Promoted wet air oxidation of polynuclear aromatic hydrocarbons

The treatment of an aqueous solution of four polycyclic aromatic hydrocarbons, namely acenaphthene, phenanthrene, anthracene and fluoranthene, under moderate conditions of temperature and pressure has been conducted in the presence and absence of free radical promoters (hydrogen peroxide or potassium monopersulfate). With no addition of promoters, the process achieves PAH conversion values in the range 80-100% at 190 degrees C and 50 bars of air pressure (80 min of reaction). Similar results are obtained in the presence of hydrogen peroxide, however, in this case, the time required is just 60 min with a sharp decrease in PAH concentration in the first 10-20 min. Additionally, temperature can be lowered to values in the range 100-150 degrees C. If potassium monopersulfate is used instead of hydrogen peroxide, an analogous behaviour is experienced, in the latter case, temperatures above 120 degrees C lead to an inhibition of anthracene oxidation, likely due to ineffective decomposition of the monopersulfate molecule.     

Effect of nanosized gold particle addition to supported metal oxide catalyst in methanol oxidation

Gold has rarely been utilized as a catalytic component because of its poor affinity to chemical species. It is however known that nanosized gold particles promote the dissociation of oxygen or hydrogen. In this study, alumina-supported metal oxide catalysts were prepared by impregnation method and applied to methanol oxidation. The dispersion form and size of the gold particles were observed by transmission electron microscopy (TEM). In the results, the maximum catalytic activity was obtained over the ZnO/Al2O3 catalyst, and the optimum loading was 4 wt%. Furthermore, nano-sized gold particles at various loadings were added to ZnO/Al2O3 catalyst by deposition method. The gold particles on Au/ZnO/Al2O3 catalyst were well dispersed and the catalyst activity was remarkably increased compared to ZnO/Al2O3 catalyst. The role of gold particles in the increased catalytic activity is discussed and a possible mechanism is presented.     

Effect of temperature on the catalytic oxidation of CO over nano-sized iron oxide

Nanocrystallite iron oxide powders were prepared by co-precipitation method using highly purified FeCl₃ and NH₄OH solution. The prepared powders were tested for the catalytic oxidation of CO to CO₂. The effect of oxidation temperature on the catalytic reaction was isothermally investigated using advanced quadrpole mass gas analyzer system. The mechanism of the catalytic oxidation reaction was estimated from the experimental data. Fe₂O₃ nanocrystallite of 78 nm shows a good response towards catalytic CO oxidation at the temperature range 200–500 °C. The catalytic oxidation efficiency reached 98% at 400–500 °C. The reaction was found to be first order with respect to CO. The average activation energy of the reaction was found to be 26.3 kJ/mol which is smaller than the values reported in the literatures. The mechanism of CO catalytic oxidation was investigated by comparing the CO catalytic oxidation data in the absence and presence of oxygen. It was found that the catalytic oxidation of CO over Fe₂O₃ nanocrystallite proceeded by adsorption mechanism. Based on the experimental results, Fe₂O₃ nanocrystallite powders can be recommended as a promising catalyst for CO oxidation.     

A comparative study of catalytic partial oxidation of methane over CeO2 supported metallic catalysts

In the present study, the catalytic partial oxidation of methane (CPOM) over various active metals supported on CeO2 (M/CeO2, M = Ir, Ni, Pd, Pt, Rh and Ru) has been investigated. The catalysts were characterized by X-ray diffraction (XRD), BET surface area, H2-temperature programmed reduction (H2-TPR), CO chemisorption and transmission electron microscope (TEM) analysis. Ir/CeO2 catalysts showed higher BET surface area, higher metal dispersion, small active metal nano-particles (approximately 3 nm) than compared to other M/CeO2 catalysts. The catalytic tests were carried out in a fixed R(mix) ratio of 2 (CH4/O2) in a fixed-bed reactor, operating isothermally at atmospheric pressure. From time-on-stream analysis at 700 degrees C for 12 h, a high and stable catalytic activity has been observed for Ir/CeO2 catalysts. TEM analysis of the spent catalysts showed that the decrease in the catalytic activity of Ni/CeO2 and Pd/CeO2 catalysts is due to carbon formation whereas no carbon formation has been observed for Ir/CeO2 catalysts.     

Pilot VOC emissions mitigation by catalytic oxidation over commercial noble metal catalysts for cleaner production

Clean Technologies and Environmental Policy - Catalytic oxidation of volatile organic compounds (VOCs) is a widely used method for VOC emissions mitigation essential for the long-term...     

Catalytic wet oxidations of aromatic compounds over supported copper oxides

Catalytic wet oxidations of naphthalene as a model compound of persistent aromatic compounds were carried out with hydrogen peroxide in a closed autoclave lined with Teflon. CuO/Al₂O₃ and CuO/AC catalyst showed the high activity for the naphthalene oxidation with hydrogen peroxide of 1.0 mol L⁻¹ at 100 °C. Naphthalene, whose initial concentration was 1.0 g L⁻¹, was converted completely and the concentration of water-soluble organic compounds in the resultant aqueous solution was less than 25 ppm-C. In contrast, platinum, and manganese oxide, silver oxide, and ruthenium oxide catalysts consumed hydrogen peroxide preferentially. Iron and nickel oxides catalysts showed lower activity than the copper oxide catalyst. During the reaction, the intermediate organic acids were formed and then were oxidized. Simultaneously, copper species of CuO catalysts were dissolved and then were precipitated. The precipitated copper species on the catalyst support showed the catalytic activity. CuO/Al₂O₃ catalysts showed high activity for the six successive batch reactions with the treatment of sodium carbonate after the reaction to precipitate copper ions.     

Benzene oxidation with ozone over supported manganese oxide catalysts: effect of catalyst support and reaction conditions

Catalytic oxidation of gaseous benzene with ozone was carried out over supported manganese oxides to investigate the factors controlling the catalytic activities. The rate for benzene oxidation linearly increased with the surface area of catalyst, regardless of the kinds of catalyst support, whereas the ratio of ozone decomposition rate to benzene oxidation rate was larger for SiO(2)-supported catalyst than Al(2)O(3)-, TiO(2)-, and ZrO(2)-supported catalysts. The rate for benzene oxidation and CO(x) selectivity increased with the reaction temperature (22-100 degrees C) and were improved by the addition of water vapor to reaction gases. Benzene conversion and carbon balance increased with ozone concentration.     

Complete oxidation of ethylene over supported gold nanoparticle catalysts

Complete oxidation of ethylene was performed over supported noble metals or transition metals oxide catalysts and on monoliths under atmospheric pressure. Gold nanoparticles on Al2O3 or MxOy(M = Mo, Fe, Mn) were prepared by impregnation, coprecipitation, deposition, and dispersion methods. Nanoparticles prepared by impregnation method were irregular and very large above 25 nm, but those by coprecipitation and deposition method were uniformly nanosized at 4-5 nm. The gold nanoparticle were outstandingly active in catalyzing oxidation of ethylene. The activity order of these catalysts with preparation methods was deposition > coprecipitation > impregnation, and Au/Co3O4 prepared by deposition method showed the best performance in ethylene oxidation. The addition of gold particles to MxOy/Al2O3 catalyst enhanced the ethylene oxidation activity significantly. The main role of the gold nanoparticles apparently was to promote dissociative adsorption of oxygen and to enhance the reoxidation of the catalyst.     

Gold supported on metal oxides for carbon monoxide oxidation

Au has been loaded (1% wt.) on different commercial oxide supports (CuO, La₂O₃, Y₂O₃, NiO) by three different methods: double impregnation (DIM), liquid-phase reductive deposition (LPRD), and ultrasonication (US). Samples were characterised by N₂ adsorption at −196 °C, high-resolution transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray spectrometry, high-angle annular dark-field imaging (Z-contrast), X-ray diffraction, and temperature programmed reduction. CO oxidation was used as a test reaction to compare the catalytic activities. The best results were obtained with Au loaded by DIM on the NiO support, with an activity of 7.2 × 10⁻⁴ mol_CO·g_Au ⁻¹·s⁻¹ at room temperature. This is most likely related to the Au nanoparticle size being the smallest in this catalyst (average 4.8 nm), since it is well known that gold particle size determines the catalytic activity. Other samples, having larger Au particle sizes (in the 2–12 nm range, with average sizes ranging from 4.8 to 6.8 nm), showed lower activities. Nevertheless, all samples prepared by DIM had activities (from 1.1 × 10⁻⁴ to 7.2 × 10⁻⁴ mol_CO·g_Au ⁻¹·s⁻¹, at room temperature) above those reported in the literature for gold on similar oxide supports. Therefore, this method gives better results than the most usual methods of deposition-precipitation or co-precipitation.      

Methanol conversion to hydrocarbons over WO3/HZSM-5 catalysts prepared by metal oxide vapor synthesis

Metal oxide vapor synthesis (MOVS) methodology was used to deposit WO₃ on the zeolite HZSM-5. Samples I, II, and III of various weight percentage-loaded (3.1, 5.4, and 10.8, respectively) WO₃ on the HZSM-5 support were prepared. These materials were characterized by powder X-ray diffraction pattern, sorption, chemical analysis, and scanning electron microscopy. The characterization studies showed good crystalline nature of the support, partial inclusion of WO₃ particles into the zeolite cavities, and a uniform deposition of amorphous WO₃ over the support. These samples were tested for their catalytic activity in the conversion of methanol into hydrocarbons. Results were compared with that of pure support under identical conditions. The product selectivity for aromatics over WO₃/HZSM-5 catalyst samples was negligible compared with the same selectivity observed over pure support, whereas the selectivity for olefins increased significantly.     

TEM characterization of metal and metal oxide particles supported by multi-wall carbon nanotubes

Composites of Sn–Pd particles and multi-walled carbon nanotubes (MWNTs), and of Ni–Co particles and MWNTs were investigated by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The Sn–Pd particle composites were prepared by impregnation deposition, and the Ni–Co particle composites were prepared by electroless deposition on MWNTs synthesized by a chemical vapor deposition method using thermal catalytic decomposition of hydrocarbon. The morphologies and the microstructure of the deposited particles were investigated upon annealing the composites with and without hydrogen. Both the crystalline particle structure and the particle morphology are observed to be different for the samples annealed with and without hydrogen.     

Catalytic wet air oxidation of chlorophenols over supported ruthenium catalysts

A series of noble metal (Pt, Pd, Ru) loaded zirconia catalysts were evaluated in the catalytic wet air oxidation (CWAO) of mono-chlorophenols (2-CP, 3-CP, 4-CP) under relatively mild reaction conditions. Among the investigated noble metals, Ru appeared to be the best to promote the CWAO of CPs as far as incipient-wetness impregnation was used to prepare all the catalysts. The position of the chlorine substitution on the aromatic ring was also shown to have a significant effect on the CP reactivity in the CWAO over 3wt.% Ru/ZrO(2). 2-CP was relatively easier to degradate compared to 3-CP and 4-CP. One reason could be the higher adsorption of 2-CP on the catalyst surface. Further investigations suggested that 3wt.% Ru/ZrO(2) is a very efficient catalyst in the CWAO of 2-CP as far as high 2-CP conversion and TOC abatement could still be reached at even lower temperature (393K) and lower total pressure (3MPa). Additionally, the conversion of 2-CP was demonstrated to increase with the initial pH of the 2-CP solution. The dechlorination reaction is promoted at higher pH. In all cases, the adsorption of the reactants and the reaction intermediates was shown to play a major role. All parameters that would control the molecule speciation in solution or the catalyst surface properties would have a key effect.     

负载型Pd催化剂的制备及其对甲醇氧化的催化活性

采用等体积浸渍法制备了一系列负载型Pd+M(M=MgO、CaO、SrO、BaO)催化剂,运用BET、CO-化学吸附、XRD、H2-TPR和XPS等表征手段对催化剂进行了表征,并考察其对甲醇的催化氧化性能。结果表明,添加碱土金属可使Pd粒子高度分散,催化剂表面易还原氧物种量增多,还原速率加快;XPS分析可知,碱土金属可增强Pd-Ce间相互作用,促使Pd向氧化态过渡,同时增加催化剂表面Ce3+浓度,改善催化剂的氧化还原性能,进而提高催化剂的催化活性。助催化效果递变规律为BaOCaOMgOSrO。     

Polycyclic aromatic hydrocarbons in road dust over Greater Cairo, Egypt

Road dust samples were collected during 2005 and polycyclic aromatic hydrocarbons (PAHs) were determined. Sites under investigation were selected to represent the different parts of Greater Cairo, Egypt. Estimation and spatial distribution pattern of PAHs in road dust were the main objectives of this study. The road dust samples were collected from 17 sites over greater Cairo. The concentration of PAHs was determined by using HPLC technique. Twelve common environmental PAHs were found to be distributed. The present data illustrated that the total average of PAHs over the investigated sites was ranged from 0.045 to 2.6 mg/kg. On individual scale, the highest concentrations were 1.031 and 1.028 mg/kg for pyrene and phenanthrene, meanwhile the lowest was benzo(a)pyrene with value 0.0001 mg/kg. The obtained results showed that the carcinogenic content of PAHs (naphthalene, benzo(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene and benzo(a)pyrene) ranged from 0.8 to 46.6% of total PAHs. It has been concluded from the present work that PAHs concentrations are greater and closer to traffic routes and industrial activities.     

纤维素负载金属基催化体系在有机反应中的研究进展EI北大核心CSCD

金属基催化剂现已成为催化领域的主流催化剂,但其存在难以分离循环使用、催化剂遗留、成本较高、催化剂与底物不稳定性等问题,采用高分子载体进行负载是解决以上问题的一种有效方法。纤维素是地球最丰富的绿色高分子,作为催化剂载体具有来源广泛、可生物降解、无毒、良好的生物相容性的优异特点,且分子结构上具有大量的羟基易改性、可通过多种方式负载金属催化剂。因此,本文综述了纤维素作为载体,负载零价金属纳米粒子、非零价金属基催化剂的进展,以及对负载后的催化体系在氧化还原反应、Heck反应、Suzuki反应等反应中的催化活性进行概述;并通过对比该体系中载体-金属等之间的作用机理,阐述了不同负载方式之间的协同作用,以及催化活性的差异性。     

Surface and catalytic properties of cobaltic oxide supported on an active magnesia

The surface and catalytic properties of Co₃O₄ loaded on MgO were investigated using nitrogen adsorption measurements conducted at −196°C and oxidation of CO by O₂ at 150–300°C. The amounts of cobaltic oxide were 23, 37.5 and 47.5 wt.% Co₃O₄. The supported samples were prepared by impregnating a known amount of magnesium carbonate with cobalt nitrate dissolved in the least amount of distilled water followed by drying and calcination at 300–700°C.The results obtained revealed that the specific surface areas of various samples decreased monotonically as a function of both precalcination temperature and extent of loading. Moreover, the activation energy of sintering, ΔE_s, was found to increase by increasing the amount of Co₃O₄ present. On the other hand, the catalytic activity of different samples were found to increase progressively by increasing the amount of Co₃O₄ present reaching a maximum value at 37.5 wt.% Co₃O₄ and decreased by increasing the extent of loading above this limit. The catalytic activity, expressed as reaction rate constant per unit surface area, was found to increase by increasing the precalcination temperature from 300°C to 400°C, then decreased progressively by increasing the temperature from 400°C to 700°C.This treatment did not modify the mechanism of the catalytic reaction but changed the number of catalytically-active sites taking place in chemisorption and catalysis CO-oxidation reaction by changing their energetic nature.