Catalytic dehydrogenation of ethylbenzene with carbon dioxide: promotional effect of antimony in supported vanadium–antimony oxide catalyst

Alumina-supported vanadium oxide, VO_x/Al₂O₃, and binary vanadium–antimony oxides, VSbO_x/Al₂O₃, have been tested in the ethylbenzene dehydrogenation with carbon dioxide and characterized by S_BET, X-ray diffraction, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction and CO₂ pulse methods. VSbO_x/Al₂O₃ exhibited enhanced catalytic activity and especially on-stream stability compared to VO_x/Al₂O₃ catalyst. Incorporation of antimony into VO_x/Al₂O₃ increased dispersion of active VO_x species, enhanced redox properties of the systems and formed a new mixed vanadium–antimony oxide phase in the most catalytically efficient V_0.43Sb_0.57O_x/Al₂O₃ system.     

Preparation and characterization of carbon-encapsulated iron nanoparticles and their catalytic activity in the hydrogenation of levulinic acid

This study describes the synthesis of carbon-encapsulated iron nanoparticles using an ultrasonic method and also investigates their catalytic activity. These nanoparticles have been prepared using ultrasonic irradiation followed by annealing at various temperatures. As the annealing temperature of as-prepared α-Fe₂O₃ nanoparticles increased, the sample transformed into γ-Fe₂O₃, Fe₃O₄, and Fe nanoparticles via the reduction process without requiring any additional reducing agents such as H₂ gas, thus, creating a carbon shell surrounding the nanoparticles. By controlling the experimental conditions, Fe nanoparticles of various sizes can be formed with diameters in the range 100–800 nm; these nanoparticles are tightly encapsulated by 20-nm-thick carbon shells. Because of their high saturation magnetization 212 emu g^?1, the carbon-encapsulated Fe nanoparticles can be used for magnetic resonance imaging with a dramatically enhanced efficiency compared to commercially available T ₂ contrast agents. Moreover, the carbon-encapsulated Fe nanoparticles showed its superior catalytic activity and reusability for the hydrogenation of biomass-derived levulinic acid to GVL (99.6 %) in liquid phase.     

Synthesis of mesoporous silica in acidic condition by solvent evaporation method

Both powder-type and film-type mesoporous silica materials have been prepared by using a sol-gel process in highly acidic, solvent-rich and mild conditions by solvent evaporation method. Powder mesoporous silica which has hexagonal arrays was well synthesized within only 10 minutes, and mesoporous film was formed on the glass plate within only several seconds by supramolecular interactions between the silicate species and surfactant-templates. In particular, the synthesis time was very short compared with that of hydrothermal synthesis owing to the solvent evaporation. This method has some characteristics different from the hydrothermal method such as the following. There is no precipitation because particles do not form in the solution before solvent evaporation, bulk powder is rigid, whereas that of hydrothermal synthesis is very soft, and mesoporous materials are synthesized in acidic condition. Solvent evaporation method for the synthesis of mesoporous materials is promising because the method is very simple and time-saving.     

Environmentally Benign Oxidation of Alkylphenols to p-Benzoquinones: A Comparative Study of Various Ti-Containing Catalysts

Catalytic properties of Ti-containing porous solids were compared in the oxidation of 2,3,6-trimethylphenol (TMP) with H₂O₂ to produce 2,3,5-trimethyl-1,4-benzoquinone (TMBQ, vitamin E key intermediate). Mesoporous titanium–silicates with di(oligo)nuclear Ti centers, metal–organic framework MIL-125 and amorphous TiO₂ demonstrated 100 % selectivity toward TMBQ. Titanium–silicates prepared by evaporation-induced self-assembly revealed superior performance in terms of product yield and catalyst reusability.

     

Hydrophobicity and catalytic properties of Ti-MFI zeolites synthesized by microwave and conventional heating

Ti-incorporated MFI zeolite (Ti-MFI-MW) has been synthesized with microwave heating. Their physicochemical properties such as surface hydrophobicity, and adsorption and catalytic properties have been compared with those of Ti-incorporated MFI zeolite (Ti-MFI-CH) prepared by conventional hydrothermal method. Competitive adsorption measurements with toluene and water revealed that the hydrophobicity index of Ti-MFI-MW (8.0) is higher than that of Ti-MFI-CH (6.2). IR spectra showed that Ti-MFI-MW also has a lower content of surface hydroxyl groups and adsorbs a larger amount of 1-hexene than Ti-MFI-CH. These results pointed out that Ti-MFI-MW is more hydrophobic than Ti-MFI-CH. Epoxidation reactions of 1-hexene and styrene with hydrogen peroxide have been conducted to investigate catalytic properties of the Ti-MFI zeolites according to the synthesis method. The conversions and epoxide selectivities over Ti-MFI-MW are higher than those over Ti-MFI-CH due to the enhanced surface hydrophobicity.     

Effect of solvent and impurity on synthesis of ethyl lactate from fermentation-derived ammonium lactate

Fermentation-derived ammonium lactate was converted into ethyl lactate by decomposition in various organic solvents followed by esterification with ethanol over Amberlyst catalyst. The ammonium lactate was decomposed more efficiently in an organic solvent with high boiling point, where the produced lactic acid was stabilized well as a monomer without oligomerization. However, only the nonreactive phosphate-type solvent such as triethyl phosphate and tributyl phosphate showed a notable ethyl lactate yield in the subsequent esterification reaction compared with dimethyl sulfoxide and N-methyl pyrolidine. The lactic acid yield in ammonium lactate decomposition and the subsequent ethyl lactate yield were also highly dependent on solvent ratio to ammonium lactate, temperature and pressure in ammonium lactate decomposition reaction. The amino acid impurity contained in the fermented ammonium lactate as well as the unreacted ammonium lactate reduced the acid strength of Amberlyst-36, which resulted in the final ethyl lactate yield.     

Selective crystallization of CoAPO-34 and VAPO-5 molecular sieves under microwave irradiation in an alkaline or neutral condition

Syntheses of cobalt- and vanadium-incorporated aluminophosphate molecular sieves (CoAPO and VAPO) with AFI and CHA structures have been studied using an alkaline or neutral gel under microwave irradiation and conventional hydrothermal heating. Microwave synthesis gives rise to the selective crystallization of CoAPO-34 with a CHA structure and VAPO-5 with an AFI structure, while the conventional hydrothermal crystallization brings CoAPO-5 and VAPO-34 through the gradual transformation of CoAPO-34 and VAPO-5, respectively, as the crystallization time increases. These results reveal that the relative stabilities of metal-incorporated aluminophosphate (MeAPO) molecular sieves between AFI and CHA structures depend on the type of incorporated metal ions. This work also suggests that microwave syntheses of MeAPO molecular sieves preferentially induce a kinetically favorable MeAPO phase in a short period of crystallization time. The synthesis of VAPO-5 in an alkaline condition is for the first time reported in this work.     

Generation of H2O2 from H2 and O2 over zeolite beta containing Pd and heterogenized organic compounds

The catalytic generation of H₂O₂ from H₂ and O₂ has been studied over zeolite beta-supported Pd and zeolite beta-adsorbed organic compounds such as 1,4-benzoquinone (BQ), hydroquinone (HQ), azobenzene (AB) and hydrazobenzene (HAB). According to catalytic results, zeolite beta-supported Pd catalysts display effective performance relative to those prepared from other types of zeolites reported and Pd-loaded zeolite beta-adsorbed HQ catalysts show enhanced activity compared to zeolite beta-supported Pd catalysts. In situ UV–Vis spectroscopic study indicates that HQ can readily be converted to BQ reversibly under H₂ and air inside zeolite beta only in the presence of Pd. The results suggest that HQ acts as a strong hydrogen transfer agent to promote the production of H₂O₂ from H₂ and O₂ in cooperation with a Pd catalyst. By contrast, adsorption of BQ, AB and HAB induces suppression of the catalytic properties of Pd/zeolite beta.     

Oligomerization of isobutene over aluminum chloride-loaded USY zeolite catalysts

Oligomerization of isobutene has been investigated over AlCl₃-loaded USY zeolite catalysts in order to produce triisobutenes or remove/separate isobutene from C₄ streams. Stable isobutene conversion and high selectivity for trimers and tetramers were attained over the modified zeolite with high ratio of Lewis acid site-to-Brønsted acid site, suggesting that a potential trimerization catalyst can be obtained easily by loading a Lewis acid into an acidic zeolite catalyst. This catalyst can be facially produced by physical mixing and can be easily restored its activity after deactivation by simple calcinations.     

Microwave synthesis of metallosilicate zeolites with fibrous morphology

In this paper, we report syntheses of silicalite (Si-MFI) zeolite crystals with tetravalent metal ions incorporated to synthesize metallosilicalite (M-MFI; M = Sn, Zr, Sn/Zr, Ti/Zr) zeolite crystals by using microwave irradiation reactions. Beta-Diketonate (acetylacetone) was used as a chelating ligand of the metal precursors, in order to reduce their hydrolysis rates and, therefore, to enhance framework incorporation of each metal in the syntheses of M-MFI zeolites. The zeolite crystals formed show puck-like morphology, and these crystals are stacked to form fibers with the degree of self-assembly varied depending on the nature of the tetravalent metal ion used. Importantly, the self-assembly of the zeolite crystals and the resultant fibrous morphology are observed only when the substituting metal ions are present. Powder X-ray diffraction, infrared and ultraviolet diffuse reflectance spectroscopic data all indicate that Sn and Ti atoms are well substituted for Si, but Zr is not well incorporated in the resulting MFI crystals. These results are discussed in terms of the ionic sizes and bulk dielectric constants of the corresponding metal oxides of the substituting metal ions.