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Abstract

The identity of surface silver hydroxides produced by hydrogenation or hydration of surface silver oxide was demonstrated. A two-route mechanism of hydrogen interaction with oxygen adsorbed on silver was suggested. The first route includes two consecutive-parallel steps: formation of adsorbed hydroxyl groups and their interaction with hydrogen; the second route consists of two consecutive steps: formation of adsorbed hydroxyl groups and their disproportionation yielding water and adsorbed oxygen.

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Abstract

The influence of working pressure on the mechanisms of the CO2/H2 reaction on a co-precipitated CuO/ZnO/Al2O3 catalyst have been studied at 230 °C and in the pressure range of 1–75 bar. In the CO2 hydrogenation using CuO/ZnO/Al2O3, the products were found to be CO, methanol and water almost exclusively. Only a trace of methane formation was observed. Methanol and carbon monoxide are competitively formed. The former is produced directly from CO2 whatever the pressure whereas carbon monoxide stems either from CO2 directly at high pressure or both methanol decomposition and CO2 directly at low pressure.

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Abstract

Pd/Al2O3 catalysts prepared from Pd nitrate dissolved in water (Pd-water) and toluene (Pd-toluene) were investigated in the gas-phase selective hydrogenation of 1,3-butadiene under various reaction conditions. As revealed by TEM and CO chemisorption results, smaller Pd particle sizes with more uniform particle size distribution were obtained on Pd-toluene catalysts. Reduction at 500 °C resulted in sintering of Pd particles with Pd-water showing higher degree of metal sintering than Pd-toluene. Sintering of Pd particles may result in low-index surfaces which promoted butane formation and lowered 1-butene selectivity. While Pd dispersion and/or Pd particle size strongly affected 1,3-butadiene hydrogenation rate and 1-butene selectivity, the selectivity to 2-butenes was quite similar at 47–55% for all the catalysts under various reaction conditions.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Saet Byul Kim, Mi Ran Lee, Eun Duck Park, Sang Min Lee, HyoKyu Lee, Ki Hyun Park, and Myung-June Park

Abstract

A kinetic model of the homogeneous conversion of d-xylose in high temperature water (HTW) was developed. Experimental testing evaluated the effects of operating conditions on xylose conversion and furfural selectivity, with furfural yields of up to 60% observed without the use of acid catalysts. The reaction order for the decomposition of d-xylose was assumed to be above two, while the conversion of d-xylose to furfural and the degradation of furfural were first order reactions. Estimated kinetic parameters were within the range of values reported in the literature. The activation energy of furfural production showed that the ionization rate was high enough for HTW to replace acid catalysts. Simulated results from this model were in good agreement with experimental data, allowing the model to aid reactor design for the maximization of productivity.

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Abstract

The role of palladium precursors and the preparation route in the catalytic properties of Pd/Al2O3-ZrO2 catalysts toward methane oxidation was investigated in this paper. The palladium precursors were Pd acetylacetonate Pd(C5H7O2)2 and palladium nitrate Pd(NO3)2. Catalysts were prepared by using either sol-gel or wet impregnation. All catalysts were characterized by N2 physiorption, H2 chemisorption, H2 TPR, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The obtained results suggested that the use of different palladium precursors and preparation routes played an important role in the properties of the catalysts. The use of palladium acetylacetonate as precursor for the impregnation method generated more active catalysts. However, sol-gel prepared catalyst presented better textural properties with moderate catalytic activities.

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Abstract

Wet oxidation was carried out for treating different industrial process wastewaters (PWW's) of pharmaceutical production, with oxygen in a stainless steel autoclave at 230 and 250 °C and total pressure of 50 bar. Beside non-catalytic, a catalytic reaction was also carried out. The catalyst applied was Ti mesh covered with Ru and Ir oxide. PWW samples were analyzed with respect to their TOC, COD (BOD) content. The tested PWW's could be oxidized but with rather different conversions. Some effluents were converted with remarkable rate due in some cases to their Fe or Cu ion content, in other cases to the Ti based precious metal oxide catalyst.

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Abstract

A nanostructured mesoporous MCM-41 supported N-heterocyclic carbene–Pd (NHC–Pd) complex was prepared through the reaction of an ionic liquid immobilized onto MCM-41 with palladium acetate. The MCM-41-supported NHC–Pd complex could serve as a highly effective catalyst for the Suzuki cross-coupling reaction under aqueous conditions. Furthermore, the Pd(II) catalyst was recovered by a simple filtration from the reaction mixture and reused without a significant loss of its catalytic activity. The heterogeneous catalyst was also air-stable and thermally stable to allow its easy use.

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Abstract

In this paper, novel kind of supports for immobilizing metalloporphyrin catalysts, poly(N-vinylimidazole)/SiO2 (PVI/SiO2) were prepared in the manner of “grafting from”. Then, various metalloporphyrins (MPs), such as cobalt, iron and manganese tetraphenylporphyrins (CoTPP, FeTPP, MnTPP), cobalt tetra (para-nitrophenyl) porphyrin (CoTNPP), and cobalt tetra (para-chlorophenyl) porphyrin (CoTClPP), were immobilized on the supports PVI/SiO2 via the axial coordination reaction between MPs and the imidazole groups of the grafted PVI, resulting in the heterogenized catalysts MPs–PVI/SiO2. The supported catalysts were characterized by IR and UV–Vis spectra. The catalytic performances of MPs–PVI/SiO2 for the oxidation of ethyl benzene in the absence of any reductant and solvent were investigated and compared in detail. The experimental results revealed that MPs–PVI/SiO2 could effectively activate dioxygen, and obviously catalyze the oxidation of ethyl benzene to acetophenone. The catalytic activities of MPs–PVI/SiO2 increased with increase of the electron-deficient degree of the peripheral substituent attached to the benzene ring outside the porphyrin ring. The catalytic activities of MPs–PVI/SiO2 differed among the different metals and the different substitutional groups according to the following sequences: Co(II) > Fe(III) > Mn(III), and CoTNPP > CoTClPP > CoTPP. In comparison, the catalytic activity of CoTNPP–PVI/SiO2 was the best. Under the reaction conditions of 120 °C and the ordinary pressure of oxygen, the catalyst CoTNPP–PVI/SiO2 gave wonderful results with 33.4 mol% yield of acetophenone.

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Abstract

Hydrogen phosphate (HPO4 2−) or poly(acrylic acid) (PAA) stabilized cobalt(0) nanoclusters were in situ generated from the reduction of cobalt(II) chloride during the catalytic hydrolysis of sodium borohydride (NaBH4) in the presence of stabilizers, HPO4 2− or PAA. Cobalt(0) nanoclusters stabilized by HPO4 2− or PAA were characterized by using UV–Visible spectroscopy, TEM, XPS and FT-IR techniques. They were employed as catalysts in the hydrolysis of NaBH4 to examine the effect of stabilizer type on their catalytic activity and stability. Detailed reaction kinetics of the hydrolysis of NaBH4 in the presence of both catalysts was studied depending on catalyst concentration, substrate concentration and temperature. PAA stabilized cobalt(0) nanoclusters provided higher total turnover number (TTON = 6,600) than that of HPO4 2− stabilized cobalt(0) nanoclusters (1,285 turnovers). However, the HPO4 2− stabilized cobalt(0) nanoclusters provided a lower activation energy (E a = 53 ± 2 kJ mol−1) than the PAA stabilized cobalt(0) nanoclusters (E a = 58 ± 2 kJ mol−1) for the hydrolysis of NaBH4. The use of two types of stabilizers in the preparation of the same metal(0) nanoclusters following the same methodology enables us to compare the electrostatic and steric stabilization in terms of the catalytic activity and stability of metal(0) nanoclusters.

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Abstract

The results of the epoxidation of allyl alcohol with 30% hydrogen peroxide over the Ti-MWW catalyst have been presented. The studies were carried out under atmospheric pressure and in the presence of methanol as a solvent. The influence of the following technological parameters on the course of epoxidation was examined: temperature (20–60 °C), the molar ratio of AA/H2O2 (1:1–5:1), methanol concentration (5–90 wt%), catalyst content (0–5.0 wt%), reaction time (5–300 min) and intensity of stirring (0–500 rpm).

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