Synthesis of Thermally Stable χ-Alumina by Thermal Decomposition of Aluminum Isopropoxide in Toluene

Thermal decomposition of aluminum isopropoxide in toluene at 315°C resulted in χ-alumina that had high thermal stability, whereas the reaction at lower temperatures resulted in formation of an amorphous product. The χ-alumina thus obtained directly transformed to α-alumina at ∼1150°C, bypassing the other transition alumina phases, whereas the amorphous product transformed to γ-alumina and then to θ-alumina before final transformation to α-alumina. When the χ-alumina, solvothermally synthesized at 315°C, was recovered by the removal of the solvent at the reaction temperature, thermal stability of the product was improved further. This procedure is convenient because it avoids bothersome work-up processes that yield large-surface-area and large-pore-volume alumina.     

Ag-ZnO catalysts for UV-photodegradation of methylene blue

High surface area Ag-ZnO catalysts have been made by flame spray pyrolysis (FSP) and characterized by X-ray diffraction (XRD), nitrogen adsorption, UV–vis spectroscopy and electron microscopy (SEM and transmission electron microscopy (TEM)) combined with energy dispersive X-ray spectroscopy (EDXS) for elemental mapping. Silver metal clusters deposited directly on ZnO nanocrystals were obtained from this process. The Ag loading (1–5 at.%) controlled the Ag cluster size from 5 to 25 nm but did not influence the ZnO crystal size. Photodegradation of 10 ppm methylene blue (MB) solution was used to evaluate the performance of these FSP-made Ag-ZnO and was compared to wet-made Ag-ZnO and reference titania photocatalysts. The rate of photodegradation was optimal for Ag loading around 3 at.%. The best photocatalytic performance was exhibited by flame-made Ag-ZnO produced at the longest high-temperature residence times having high crystallinity as determined by XRD and UV–vis.     

Color improvment of C9 hydrocarbon resin by hydrogenation over 2% Pd/γ‐alumina catalyst: Effect of degree of aromatic rings hydrogenation

Color improvement of commercial C₉ hydrocarbon resin (c‐C₉HR) and prepared C₉ hydrocarbon resin (p‐C₉HR) has been investigated under various hydrogenation conditions over 2% Pd/γ‐alumina catalysts. The degrees of aromatic rings hydrogenation (DHs) and molecular structure of resin were determined from nuclear magnetic resonance of ¹H and ¹³C (¹H‐NMR and ¹³C‐NMR) and Fourier transform infrared spectroscopy (FTIR) analyses. The starting c‐C₉HR presented in yellow color (Gardner color No. 8.4). Under the hydrogenation conditions used (H₂ pressure 70 bar, 250°C, and 8 h), the ethylenic proton in c‐C₉HR was completely removed, but the aromatic rings content remained unaltered and very little change in resin color was observed (Gardner color No.8.1). On the other hand, the starting p‐C₉HR contained only unsaturated aromatic proton with Gardner color No.17.1. Under similar conditions, aromatic rings in p‐C₉HR were converted to alicyclic rings, and its color was reduced to Gardner color No.5.7. By varying the DH of aromatics in p‐C₉HR, two‐step decolorization was observed in which at lower DH (≤10%) the color decreased sharply from 17.1 to 9.3, while further color reduction to 5.7 was obtained when the DH was increased to 94%. It is suggested that both color body and aromatic rings were the main sources contributing to C₉HR color. Nevertheless, color stability of the resin during heat treatment was significantly improved by hydrogenation especially at DH ≥ 50%. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Phase transformation behavior of nanocrystalline χ-alumina powder obtained by thermal decomposition of AIP in inert organic solvent

Thermal decomposition of aluminum isopropoxide (AIP) in inert organic solvents (toluene and mineral oil) resulted in the formation of -alumina. Phase evolution by calcination at various temperatures for this alumina was studied via X-ray diffraction. The results suggest a direct transformation from -alumina to -alumina at approximately 1180°C, without the formation of -alumina phase, while still maintaining the small particle size (<100 nm). The transformation behavior was observed by TEM and the crytallite size was calculated by the Scherrer equation. The results indicate one -alumina crystal transforms into one -alumina crystal at its critical size in a nucleation step. This crystal exhibits a rapid grain growth following the transformation.     

Effect of Cobalt Precursors on the Dispersion of Cobalt on MCM-41

The photocatalytic activity of titanium dioxide supported on zeolites HZSM-5, HY and H was evaluated for a novel intermolecular cyclization of ethylenediamine with propylene glycol leading to dihydropyrazine. Titanium dioxide supported on zeolites has been prepared with 2 and 5 wt% of TiO₂ by solid-state reaction, impregnation and sol impregnation methods. From the characterization by XRD, BET, EDAX and TPD of NH₃, it is deduced that in all cases titanium dioxide is in small particles of anatase on zeolites. The highest photocatalytic activity was obtained with 2 wt% TiO₂/H prepared by solid-state reaction. The acidity determined by TPD of NH₃ was found to be lower for TiO₂/H than for TiO₂/HZSM-5 and TiO₂/HY. From the above observations, it can be concluded that adsorption, acidity and structure of zeolites have an influence on the activity of supported TiO₂.     

Surfactant‐dispersed carbon black in polyimide nanocomposites: Spectroscopic monitoring of the dispersion state in the polymer matrix

The effects of an anionic surfactant on the dispersion of carbon black (CB) for the purpose of forming conducting composite films were examined with ultraviolet–visible (UV–vis) absorption spectroscopy. To obtain a good dispersion and size reduction of aggregated CB in a polymer matrix, sodium dodecyl sulfate (SDS), used as a surfactant, was introduced into a CB suspension. A set of concentrations with various ratios of CB to SDS (ranging from 1 : 0.4 to 1 : 10) was established before mixing with poly(amic acid) (PAA), a precursor of pyromellitic dianhydride and oxydianiline, was performed. The CB/PAA solution mixtures were submerged under an ultrasonic bath for several hours, then cast onto dry plate glasses, and finally subjected to thermal imidization to produce CB/polyimide (PI) nanocomposite films with various CB weight fractions ranging from 0.025 to 0.50 wt %. A method for evaluating the absorbance at 500 nm of the CB/PI nanocomposite films was established. The absorbance of CB/PI nanocomposite samples of various thicknesses was also normalized to get rid of the effects of the different thicknesses. UV–vis spectra showed that the minimum weight ratio of CB to SDS in the nanocomposite films that achieved well‐dispersed CB and still had transparent properties was 1 : 2.0. Transmission electron microscopy demonstrated that CB was dispersed homogeneously in the PI matrix, and the size of the aggregated CB was affected by the amount of the surfactant. The dielectric properties of the nanocomposite films without the surfactant increased by approximately 2 orders of magnitude with an increasing mass weight fraction of CB and decreased when the surfactant was added. The surfactant also reduced the tensile strength of the CB/PI nanocomposites when the CB/SDS ratio was higher than 1 : 2.0. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of calcination temperature on characteristics of sulfated zirconia and its application as catalyst for isosynthesis

The effect of catalyst calcination temperature (450 °C, 600 °C, and 750 °C) on catalytic performance of synthesized and commercial grade sulfated zirconia catalysts towards isosynthesis was studied. The characteristics of these catalysts were determined by using various techniques including BET surface area, XRD, NH₃- and CO₂-TPD, ESR, and XPS in order to relate the catalytic reactivity with their physical, chemical, and surface properties. It was found that, for both synthesized and commercial sulfated zirconia catalysts, the increase of calcination temperature resulted in the increase of monoclinic phase in sulfated zirconia, and the decrease of acid sites. According to the catalytic reactivity, at high calcination temperature, lower CO conversion, but higher isobutene production selectivity was observed from commercial sulfated zirconia. As for synthesized sulfated zirconia, the isobutene production selectivity slightly decreased with increasing calcination temperature, whereas the CO conversion was maximized at the calcination temperature of 600 °C. We concluded from the study that the difference in the calcination temperatures influenced the catalytic performance, sulfur content, specific surface area, phase composition, the relative intensity of Zr³⁺, and acid-base properties of the catalysts.     

Isosynthesis via CO hydrogenation over SO4–ZrO2 catalysts

Catalytic performances of sulfated zirconia catalysts with various contents of sulfur (from 0.1 to 0.75%) on isosynthesis were studied. It was firstly found that undoped-zirconia synthesized from zirconyl nitrate provided higher activity towards isosynthesis reaction (106 μmol kg-cat^?1 s^?1) compared to that synthesized from zirconyl chloride (84.9 μmol kg-cat^?1 s^?1). Nevertheless, the selectivity of isobutene in hydrocarbons was relatively lower. It was then observed that the catalytic reactivity and selectivity significantly improved by sulfur loading. The most suitable sulfur loading content seems to be at 0.1%, which gave the highest reaction rate and selectivity of isobutene. By applying several characterization techniques, i.e. BET, XRD, NH₃- and CO₂-TPD and SEM, it was revealed that the high reaction rate and selectivity towards isosynthesis reaction of sulfated zirconia catalysts are related to the acid–base properties, Zr³⁺ quantity and phase composition.     

The influence of Si-modified TiO2 on the activity of Ag/TiO2 in CO oxidation

Nanocrystalline TiO₂ and Si-modified TiO₂ with Si/Ti ratios 0.01, 0.05, 0.1, and 0.3 were prepared by the solvothermal method and employed as the supports for Ag/TiO₂ catalysts for CO oxidation reaction. The incorporation of Si into the TiO₂ lattice in the form of Ti–O–Si as revealed by FT-IR results could inhibit the agglomeration of TiO₂ crystallites, resulting in an increase of both surface area and metal dispersion. However, there existed an optimum content of Si/Ti at ca. 0.05–0.1 which resulted in an improved catalytic activity of Ag/TiO₂ in CO oxidation. Based on the O₂-temperature program desorption (O₂-TPD) results, the catalysts with appropriate amounts of Si/Ti exhibited higher amount of O₂ adsorption and much lower desorption temperature. It is suggested that the presence of Ti–O–Si promoted the formation of active oxygen species and increased the mobility of lattice oxygen so that the catalytic activity was enhanced. There was no improvement in CO oxidation activity of the Ag/TiO₂ catalyst when the Si/Ti was further increased to 0.3 due probably to the formation of amorphous SiO₂ instead of the Ti–O–Si bond.     

A Comparative Study of Ethylene/α-Olefin Copolymerization with Silane-Modified Silica-Supported MAO Using Zirconocene Catalysts

Activities of ethylene/α-olefin copolymerization were found to increase with silane-modified silica-supported MAO using ansa-zirconocene catalyst. The increase in activities was less pronounced when higher α-olefins were used. However, silane modification resulted in the narrower molecular weight distribution of polymers. ¹³C NMR revealed that ethylene incorporation in all systems gave polymers with the similar triad distribution.