Showing papers in "Journal of Molecular Catalysis A-chemical in 2007"
TL;DR: In this article, the photocatalytic activity of La-doped ZnO nanoparticles in the degradation of monocrotophos (MCP) was studied.
Abstract: La-doped ZnO nanoparticles with different La contents were synthesized and characterized by various sophisticated techniques such as XRD, UV–vis, AFM, XPS, and HR-SEM. The XRD results revealed that La3+ is uniformly dispersed on ZnO nanoparticles in the form of small La2O3 cluster. It was found that the particle size of La-doped ZnO is much smaller as compared to that of pure ZnO and decreases with increasing La loading. Rough and high porous surface of La-doped ZnO was observed by AFM, which is critical for enhancing the photocatalytic activity. The photocatalytic activity of La-doped ZnO in the degradation of monocrotophos (MCP) was studied. The effects of the adsorption of MCP, lights of wavelength, and the solution pH on the photocatalytic activity of La-doped ZnO with different La loading were studied and the results were compared with pure ZnO and pure TiO2. It was observed that the rate of degradation of MCP over La-doped ZnO increases with increasing La loading up to 0.8 wt% and then decreases. It was found that the doping of La in ZnO helps to achieve complete mineralization of MCP within a short irradiation time. Among the catalyst studied, the 0.8 wt% La-doped ZnO was the most active, showing high relative photonic efficiencies and high photocatalytic activity for the degradation of MCP.
329 citations
TL;DR: In this paper, the impact of early transition-metal oxygen-anion cluster (polyoxometalate or “POM”) geometric and electronic structural properties on POM-based catalysis is addressed.
Abstract: The impact of early transition-metal oxygen-anion cluster (polyoxometalate or “POM”) geometric and electronic structural properties on POM-based catalysis is addressed. Three specific areas of general challenge in POM-based catalysis and catalytic materials are elaborated: (1) the role of ion pairing in catalyst stability, selectivity, and reactivity; (2) the presence of multiple reactive forms of the POMs and the interconvertability of these forms under turnover conditions; and (3) the impact of POM ground state and excited state electronic structure on turnover and selectivity.
304 citations
TL;DR: In this article, the effects of H2S on the HDO of aromatic and aliphatic oxygenates on sulphided NiMo/γ-Al2O3 and CoMo/β-Al 2O3 catalysts were compared in liquid and gas phases.
Abstract: A sulphiding agent added to maintain catalyst activity affects hydrodeoxygenation (HDO) of bio-oils. Aromatic compounds are dominant oxygenates in wood-based biofuels, and aliphatic oxygenates in vegetable oils and animal fats. The effects of H2S on the HDO of aromatic and aliphatic oxygenates on sulphided NiMo/γ-Al2O3 and CoMo/γ-Al2O3 catalysts were compared in liquid and gas phases.
Direct hydrogenolysis and hydrogenation reactions played a major role in the HDO of phenol. H2S suppressed these reactions on the NiMo catalyst and mainly direct hydrogenolysis on the CoMo catalyst, inhibiting thereby the HDO of phenol. The inhibition by H2S was attributed to the competitive adsorption of phenol and H2S. The effect was in contrast to the promoting effect of H2S on the HDO of aliphatic oxygenates, in which acid-catalysed and hydrogenation reactions predominate. The differences were attributed to the different reaction mechanisms due to the distinct molecular and electronic structures of aromatic and aliphatic oxygenates. Phenol was found to be less reactive than aliphatic oxygenates. Further, the NiMo catalyst exhibited lower activity for the HDO of phenol than did the CoMo catalyst, while the reverse was the case for the HDO of aliphatic oxygenates.
259 citations
TL;DR: In this article, the catalytic vapor phase hydrogenation of furfural (FAL) to furfuryl alcohol (FOL) at atmospheric pressure, the gas hourly space velocity (GHSV) has been maintained at 0.5.
Abstract: Cu–MgO catalysts have been employed for the catalytic vapor phase hydrogenation of furfural (FAL) to furfuryl alcohol (FOL) at atmospheric pressure, H 2 /furfural (molar ratio) = 2.5 and the gas hourly space velocity (GHSV) has been maintained at 0.05 mol h −1 g cat −1 . Cu–MgO catalysts with variable Cu loadings (5.2–79.8 wt.%) are prepared by coprecipitation method and are characterized by BET surface area, AAS (atomic adsorption spectroscopy), XRD, XPS and DTA/TGA. Hydrogenation activities of the catalysts, reduced at 523 K in H 2 flow for 4 h prior to the reaction are studied in the temperature range of 453–523 K. Cu–MgO catalyst with 16 wt.% of Cu showed hydrogenation activity with 98% conversion of furfural producing furfuryl alcohol with a higher selectivity of 98%. XPS analysis showed the presence of Cu 0 /Cu + sites on the catalyst surface that may be responsible for the higher activity compared to other Cu–MgO catalysts studied. The turnover frequency of furfural conversion in the catalysts containing lower composition of Cu is very high. However, due to the lack of required number of Cu 0 particles and the absence of Cu + species in these catalysts, the overall conversion of furfural is low.
249 citations
TL;DR: In this article, the authors discuss the perspectives of acid catalysis by solid HPAs, in particular focusing on several approaches that could help overcome the deactivation of HPA catalysts to achieve sustainable catalyst performance.
Abstract: Heterogeneous acid catalysis by heteropoly acids (HPAs) has the potential of substantial economic and green benefits. Its application, however, has been limited because of the difficulty of catalyst regeneration due to a relatively low thermal stability of HPAs. The aim of this paper is to discuss the perspectives of acid catalysis by solid HPAs, in particular focusing on several approaches that could help overcome the deactivation of HPA catalysts to achieve sustainable catalyst performance. These approaches include: developing novel HPA catalysts possessing high thermal stability, modification of HPA catalysts to enhance coke combustion, inhibition of coke formation on HPA catalysts during operation, reactions in supercritical fluids and cascade reactions using multifunctional HPA catalysis.
239 citations
TL;DR: In this article, the scope and limitations of the two catalysts in various reaction conditions examined were described, and both HClO4−SiO2 and PPA-SiO 2 catalysts yielded only 4 as the product in aqueous medium.
Abstract: Efficient one-pot Knoevenagel condensation, Michael addition and cyclodehydration of dimedone with various aldehydes in acetonitrile and solvent free conditions using PPA–SiO2 catalyst gave 1,8-dioxo-octahydroxanthenes 3 in excellent yields; whereas in the presence of HClO4–SiO2 catalyst the reaction is limited to give only 2,2′-arylmethylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one) 4 in very good yields. In aqueous medium both HClO4–SiO2 and PPA–SiO2 catalysts yielded only 4 as the product. The scope and limitations of the two catalysts in various reaction conditions examined were described.
235 citations
TL;DR: A review of the progress made in the past few years on homogeneous and heterogeneous catalytic reactions in the non-conventional solvents, water, ionic liquids, supercritical carbon dioxide and fluorous carbons, with the focus on those catalyzed by transition metal complexes is given in this paper.
Abstract: Solvents play a critical role in “greening” synthetic chemistry, and this is also true in catalytic organic synthesis. This review attempts to summarize the progress made in the past a few years on homogeneous and heterogeneous catalytic reactions in the non-conventional solvents, water, ionic liquids, supercritical carbon dioxide and fluorous carbons, with the focus on those catalyzed by transition metal complexes. The reactions covered include hydrogenation, hydroformylation, carbonylation, Heck reactions, Suzuki and Stille couplings, Sonogashira reactions, allylic substitution, olefin metathesis, olefin epoxidation and alcohol oxidation.
230 citations
TL;DR: In this article, the authors synthesized barium doped nano-TiO2 nanoparticles by sol-gel method and characterized them by XRD, BET, FT-IR, TGA, UV-vis, SEM and TEM techniques.
Abstract: Magnesium and barium doped TiO2 nanoparticles were synthesized by sol–gel method. The materials were characterized by XRD, BET, FT-IR, TGA, UV–vis, SEM and TEM techniques. The pure TiO2 nanoparticles contained both anatase and rutile phases together, but Mg2+ or Ba2+ metal ion doped nano TiO2 gave only anatase phase. The framework substitution of Mg2+ in nano TiO2 was established by XRD and FT-IR techniques. However, Ba2+ was retained only on the surface of nano TiO2 as BaCO3 and the absence of framework substitution of Ba2+ in nano TiO2 was evident from XRD and FT-IR analysis. The band gap values of Mg2+ and Ba2+ doped nano TiO2 were higher than the pure nano TiO2. The presence of anatase type structure in nano TiO2 with high crystallinity and high phase stability even after annealing at 800 °C substantially indicates that the dopants might inhibit densification and crystallite growth in nano TiO2 by providing dissimilar boundaries. The photocatalytic activity in the degradation of 4-chlorophenol was found to be higher for Mg2+ and Ba2+ doped nano TiO2 than both pure nano TiO2 and commercial TiO2 (Degussa P-25). The influence of various parameters such as initial concentration of 4-chlorophenol, catalyst loading, pH and light intensity were optimized to obtain maximum degradation.
221 citations
TL;DR: In this article, a series of novel water-tolerant polyoxometalate-containing composite photocatalysts such as amine-functionalized mesoporous silica/anatase titania impregnated with transition metal substituted polyoxometricalates, bimodal porous polyoxotungstate-anatases TiO2 nanocomposites, Fe-polytungstate−silica-structured fabrics, and highly ordered macroporous monovacant Keggin unit-titania composite films, including their design,
Abstract: This paper reviews a series of novel water-tolerant polyoxometalate-containing composite photocatalysts such as amine-functionalized mesoporous silica/anatase titania impregnated with transition metal substituted polyoxometalates, bimodal porous polyoxotungstate–anatase TiO2 nanocomposites, Fe–polytungstate–silica-structured fabrics, monovacant Keggin unit-silica/titania composite films, and highly ordered macroporous monovacant Keggin unit-titania composite films, including their design, preparation, optical absorption property, surface physico-chemical property, morphology, and heterogeneous photocatalytic behaviors. Emphases are addressed on the efficient photocatalytic activity of as-prepared solid polyoxometalates in the near UV- and/or visible-light region and easier recovery of the catalyst from the reaction system.
211 citations
TL;DR: Zr 4+ doped nano titania was prepared by sol-gel method using titanium(IV) isopropoxide and zirconium nitrate as precursors as mentioned in this paper.
Abstract: Zr 4+ doped nano titania was prepared by sol–gel method using titanium(IV) isopropoxide and zirconium nitrate as precursors. The materials were characterized by XRD, BET, UV–vis, FT-IR, SEM-EDX and TEM techniques. The nanoparticles of pure TiO 2 contained both anatase and rutile phases together but Zr 4+ doped TiO 2 gave anatase phase only. The framework substitution of Zr 4+ in TiO 2 was established by XRD, SEM-EDX and FT-IR techniques. The band gap value of Zr 4+ doped TiO 2 was higher than the parent nano TiO 2 . TEM observations confirmed the nanocrystalline nature of Zr 4+ doped TiO 2 . The presence of dopants therefore could suppress the growth of TiO 2 grains, increase the surface area, decrease the anatase–rutile phase transformation and accelerate the surface hydroxylation. These properties resulted higher photocatalytic activity for Zr 4+ doped nano TiO 2 than undoped nano TiO 2 . The presence of anatase type structure in TiO 2 with high crystallinity and high phase stability, even after annealing at 800 °C substantially indicated that the dopants might inhibit densification and crystallite growth by providing dissimilar boundaries. The photocatalytic activity in the degradation of 4-chlorophenol was found to be higher for Zr 4+ doped TiO 2 than both nano TiO 2 and commercial TiO 2 (Degussa P25). The experimental parameters such as initial concentration of 4-chlorophenol, catalyst loading, pH and light intensity were optimized for maximum degradation efficiency.
205 citations
TL;DR: In this paper, the synthesis of group 4 transition metal (Ti, Zr, Hf) complexes, especially nonbridged half-metallocenes containing anionic donor ligands of the type, Cp′MX 2 (L) (Cp′ ǫ = cyclopentadienyl group; Mǫ, Zr, Hf; X,=halogen, alkyl etc., Lǫ,=anionic donor l ligands), as catalysts for precise olefin polymerization was reviewed.
Abstract: Recent examples for synthesis of group 4 transition metal (Ti, Zr, Hf) complexes, especially nonbridged half-metallocenes containing anionic donor ligands of the type, Cp′MX 2 (L) (Cp′ = cyclopentadienyl group; M = Ti, Zr, Hf; X = halogen, alkyl etc.; L = anionic donor ligands), as catalysts for precise olefin polymerization have been reviewed. It has been revealed that these complex catalysts displayed unique characteristics especially for ethylene copolymerizations and some examples are known to produce new polyolefins that cannot be prepared by ordinary catalysts such as classical Ziegler–Natta, metallocenes. Modification of both cyclopentadienyl fragment and anionic ancillary donor ligands are the key for precise olefin (co)polymerization.
TL;DR: The significant features of the iodine-catalyzed condensation are operational simplicity, inexpensive reagents, high yield of products and the use of non-toxic reagents.
Abstract: Molecular iodine has been used an efficient catalyst for an improved and rapid one-pot synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetra substituted imidazoles in excellent yields. The significant features of the iodine-catalyzed condensation are operational simplicity, inexpensive reagents, high yield of products and the use of non-toxic reagents.
TL;DR: In this paper, nano-TiO 2 particles prepared by the sol-gel method were used as catalyst for the degradation of nitrobenzene by ozone, and the mechanism of catalytic ozonation was also discussed.
Abstract: Nano-TiO 2 particles prepared by the sol–gel method were used as catalyst for the degradation of nitrobenzene by ozone. Catalyst samples were characterized by measuring the specific area ( S BET ), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Removal efficiency of nitrobenzene (NB) was significantly promoted in the presence of catalyst compared with ozone alone. TiO 2 calcined at 500 °C showed the best activity. Different experimental conditions like catalyst dose, ozone dosage, initial nitrobenzene and pH have been examined. The mechanism of catalytic ozonation was also discussed. Both ozonation and catalytic ozonation were significantly influenced by carbonate and tert -butyl alcohol, which confirmed that TiO 2 -catalyzed ozonation follows a radical-type mechanism. And hydroxyl radicals were truly identified by spin-trapping/EPR technique.
TL;DR: In this paper, an ultrasonic-assisted method was used to synthesize visible-light-induced photocatalysts using Bi2MoO6 (M = W, Mo) nanocrystals.
Abstract: Visible-light-induced photocatalysts Bi2MO6 (M = W, Mo) nanocrystals have been successfully synthesized via a new ultrasonic-assisted method. Laminar structured Bi2WO6 nanoplates with size of ca. 100 nm and Bi2MoO6 nanoparticles with size of ca. 150 nm were prepared via ultrasonic pretreatment followed by calcination at 500 °C. The photocatalytic activities of as-prepared Bi2MO6 were about 4–6 times higher than that of the products prepared by traditional solid-state reaction (SSR), which were evaluated by the degradation of RhB dye in water under visible light irradiation (λ > 400 nm). It was found that ultrasonic irradiation played an important role in the formation of the nanomaterials with a smaller crystal size and larger surface area, which was beneficial to their photocatalytic activities. The present study suggested a promising method, as an effective improvement of traditional SSR-process, for the synthesis of other photocatalysts.
TL;DR: In this article, Nitrogen-containing carbon nanostructures were prepared from the decomposition of acetonitrile at 900°C over silica and magnesia supports impregnated with Fe, Co, or Ni.
Abstract: Nitrogen-containing carbon nanostructures were prepared from the decomposition of acetonitrile at 900 °C over silica and magnesia supports impregnated with Fe, Co, or Ni For the carbon grown from supported Fe and Co particles, compartmentalized fibers with a stacked cup structure predominantly formed, while mostly broken multi-walled nanotubes formed from Ni particles The fibers were purified from the support by removing silica with 1 M KOH, or removing metal particles and magnesia with 1 M HCl Surface analysis was performed with XPS and hydrophobicity comparisons Surface properties were related to nanostructure and edge plane exposure Activity for the ORR was highest over CNx fibers grown from supported Fe and Co particles, which may also be related to edge plane exposure, and not necessarily to the presence of metal contamination The most active materials were generally the most selective catalysts as well Moreover, from Tafel plot slopes a trend was observed depending on the precursor metal used to prepare the CNx The magnitude of the Tafel slope was smallest for the samples prepared from Fe or Co precursors Compared to a state-of-the-art platinum catalyst, the most active alternative non-noble metal catalysts had less than 100 mV potential drop difference, high selectivity for complete oxygen reduction, a similar Tafel slope, and good electrical conductivity
TL;DR: In this paper, a short focused review shows the usefulness of polyoxometalates (POMs) in selected electrocatalytic processes, including hydrogen production, NOx reduction, dioxygen reduction, coenzyme oxidation.
Abstract: Polyoxometalates (POMs) constitute a broad family of molecular oxides showing promise in several efficient and clean electrocatalytic processes, when they are handled in appropriate conditions. Reduction and oxidation possibilities exist as well. The present short focused review shows the usefulness of POMs in selected electrocatalytic processes. Quantitative transformations were demonstrated in several examples, including hydrogen production, NOx reduction, dioxygen reduction, coenzyme oxidation… This selection leaves room for a wealth of other possibilities. It appears clearly that several parameters must be taken into account in the design and study of these processes. Among them, the stability in aqueous or non aqueous solutions is an absolute prerequisite, which excludes the use of several newly synthesised fragments solely stable in the solid state. New parameters, in addition of those highlighted here, might emerge because POMs with new atomic compositions, new structures and new reactivities, continue to be synthesised and characterised. The challenge, however, is to find new POMs or new POM-based systems to decrease overpotentials which remain high for most reactions and improve the overall kinetics.
Finally, an optimistic prediction is that POMs, owing to their versatility and possibility to accommodate nearly all the atoms of the periodic classification, will become popular to drive selected electrocatalytic processes.
TL;DR: In this paper, the synthesis of 2,4,5-triaryl-imidazoles from benzyl, aldehydes and NH4OAc, as ammonia source, in the presence of catalytic amount of NiCl2·6H2O supported onto acidic alumina in very good yields under heterogeneous system is reported.
Abstract: The synthesis of 2,4,5-triaryl-imidazoles from benzyl, aldehydes and NH4OAc, as ammonia source, in the presence of catalytic amount of NiCl2·6H2O supported onto acidic alumina in very good yields under heterogeneous system is reported.
TL;DR: In this paper, the authors investigated solid phase photocatalytic degradation of polyethylene (PE) plastic with TiO2 in the ambient air under solar and ultraviolet light irradiation.
Abstract: This paper investigated solid-phase photocatalytic degradation of polyethylene (PE) plastic with TiO2 in the ambient air under solar and ultraviolet light irradiation. The photodegradation of the composite plastic was compared with that of pure PE through weight loss monitoring, scanning electron microscopic (SEM) analysis, gas chromatography (GC), FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS). PE-TiO2 composite plastic can be efficiently decomposed and the main products are CO2 and water. The weight-loss of PE-TiO2 (1 wt%) film reached 42% under solar irradiation for 300 h. The degradation rate can be controlled by changing the content of TiO2 nanoparticles in PE plastic. The degradation of composite plastic initiated on PE-TiO2 interface and then extended into polymer matrix induced by the diffusion of the reactive oxygen species generated on TiO2 particle surface. The present study demonstrates that the polymer-TiO2 compositing is a practical and promising way to degrade the plastic waste under solar light without any pollution.
TL;DR: In this article, the condensation of various aldehydes, benzil, aliphatic or aromatic primary amines and ammonium acetate under solvent free conditions using perchloric acid adsorbed on silica gel (HClO 4 -SiO 2 ) as catalyst in excellent yields.
Abstract: Highly efficient, one-pot, four-component synthesis of 1,2,4,5-tetrasubstituted imidazoles was reported the condensation of various aldehydes, benzil, aliphatic or aromatic primary amines and ammonium acetate under solvent free conditions using perchloric acid adsorbed on silica gel (HClO 4 –SiO 2 ) as catalyst in excellent yields. HClO 4 –SiO 2 exhibited remarkable catalytic activity with respect to the reaction time (2–20 min), amount of catalyst. Present protocol with HClO 4 –SiO 2 catalyst is convincingly superior to the recently reported catalytic methods.
TL;DR: In this paper, the authors investigated reactions of methyl heptanoate on sulphided NiMo/γ-Al 2 O 3 and CoMo/β-Al O 3 catalysts in gas and liquid phases.
Abstract: Reactions of methyl heptanoate on sulphided NiMo/γ-Al 2 O 3 and CoMo/γ-Al 2 O 3 catalysts in gas and liquid phases were investigated in detail. Experiments with heptanol and heptanoic acid were carried out in support of the conclusions. Hydrodeoxygenation (HDO) of the ester produced C 7 and C 6 hydrocarbons. Alcohols, aldehyde, carboxylic acid and ethers were formed as intermediates. In addition, a few sulphur-containing compounds were formed as intermediates and they led to desulphurisation of the catalysts. The reactions of the ester and the intermediates are explained in terms of hydrogenation and acid-catalysed reactions such as hydrolysis, esterification and dehydration. The E 2 elimination and S N 2 nucleophilic substitution mechanisms are proposed to play a role in the reactions. HDO and hydrogenation activities were higher on the NiMo catalyst than the CoMo catalyst. The NiMo catalyst might thus seem to be preferred for the conversion of aliphatic esters, alcohols and carboxylic acids. According to the proposed reaction scheme, however, hydrogen consumption will be greater with this catalyst.
TL;DR: In this article, a three-component reaction of 2-naphthol, aldehydes and urea or amides has been carried out in the presence of iodine in dichloroethane at room temperature or under solvent-free conditions at higher temperature to form the corresponding amidoalkyl naphthols in high yields.
Abstract: A one-pot three-component reaction of 2-naphthol, aldehydes and urea or amides has efficiently been carried out in the presence of iodine in dichloroethane at room temperature or under solvent-free conditions at higher temperature to form the corresponding amidoalkyl naphthols in high yields.
TL;DR: In this paper, the degradation of oxalic acid has been studied in aqueous solution photocatalyzed by band-gap-irradiated TiO2, modified with nanosized gold particles.
Abstract: The commercially available TiO2-photocatalyst (Degussa P25) was modified with nanosized gold particles by the photoreduction method at four different values of the pH factor of the medium. The characterization of the synthesized catalysts was carried out by the BET method, X-ray photoelectron spectroscopy (XPS), TEM and the adsorption of the model pollutant. A remarkable influence of the pH on the particle size of Au was registered upon investigating the catalysts by XPS and TEM methods. The size of the gold nanoparticles on the TiO2 surface decreases with increase in the pH of the medium. The degradation of oxalic acid has been studied in aqueous solution photocatalyzed by band-gap-irradiated TiO2, modified with nanosized gold particles. The photocatalytic activity of TiO2, modified with gold, was found to increase with the decrease of the size of the gold nanoparticles on the surface of the photocatalytic material. The maximal value of the photocatalytic activity (twice higher than that of the semiconducting support) is registered in the case of gold photoreduction at pH 7. The adsorption properties of the catalysts, as well as the size of the noble metal nanoparticles on the surface of the support, influence the efficiency of the photocatalytic process. The reaction rate of photocatalytic degradation of the oxalic acid follows a zero kinetic order according to the Langmuir–Hinshelwood model. The increase of the quantum yield of the photodestruction reaction of the studied model pollutant is due to the formation of Schotky barriers on the metal-semiconductor interface, which serve as efficient electron traps, preventing the electron–hole recombination.
TL;DR: In this article, an efficient and improved procedure for the synthesis of tetrasubstituted imidazoles is developed by Keggin-type heteropolyacid (HPA) catalyzed four-component one-pot coupling protocol in refluxing ethanol.
Abstract: An efficient and improved procedure for the synthesis of tetrasubstituted imidazoles is developed by Keggin-type heteropolyacid (HPA) catalyzed four-component one-pot coupling protocol in refluxing ethanol.
TL;DR: A quaternary ammonium salt covalently bound to chitosan is reported as an efficient and recyclable single-component catalyst for the synthesis of propylene carbonate (PC) from propylene oxide (PO) and carbon dioxide without any organic solvent or co-catalyst as discussed by the authors.
Abstract: A quaternary ammonium salt covalently bound to chitosan is reported as an efficient and recyclable single-component catalyst for the synthesis of propylene carbonate (PC) from propylene oxide (PO) and carbon dioxide without any organic solvent or co-catalyst. The catalyst can be easily recovered by filtration and reused for at least five times without obvious loss of its catalytic activity. The effects of the catalyst structure and various reaction parameters on the catalytic performance were in detail investigated. Moreover, the catalyst was found to be applicable to a variety of terminal epoxides, producing the corresponding cyclic carbonates in high yield and selectivity. Notably, this environmentally benign and cost-effective process has great potential to be applied in various continuous flow reactors in industry.
TL;DR: This aqua mediated Michael addition of various aromatic and heteroaromatic aldehydes with 4-hydroxycoumarin or dimedone using catalytic amount of molecular iodine devoids the use of expensive, corrosive reagents, toxic sovents and provides the operational simplicity.
Abstract: Molecular iodine has been used an efficient catalyst for an improved and rapid one-pot synthesis of 3,3′-arylmethylenebis-(4-hydroxycoumarin) and 2,2′-arylmethylenebis(3-hydroxyl-5,5-dimethyl-2-cyclohexen-1-one) in excellent yields using water as a reaction medium. This aqua mediated Michael addition of various aromatic and heteroaromatic aldehydes with 4-hydroxycoumarin or dimedone using catalytic amount of molecular iodine devoids the use of expensive, corrosive reagents, toxic sovents and provides the operational simplicity.
TL;DR: In this article, a series of Ni-Co catalysts with molar ratios of 0.25:1 between Ni and Co was used for catalytic generation of hydrogen by steam reforming of acetic acid.
Abstract: Catalytic generation of hydrogen by steam reforming of acetic acid over a series of Ni–Co catalysts have been studied. The catalyst with the molar ratio of 0.25:1 between Ni and Co was superior to other catalysts. The effects of reaction temperature, liquid hourly space velocity (LHSV) and molar ratios of steam-to-carbon (S/C) were studied in detail over this catalyst. At T = 673 K, LHSV = 5.1 h −1 , S/C = 7.5:1, the catalyst exhibited the best performances. Acetic acid was converted completely to hydrogen, while H 2 selectivity reached up to 96.3% and CO 2 selectivity up to 98.1% was obtained, respectively. Ni–Co catalyst showed rather stable performances for the 70 h time-on-stream without any deactivation.
TL;DR: The Bronsted acidities of sulfonic acid-functionalized ionic liquids (SFILs) with pyridinium cations were investigated in this article, where the acidity order of SFILs is consistent with their activity order observed in some acid-catalyzed reactions.
Abstract: The Bronsted acidities of sulfonic acid-functionalized ionic liquids (SFILs) with pyridinium cations were investigated. The Hammett function values of SFILs are between −1.5 and −3.6 at 110 °C. The acidities of SFILs depend on the anions, and have the order as follows: [PSPy][BF 4 ] > [PSPy][HSO 4 ] > [PSPy][ p TSA] > [PSPy][H 2 PO 4 ] ([PSPy] = N -propane–sulfonic acid pyridinium). The acidity order of SFILs is consistent with their activity order observed in some acid-catalyzed reactions. The minimum-energy geometries of SFILs manifest that anions have strong interactions with the sulfonic acid proton. It is considered that in addition to the alkyl sulfonic acid group, the anion is likely to serve as available acid sites. Hence the acidities and catalytic activities of SFILs depend on the kinds of anions.
TL;DR: An efficient method for the synthesis of 1.2,4,5,5-tetrasubtituted imidazoles by four-component condensation of benzil or benzoin, aldehydes, amines and ammonium acetate under microwave irradiation or classical heating conditions using potassium dodeca tungstocobaltate trihydrate [K5CoW12O40·3H2O (1.1
Abstract: An efficient method for the synthesis of 1,2,4,5-tetrasubtituted imidazoles by four-component condensation of benzil or benzoin, aldehydes, amines and ammonium acetate under microwave irradiation or classical heating conditions using potassium dodeca tungstocobaltate trihydrate [K5CoW12O40·3H2O (01 mol%)] as catalyst is reported The catalyst exhibited remarkable reusable activity
TL;DR: In this article, a homogeneous kinetic model for preparation of peracetic acid (PAA) from acetic acid and hydrogen peroxide (HP) under the catalysis of sulfuric acid (SA) in the liquid phase was investigated.
Abstract: A homogeneous kinetic model for preparation of peracetic acid (PAA) from acetic acid (AA) and hydrogen peroxide (HP) under the catalysis ofsulfuric acid (SA) in the liquid phase was investigated. The kinetic equations of PAA synthesis and hydrolysis were given and the kinetic constantswere estimated according to the experimental data by a simplex optimization method. It was found that the synthesis and hydrolysis of PAA wereboth first-order reactions with respect to reactant concentrations and H + concentration. Linear relationships were discovered between the observedrate constants and H + concentrations at a certain temperature, with the slopes being corresponding intrinsic rate constants. The intrinsic activationenergies of PAA synthesis and hydrolysis were 57.8 and 60.4kJmol −1 , respectively. The mechanisms of PAA synthesis and hydrolysis werediscussed. It has been proved that the rate-determining step in the synthesis of PAA is the reaction between H 2 O 2 with active carbonyl intermediary,and in the hydrolysis of PAA the reaction between water and corresponding active carbonyl intermediary.© 2007 Elsevier B.V. All rights reserved.
TL;DR: In this paper, the influence of zinc addition to alumina supported Pt and PtSn catalysts is analyzed not only on the activity, selectivity and deactivation in the propane dehydrogenation reaction, but also on the characteristics of platinum metal phase.
Abstract: The influence of the zinc addition to alumina supported Pt and PtSn catalysts is analyzed in this paper, not only on the activity, selectivity and deactivation in the propane dehydrogenation reaction, but also on the characteristics of platinum metal phase. Zinc can give a remarkable improvement in dehydrogenation performance of catalysts. High propylene selectivity (≥97%) can be obtained over zinc-doped catalysts. Physicochemical technologies like BET, NH 3 -TPD, H 2 -TPR, H 2 -chemisorption, C 3 H 6 -TPD, CO-FTIR and TPO were used to characterize the metal phase of catalysts. The presence of zinc modifies the metallic phase, mainly by geometric and electronic modifications of the metallic phase. These modifications could be responsible for the improvement of catalytic performance.