Showing papers in "Journal of Molecular Catalysis A-chemical in 2009"

Reduction of 4-nitrophenol to 4-aminophenol over Au nanoparticles deposited on PMMA

Abstract: Gold nanoparticles (Au NPs) were directly deposited on commercially available poly(methyl methacrylate) (PMMA) beads by the deposition reduction method by adding dropwise of NaBH4 into the aqueous solution of Au(en)2Cl3. The average diameter of Au NPs was 6.9 nm and, in contrast to the case of rapid addition, there were no aggregated particles larger than 20 nm. Catalytic activity of Au/PMMA was tested for the reduction of 4-nitrophenol to 4-aminophenol with an excess amount of NaBH4. Gold NPs on PMMA showed the highest catalytic activity among polymer supported Au NPs previously reported. The reaction rate is the pseudo-first-order with respect to 4-nitrophenol. The pseudo-first-order rate constant and the activation energy were estimated to be 7.2–7.9 × 10−3 s−1 at 295 K and 38 kJ mol−1, respectively.

Prevention of zeolite deactivation by coking

Abstract: The deactivation of acid zeolite catalysts is essentially due to the formation and trapping of heavy secondary products (coke) within the pores (channels and cages). As in these nanosized pores the growth of these products is sterically limited, the coke composition, i.e., the quantitative distribution in nature and size of the components, can be determined and the scheme and mechanisms of coke formation established. Moreover, coupling activity, acidity and adsorption data with coke composition leads to information on the location and deactivating effect of coke molecules. Based on the influence on coking and deactivation rates of the features of reactions and zeolite catalysts, general rules are proposed for limiting the rate of formation of coke molecules and minimising their deactivating effect.

Acidic catalysts for the dehydration of glycerol: Activity and deactivation

Abstract: Al2O3 and TiO2 supports modified by impregnation with PO4-ions and SAPO-11 and SAPO-34 samples were synthesized and characterized by physico-chemical methods. The acidic properties of these catalysts were determined by ammonia TPD. The gas-phase dehydration of glycerol in presence of water was investigated at 280 °C. Glycerol conversion and acrolein selectivity depended on the total acidity and on the textural properties. Additionally, the formation of by-products during the dehydration of glycerol and the conversion of 1-hydroxyacetone and 3-hydroxypropionaldehyde catalysts was studied. The SAPO samples showed high selectivity at low reaction times. Rapid deactivation and formation of carbonaceous deposits was observed for all tested catalysts. The properties of the deactivated catalysts were studied by TPD-NH3 and TPO analysis.

Durable Ni/MgO catalysts for CO2 reforming of methane: Activity and metal–support interaction

Abstract: Two series of Ni/MgO catalysts were prepared by reducing NiO/MgO samples of fixed Ni loading but different calcination temperatures and of varying Ni loadings but fixed calcination temperature. These catalysts were investigated in CO2 reforming of methane under atmospheric pressure and characterized with XRD, TPR and H2-TPD techniques. A complete incorporation of NiO into the MgO “support” to form NiO–MgO solid solution during the calcination stage of the catalyst preparation was identified essential for the formation of stable Ni/MgO catalysts, and the presence of readily reducible “free” NiO in the calcined (unreduced) NiO/MgO samples was shown to produce the deactivating Ni/MgO catalysts during the CO2/CH4 reaction. The reactivities of CO2/CH4 were found sensitive to the particle size (or dispersion) of metallic Ni; the catalytic activity by CH4 turnover frequency (TOF) decreased with increasing the Ni particle size. The reduced catalysts showed two H2-TPD peaks and the nickel sites corresponding to H2-TPD peak at higher temperature showed a higher activity than those associated with the peak at lower temperature. Our data demonstrate that the support in the stable catalysts was actually a kind of NixMg1−xO (x = 0.02–0.15) solid solution and the stable catalytic sites were associated with nanosized Ni particles (3–20 nm) in strong interaction with the solid solution support.. © 2008 Elsevier B.V. All rights reserved.

Effect of chelating agent on the oxidation rate of PCP in the magnetite/H2O2 system at neutral pH

Abstract: The effect of chelating agents on the Fenton heterogeneous oxidation rate of pentachlorophenol (PCP) in the presence of magnetite (Fe3O4) was investigated in opened batch reactor at neutral pH. Six kinds of chelating agents (CA) were selected including EDTA, CMCD, oxalate, tartrate, citrate and succinate. The PCP oxidation rate in the Fenton-like system was significantly improved by using chelating agents at neutral pH. This observation was supported by the increased concentration of chloride produced by the degradation of PCP. The enhancement factor of heterogeneous oxidation rate was found to be not correlated with that of dissolved iron amount. However, the propagation of homogeneous reaction by the dissolved iron contributed to the improvement of the whole oxidation rate. In homogeneous Fenton system (dissolved Fe2+ or Fe3+), EDTA-driven Fenton reaction showed the highest oxidation rate, while oxalate seems to be more efficient in heterogeneous Fenton system (Fe3O4). In fact, EDTA can bind more strongly than oxalate to magnetite surface and compete more actively than H2O2 or PCP for the sorption on the surface active sites. Decrease in H2O2 decomposition rate value was observed when EDTA is previously adsorbed on the catalyst surface. The surface mechanism of oxidant with iron sites on the catalyst surface appears to be the rate-determining step in heterogeneous Fenton system.

Amine functionalized MCM-41: An active and reusable catalyst for Knoevenagel condensation reaction

Abstract: This paper reports preparation, characterization of amine modified mesoporous crystalline MCM-41 and its application in Knoevenagel condensation reaction. Amine modified MCM-41 was prepared by co-condensation and post-synthesis methods. The samples were characterized by X-ray powder diffraction, Fourier-transfer infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron micrograph (SEM), 29Si magic-angle spinning (MAS), nuclear magnetic resonance (NMR), diffuse reflectance spectra (DRS), nitrogen adsorption–desorption and CHN analysis. X-ray diffraction patterns indicate that the modified materials retain the standard MCM-41 structure. SEM study exhibits that the arrangement of particles for 12.8% amine modified MCM-41 is well ordered and spherical in nature. CHN analysis supports that complete hydrolysis of ethoxy groups take place in 12.8% amine modified sample. From the NMR study it is confirmed that the surface coverage is 40% in 12.8% amine modified sample. The base catalytic activity of hybrid MCM-41 materials such as amine (post-synthesis and co-condensation methods) and surfactant functionalized materials for condensation reaction between benzaldehyde and diethyl malonate in solvent free, room temperature synthesis of cinnamic acid was evaluated and correlated with the surface and textural properties. Sample containing 12.8 wt% amine loaded by co-condensation method showed highest malonic ester conversion (92%) and selectivity (98%) for cinnamic acid.

Methanol assisted selective formation of 1,2-glycerol carbonate from glycerol and carbon dioxide using nBu2SnO as a catalyst

Abstract: Selectively 1,2-glycerol carbonate was obtained from glycerol and carbon dioxide in methanol using 1 mol% n Bu 2 SnO (dibutyltin(IV)oxide, 1 ) as a catalyst. The reaction attained equilibrium in 4 h and the yield of 1,2-glycerol carbonate obtained was as high as 35%. We observed the rate of the reaction depends on the amount of the catalyst and methanol used. During the reaction we could trap the intermediates and identify it by 13 C NMR, IR and mass spectrum of the reaction mixture. The reaction proceeds upon activation of 1 by methanol forming dibutyltindimethoxide followed by dibutyltinglycerate, which undergoes CO 2 insertion to produce non-isolable 7-membered tin–glycerolcarbonato complex that finally yield glycerol carbonate. Catalyst 1 was found to be successful even with 1,2-propanediol and ethylene glycol yielding the corresponding cyclic carbonate.

Effect of morphology and crystallite size on solar photocatalytic activity of zinc oxide synthesized by solution free mechanochemical method

Abstract: Zinc oxide crystallites were synthesized by two steps, solution free mechanochemical method. In order to obtain zinc oxide of different morphology and crystallite size, calcination temperature was varied from 400 to 900 °C. These photocatalysts are then characterized by X-ray diffraction (XRD), Scanning Electron Micrograph (SEM), Energy dispersive X-ray spectra (EDXS), Fourier transform infrared spectra (FT-IR) and UV–Visible spectrophotometer. X-ray diffraction data suggest that the obtained ZnO crystallites are of wurtzite structure. The zinc oxide crystallite growth rate is found to be different in different calcination temperature range. Photocatalytic activity of ZnO was checked by means of oxidative photocatalytic degradation (PCD) of resorcinol a potent endocrine disrupter in water under irradiation of sunlight in a batch photoreactor. The PCD efficiency was found to be dependent on crystallite growth rate and morphology of zinc oxide. The zinc oxide calcined from 400 °C to 550 °C exhibit same crystallite growth rate and showed maximum photocatalytic degradation of resorcinol. The PCD efficiency of zinc oxide was found to decrease with increase in calcination temperature as the particle size was increased. In addition to effect of calcination temperature, the influence of various other parameters such as photocatalyst amount, initial concentration of resorcinol and pH was also examined for maximum PCD of resorcinol. Neutral and basic pH is found to be favorable for chemical oxygen demand (COD) removal of resorcinol.

Effects of pH on hydrothermal synthesis and characterization of visible-light-driven BiVO4 photocatalyst

Abstract: BiVO 4 powders were hydrothermally synthesized at different pHs and characterized by XRD, SEM, DRS, nitrogen adsorption and Raman techniques. It revealed that the pH values of the precursors can influence significantly on the morphologies and structures of the products. The photocatalytic activities of the catalyst obtained were evaluated by the decolorization of methyl orange in aqueous solution under visible light irradiation. It was found that monoclinic BiVO 4 showed better photocatalytic activities than those shown by the tetragonal phase under visible light, which are attributed to its wider bandgap. The results also revealed that the dispersive particles with larger surface area represented higher activities than the coagulate ones when considering their photocatalysis.

Studies on catalytic behavior of Co–Ni–B in hydrogen production by hydrolysis of NaBH4

Abstract: Catalyst powders of Co–B, Ni–B, and Co–Ni–B, with different molar ratios of Co/Ni, were synthesized by chemical reduction of cobalt and nickel salts with sodium borohydride at room temperature. Surface morphology and structural properties of the catalyst powders were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. Surface electronic states and composition of the catalysts were studied by X-ray photoelectron spectroscopy (XPS). The catalytic activity of the powders has been tested by measuring the H 2 generation rate and yield by the hydrolysis of NaBH 4 in basic medium. Co–Ni–B with the Co/(Co + Ni) molar ratio ( χ Co ) of 0.85 exhibited much superior activity with highest H 2 generation rate as compared to the other powder catalysts. The enhanced activity obtained with Co–Ni–B ( χ Co = 0.85) powder catalyst could be attributed to: large active surface area and electron transfer by alloying large quantity of B to active Co and Ni sites on the surface of the catalyst. The electron enrichment, detected in the XPS spectra on active Co and Ni sites in Co–Ni–B, higher than that of Co–B and Ni–B seems to be able to facilitate the catalysis reaction by providing the negative charge electron required by the reaction. Synergetic effect of the Co and Ni atoms in Co–Ni–B catalyst is able to lower the activation energy up to 34 kJ mol −1 as compared to 45 kJ mol −1 obtained with Co–B powder. Structural modification, caused by the heat-treatment at 773 K for 2 h in Ar atmosphere, was not able to change the activity of the Co–Ni–B powder.

Basic ionic liquids supported on hydroxyapatite-encapsulated γ-Fe2O3 nanocrystallites: An efficient magnetic and recyclable heterogeneous catalyst for aqueous Knoevenagel condensation

Abstract: A series of basic ionic liquids functionalized hydroxyapatite-encapsulated γ-Fe2O3 magnetic nanoparticles were synthesized and characterized by XRD, XPS, HRTEM, IR and BET. These magnetic nanoparticles were used as efficient heterogeneous catalysts for aqueous Knoevenagel condensation under mild conditions and excellent results for extended substrates were obtained. In comparison with the control experiments, the high activity is ascribed to the cooperativity between the base sites generated by framework hydroxyapatite and supported basic ionic liquids. Separation of the catalyst from the reaction mixture was readily achieved by simple magnetic decantation and the catalyst could be easily recycled without appreciable loss of catalytic activity.

The confinement effect in zeolites

Abstract: As microporous materials, zeolites entrap molecules allowing their diffusion, adsorption and reaction within the channel system. This confinement affects the physico-chemistry of such incoming molecules in different ways. Derouane pioneered research onto the confinement effect in zeolites and extracted ideas and conclusions regarding physisorption, catalytic cracking and diffusion. His work on this topic is reviewed in this article and further updates on the confinement effects by other groups are also analysed.

Acetalization of glycerol using mesoporous MoO3/SiO2 solid acid catalyst

Abstract: Acetalization of glycerol with various aldehydes has been carried out using mesoporous MoO3/SiO2 as a solid acid catalyst A series of MoO3/SiO2 catalysts with varying MoO3 loadings (1–20 mol%) were prepared by sol–gel technique using ethyl silicate-40 and ammonium heptamolybdate as silica and molybdenum source respectively The sol–gel derived samples were calcined at 500 °C and characterized using various physicochemical characterization techniques The XRD of the calcined samples showed the formation of amorphous phase up to 10 mol% MoO3 loading and at higher loading of crystalline α-MoO3 on amorphous silica support TEM analyses of the materials showed the uniform distribution of MoO3 nanoparticles on amorphous silica support Raman spectroscopy showed the formation of silicomolybdic acid at low Mo loading and a mixture of α-MoO3 and polymolybdate species at high Mo loadings Moreover the Raman spectra of intermediate loading samples also suggest the presence of β-MoO3 Acetalization of glycerol with benzaldehyde was carried out using series of MoO3/SiO2 catalysts with varying MoO3 loadings (1–20 mol%) Among the series, MoO3/SiO2 with 20 mol% MoO3 loadings was found to be the most active catalyst in acetalization under mild conditions Maximum conversion of benzaldehyde (72%) was obtained in 8 h at 100 °C with 60% selectivity for the six-membered acetal using 20% MoO3/SiO2 Interestingly with substituted benzaldehydes under same reaction conditions the conversion of aldehydes decreased with increase in selectivity for six-membered acetals These results indicate the potential of this catalyst for the acetalization of glycerol for an environmentally benign process

Photocatalytic activity of V5+, Mo6+ and Th4+ doped polycrystalline TiO2 for the degradation of chlorpyrifos under UV/solar light

Abstract: TiO 2 photocatalysts were prepared by doping transition metal ions like V 5+ , Mo 6+ and an inner transition metal Th 4+ in the concentration range of 0.02–0.1% and were characterized by various analytical techniques. The photocatalytic activities of these catalysts were studied for the mineralization of chlorpyrifos (CP) as a probe molecule. X-ray diffraction results showed only anatase phase irrespective of nature, oxidation state and concentration of these dopants. The photocatalytic activity of undoped TiO 2 showed a better activity under UV light compared to doped catalysts. Under solar light illumination, the Th 4+ (0.06%)–TiO 2 showed highest activity for the mineralization of CP. This was attributed to the prolonged separation of photogenerated electron–hole pairs, high specific surface area of the catalyst and high concentration of surface adsorbed water/hydroxyl groups. Further large shift in the absorption band (460 and 482 nm) due to the creation of mid band gap states by Th 4+ dopant and also by its small crystallite size additionally contributes to the enhancement of the degradation process. The degradation pathway was followed by UV–vis spectroscopic and GC–MS analysis.

Hydrogen production from photocatalytic water splitting over mesoporous-assembled SrTiO3 nanocrystal-based photocatalysts

Abstract: Mesoporous-assembled SrTiO3 nanocrystal-based photocatalysts were synthesized via the sol–gel method with the aid of a structure-directing surfactant. The photocatalytic water splitting activity for hydrogen production over the mesoporous-assembled SrTiO3 nanocrystal-based photocatalysts with various hole scavengers: methanol, ethanol, 2-propanol, d -glucose, and Na2SO3, was investigated. The pristine mesoporous-assembled SrTiO3 photocatalysts exhibited much higher photocatalytic activity in hydrogen production via the photocatalytic water splitting using methanol as the hole scavenger than both non-mesoporous-assembled commercial photocatalysts: commercial SrTiO3 and commercial TiO2 (Degussa P-25), even if their specific surface areas were lower than those of both commercial photocatalysts. These results point out that the mesoporous assembly of nanocrystals with high pore uniformity plays a significant role, affecting the photocatalytic hydrogen production activity of the SrTiO3 photocatalysts. The Pt co-catalyst enhances the visible light harvesting ability of the mesoporous-assembled SrTiO3 photocatalyst and behaves as the active site for proton reduction, leading to photocatalytic activity enhancement under both UV and visible light irradiation. Methanol provided the highest photocatalytic hydrogen production enhancement. An optimum Pt loading of 0.5 wt.% on the mesoporous-assembled SrTiO3 photocatalyst provided the highest photocatalytic activity, with hydrogen production rates (from 50 vol.% methanol aqueous solution systems) of 276 and 188 μmol h−1 gcat−1 and quantum efficiencies of 1.9 and 0.9% under UV and visible light irradiation, respectively.

Heterogeneous acid catalysis by heteropoly acids: Approaches to catalyst deactivation

Abstract: Heterogeneous acid catalysis by heteropoly acids (HPAs) has the potential of great economic rewards and green benefits. Its application, however, has been limited to some extent because of a relatively low thermal stability of HPAs, hence difficulty of catalyst regeneration (decoking). The aim of this paper is to discuss approaches to the problem of catalyst deactivation that could be instrumental to achieve sustainable performance of solid HPA catalysts. These approaches include: developing new 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.

Synthesis and characterization of mesoporous phosphotungstic acid/TiO2 nanocomposite as a novel oxidative desulfurization catalyst

Abstract: A series of mesoporous phosphotungstic acid/TiO 2 (HPW/TiO 2 ) nanocomposites with various HPW contents have been synthesized by evaporation-induced self-assembly method. These nanocomposites were used as catalysts for oxidative desulfurization of model fuel, which was composed of dibenzothiophene (DBT) and hydrocarbon, and used H 2 O 2 as oxidant. These catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption isotherm, transmission electron microscopy (TEM), FTIR and UV–vis. Characterization results suggest that these mesoporous HPW/TiO 2 possessed relatively uniform channel-like pores with Barrett–Joyner–Halenda (BJH) pore size of about 4 nm. The Brunauer–Emmett–Teller (BET) surface of the mesoporous HPW/TiO 2 slightly increases with the increase of HPW content and reach to a peak value of 176 m 2 /g and 0.25 cm 3 /g when the HPW content is 30 wt%. Keggin-type heteropolyacids (HPAs) has been encapsulated into anatase TiO 2 framework and the average size of TiO 2 nanoparticles is 8 nm. Catalytic oxidation results show that the catalysts are very active in refractory bulky molecule organosulfur compounds in fuel oil. The oxidative removal of DBT increases as the HPW content increases. The mesoporous HPW/TiO 2 also shows high selectivity for DBT oxidation in the DBT–petroleum ether–benzene system. The selective desulfurization ratio reach to 95.2% with mesoporous HPW/TiO 2 (20 wt%) catalyst under the reaction condition of 333 K, 2 h. In addition, the mesoporous HPW/TiO 2 catalyst shows excellent reusing ability, which makes it a promising catalyst in oxidative desulfurization process.

Bismuth ferrite (BiFeO3) nanopowder prepared by sucrose-assisted combustion method: A novel and reusable heterogeneous catalyst for acetylation of amines, alcohols and phenols under solvent-free conditions

Abstract: Bismuth ferrite (BiFeO3) nanopowder was prepared by the novel combustion technique using sucrose as a fuel. The catalyst was characterized by using XRD, FT-IR, scanning electron microscope (SEM), transmission electron microscope (TEM), and BET surface area measurement and used as the heterogeneous catalyst for the acetylation reaction under solvent-free conditions. Efficient and selective acetylation of various amines, alcohols and phenols was carried out over BiFeO3 nanopowder by using acetic anhydride and/or acetyl chloride as the acetylating agents at room temperature under solvent-free conditions. The method is highly chemoselective – alcoholic hydroxyl group can be protected while phenolic hydroxyl group remains intact and the amine group can be acetylated in the presence of hydroxyl. This method is fast, high yielding, clean, safe, cost effective, compatible with the substrates having other functional groups and very suitable for practical organic synthesis. The catalyst can also be reused for acetylation without loss of catalytic activity.

Effect of preparation method on structural characteristics and propane steam reforming performance of Ni–Al2O3 catalysts

Abstract: Propane steam reforming was studied over Ni–Al 2 O 3 catalysts that were prepared by a conventional impregnation (IM) method and a one-step sol–gel (SG) technique. Both Ni–Al 2 O 3 catalysts showed similar initial activity. However, IM-Ni–Al 2 O 3 deactivated severely with time-on-stream of propane steam reforming. The catalyst prepared using a SG technique demonstrated stable catalytic performance. The two catalysts also showed major differences in product distribution, with SG catalyst giving much higher yields of hydrogen. Catalysts were characterized with temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), temperature-programmed oxidation (TPO), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. It was revealed that, with sol–gel preparation, highly dispersed small Ni crystallites are formed with a strong interaction with the support. This is shown to be important for coke suppression and catalyst stability.

Knoevenagel condensation and cyanosilylation reactions catalyzed by a MOF containing coordinatively unsaturated Zn(II) centers

Abstract: An aqueous solution of Zn(NO 3 ) 2 ·6H 2 O reacts with tetraethylammonium salt of the tripodal ligand tris -(4-carboxy-2-phenoxyethyl)amine (ptaH 3 ) at room temperature, to form infinite interlinked 2D metallocycles. These 2D networks stack to form an overall 3D structure ( 1 ) where lattice water molecules occupy the metallocyclic cavities. On heating to 110 °C for 5 h under vacuum, 1 loses metal bound water molecules as well as lattice ones without framework collapse and leaves the metal ion coordinatively unsaturated. The coordination space in the structure ( 1a ) can be utilized for Knoevenagel and cyanosilation reactions to give biologically important molecules. These reactions are catalyzed by Zn(II) centers which are coordinatively unsaturated. Larger carbonyl substrates cannot diffuse through the pores of 1a , and afford poor yields of the desired products.

Heteropolyacid (H3PW12O40) supported MCM-41: An efficient solid acid catalyst for the green synthesis of xanthenedione derivatives

Abstract: HPWA/MCM-41 mesoporous molecular sieves of appropriate ratios were prepared by loading HPWA on siliceous MCM-41 by the wet impregnation method. The prepared HPWA/MCM-41 materials were characterized by X-ray diffraction analysis (XRD) and BET surface area and FT-IR measurements. The morphology of mesoporous materials was studied by TEM observation. The catalytic activity of the above materials was tested for the condensation of dimedone (active methylene carbonyl compound) and various aromatic aldehyes under liquid phase conditions at 90 °C. The products were confirmed by FT-IR, 1H NMR and 13C NMR studies. HPWA supported MCM-41 catalysts catalyses efficiently the condensation of dimedone and aromatic aldehydes in ethanol and other solvents under liquid phase conditions to afford the corresponding xanthenedione derivatives. Activities of the catalysts follow the order: HPWA/MCM-41(20 wt.%) > HPWA/MCM-41(30 wt.%) > H3PW12O40·nH2O > HPWA/MCM-41(10 wt.%) > HPWA/SiO2 (20 wt.%) > HM (12) > Hβ (8) > Al-MCM-41 (50). Various advantages associated with these protocols include simple workup procedure, short reaction times, high product yields and easy recovery and reusability of the catalyst.

Sulfonated organic heteropolyacid salts: Recyclable green solid catalysts for esterifications

Abstract: A family of solid organic heteropolyacid (HPA) salts were prepared by combining Keggin heteropolyanions with ionic liquid (IL)-forming cations functionalized by propane sulfonate (PS). Their catalytic activities were evaluated in esterifications, including the testing of the influence of organic cations, function of heteropolyanions, scope of reactions, optimization of reaction conditions, and catalytic reusability. The obtained catalysts caused a liquid–liquid biphasic esterification system, presenting high yield and selectivity for target esters, and after reaction, they appeared in solid state again, which could be easily recovered and quite steadily reused demonstrated by a seven-run recycling test. The highly efficient and environmentally benign performance of this family of catalysts is due to the pseudoliquid behavior of HPA salts that allows PS acidic species in the bulk of the heteropoly compound acting fully as active centers for esterification, as well as the stabilization function of heteropolyanion on carbonium ion intermediates created at acid sites.

A Novel Homogeneous Fenton-like System with Fe(III)-Phosphotungstate for Oxidation of Organic Compounds at Neutral pH Values.

Abstract: Ferric ion (Fe[III]) catalyzes the decomposition of hydrogen peroxide (H(2)O(2)) into strong oxidants such as hydroxyl radical ((•)OH) and ferryl ion (Fe[IV]) through the redox cycling of the iron couple (Fe[II]/Fe[III]). The use of these reactions for the catalytic oxidation of organic compounds is usually limited to the acidic pH region due to the low solubility of Fe(III) and the low efficiency of oxidant production at neutral pH values. The addition of phosphotungstate (PW(12)O(40) (3-)), a polyoxometalate extends the working pH range of the Fe(III)/H(2)O(2) system up to pH 8.5. PW(12)O(40) (3-) forms a soluble complex with iron that converts H(2)O(2) into oxidants. The coordination of Fe(II) by PW(12)O(40) (3-) also alters the mechanism of the reaction of Fe(II) with H(2)O(2) at neutral pH, resulting in formation of an oxidant capable of oxidizing aromatic compounds. The base-catalyzed hydrolysis of PW(12)O(40) (3-) gradually results in inactivation of the catalyst. In the absence of Fe(III), PW(12)O(40) (3-) was completely hydrolyzed after 1 day at pH 7.5, whereas the Fe(III)-PW(12)O(40) (3-) complex was active for at least four days under the same conditions.

Structure-dependent photocatalytic activities of MWO4 (M = Ca, Sr, Ba)

Abstract: The photocatalytic activities of the isostructural photocatalysts MWO4 (M = Ca, Sr, Ba) for decomposing methyl orange, which were synthesized by a solid state reaction, were investigated. In the experiments, the photocatalytic activity is in the increasing order of CaWO4 < SrWO4 < BaWO4 under both neutral and acidic conditions. The factors, which influence the photocatalytic processes and the final activity, were analyzed the difference of their photocatalytic behaviors. The further investigation indicates that the higher structural openness degree, corresponding to a lower packing factor, leads to the better photocatalytic activity.

Cellulose sulfuric acid: An efficient biodegradable and recyclable solid acid catalyst for the one-pot synthesis of aryl-14H-dibenzo[a.j]xanthenes under solvent-free conditions

Abstract: The condensation of β-naphthol with aromatic aldehydes in the presence of cellulose sulfuric acid under solvent-free media to afford the corresponding aryl-14H-dibenzo [a.j]xanthenes in excellent yields and short reaction times is described. The reaction work-up is very simple and the catalyst can be easily separated from the reaction mixture and reused several times in subsequent reactions.

Selective oxidation of benzyl alcohol to benzaldehyde with hydrogen peroxide over alkali-treated ZSM-5 zeolite catalysts

Abstract: A stable, economic and high active catalyst for selective oxidation of benzyl alcohol (BzOH) was developed by treating ZSM-5 zeolite with sodium hydroxide solution. The changes resulted by alkali-treatment in crystallinity, composition, structure parameters and acidities of alkali-treated ZSM-5 zeolites were examined by XRD, ICP, N2 adsorption-desorption, scanning electron micrographs (SEM), temperature program desorption (TPD) and Fourier transform infrared spectroscopic (FT-IR). The results showed that the specific MFI structure was preserved and the intrinsic micropores were kept without obvious change, the amount of Lewis acid sites and the external surface area were evidently increased after alkali-treatment. Without any organic solvent, the catalytic performance of alkali-treated ZSM-5 zeolite was investigated in selective oxidation of BzOH with hydrogen peroxide (H2O2), and the effects of reaction temperature, reaction time, dosage of catalyst, dosage of H2O2 and SiO2/Al2O3 ratio of as-received zeolites on catalytic selective-oxidation of BzOH were investigated. The results showed that the conversion of BzOH and the selectivity to benzaldehyde (BzH) were about 53% and about 86% respectively under reflux for 4 h in water. At the same time, the catalyst was very stable and could be reused for more than six times.

Kinetic studies on the photocatalytic degradation of Direct Yellow 12 in the presence of ZnO catalyst

Abstract: The photocatalytic degradation of Direct Yellow12 (DY12) was studied by a batch process using ZnO as the catalyst on irradiation with UV light. The influence of pH, catalyst weight and initial concentration of the dye on the degradation of the dye was investigated. The degradation of the dye was found to be effective in alkaline media. The dye degradation obeyed first order kinetics and explained on the basis of Langmuir–Hinshelwood mechanism. The oxidants involved were identified as positive hole, hydroxyl radical and superoxide anion radical.

The role of water in the catalysis on solid heteropolyacids

Abstract: Heteropolyacids (HPAs) are used as catalysts for many acid reactions in both homogeneous and heterogeneous systems. For such systems water, as a vapour and/or the crystallization water, plays an essential role. The review surveys the structure of HPA hydrates and the physicochemical properties of HPA–water system. Especially, tendency to the formation of protonated water clusters in the bulk of the solid, together with acid strength and sorption properties are described. The catalytic part of the paper includes following topics: the role of water as a substrate (hydration of olefins), product (dehydration of alcohols) and as water formally not participating in the catalytic reaction (etherification).

A simple preparation of an efficient heterogeneous gold catalyst for aerobic amine oxidation

Abstract: Numerous sophisticated techniques have been applied in the past years for the preparation of supported gold catalysts designed for oxidation reactions. Here we show that it is possible to arrive at an efficient catalyst without using any conventional step for the synthesis of supported gold nanoparticles. The reaction studied was the oxidative dehydrogenation of amines to imines with molecular oxygen. The catalyst precursors Au(OAc)3 and an oxide support were simply added to the reaction mixture and the active gold nanoparticles on the support were formed in situ. The corresponding imines were produced in 89–100% yield and the catalyst was proved to be truly heterogeneous and recyclable. Despite of the simplicity of the method, the activity of the catalysts was comparable, or even superior, to other known catalysts of the oxidative dehydrogenation of amines and to some commercially available supported gold catalysts.

Role of yttrium loading in the physico-chemical properties and soot combustion activity of ceria and ceria-zirconia catalysts

Abstract: Ce 1− x Y x O 2 and Ce 0.85− x Zr 0.15 Y x O 2 mixed oxides have been prepared by 1000 °C-nitrates calcination to ensure thermally stable catalysts. The physico-chemical properties of the mixed oxides have been studied by N 2 adsorption at −196 °C, XPS, XRD, Raman spectroscopy and H 2 -TPR, and the catalytic activity for soot oxidation in air has been studied by TG in the loose and tight contact modes. Yttrium is accumulated at the surface of Ce 1− x Y x O 2 and Ce 0.85− x Zr 0.15 Y x O 2 , and this accumulation is more pronounced for the former formulation than for the latter, because the deformation of the lattice due to zirconium doping favours yttrium incorporation. Yttrium and zirconium exhibit opposite effects on the surface concentration of cerium; while zirconium promotes the formation of cerium-rich surfaces, yttrium hinders the accumulation of cerium on the surface. For experiments in tight contact between soot and catalyst, all the Ce 1− x Y x O 2 catalysts are more active than bare CeO 2 , and Ce 0.99 Y 0.01 O 2 is the most active catalyst. The benefit of yttrium doping in catalytic activity of ceria can be related to two facts: (i) the Y 3+ surface enrichment hinders crystallite growth; (ii) the surface segregation of Y 3+ promotes oxygen vacancies creation. High yttrium loading ( x = 0.12) is less effective than low dosage ( x = 0.01) because yttrium is mainly accumulated at the surface of the particles and hinders the participation of cerium in the soot oxidation reaction, which is the active component. For the mixed oxides with formulation Ce 0.85− x Zr 0.15 Y x O 2 (operating in tight contact) the effect of zirconium on the catalytic activity prevails with respect to that of yttrium. For experiments in loose contact between soot and catalyst, the catalytic activity depends on their BET surface area, and the catalysts Ce 0.85− x Zr 0.15 Y x O 2 (BET = 10–13 m 2 /g) are more active than the catalysts Ce 1− x Y x O 2 (BET = 2–3 m 2 /g). In the loose contact mode, the yttrium doping and loading have a minor or null affect on the activity, and the stabilising effect of the BET area due to zirconium doping prevails.