of KMnO4. The hydrothermal reduction yielded products exhibiting larger surface area and higher specific catalytic activity when carried out under stoichiometric conditions. Comparable kinetic parameters were determined using both catalytic reactors. Unsupported and alumina supported catalysts displayed comparable activity per gram of manganese. [Copyright &y& Elsevier]

In this investigation, well defined mesoporous zirconia nanoparticles (ZrO 2 NPs) with cubic, tetragonal or monoclinic pure phase were synthesized via thermal recovery (in air) from chitosan (CS)- or polyvinyl alcohol (PVA)-ZrO x hybrid films, prepared using sol-gel processing. This facile preparative method was found to lead to an almost quantitative recovery of the ZrOx content of the film in the form of ZrO 2 NPs. Impacts of the thermal recovery temperature (450, 800 and 1100 °C) and polymer type (natural bio-waste CS or synthetic PVA) used in fabricating the organic/inorganic hybrid films on bulk and surface characteristics of the recovered NPs were probed by means of X-ray diffractometry and photoelectron spectroscopy, FT-IR and Laser Raman spectroscopy, transmission electron and atomic force microscopy, and N 2 sorptiometry. Results obtained showed that the method applied facilates control over the size (6-30 nm) and shape (from loose cubes to agglomerates) of the recovered NPs and, hence, the bulk crystalline phase composition and the surface area (144-52 m 2 /g) and mesopore size (23-10 nm) and volume (0.31-0.11 cm 3 /g) of the resulting zirconias.