A set of three new polymer-anchored palladium(II) Schiff base catalysts have been synthesized, characterized and their catalytic activity was investigated in the Suzuki cross-coupling reaction between aryl halides and arylboronic acid in the presence of Cs2CO3 as a base. They show excellent catalytic activity in coupling of aryl bromides or aryl iodide with phenylboronic acid under the optimized reaction conditions in water. Polymer-anchored Pd(II) complexes provided turnover frequency of 29,700 or 58,200 h(-1) in Suzuki coupling reactions of phenylboronic acid with p-bromoacetophenone or p-iodobenzene, respectively, which are the highest values ever reported for the Suzuki coupling reactions in water as sole solvent. The catalyst 1 could be used for 15 reaction cycles in the Suzuki coupling of p-acetobromobenzene at 100 degrees C with no loss of catalytic activity. (C) 2012 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.apcata.2012.09.048
Sayi :449 Sayfa :172-182
A series of alumina supported Ni, Mo and Ni-Mo catalysts were prepared for investigating the interaction between Ni and Mo in terms of their structural properties and catalytic activities. The catalysts containing 0-15 wt% Ni and/or Mo were prepared by impregnation or coimpregnation and were tested for BET surface area and total pore volume. CO chemisorption was used for metal surface area measurements. The catalytic activities of the samples were tested by CO2 methanation. Selected Ni/Al2O3 and Ni-Mo/Al2O3 catalysts with Ni and Mo loadings in the 5-15 wt% range were also examined by TEM and SEM-EDX, The results show that Mo changes the structural properties and the methanation activities of the catalysts. TEM and SEM-EDX studies support the synergetic interaction between Ni sites and MoOx species and show that the nature of the Ni-Mo interaction changes with the level of Ni and Mo loading. At low Mo loadings, Mo species act as a diluent of the matrix, promoting Ni particle distribution. At higher Mo loadings, partial coverage of the nickel particles is observed especially on catalysts with high total metal loading. SEM backscattered composition images indicate the presence of molybdenum in the oxide form which means that the active sites are the nickel crystallites. (C) 1998 Elsevier Science B.V.
DOI : 10.81043/aperta.101489
Sayi :168 issue :2 Sayfa :385-397
Calixarene-based chiral organocatalyst derived from L-proline supported onto well-defined (15 +/- 3 nm) magnetic Fe3O4 nanoparticles was used as a highly active, recoverable, and reusable catalyst for the asymmetric aldol reaction in water without need for organic solvents. The chiral organocatalyst showed high catalytic activity (up to 94%), enantioselectivity (up to 93%) and diastereoselectivity (up to 97:3) for the reaction between cyclohexanone and aromatic aldehydes. The catalyst could easily separated using an external magnetic field and reused for several times without any significant loss of activity. (C) 2015 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.apcata.2015.04.018
Sayi :499 Sayfa :205-212
In this study, isobutyl acetate, a valuable solvent in cosmetics, aroma and paint industries, is produced by pervaporation-esterification equilibrium reaction in a batch pervaporation membrane reactor (PVMR) using homogeneous (sulphuric acid) and heterogeneous (Dowex 50W-X8) catalysts. The effects of catalyst loading, catalyst type, reaction time, membrane thickness, temperature and initial molar ratio of reactants were investigated. A cross-linked polydimethylsiloxane (PDMS) membrane selective to esters was prepared and used in PVMR. Batch reactions were carried out also in a simple batch reactor (SBR) without pervaporation under the same conditions to compare the conversions for the reactions with and without pervaporation. In conclusion, PVMR experiments showed that the PDMS membrane can be used to remove the isobutyl acetate formed selectively with acceptable conversions and pervaporation fluxes. (C) 2009 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.apcata.2009.06.037
Sayi :366 issue :1 Sayfa :102-107
A new hybrid of nanoparticles designed to enable efficient catalysis for hydrogen generation (NPs) include a dual combination of Co, Ni, and Cu transition metals. These nanoparticles are made by altering metals and molar ratios (x: 0.25, 0.50, and 0.75) and synthesized for hydrogen generation by hydrolytic dehydrogenation of ammonia borane (NH3BH3). A synergistic effect of dual combination on the induction period and dehydrogenation rate (DR) is found. Kinetic interpretation and thermodynamic studies demonstrate that the Co0.50Cu0.50/NPs catalyst shows superior activation (DR = 10.561 H-2 min(-1).g(-1)cat and E-a = 38.12 kJ mol(-1)) with a synergistic effect and meet the criteria of The United States Department of Energy (DOE) targets for onboard hydrogen production systems for light-duty vehicles.
DOI : 10.1016/j.apcata.2017.11.022
Sayi :550 Sayfa :320-330
Reactor operation parameters for the liquid-phase acid-catalyzed decomposition of 2-isopropylnaphthalenehydroperoxide (2-IPNHP) were investigated to produce simultaneously 2-naphthol and acetone with a high yield. The 2-naphthol and acetone are produced from 2-IPNHP by ionic reactions, nevertheless, dimethyl-2-naphthylcarbinol (DMNC) and 2-acetonaphthone (AN) formations through radical reactions cannot be avoided because of the induced decomposition effects but can be decreased. The decomposition of 2-IPNHP was carried out in the presence of two different aprotic solvents of low dielectric (DE) constant, i.e. 2-isopropylnapthalene (IPN) and acetone (AC), and the protogenic solvent acetic acid (AcOH), with two different oxyacid catalysts, i.e. HClO4 and H2SO4. The production rate of 2-naphthol increases with the increase in the dipole moment (DM) of aprotic solvents. The increase in the initial 2-IPNHP concentration increases 2-IPNHP, decomposition and 2-naphthol production rates. 2-Naphthol production rate decreases and the radical by-product AN formation rate increases with increasing temperature. The presence of the impurities DMNC and AN of the reactant mixture and a radical scavenger in the decomposition reaction medium decreased the 2-naphthol production rate. A 70% yield of 2-naphthol was obtained in the presence of IPN by 0.047 mol dm(-3) HClO4 with the initial concentrations of 1.155 mol dm(-3) 2-IPNHP, 0.470 mol dm(-3) DMNC and 0.011 mol dm(-3) AN at T = 22degreesC and N = 1000 rpm. The reaction rate equations for the decomposition reaction of 2-IPNHP and production of 2-naphthol are also presented. (C) 2002 Elsevier Science B.V. All rights reserved.
DOI : 10.81043/aperta.96471
Sayi :238 issue :1 Sayfa :85-97
Treatment of textile wastewaters containing dyes has not been very successful by conventional methods such as biological treatment. In order to overcome this problem, ozonation based on the oxidation of organic pollutants has been studied by researchers. Catalytic ozonation and advanced oxidation processes (ACPs) are used in order to increase the efficiency of sole ozonation further. In this work, catalytic ozonation in the presence of copper sulfide (CuS) powder as a catalyst was investigated in the treatment of aqueous single dye solutions, namely solutions of Acid Red-151 (AR-151), Remazol Brilliant Blue-R (RBBR) and Reactive Black-5 (RB-5). In the catalytic ozonation experiments, the effects of important ozonation parameters such as solution pH, ozone and catalyst dosages and the initial concentration of each dye on reaction kinetics and mechanism were studied.
DOI : 10.1016/j.apcata.2009.05.011
Sayi :363 issue :1-2 Sayfa :157-163
Boron tri-isopropoxide, B((OPr)-Pr-i)(3), was immobilized on mesoporous material, MCM-41, and denoted as "B((OPr)-Pr-i)3-MCM-41". The prepared new heterogeneous catalyst, B((OPr)-Pr-i)(3)-MCM-41, was characterized in details by using PXRD, FT-IR-, B-11 NMR-, Si-29 NMR-, C-13 NMR-, TEM, EDX, N-2 adsorption and ICP-OES. The results demonstrated the successful homogenous distribution of the B((OPr)-Pr-i)(3) on the MCM-41 support. Heterogeneous B((OPr)-Pr-i)(3)-MCM-41 catalyst in comparison with the homogeneous B((OPr)-Pr-i)(3) and B(OEt)(3) catalysts, display similiar catalytic activity in the Meerwein-Ponndorf-Verley (MPV) reduction of unsaturated aldehydes and ketones with alcohols as reductants. Reduced reaction times, higher rate constants and very high selectivities for the unsaturated alcohols were obtained with the heterogenous catalyst than the homogeneous catalysts. In most cases, there were no side products other than the desired alcohol. The B((OPr)-Pr-i)(3)-MCM-41 catalyst was found to be encouraging as the catalyst is recyclable up to six cycles without any significant loss in its catalytic activity. This work enriches the family of heterogeneous MPV catalysts for chemoselective reductions of unsaturated aldehydes and ketones. (c) 2012 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.apcata.2012.06.004
Sayi :435 Sayfa :204-216
The influence of the acid-base properties of TiO2-based supports on the performances of Pd-Cu bimetallic catalysts for the hydrogenation of nitrates in water has been investigated. Nanostructured TiO2 and TiO2 doped with various amounts of Mg and Nb (1-7 wt%) were prepared by co-hydrolysis of metal alkoxides. The surface area increased and the crystallinity decreased for Mg- and Nb-doped TiO2, all solids exhibiting mesoporosity with average pore sizes smaller than 20 nm. The acid-base properties of TiO2 were strongly modified by doping, Mg introducing a basic character whereas Nb-doped TiO2 becomes acidic. Pd-Cu bimetallic catalysts deposited on TiO2 and Mg- or Nb-doped TiO2 were found very active for the catalytic hydrogenation of nitrates, but the selectivity to ammonium was high. Nb-doping slightly decreased the reactivity of nitrates and Mg-doping slightly improved the reactivity of nitrites, whereas the selectivity to ammoniums was only marginally modified. The activity and products selectivity were very moderately affected by the acid or basic character of the support, which suggests that this property is not relevant to the reaction mechanism. (C) 2013 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.apcata.2013.07.038
Sayi :467 Sayfa :414-420
Tungsten loaded and Zr incorporated SBA-15 catalysts (WO3/Zr-SBA-15 and Zr-SBA-15) were developed for esterification of cetyl alcohol and palmitic acid. The influence of the Zr content, tungsten loading amount, calcination temperature, feed composition and catalyst amount has been studied. Higher tungsten loading decreased the acidity due to formation of WO3 crystals whereas-calcination temperature enhanced the acidity by favoring the dispersion of WO. species. Activities of the catalyst changed depending on their amount of Bronsted sites and total number of acid sites. Zr-SBA-15 catalyst which had the highest amount of Bronsted acid sites gave maximum cetyl palmitate yield (63.1%). This catalyst retained its activity up to 3 reuse cycles without significant loss of activity. (C) 2016 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.apcata.2016.05.010
Sayi :522 Sayfa :194-200
A series of iron containing zeolites with varying Si/Al ratios (11.5-140) and low iron content (similar to 0.9 wt.% Fe) have been synthesised by solid-state ion exchange with commercially available zeolites and tested, for the first time, in the oxidative dehydrogenation of propane (ODHP) with N2O. The samples were characterised by XRD, N-2-Adsorption, NH3-TPD and DR-UV-vis spectroscopy. The acidity of the Fe-ZSM-5 can be controlled by high temperature and steam treatments and Si/Al ratio. The selectivity and yield of propene were found to be the highest over Fe-ZSM-5 with low Al contents and reduced acidity. The initial propene yield over Fe-ZSM-5 was significantly higher than that of Fe-SiO2 since the presence of weak and/or medium acid sites together with oligonuclear iron species and iron oxides on the ZSM-5 are found to enhance the N2O activation. The coking of Fe-ZSM-5 catalysts could also be controlled by reduction of the surface acidity of ZSM-5 and by the use of O-2 in addition to N2O as the oxidant. Fe-ZSM-5 zeolites prepared with solid-state method have been shown to have comparable activity and better stability towards coking compared with Fe-ZSM-5 zeolites prepared by liquid ion exchange and hydrothermal synthesis methods. (C) 2012 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.apcata.2012.06.038
Sayi :441 Sayfa :30-41
The aim of this work is the parametric investigation of methane steam reforming (MSR) to synthesis gas (syngas, CO + H-2) in a wall-coated catalytic microchannel reactor. Methane conversion and CO selectivity on coated Rh, Ru, Pt and Ni catalysts, all supported on Al2O3, are compared in the parameter ranges of 12.86-77.14 ms residence time, 600-800 degrees C temperature and 0.5-3.0 M steam-to-carbon ratio at the reactor inlet. Among the active metals, Rh is the best one in terms of both methane conversion and productivity (rate of methane consumption per weight of catalyst). Productivity decreases in the order of Rh > Ru > Pt approximate to Ni. For all catalysts, conversion increases with residence time, temperature and steam-to-carbon ratio. CO selectivity is highest in all cases on Rh, and increases with increasing temperature and decreasing steam-to-carbon ratio. However, in the range of residence times considered, a maximum CO selectivity for each catalyst is encountered where the water-gas shift equilibrium becomes significant, and converts more of the CO produced by MSR to CO2. Time-on-stream runs conducted on Rh and Ni show that the former has excellent chemical and mechanical stability for 72 h even at extreme conditions such as steam-to-carbon ratio of 0.5 and residence time of 12.86 ms. Activity of Ni starts to decrease after 20 h even though it is operated at a steam-to-carbon ratio of 3.0. Comparative tests conducted between microchannel and packed-bed reactors show that the former outperforms the packed bed in terms of productivity and CO selectivity. (C) 2011 Elsevier BY. All rights reserved.
DOI : 10.1016/j.apcata.2011.10.028
Sayi :411 Sayfa :114-122
Lipases are enzymes that catalyses a variety of reactions, such esterifications, interesterification and hydrolysis. Several methods have been reported for the immobilization of lipases, such as deposition onto solid supports, covalent binding and encapsulation within a polymer matrix or silica glasses obtained by sol-gel techniques. In this study, the Candido rugosa lipase was encapsulated within a chemically inert sol-gel support prepared by polycondensation by tetraetoxysilane (TEOS)and octyltrietoxysilane(OTES) in the presence and absence of calix[n]arene, calix[n]-NH2 and calix[n]-COOH (n = 4,6,8) compounds as additives. The catalytic activity of the encapsulated lipases was evaluated into model reactions, i.e. the hydrolysis of p-nitrophenylpalmitate (p-NPP), and the enantioselective hydrolysis of rasemic Naproxen methyl ester that was studied in aqueous buffer solution/isooctane reaction system. The results indicated that the particularly calix[4,6]-NH2 and calix-COOH based encapsulated lipases had higher conversion and enantioselectivity compared to the sol-gel free lipase. (C) 2009 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.apcata.2009.08.030
Sayi :369 issue :1-2 Sayfa :36-41
Nickel nanoparticles inside poly(2-acrylamido-2-methyl-1-propansulfonic acid) (p(AMPS)) hydrogel were prepared by reduction of Ni(II) ions absorbed within hydrogel network. TEM images confirmed that in situ formed nickel particle in p(AMPS) hydrogel networks are about 100 nm. These nickel metal nanoparticles containing hydrogel-composites were utilized as catalysts and reaction media for the reduction reactions of aromatic nitro compounds, 2- and 4-nitrophenols with aqueous NaBH(4). The reduction rate constants at four different temperatures (30, 40,50 and 60 degrees C) and activation parameters were calculated. The activation energies (E(a)) for 4- and 2-nitrophenols are 25.70 and 38.69 kJ mol(-1), respectively. It was found that these types of hydrogel-composite catalyst systems can be used repetitively up to five times with 100% conversion and only with 25% reduction in the initial reduction rate. (c) 2010 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.apcata.2010.07.004
Sayi :385 issue :1-2 Sayfa :201-207
In this work, modular neural network modeling was applied to analyze the experimental data for the selective CO oxidation over promoted Pt/Al2O3 catalysts. The effects of preparation (Pt wt.% and promoter type) and operational (reaction temperature, feed composition and time on stream) variables on CO conversion were modeled. As a novel approach to neural network modeling of the catalytic performance, the preparation and the operational variables were used together but processed differently in the network so that the accuracy of the model could be improved since the nature of these two variables are quite different although they are both important. Similarly, the continuous (like Pt wt.%) and categorical (like promoter type) variables were also treated in different manner. After the most successful network structure was determined, the relative importances of the preparation and the operational variables as well as their effects on CO conversion were analyzed in detail. It was found that modular neural networks used this way are quite successful in predicting and explaining the experimental results, and they are superior to the monolithic neural network models. (C) 2010 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.apcata.2010.01.033
Sayi :377 issue :1-2 Sayfa :174-180
Effects of reaction temperature and feed composition on reactant conversion, product distribution and catalytic stability were investigated on syngas production by reforming of glycerol, a renewable waste, with CO2 on Rh/ZrO2 and Rh/CeO2 catalysts. For the first time in the literature, fresh and spent catalysts were characterized by in-situ FTIR, Raman spectroscopy, transmission electron microscopy and energy dispersive X-ray analysis techniques in order to unravel novel insights regarding the molecular-level origins of catalytic deactivation and aging under the conditions of glycerol dry reforming. Both catalysts revealed increased glycerol conversions with increasing temperature, where the magnitude of response became particularly notable above 650 and 700 degrees C on Rh/ZrO2 and Rh/CeO2, respectively. In accordance with thermodynamic predictions, CO2 transformation occurred only above 700 degrees C. Syngas was obtained at H-2/CO similar to 0.8, very close to the ideal composition for Fischer-Tropsch synthesis, and carbon formation was minimized with increasing temperature. Glycerol conversion decreased monotonically, whereas, after an initial increase, CO2 conversion remained constant upon increasing CO2/glycerol ratio (CO2/G) from 1 to 4. In alignment with the slightly higher specific surface area of and smaller average Rh-particle size on ZrO2, Rh/ZrO2 exhibited higher conversions and syngas yields than that of Rh/CeO2. Current characterization studies indicated that Rh/CeO2 revealed strong metal-support interaction, through which CeO2 seemed to encapsulate Rh nanoparticles and partially suppressed the catalytic activity of Rh sites. However, such interactions also seemed to improve the stability of Rh/CeO2, rendering its activity loss to stay below that of Rh/ZrO2 after 72 h time-on-stream testing at 750 degrees C and for CO2/G = 4. Enhanced stability in the presence of CeO2 was associated with the inhibition of coking of the catalyst surface by the mobile oxygen species and creation of oxygen vacancies on ceria domains. Deactivation of Rh/ZrO2 was attributed to the sintering of Rh nanoparticles and carbon formation.T
DOI : 10.1016/j.apcata.2018.07.027
Sayi :564 Sayfa :157-171
In this work, the literature for CO oxidation kinetics over Au based catalysts was analyzed using artificial neural networks to test the possibility of developing global reaction rate models representing the entire literature. A database was constructed using the data obtained from nineteen papers published between the years 1997 and 2011; then, the reaction rate was modeled as a function of catalyst preparation and operational variables by using neural networks. Next, global reaction rate equations in the form of power law were developed for each support type by the help of the neural network model, and the order of reaction with respect to each reactant and the parameters of Arrhenius relation were estimated. These power law models were successfully validated by using the information reported in the literature; hence, it was concluded that they can be used for the initial estimation of the reaction rates in the absence of more specific rate equations. (C) 2013 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.apcata.2013.08.056
Sayi :468 Sayfa :395-402
In this study, we reported a novel poly(N-vinylimidazole) (PVI)-supported latent ruthenium catalyst for olefin metathesis applications in aqueous media. The catalysts were synthesized using direct immobilization of first- and second-generation Grubbs catalysts on poly(N-vinylimidazole). The immobilized catalysts were characterized using FT-IR, SEM and EDX. The catalysts are metathesis inactive in both organic and aqueous media but can be activated via the introduction of acid to the reaction medium. The activity of the catalysts was tested on ring closing metathesis (RCM) and ring opening metathesis polymerization (ROMP) reactions. It was shown that the molecular weight of the ROMP polymers can be controlled by initiating the reaction with varying HCl/Ru ratios. Additionally, the reusability of the catalysts for RCM of diethyldiallylmalonate was studied. In addition, the RCM reaction of diethyldiallylmalonate can be switched on and off via the introduction of acids and bases to the reaction media using PVI-supported ruthenium catalysts. (C) 2014 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.apcata.2014.06.024
Sayi :483 Sayfa :19-24
Herein we report the use of zeolite confined palladium(0) nanoclusters as efficient and recyclable catalyst for Suzuki cross-coupling reactions of aryl bromides with phenylboronic acid. Zeolite confined palladium(0) nanoclusters are highly active catalyst for the Suzuki cross-coupling reactions under mild conditions (room temperature, in air) in DMF/water (1:9) mixture. A variety of aryl bromides undergo Suzuki cross-coupling with phenylboronic acid with quantitative GC yields of biaryl derivatives. Recycling experiments showed that zeolite confined palladium(0) nanoclusters can be used as recyclable catalyst in the Suzuki cross-coupling reactions. (c) 2010 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.apcata.2010.05.021
Sayi :382 issue :2 Sayfa :339-344
The study of catalytic membranes is a multidisciplinary activity, which in recent years has attracted the attention of scientists in a number of disciplines, including material science, chemistry and chemical engineering. Membrane based reactive separation processes, which seek to combine two distinct functions, i.e. reaction and separation, have been around as a concept since the early stages of the membrane field, itself, but have only attracted substantial technical interest the last decade or so. According to the literature, most studies combining membranes and catalysts concern gas phase reactions at relatively high temperature. In most of these applications inorganic membrane made from ceramic or metals are applied. Polymeric membranes (porous or dense) are used when the reaction temperatures are lower, i.e. in the field of fine chemicals or when biocatalysts are present. Dense polymeric membranes in use to separate gases or liquids from mixtures by a sorption-diffusion mechanism can be coupled to catalytic reaction and then be used to separate and react in one step. The polymeric membrane should be not only highly selective, but it should also be permeable enough to give a sufficient separation.
DOI : 10.1016/j.apcata.2006.03.058
Sayi :307 issue :2 Sayfa :167-183
Performance of an ordinary supported nickel catalyst was tuned to reach an almost complete selectivity for partial hydrogenation of 1,3-butadiene by coating it with a phosphonium-type ionic liquid (IL), tributyl(methyl) phosphonium methyl sulfate, [P-4441] [MeSO4]. Thanks to high chemical and thermal stability of (P-4441) [MeSO4], the reaction conditions could be pre-optimized for high partial hydrogenation performance before the deposition of the IL coating. When the catalyst was coated with IL, it provided a total butene selectivity of 99.5 +/- 0.2%, a record high partial hydrogenation selectivity ever reported for a nickel-based catalyst. X-ray photoelectron spectroscopy results illustrated that the IL donates electrons to nickel sites and makes them selective for partial hydrogenation. The conductor like screening model for realistic solvents (COSMO-RS) calculations indicated that the IL coating also exerts a filter effect, which helps to maintain this high partial hydrogenation selectivity at all conversion levels.
DOI : 10.1016/j.apcata.2018.06.016
Sayi :562 Sayfa :321-326
The natural zeolite obtained from the Sivas-Yavu region in Turkey and iron modified forms were studied for the decomposition of N2O and selective catalytic reduction of N2O with NH3. The natural and iron modified zeolites were characterised by XRD, SEM, H-2-TPR, NH3-TPD and low temperature nitrogen sorption. The effect iron loading, precursor and valency on the catalytic performance of catalysts were studied. The catalytic activity of the zeolites increased up to about 7.0 wt.% Fe. Above this value, the activity decreased as a result of a reduction in the surface area and pore volume of the zeolite. The highest catalytic activity was observed using catalysts prepared with FeCl2 due to the formation of more reducible iron species in the zeolites. When FeSO4 was used as the iron precursor, sulphate remained on the surface even after extensive washing resulting in a decrease in the N2O decomposition activity and a shift the N2O reduction temperature to higher values. Since the natural and iron exchanged natural zeolites prepared using FeCl2 have comparable activity with synthetic zeolites, the offer a promising alternative catalyst for the abatement of N2O, particularly for the selective reduction of N2O with NH3. (C) 2011 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.apcata.2011.08.026
Sayi :407 issue :1-2 Sayfa :67-75
In this work, oxidative coupling of methane was studied over monolithic Mn/Na2WO4/SiO2 catalysts. The monolithic catalysts were prepared by three different ways as (1) preparation of monolithic silica (monosil) followed by impregnation of Mn and Na2WO4, (2) preparation of monolithic silica with Mn addition during gelation (Mn-monosil) followed by impregnation of Na2WO4 and (3) preparation of monolithic silica as MCM-41 structure (MCM-monosil) followed by impregnation of Mn and Na2WO4. The catalysts were tested in a microflow reactor and the results were compared with those obtained over particulate catalysts. It was found that Mn-monosil performed best and produced C-2 yield of 16.2%, which is close to the values obtained over particulate catalyst (19.3%). Mn-monosil was also passed the 10 h stability and hysteresis tests successfully. SEM characterization revealed that monolithic catalysts prepared by three different methods had different pore structure; it was also seen from SEM images that Mn-monosil preserved its original form better, and this was also verified by XRD analysis.
DOI : 10.1016/j.apcata.2017.08.020
Sayi :547 Sayfa :22-29
Addressed herein is a general and facile route for the reduction of aromatic nitro, nitrile, and carbonyl compounds to the corresponding primary amines and alcohols, respectively, under ambient conditions. Our reduction approach comprises the tandem AB dehydrogenation and hydrogenation of unsaturated organic groups catalyzed by reduced graphene oxide supported Co30Pd70 alloy nanoparticles (rGO-Co30Pd70) in water/methanol mixture (v/v = 7/3) at room temperature. Monodisperse Co30Pd70 alloy NPs were synthesized by using an organic solution phase protocol involving the co-reduction of cobalt(II) acetylacetonate and palladium(II) acetylacetonate in oleylamine and borane-tert-butylamine mixture at 100 degrees C. The colloidal Co30Pd70 NPs were assembled on reduced graphene oxide (rGO-Co30Pd70) before their use as catalysts in the tandem reactions. A variety of aromatic nitro, nitriles, and carbonyl compounds were tested by the rGO-Co30Pd70 catalyzed tandem reaction and all the corresponding primary amines or alcohols were obtained by the yields reaching up to 99% within reaction times of 5-15 min. (C) 2014 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.apcata.2014.09.043
Sayi :488 Sayfa :176-182
The purpose of this study is to investigate how the property of third phase affects the reaction rate in a phase transfer catalytic reaction system. Dibenzyl sulfide was produced by the reaction between sodium sulfide in an aqueous phase and benzyl chloride in an organic phase by using tetrahexylammonium bromide ((Hex)4NBr) as a phase transfer catalyst. As the concentration of sodium sulfide in the aqueous phase and the temperature increased, the third phase was more easily formed. Three types for temperature dependencies on the reaction rate were observed. The reaction rate in one type initially increased, suddenly decreased, and then increased again. The other reaction rates in two types increased with the increase in temperature but the difference between them was 20–50 times at the same temperature. These behaviors could be explained by the property of third phase, especially, the lipophilicity or the hydrophilicity.
DOI : 10.1016/s0926-860x(00)00436-1 Anahtar Kelimeler :
Chemical reaction, Phase transfer catalyst, Third phase, Catalytic activity
ISSN: 0926-860X Sayı: 1 Cilt: 201 Sayfa: 139-143
Alkylation of aniline with methanol over AlPO4-5, AlPO4-11, CoAPO-5, CoAPO-11, ZAPO-5 and ZAPO-11 in the vapour phase has been studied. The products formed are N-methylaniline (N-MA), N,N-dimethylaniline (NN-DMA) and N-methyltoluidine (N-MT). The product distribution is influenced by temperature, (WHSV)−1 and ratio of aniline and methanol. Acidity of the catalysts plays an important role in the methylation of aniline. A direct relationship between total acidity and conversion was observed.
Selectivity and yield of ethane and ethylene in the conversion of methane without O2 increased remarkably with increasing partial pressure of carbon dioxide over CeO2 modified with CaO. The chemisorbed carbon dioxide is proposed to be responsible for the selective formation of ethane and ethylene.
The selectivity to styrene and ethylbenzene (C8 selectivity), their yields (C8 yield), and the stability with time-on-stream in the oxidative methylation of toluene with methane have been compared for superbasic catalysts prepared by promoting MgO, CaO, SrO or BaO with binary alkali metal compounds. The bi-alkali-promoted substrates are more effective than the mono-alkali promoted systems. The most effective catalytic system (5 mol-% Na+ + 5 mol-% Cs+)/CaO gave a toluene conversion as high as 45.0 mol-% and a total C8 selectivity of 60.0 mol-% (styrene/ethylbenzene = 2.2) resulting in a total C8 yield of 27%, and operated in a stable manner for 60 h. These are the highest values ever reported in the open literature. The bi-alkali-promoted MgO also showed similar performances but somewhat smaller than those of promoted CaO. In contrast, the bi-alkali-promoted SrO and BaO were less effective under the same conditions, both exhibiting much lower performances than the promoted CaO or MgO. In terms of the toluene conversion, the C8 selectivity and the stability with time-on-stream, the following sequence was observed for the bi-alkali-promoted substrates: CaO > MgO > BaO > SrO. The relatively high performances of the bi-alkali-promoted CaO or MgO compared to the mono-alkali ones are attributed to the synergistic increase in surface basicity (superbasicity) caused by the enrichment of the surface with the bi-alkali mixtures. Unlike SrO and BaO, which form stable carbonates with the CO2 formed during the reaction which inhibits the surface basicity, the Ca or Mg carbonates decompose to oxides under the reaction conditions, thereby ensuring a higher catalytic performance. It is shown that there exists an optimum substrate, CaO, which upon promotion with bi-alkali becomes the most effective in the oxidative methylation of toluene.
In this work, activities of HUSY and Ce/HUSY zeolites were studied in transesterification cycles of soybean oil and ethanol to produce biodiesel. The characterization of the materials was performed by FT-IR, XRD, BET method and pyridine adsorption followed by thermal analyses. TG/DTG results indicated a decrease of acid sites for both samples after each reaction cycle. However, Ce/HUSY zeolite showed a superior stabilization of acidic sites after three catalytic cycles and intermediary activation procedures. Biodiesel production exhibited high conversion levels (>96%) for both zeolites in all transesterification cycles. Surface area and pore volume measurements evidenced that cerium incorporation reduced the number of acid sites by interacting with OH groups in the micropore and external area of the zeolitic surface. This interaction resulted in an acid and structural stability, which provided a better activity (99%) than HUSY (96%). The higher conversion values obtained by zeolites showed a final product with a different distribution when compared with the traditional transesterification process. The identification of free fatty acids, diethyl and glycerol ethers in the final products and the reduction of unsaturated compounds indicated that parallel reactions also occurred in the studied systems. Nonetheless, the biofuel produced showed high ester content and did not present changes in its calorific power.