Applied Catalysis A, General (v.433-434, #C)
Editorial Board (CO2).
Platinum supported on alkaline and alkaline earth metal-doped alumina as catalysts for dry reforming and partial oxidation of methane by A. Ballarini; F. Basile; P. Benito; I. Bersani; G. Fornasari; S. de Miguel; S.C.P. Maina; J. Vilella; A. Vaccari; O.A. Scelza (1-11).
Catalytic activity in the DR reaction at 750 °C (τ = 0.15 s)Display Omitted► Pt catalysts supported on Na, K or Mg-doped alumina were tested in the CPO and DR. ► The catalytic performances in the tests were dependent on the support dopants. ► Highest Pt content supported on Mg-Al2O3 promoted the catalytic activity in the CPO. ► Highest Pt content supported on K-Al2O3 promoted the catalytic activity in the DR. ► No difference was observed due to the addition of doping element in the PtO x Cl y reduction.Pt catalysts with low metal loadings (0.02, 0.1 and 0.5 wt%) supported on alkaline (Na and K) or alkaline earth (Mg) metals-doped alumina were tested in the catalytic partial oxidation and dry reforming of methane. Supports were characterized by X-ray diffraction and also by determining their BET surface area, temperature-programmed desorption of CO2, and isopropanol dehydration; while catalysts were characterized by X-ray diffraction, temperature programmed reduction, tests of cyclohexane dehydrogenation, temperature-programmed oxidation, and transmission electronic microscopy. The presence of the dopants modified the thermal stability of the γ-Al2O3 phase by calcination at 1000 °C and the acidity of the support. The γ → θ transition took place for K- and Na-doped catalysts, the acidity being almost suppressed. Conversely, the Mg-doped γ-Al2O3 was thermally stable, and the catalysts still showed some acidic sites. The catalytic performances in both partial oxidation and dry reforming processes were dependent on the support dopants, with a more notable effect observed at low-noble-metal loadings. K- and Na-doped catalysts showed poor activities in the catalytic partial oxidation reaction, whereas the presence of Mg in the alumina promoted the catalytic activity. In the dry reforming reaction an improvement was found in the catalytic activity for the sample with the highest Pt content; moreover, the K-doped catalysts were slightly more efficient.
Keywords: Methane; H2 production; Catalytic partial oxidation; Dry reforming; Supported Pt; Alkaline or alkaline earth metal-doped alumina;
A new heterogeneous acid catalyst system for esterification of free fatty acids into methyl esters by Peng-Lim Boey; Shangeetha Ganesan; Gaanty Pragas Maniam; Melati Khairuddean; Siew-Ee Lee (12-17).
Display Omitted► Lauric acid esterification with ferric-alginate beads gave 98% methyl laurate. ► The beads were reusable up to 7 times without pre-treatment. ► Iron content determined by AAS and TGA was 0.175 and 0.189 g Fe/g, respectively. ► The catalyst is desirable for biodiesel production from low quality oil or fats.A new heterogeneous acid catalyst system for production of environmentally friendly fuel, biodiesel was created from ferric sulfate and non-toxic, inexpensive source of biopolymer, sodium alginate. The catalyst, in the form of ferric-alginate beads produced from the reaction of 2 wt.% sodium alginate gel with 0.1 M ferric sulfate solution gave excellent methyl ester conversion of 98% with mild reaction conditions. The esterification of 0.5 g lauric acid was carried out at optimum conditions; 16 wt.% of ferric-alginate beads (2.8 wt.% Fe) methanol refluxing temperature, 15:1 methanol to lauric acid molar ratio for 3 h. The ferric-alginate beads were reusable up to 7 times without any pre-treatment. Characterization of the ferric-alginate beads showed the formation of FeOOH that held the alginate chain in place. Thermal analysis showed that the beads are able to withstand the refluxing temperature without degradation. Iron content was found to be 0.175 g Fe/g beads as determined by AAS and 0.189 g Fe/g beads as determined by TGA. Easy catalyst separation, reusability and ability of the ferric-alginate beads to esterify lauric acid to give high conversion of methyl laurate makes this catalyst desirable for biodiesel production from high free fatty acid oils.
Keywords: Sodium alginate; Ferric-alginate; Heterogeneous acid catalyst; Biodiesel; Methyl ester;
Mesoporous I-Ag codoped titania and alumina modified titania catalysts: Synthesis, characterization and photocatalytic properties by Liang Liao; Conrad W. Ingram (18-25).
.Display Omitted► High surface area mesoporous I-Ag-TiO2 and I-Ag-TiO2-Al2O3 photocatalyts synthesized. ► I-Ag-TiO2 and I-Ag-TiO2-Al2O3 shifted UV–vis adsorption into the visible range.► The presence of Ag facilitated the incorporation of I in the structure. ► Ag-I-TiO2 and Ag-I-TiO2-Al2O3 with visible light photocatalysis up to 12× P25.Mesoporous iodine and silver codoped titania and alumina modified titania photocatalysts were synthesized by a two-step surfactant-templated hydrothermal route and characterized by X-ray diffraction, XPS, UV–visible diffuse reflectance spectroscopy and nitrogen adsorption. The mesoporous materials had surface areas of 2.6–5.3 times that of Degussa P25. The I-Ag codoped mesoporous titania samples exhibited a bicrystalline framework of rutile and anatase with rutile fractions of 23% and 26%, respectively, whereas the alumina-containing I-Ag codoped materials yielded anatase as the only crystalline phase. The I-Ag codoped photocatalysts with Ag/Ti mole ratio of 1.6% and 2.0% showed catalytic activity 3.3 times and 12 times higher than Degussa P25 under halogen visible and visible light (>400 nm) in photodecomposing methyl orange, respectively. The high performance of I-Ag codoped titania and alumina modified titania photocatalysts under visible light is attributed to the combined effects of large surface area, lower band gap energies and mesoporous structure.
Keywords: Iodine and silver modified titania; Photocatalysts; Mesoporous titania; Methyl orange photodecomposition; Anatase–rutile titania;
Enhancement of catalytic activity over TiO2-modified Al2O3 and ZnO–Cr2O3 composite catalyst for hydrogen production via dimethyl ether steam reforming by Mei Yang; Yong Men; Shulian Li; Guangwen Chen (26-34).
Display Omitted► ZnO–Cr2O3 coupled with Al2O3 or TiO2–Al2O3 was an efficient catalyst for DME SR. ► DME hydrolysis and SR was remarkably improved by the addition of TiO2 to Al2O3. ► TiO2 dopant tuned the acid properties of Al2O3, resulting in a superior activity. ► The catalytic activity of ZnCr–3% TiAl = 2:1 was stable in 150 h continuous test.The dimethyl ether steam reforming (DME SR) was carried out over the composite catalyst of ZnO–Cr2O3 coupled with Al2O3, TiO2 or TiO2–Al2O3 in the microreactor. The results showed that the catalytic activities were greatly enhanced over the composite catalyst of ZnO–Cr2O3 combined with TiO2–Al2O3 (ZnCr–TiAl) in comparison to those combined with Al2O3 or TiO2 in DME SR. By evaluating the catalytic activity of solid acids in DME hydrolysis, it was proposed that the better performance of TiO2–Al2O3 in DME hydrolysis contributed to the superior activity of ZnCr–TiAl in DME SR, indicating a higher DME hydrolysis activity favored DME SR. In view of the characterization of N2 physisorption, scanning electron microscope, X-ray diffraction and NH3 temperature-programmed desorption, the promotion effect of TiO2 on both DME hydrolysis and steam reforming was discussed in terms of the modification effect of TiO2 on the acid properties of Al2O3 surface. The acid strength or total acid amount was enhanced by the addition of different TiO2 content. In the 150 h medium stability test, there was no obvious deactivation for ZnCr–TiAl catalyst with the H2 production rate of 345 mol h − 1 k g cat − 1 and the CO selectivity in the dry reformate remained below 6%. The characterization results of the used catalyst revealed that no change in the crystalline phase and size occurred on the spent catalyst.
Keywords: Dimethyl ether; Steam reforming; Activity enhancement; H2 production; ZnO–Cr2O3; TiO2–Al2O3;
Isolation and characterization of intermediate catalytic species in the Zn-catalyzed glycerolysis of urea by Jong-Ho Park; Ji Sik Choi; Soo Kyoung Woo; Sang Deuk Lee; Minserk Cheong; Hoon Sik Kim; Hyunjoo Lee (35-40).
Display Omitted► ZnCl2 showed the highest catalytic activity. ► Zinc glycerolate (Zn(C3H6O3)) and NH4Cl were formed from ZnCl2 via Zn(NH3)2Cl2. ► Zn(C3H6O3) plays a role in activating urea and NH4Cl functions to activate glycerol.Homogeneous zinc-catalyzed synthesis of glycerol carbonate from the reaction of glycerol with urea was investigated. Among the zinc-based catalysts tested, ZnCl2 showed the highest catalytic activity. Spectroscopic and elemental analyses of the zinc species, isolated from the reaction conducted in the presence of ZnCl2, revealed that Zn(NH3)Cl2 was generated first as an intermediate species, which in turn reacted with glycerol to produce zinc glycerolate, Zn(C3H6O3) and NH4Cl. The activity of Zn(C3H6O3) was considerably lower than that of ZnCl2, but the activity was greatly enhanced by the combined use of NH4Cl, implying that both Zn(C3H6O3) and NH4Cl were functioning as essential ingredients for the carbonylation of glycerol by urea. The formation of Zn(C3H6O3) was also observed when ZnBr2, ZnI2, ZnF2, Zn(NO3)2, Zn(CH3CO2)2, or ZnO was used as the catalyst.
Keywords: Glycerol; Glycerol carbonate; Urea; Glycerolysis; Zinc halides; Homogeneous catalysis;
Catalytic performance of MoVTeNbO catalyst supported on SiC foam in oxidative dehydrogenation of ethane and ammoxidation of propane by T.T. Nguyen; L. Burel; D.L. Nguyen; C. Pham-Huu; J.M.M. Millet (41-48).
Display Omitted► Novel catalysts based on silicon carbide foam coated by MoVTeNbO oxides were synthesized. ► Catalyst's coatings exhibited good mechanical properties and contain M1 phase as major component. ► The structured catalyst appeared highly efficient and stable for propane ammoxidation.MoVTeNbO catalysts have been supported on pre-oxidized SiC foam by dip coating from slurry containing the precursors for all constituents and tested as catalysts for the oxidative dehydrogenation of ethane and the ammoxidation of propane. The characterization of the coating obtained by different techniques showed that a one layer coating contained almost no active M1 phase and mainly M2 phase whereas a two layers coating presented a significant amount of M1 phase. The structured catalyst thus obtained with two layers appeared highly efficient and stable in both reactions between 380 and 420 °C and the oxide coating exhibited fairly good mechanical properties. When compared to the most efficient powdered pure M1 phase in the case of ethane oxidative dehydrogenation and M1 + M2 phase mixture in the case of propane ammoxidation, the coated foam appeared less active; the reduced activity was attributed to the lower content in M1 phase of the supported catalyst. The selectivity to ethylene was lower, that to acrylonitrile was comparable; the decrease in ethylene selectivity was due to the presence of other active but not selective phases like TeMo5O15 and Mo0.97V0.95O5. In the case of acrylonitrile the synergy effect that takes place between the M1 and M2 phases also took place between the Mo0.97V0.95O5 phase and the M2 phase and maintained the selectivity to acrylonitrile. Improvements in preparation conditions are still possible to open the door to intensification and miniaturization on the process of propane ammoxidation on these efficient coated SiC foam structured reactors.
Keywords: Ethane oxidative dehydrogenation; Ethylene; Propane ammoxidation; Acrylonitrile; M1-phase; MoVTeNbO oxide catalysts; Milli-structured reactor; Silicon carbide foam;
WO3 monolayer loaded on ZrO2: Property–activity relationship in n-butane isomerization evidenced by hydrogen adsorption and IR studies by Ainul Hakimah Karim; Sugeng Triwahyono; Aishah Abdul Jalil; Hideshi Hattori (49-57).
Display Omitted► The addition of WO3 modified the nature and concentration of the acidic sites. ► 13 wt% WO3 ―ZrO2 (13WZ) led to the strongest Lewis and Brønsted acid sites. ► 13WZ exhibited the greatest ability and capacity to form and to take up H+. ► The H2 uptake capacity was shown to be directly correlated with the activity of WZ. ► Permanent H+ could not be directly associated with the activity of WZ.The property–activity relationship of WO3 supported on ZrO2 (WZ) was evaluated in n-butane isomerization for a series of catalysts with WO3 loading ranging from 5 to 20 wt% on ZrO2. The catalysts were prepared by incipient-wetness impregnation of Zr(OH)4 with an aqueous solution of (NH4)6[H2W12O40·nH2O], followed by drying and calcination at 1093 K. The introduction of WO3 continuously increased the tetragonal phase of ZrO2, WO3 surface density and coverage. The specific surface area and total pore volume passed through a maximum of WO3 loading at 13 wt%; this loading corresponds to 5.9 WO3/nm2 and is near the theoretical monolayer-dispersed limit of WO3 on ZrO2. The IR results indicate that the presence of WO3 eroded the absorbance bands at 3738 and 3650 cm−1 corresponding to bibridged and tribridged hydroxyl groups up to near the monolayer-dispersed limit of WO3. A new broad and weak band appeared, centered at 2930 cm−1, indicating the presence of bulk crystalline WO3 for WO3 coverage exceeding the theoretical monolayer-dispersion limit. In addition to the band at 2930 cm−1, two W＝O stretching bands were observed at about 1021 and 1014 cm−1 for all WZ catalysts, confirming the existence of W＝O connected to coordinative unsaturated (cus) Zr4+ through O and to the other W through O, respectively. Pyridine adsorbed IR and NH3-TPD revealed that the presence of WO3 modified the nature and concentration of acidic sites. The highest acidity was observed with 13 wt% loading WO3. The decrease in the intensity of peaks due to increasing WO3 loading was much higher on Lewis acid sites than on Brønsted acid sites. Hydrogen adsorption isotherms and the IR results for hydrogen adsorption on preadsorbed pyridine were used to evaluate the formation of active protonic acid sites from molecular hydrogen. The catalyst with 13 wt% WO3 loading showed the maximum hydrogen uptake capacity and formation of protonic acid sites. These results show a direct correlation with the activity of WZ in n-butane isomerization at 573 K in which 13 wt% WO3 loading on ZrO2 yielded the highest amount of isobutane. It is suggested that the presence of strong Lewis acid sites on monolayer-dispersed WO3 facilitates the formation of protonic acid sites from hydrogen in the gas phase which act as active sites in n-butane isomerization. The presence of permanent Brønsted acid sites could not be directly associated with activity. In fact, no isomerization activity was observed in the absence of hydrogen.
Keywords: WO3 ―ZrO2; Protonic acid sites; Lewis acid sites; Hydrogen uptake; n-Butane isomerization;
Fischer–Tropsch synthesis using H2/CO/CO2 syngas mixtures: A comparison of paraffin to olefin ratios for iron and cobalt based catalysts by Yali Yao; Xinying Liu; Diane Hildebrandt; David Glasser (58-68).
Display Omitted► The product selectivities between the feeds of CO2-rich syngas and CO-rich syngas are far different. ► P/O ratio for FTS is strongly dependent on the operating conditions. ► Linear relationship between P (n+1)/O (n+1) and P (n)/O (n) holds for many experiments. ► Vapor–liquid equilibrium and quasi reaction equilibrium have been used to explain the phenomenon.Fischer–Tropsch synthesis (FTS) using H2/CO/CO2 syngas mixtures over cobalt and iron based catalysts was carried out in a fixed-bed reactor. CO2 rich feeds produce products that are mostly light hydrocarbons with higher molar paraffin to olefin (P/O) ratio, whereas CO rich feeds shift the product composition to an FT type product with higher olefin product selectivity over both iron and cobalt based catalysts. Although the P/O ratio for FTS is strongly dependent on the operating conditions, the experimental evidence shows that the linear relationship between P (n+1)/O (n+1) and P (n)/O (n) holds for a large number of experiments. It is also shown to be independent of the type of the reactor, the composition of the syngas, reaction conditions and the kind of catalyst. Two features about the ratio of ξ = [P (n+1)/O (n+1)]/[P (n)/O (n)] for the FT products have been identified: (1) with n > 2, the experimental values of ξ n>2 are higher than 1, fairly constant and independent of chain length n; (2) with chain length n = 2, the ratio of P 3/O 3 to P 2/O 2 (ξ n=2) is significantly different, and shows that ξ n=2 ≪ ξ n>2. An equilibrium hypothesis is considered in an attempt to explain this experimental phenomenon.A simple vapor–liquid equilibrium (VLE) model indicates that the ratio of P (n+1)/O (n+1) to P (n)/O (n) changes in a range of (1, 1/β), where β is the variation of the vapor pressure coefficient, which is related to the incremental energy of vaporization per CH2 unit of the hydrocarbon chain. Our experimental results support the expression when the chain length n > 2. But with chain length n = 2, this expression is unable to explain the relationship between P 3/O 3 and P 2/O 2. Another model, based on quasi reaction equilibrium, is developed to explain the linear relationship between P (n+1)/O (n+1) and P (n)/O (n). We assume that the reaction of C n+1H2n+2 + C n H2n+2 = C n+1H2n+4 + C n H2n reaches quasi-equilibrium. Because the experimental results are quite close to the equilibrium calculations, we postulate that the product distribution might be determined by considering reaction equilibrium.
Keywords: Fischer–Tropsch synthesis; CO hydrogenation; CO2 hydrogenation; Paraffin to olefin ratio; Vapor–liquid equilibrium; Quasi-equilibrium;
In2O3-doped Pt/WO3/ZrO2 as a novel efficient catalyst for hydroisomerization of n-heptane by Yingying Nie; Shuning Shang; Xin Xu; Weiming Hua; Yinghong Yue; Zi Gao (69-74).
Display Omitted► Pt/WO3/ZrO2 catalyst was modified by small amounts of In2O3. ► Doping In2O3 into Pt/WO3/ZrO2 enhanced Pt dispersion and Pt0/Pt2+ ratio. ► Brønsted acid sites were generated under reaction conditions. ► The addition of In2O3 to Pt/WO3/ZrO2 improved the catalytic performance markedly. ► Pt/WO3/In2O3-ZrO2 exhibited a constant catalytic performance for at least 80 h.A series of Pt catalysts supported on In2O3-doped (In/Zr molar ratio = 0.01–0.04) WO3/ZrO2 (9–24 wt.% WO3) have been tested for the hydroisomerization of n-heptane at 473 K. Several techniques including X-ray diffraction, N2 adsorption, CO chemisorption and X-ray photoelectron spectroscopy were applied to characterize the physicochemical properties of the as-synthesized materials. The catalytic activity is strongly dependent on the surface WO3 loading and In/Zr ratio. The maximum activity was observed for the sample with a In/Zr molar ratio of 0.02, which gave 72% n-heptane conversion and 96% C7 isomer selectivity at 473 K, and can be kept constant over 80 h under reaction reactions. The incorporation of small amounts of In2O3 into Pt/WO3/ZrO2 increases the activity significantly (from 37% to 72%) and improves the isomerization selectivity moderately (from 90% to 96% at a conversion of 72%). The results of cumene cracking reveal that the remarkable activity and selectivity of the In2O3-promoted catalysts are caused by an enhancement in the number of Brønsted acid sites under reaction conditions and in the hydride transfer reaction rate of isomerized carbenium ions with hydride ions originating from hydrogen molecules.
Keywords: n-Heptane isomerization; Pt/WO3/ZrO2; In2O3 doping; Promoting effect;
Hydrothermal crystallization of titania on silver nucleation sites for the synthesis of visible light nano-photocatalysts—Enhanced photoactivity using Rhodamine 6G by Chee Meng Ng; Pao-Chi Chen; Sivakumar Manickam (75-80).
Display Omitted► Silver-titania nanoparticles has been developed by using a hydrothermal process. ► Silver has been used as nucleation sites to induce crystallization. ► The pH of titania precursor was observed to influence the phase of titania formed. ► The visible light photodegradation rate of Rhodamine 6G were significantly higher. ► A lower (1%) or higher (≥5%) silver concentration diminished the degradation rates.The doping of titania with metal ions is a well-established method for prolonging the recombination rate of photoexcited electrons to enhance its photocatalytic activity in the visible light region. In this work, silver–titania nanocomposite catalysts were successfully synthesized using an alternative hydrothermal synthetic pathway where suspended silver nanoparticles served as nucleation sites for the crystallization of titania. EDX analysis and TEM imaging were used to confirm the presence of silver on the titania. From the XRD results, titania produced by the present hydrothermal method were mainly in the anatase phase, while the addition of silver seemed to lower the content of rutile and brookite forms. Photocatalytic studies conducted by observing the photodegradation of Rhodamine 6G showed a marked improvement in visible light photocatalytic activity for silver-doped samples, although a diminishing effect in degradation rates was observed when silver concentration was increased beyond 3 mol%.
Keywords: Hydrothermal crystallization; Silver; Titania; Visible light; Nano; Photocatalysis; Nucleation; Rhodamine 6G;
New insights into the relationship between photocatalytic activity and photocurrent of TiO2/WO3 nanocomposite by Yuan Liu; Changsheng Xie; Jie Li; Tao Zou; Dawen Zeng (81-87).
Display Omitted► The relationship between photocatalytic activity and photocurrent is important. ► We disproved the common sense of the relationship in the previous researches. ► A more comprehensive relationship was proposed based on TiO2/WO3 composite. ► Carrier mobility and photocurrent in pollutant ambience should be considered. ► The pluralism of the conception of photocatalytic activity should be noted.The photocurrent has been regarded as the most efficient method to evaluate the photocatalytic activity of composite photocatalyst. A relationship is commonly recognized: the higher the photocurrent is, the higher the e−–h+ separation efficiency is, and thus the higher the photocatalytic activity is. In this paper, we use the TiO2/WO3 composite as a model heterojunction system to argue about this viewpoint, and try to explore a more comprehensive relationship. Our research reveals that there is no direct relation between photocurrent, charge separation efficiency and photocatalytic activity. It is shown that the photocurrent combined with the carrier mobility is essential in the analysis of the charge separation efficiency. In addition, the charge separation efficiency cannot be responsible for the photocatalytic activity, since it does not include the information on the redox ability of the charge carrier. It is confirmed that the photocatalytic activity which is a pluralistic concept includes three levels of degradation efficiency, initial reaction rate and mineralization ability. The difference in each level is determined by the band structures, the matched band potentials and the target pollutants. Therefore, we also propose that the introduction of pollutant ambience is needed in photocurrent test. The ratio of photocurrent in air to that in pollutant ambience can be used as an index to evaluate the initial reaction rate of photocatalytic activity.
Keywords: Photocatalysis; Photocurrent; Heterojunction; TiO2/WO3; Toluene;
Low temperature gas-phase oxidation of ethanol over Au/TiO2 by Vladimir I. Sobolev; Konstantin Yu. Koltunov; Olga A. Simakova; Anne-Riikka Leino; Dmitry Yu. Murzin (88-95).
Display Omitted► Au/TiO2 catalysts with Au loadings ranging from 0.5 to 7.0 wt% are prepared. ► Gas-phase aerobic oxidation of ethanol is catalyzed by Au/TiO2 to give acetaldehyde. ► The catalytic activity occurred at extraordinarily low temperature, around 125 °C. ► The mechanistic aspects of the unusual catalytic behavior of Au/TiO2 are discussed.A set of nanostructured gold catalysts with Au loadings ranging from 0.5 to 7.0 wt% on a TiO2 support was prepared and evaluated in a gas-phase oxidation of ethanol with molecular oxygen. The catalytic activity was measured in a flow reactor under atmospheric pressure using temperature programmed heating. The catalysts with Au loadings varying from 2 wt% to 7 wt% displayed two distinct temperature dependent peaks of catalytic activity in ethanol oxidation to acetaldehyde. The temperature, at which the first peak occurred, 125 °C, is extraordinarily low for the gas-phase oxidation of ethanol. In contrast, gold supported on Al2O3 and SiO2, which was prepared and tested in the same reaction for the purpose of comparison, showed conventional, steady increase of ethanol conversion at temperatures above 200 °C. The results demonstrated a possibility to employ Au/TiO2 catalysts in selective low temperature gas phase oxidation of ethanol. The probable reasons of the unusual catalytic behavior of Au/TiO2 are discussed.
Keywords: Ethanol; Selective oxidation; Gold; Nanoparticles; Au/TiO2;
A kinetics study for the oxidative coupling of methane on a Mn/Na2WO4/SiO2 catalyst by T.P. Tiemersma; M.J. Tuinier; F. Gallucci; J.A.M. Kuipers; M. van Sint Annaland (96-108).
Display Omitted► Mn/Na2WO4/SiO2 catalyst for OCM was prepared and investigated. ► The catalyst has excellent long-term stability and moderate catalytic activity. ► A possible reaction path has been proposed for OCM. ► The effect of both homogeneous and heterogeneous reactions has been evaluated. ► Kinetic expressions have been derived to be used for modeling of chemical reactors.This paper presents an experimental kinetic study for the oxidative coupling of methane (OCM) over a Mn/Na2WO4/SiO2 catalyst prepared by incipient wetness impregnation. Because the catalyst is a reducible metal oxide, the stability of the catalyst has been assessed by Thermo Gravimetric Analysis (TGA). These experiments show that the catalyst has to be pre-treated with oxygen in order to obtain high C2 selectivity (around 85%) and that a low oxygen partial pressure during the OCM reactions is already sufficient to maintain the catalyst stable in the oxidized state.The catalyst has subsequently been tested in a micro-catalytic fixed bed reactor. The overall reaction orders and rate constants of the primary reactions were determined by measuring the intrinsic reaction rates at different methane and oxygen inlet concentrations. It was found that the reaction order in oxygen for the coupling reaction is 0.38, while the reaction order in oxygen for ethylene oxidation approaches unity, indicating that low oxygen concentration levels are beneficial for obtaining a high C2 selectivity (up to 80–90%). Such a low oxygen concentration can be obtained with distributive feeding in a membrane reactor.Based on the experiments and least-squares minimization, a simplified reaction mechanism is proposed, where the dependency of the ethane (coupling) and carbon dioxide (oxidation) production rates and the secondary ethylene production and C2 oxidation rates can be described with power-law type reaction rate expressions.
Keywords: Methane oxidative coupling; Catalysis; Kinetics; Mn/Na2WO4/SiO2;
Selective partial biodiesel hydrogenation using highly active supported palladium nanoparticles in imidazolium-based ionic liquid by Bruno S. Souza; David M.M. Pinho; Elder C. Leopoldino; Paulo A.Z. Suarez; Faruk Nome (109-114).
Display Omitted► Heterogeneous catalyst with surfactant stabilized palladium nanoparticles on Al2O3. ► This catalyst is used for partial biodiesel hydrogenation. ► Ionic liquid as a reaction media allows selective hydrogenation of polyenes. ► Partially hydrogenated biodiesel if more stable against oxidation. ► The ionic liquid allows simple separation of products and catalyst recovery.The low oxidative stability of biodiesel derived from polyunsaturated oils is one of the great challenges to be overcome in biodiesel technology. Here, we use a high activity catalyst Pd/ImS3-12@Al2O3, prepared by adsorption of water-prepared palladium nanoparticles on aluminum oxide, for partial biodiesel hydrogenation. The catalyst shows higher hydrogenation activity than conventional Pd/C, leading in the absence of ionic liquid (IL) to fully hydrogenated product. In the presence of BMIM·NTf2 (1-butyl-3-methylimdazolium bis(trifluoromethylsulfonyl)imide) IL the activity of the Pd/ImS3-12@Al2O3 catalyst could be controlled and selective reduction to monoene product, with large preference for formation of the cis isomer, could be achieved at low temperature and pressure, with very low catalyst loading, no detectable metal leaching and good recyclability. The partially hydrogenated biodiesel is far more stable to oxidation than the crude, without compromising its cold-flow properties.
Keywords: Biodiesel; Fame; Palladium; Nanoparticles; Hydrogenation; Ionic liquid;
Tungsten disulfide catalysts from tetraalkylammonium thiotungstates by ex situ activation, their properties and HDS activity by R. Romero-Rivera; G. Berhault; G. Alonso-Núñez; M. Del Valle; F. Paraguay-Delgado; S. Fuentes; S. Salazar; A. Aguilar; J. Cruz-Reyes (115-121).
Display Omitted► Ex situ activation of ammonium thiotungstate leads to highly active catalysts. ► The role of carbon coming from thiotungstate precursors is analyzed. ► The nature of the atmosphere used during activation plays a minor role. ► Carbon-containing thiotungstate leads to excessive formation of amorphous carbon. ► Depleted hydrogenating character if carbon-containing precursor is used.The role of carbon coming from tetraalkylammonium thiotungstate precursors during the ex situ activation of WS2 catalysts was herein studied through the comparison of two different thiosalts, ammonium tetrathiotungstate (ATT, without carbon) and cetyltrimethylammonium tetrathiotungstate (CTATT, with carbon). The influence on the resulting WS2 catalysts, of a N2 vs a H2S/H2 (20% H2S) atmosphere during ex situ activation was also evaluated. Freshly obtained catalysts were characterized by N2 adsorption–desorption isotherms, X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX), while their catalytic properties were evaluated in the hydrodesulfurization of dibenzothiophene at 3.1 MPa and 623 K. No significant difference was found in the textural and morphological properties of the final WS2 catalysts derived from thermal decomposition of ATT under N2 flow, compared to 20% H2S/H2 flow. In contrast, the textural, morphological and catalytic properties of WS2 catalysts derived from CTATT were strongly influenced by the nature of the atmosphere. Samples of WS2 derived from ATT showed an absence of porosity, while WS2 catalysts formed from CTATT presented a mesoporous organization characterized by type IV N2 isotherms. XRD and TEM showed that the use of CTATT induces a strong destacking of the WS2 particles and the excessive formation of amorphous carbon, thus yielding less active WS2 catalysts which confirm the negative role of carbon-containing tetraalkylammonium precursors in the activation of WS2 catalysts, as opposed to their positive influence in the activation of MoS2 catalysts. The very high activity of the WS2 catalyst obtained from ATT is attributed to an optimized incorporation of structural carbon inside the WS2 structure. Finally, selectivity results show the depleted hydrogenating character of the WS2 catalysts formed from CTATT.
Keywords: Hydrodesulfurization; WS2; Tetraalkylammonium; Carbon; Activation;
Design of zeolite catalysts for nitroaldol reaction under mild condition by Rasna Devi; Ruli Borah; Ramesh C. Deka (122-127).
Display Omitted► Henry nitroaldol reaction conditions were optimized with moderately weak base catalysts under various reaction conditions. ► Basic zeolites NaY, KL and their alkali metal impregnated form are found to be effective catalysts for nitroaldol reaction. ► Framework structure of zeolites does not break after modification. ► The reaction gives nitroaldol product in good yield.NaY and KL zeolites were modified by impregnating with potassium fluoride for investigating their basicity and catalytic activity towards Henry nitroaldol reaction under different reaction conditions. Effects of solvents, temperature, catalysts and ratio of substrate versus reagents were studied to optimize the reaction conditions. The catalysts were characterized by FTIR, XRD and SEM techniques and the products were characterized by 1H NMR, 13C NMR and FTIR techniques. It was observed that NaY/KF zeolite with H2O–MeOH pair as solvent showed good conversion and selectivity at room temperature. Both XRD and FTIR study showed no change of spectral patterns for both modified and parent zeolites. We have again showed a plot of Hammett free energy linear relationship in terms of percentage yield and Hammett substituent constant.
Keywords: Zeolite; Base catalyst; Henry nitroaldol reaction; β-Nitro alcohols; Hammett's constant;
Solid acid co-catalyst for the hydrogenolysis of glycerol to 1,3-propanediol over Ir-ReO x /SiO2 by Yoshinao Nakagawa; Xuanhe Ning; Yasushi Amada; Keiichi Tomishige (128-134).
Display Omitted► The combination of Ir-ReO x /SiO2 and solid acids catalyzes glycerol hydrogenolysis. ► Acid addition enhances hydrogenolysis of the internal C―OH bond of glycerol. ► Amberlyst 70 is the most effective solid acid in enhancing the activity. ► H-ZSM-5 is a suitable solid acid in terms of activity and reusability.Hydrogenolysis of aqueous glycerol was conducted with Ir-ReO x /SiO2 catalyst and solid acid co-catalyst. Considering the reusability and activity, H-ZSM-5 is the most suitable solid co-catalyst. The property of Ir-ReO x /SiO2 + H-ZSM-5 system including kinetics and selectivity trends in various reaction conditions is similar to the case of Ir-ReO x /SiO2 + H2SO4. The catalyst stability, activity, and the maximum yield of 1,3-PrD of Ir-ReO x /SiO2 + H-ZSM-5 were slightly lower than Ir-ReO x /SiO2 + H2SO4. The role of added acid may be to protonate the surface of ReO x cluster to increase the number of hydroxorhenium site, which activates glycerol by the formation of glyceride species.
Keywords: Hydrogenolysis; Glycerol; Iridium; Rhenium; Zeolite;
Comprehensive IR study on acid/base properties of metal oxides by Masazumi Tamura; Ken-ichi Shimizu; Atsushi Satsuma (135-145).
Display Omitted► IR indexes for acid/base properties (type, strength, number) of a wide range of metal oxides. ► CD3CN for the strength of acid sites. ► CHCl3 for the strength of basic sites. ► Pyridine for the number of Brønsted/Lewis acid sites. ► Nitrobenzene for the number of basic sites.Acid/base properties (type, strength, number) of a wide range of metal oxides were studied by IR (infra-red) spectroscopy. Ammonia, pyridine and CD3CN were used as probe molecules for acidity measurement. CO2, CHCl3, benzaldehyde and nitrobenzene were used for basicity measurement. Pyridine for the nature and number of acid sites, CD3CN for the strength of acid sites, CHCl3 for the strength of basic sites and nitrobenzene for the number of basic sites were found to be suitable probes. The absorption coefficients of pyridine for acidic sites and nitrobenzene for basic sites, estimated for various metal oxides by IR coupled with mass spectrometry, were within ±10% of the average value, which indicates that the integrated molar extinction coefficients could be used for semi-quantification of acid/base sites of various oxides samples. The comprehensive IR results in this study will be available to characterize properties of Lewis and Brønsted acid sites and basic sites on metal oxides by a simple IR experiment.
Keywords: Solid acid; Solid base; Characterization; IR; Metal oxides; Heterogeneous catalysis;
Silica-supported Au–Cu alloy nanoparticles as an efficient catalyst for selective oxidation of alcohols by Wanjun Li; Aiqin Wang; Xiaoyan Liu; Tao Zhang (146-151).
Display Omitted► Au–Cu/SiO2 catalysts are highly active and selective for oxidation of alcohols. ► There is a strong synergistic effect between Au and Cu. ► Reduction pretreatment is necessary for a good performance.Silica-supported Au–Cu and Au–Ag alloy nanoparticles were synthesized, characterized, and tested for the aerobic oxidation of alcohols. The results showed that Au–Cu alloy catalyst exhibited good activity and selectivity to aldehydes for a variety of structurally diverse alcohols and a strong synergistic effect was found between Au and Cu. In contrast, Au–Ag alloy catalysts were less active and selective for the oxidation of alcohols although they have very similar particle sizes to the Au–Cu alloy catalysts. Besides the chemical compositions, the pretreatment conditions were found to affect significantly the catalytic performances, and the reduction treatment is necessary for obtaining a high activity and selectivity, suggesting Au–Cu alloy is the active phase. Moreover, the catalyst could be reused if only the catalyst after the reaction was subjected to reduction treatment.
Keywords: Gold; Copper; Au–Cu; Au–Ag; Synergetic effect; Alcohol oxidation;
Synthesis of hybrid SBA-15 functionalized with molybdophosphoric acid as efficient catalyst for glycerol esterification to fuel additives by M.S. Khayoon; B.H. Hameed (152-161).
Display Omitted► Hybrid silicate material was synthesized using Brij S100 as a co-surfactant. ► SBAH-15 functionalized with β-MoO3 employed to catalyze glycerol esterification. ► Complete glycerol conversion was achieved within 1 h of reaction time. ► The stability of the catalytic activity was examined and proved. ► Catalyst surface acidity plays a prominent role in promoting the catalytic activity.Fibrous mesoporous hybrid silica (SBAH-15) with mesopore diameter of 70 Å was synthesized using pluronic P123 (EO20PO70EO20) as surfactant, with Brij S100 as nonionic co-surfactant. Series of catalysts with different molybdophosphoric acid (MPA) loading (5–25%) were synthesized by the thermal decomposition of MPA species in the lattice of SBAH-15. Catalysts calcined at 560 °C undergone a thermal decomposition of MPA resulted in the formation of β-MoO3 active species. The effectiveness of the hybrid support was evaluated by comparison with analogous catalyst prepared by incorporating MPA into the framework of classical SBA-15. The catalytic performance of the prepared acid catalysts was examined during glycerol esterification with acetic acid. Mono-, di- and triacetyl glycerol (MAG, DAG and TAG, respectively) were the esterification reaction products. SBAH-15(15) catalyst, with 15 wt.% MPA loading, exhibited an excellent activity during this reaction, indicated by the complete glycerol conversion (after 1 h) with a corresponding combined selectivity of 86% toward both DAG and TAG. The best reaction conditions are: reaction temperature of 110 °C, glycerol to acetic acid molar ratio of 1:6 and reaction time of 3 h. The SBAH-15(15) catalyst demonstrated good stability in activity upon recycling for four times.
Keywords: Glycerol; Esterification; SBA-15; Molybdophosphoric acid; MoO3;
SO2 promoted alkali metal doped Ag/Al2O3 catalysts for CH4-SCR of NOx by Komateedi N. Rao; Heon Phil Ha (162-169).
Display Omitted► Lean NOx reduction activity was carried out in alkali doped Ag/Al2O3 catalysts. ► K–Ag/Al2O3 and Cs–Ag/Al2O3 exhibited higher NOx conversions and thermal stability. ► XANES and UV–Vis DRS revealed the presence of appropriate ratio of Ag0 and Ag+. ► The enhancement in the NO conversion is attributed to the strong adsorption sites for NO and substantial inhibition for SO2.A study of the lean NOx reduction activity in the presence of SO2 and water over alkali promoted Ag/Al2O3 catalysts has been done using methane as a reductant. The alkali doped materials are synthesized by the co-impregnation method. Their promotional behavior, existence of several silver species and improved adsorption properties have been thoroughly investigated by various techniques: XRD, XANES, TEM, UV–Vis DRS, SO2 TPD and NO TPD. The evaluated samples exhibited high surface area around 220 m2 g−1. TEM results demonstrated the presence of highly dispersed nano sized silver particles on surface, where the addition of alkali metals slightly enhanced the crystallization of silver. Moreover, standard XRD profiles of fresh and used samples indicate the high durability and mechanical strength of catalysts. These findings are in line with the time-on-stream studies. The XANES results revealed that the edge spectra of prepared materials are similar to that of the reference Ag2SO4. From XANES and UV–Vis DRS, the presence of crystalline Ag0 and Ag+ species were identified. Poor activity of Na promoted sample is attributed to absence of suitable amount of ionic silver compounds. However, the synthesized alkali doped materials showed the promotional deNOx conversions in the presence of SO2 and H2O stream. Among the investigated samples K–Ag/Al2O3 and Cs–Ag/Al2O3 exhibited higher NOx conversions and thermal stability. The higher SCR of NOx was explained by the NO adsorption properties identified from the NO TPD studies.
Keywords: SCR of NOx; Methane; Alkali metals; Ag/Al2O3; XANES; SO2 influence;
Liquid hydrocarbon fuels from jatropha oil through catalytic cracking technology using AlMCM-41/ZSM-5 composite catalysts by G. Ramya; R. Sudhakar; J. Amala Infant Joice; R. Ramakrishnan; T. Sivakumar (170-178).
Display Omitted► Catalytic cracking of jatropha oil has not been reported so far in the literature. ► AlMCM-41/ZSM-5 composite catalyst showed remarkable catalytic activity. ► 99% of jatropha oil converted with 70% of BLF yield and 61% of GG selectivity. ► SEM confirmed core–shell architecture of composite catalyst.Biofuels, the hydrocarbons less than C18, produced by catalytic cracking of nonedible vegetable oils are the potential source to battle energy demand and pollution. Among the non edible oils, jatropha is the apt candidate for the production of biofuel. Jatropha oil can be cracked catalytically over solid acid catalysts to yield liquid fuels with superior characteristics. We present here the hydrothermal syntheses of a microporous solid acid catalyst (HZSM-5 with Si/Al = 14), mesoporous materials (AlMCM-41) with varying Si/Al ratios (Si/Al = 18, 41, 72 and 95) and composite catalyst comprising HZSM-5 (as core) and varying coating percentages (5, 10 and 20%) of AlMCM-41 (as shell). All the synthesized catalysts were characterized by using XRD, BET N2 sorption studies, ICP, TPD and SEM techniques. Herein we report the catalytic activities of all the synthesized catalysts towards the cracking of jatropha oil obtained at the optimized conditions of temperature – 400 °C, WHSV – 4.6 h−1 and reaction time – 1 h. Of all the mesoporous catalysts with varying Si/Al ratios, AlMCM-41 (Si/Al = 18) was found to be the most active catalyst as it converted 65% of jatropha oil yielding 39% of bioliquid fuel with 47% and 36% selectivities towards green diesel and green gasoline respectively. In the core–shell architecture of the composite catalyst, different % coatings of the best active mesoporous material (AlMCM-41, Si/Al = 18) over the best active microporous material (ZSM-5, Si/Al = 14) were done. AlMCM-41/ZSM-5 (25, 15, 10) showed remarkable performance in the conversion of jatropha oil (99%) yielding 70% of bioliquid fuel with very high selectivity (61%) towards green gasoline.
Keywords: Composite catalyst; Green gasoline; Vegetable oil; Cracking; Bioliquid fuels, Porous materials;
Zirconium doped mesoporous silica catalysts for dehydration of glycerol to high added-value products by C. García-Sancho; R. Moreno-Tost; J. Mérida-Robles; J. Santamaría-González; A. Jiménez-López; P. Maireles-Torres (179-187).
Display Omitted► SiZrx catalysts display both Brönsted and Lewis acid sites. ► They are active in the gas-phase dehydration of glycerol. ► Long-term stability is ameliorated by steaming treatment of catalysts. ► The selectivity can be explained by considering the nature of acid sites.A series of zirconium doped mesoporous silica, with different Si/Zr molar ratios, has been synthesized and tested in the gas-phase dehydration of glycerol. The surface characterization of these solids by using NH3-TPD and pyridine adsorption coupled to FTIR spectroscopy has revealed the existence of well dispersed acid sites, mainly of Lewis type, associated to Zr(IV) species deficiently coordinated located on the pore walls of the siliceous framework. These acid catalysts are active in the glycerol dehydration, increasing the conversion with the zirconium content until values higher than 90 mol% for a Si/Zr molar ratio of 4, at 325 °C after 5 h of reaction. However, the catalysts suffer deactivation, which is more important when zirconium oxide is incorporated by impregnation of mesoporous MCM-41 silica. The main reaction products were acrolein, acetaldehyde and acetol. Moreover, the catalysts with a SiZr molar ratio higher than 5 are more selective to acetaldehyde. The acrolein yield was, in all cases, lower than 15 mol% after 24 h of TOS, but a pretreatment under a helium flow saturated with water vapour allows reaching an acrolein yield of 28 mol% and ameliorates the stability of catalysts. The selectivity towards acrolein and hydroxyacetone can be explained by considering the influence of the nature of active sites.
Keywords: Mesoporous silica; Glycerol; Zirconium oxide; Acid catalysis; Acrolein;
Isoprene hydroamination catalyzed by palladium xantphos complexes by Bahareh Tamaddoni Jahromi; Ali Nemati Kharat; Sara Zamanian; Abolghasem Bakhoda; Kobra Mashayekh; Sadegh Khazaeli (188-196).
Display Omitted► Pd–Xantphos complexes are potent isoprene hydroamination catalysts. ► An efficient synthesis of pharmaceutically important amines could be achieved. ► Amines with high steric hindrance yield 4-(3-methylbut-2-enyl) amines before reduction.Pd(II) Xantphos or Xantphos chalcogenide complexes with general folmula [PdCl2(X∩X)] (where X = P, O, S or Se) were synthesized by the addition of corresponding ligands to [PdCl2(COD)] (COD = 1,5-cyclooctadiene). Prepared Complexes [PdCl2(Xantphos)] and [PdCl2(Xantphos = S)] showed distorted square planar geometries, from X-ray crystallographic analysis. All of the prepared complexes showed activity toward intermolecular hydroamination of isoprene with a variety of secondary amines. Complete conversion (∼100%) of pyrrolidine was observed using Pd–Xantphos as catalysts. Hydroamination reactions exhibited regioselectivity when crowded secondary amines were used.
Keywords: Isoprene; Secondary amines; Hydroamination; Palladium complexes; Xantphos;
N-Substituted 3,4-dihydroisoquinolinium ionic liquids as catalysts in alkenes epoxidation reactions by Stefan Baj; Maciej Bełch; Mirosław Gibas (197-205).
Display Omitted► 3,4-Dihydroisoquinolinium ionic liquids were obtained with yield up to 91%. ► The structure of synthesised ionic liquids was characterised using 1H and 13C NMR. ► Synthesised ionic liquids as catalysts in olefin epoxidation was investigated. ► The major products of these reactions were the epoxides with yield up to 70%.Because of their high reactivity, epoxides are one of the most important groups of organic compounds. These substances are synthesised primarily by the catalytic oxidation of alkenes in the liquid or gaseous phase. This study investigated new catalytic systems for epoxidation reactions using functionalised ionic liquids. These ionic liquids serve as oxygen transfer agents during the reactions. Several N-substituted 3,4-dihydroisoquinolinium ionic liquids were synthesised, and their potential as catalysts for epoxidation reactions was investigated. Cyclic alkenes such as cyclohexene and cyclooctene were used as model olefins.
Keywords: 3,4-Dihydroisoquinolinium ionic liquids; Alkenes epoxidation; Oxygen transfer agents;
Rod-, flower-, and dumbbell-like MnO2: Highly active catalysts for the combustion of toluene by Fengjuan Shi; Fang Wang; Hongxing Dai; Jianxing Dai; Jiguang Deng; Yuxi Liu; Guangmei Bai; Kemeng Ji; Chak Tong Au (206-213).
Display Omitted► α-, ɛ-, and β-MnO2 with various shapes are prepared by hydrothermal or water-bathing method. ► Rod-like α-MnO2, flower-like ɛ-MnO2, and dumbbell-like β-MnO2 show a surface area of 30–114 m2/g. ► Well-defined morphological MnO2 possess high Oads concentrations and good reducibility. ► Rod-, flower-, and dumbbell-like MnO2 catalysts perform well for toluene combustion. ► High Oads concentration and good reducibility account for the good catalytic activity.The rod-like tetragonal α-MnO2, flower-like hexagonal ɛ-MnO2, and dumbbell-like tetragonal β-MnO2 were prepared using the hydrothermal or water-bathing method under different conditions. It is shown that the α-MnO2, ɛ-MnO2, and β-MnO2 catalysts possessed a surface area of ca. 53, 30, and 114 m2/g, respectively. The oxygen adspecies concentration and low-temperature reducibility decreased in the order of α-MnO2 > ɛ-MnO2 > β-MnO2, coinciding with the sequence of their catalytic activities for toluene combustion. The well-defined morphological MnO2 catalysts performed much better than the bulk counterpart. At a space velocity of 20,000 mL/(g h), the temperature for 90% toluene conversion was 238, 229, and 241 °C over α-MnO2, ɛ-MnO2, and β-MnO2, respectively. The apparent activation energies of α-MnO2, ɛ-MnO2, and β-MnO2 were in the range of 20–26 kJ/mol. It is concluded that higher oxygen adspecies concentrations and better low-temperature reducibility were responsible for the good catalytic performance of the α-MnO2, ɛ-MnO2, and β-MnO2 materials.
Keywords: Hydrothermal preparation method; Water-bathing preparation method; Well-defined morphology; Manganese oxide catalyst; Toluene combustion;
A practical ruthenium based catalytic system bearing a switchable selectivity between the dimerization and cyclotrimerization reactions of alkynes by Bengi Özgün Öztürk; Solmaz Karabulut; Yavuz İmamoğlu (214-222).
Display Omitted► [RuCl2(p-cymene)]2/PCy3 emerges as a practical and inexpensive catalytic system for alkyne dimerization reactions. ► The catalytic system has switchable selectivity between cyclotrimerization and dimerization reactions of alkynes. ► Excellent yields and regioselectivities were observed for both processes.In this study, a practical and inexpensive switchable catalytic system (cyclotrimerization vs. dimerization), [RuCl2(p-cymene)]2/PR3 has been developed for the catalytic dimerization of terminal alkynes. Bulky and basic phosphine derivatives, PCy3 and P(i-Pr)3, were used with [RuCl2(p-cymene)]2 and excess of terminal alkyne to in situ formation of vinylidenic intermediates which are active towards dimerization reactions. Effect of phosphine/ruthenium ratio has been investigated. A solvent study was carried out and toluene was found to be the most versatile solvent for both cyclotrimerization and dimerization reactions. A set of aryl and alkyl acetylenes were chosen as substrates to investigate the effect of the nature of the substrates on alkyne dimerization reactions catalyzed by [RuCl2(p-cymene)]2/PR3. In conclusion, we have shown that [RuCl2(p-cymene)]2/PCy3 can be used as a practical and inexpensive catalytic system which has a switchable selectivity towards cyclotrimerization and dimerization reactions. Best results in means of regioselectivity and yield were observed by using arylacetylene derivatives in these reactions. This catalytic system emerges as an economical method for the transformation of arylacetylenes to corresponding enyne and arene derivatives in excellent yields and selectivity.
Keywords: Alkyne dimerization; Ruthenium; Enynes; Switchable catalysis;
Synthesis and characterization of Zr, Ti, Al-phthalate and pyridine-2-carboxylate compounds and their use in ring opening polymerization by Gamze Yalcin; Asgar Kayan (223-228).
.Display Omitted► Synthesis of new catalysts of zirconium, titanium and aluminum. ► High activity of the catalysts in mild conditions with respect to the reported acid catalysts. ► Application of solvent free conditions in the polymerization reactions. ► Characterization of poly-GPTS by GPC and spectroscopic methods.Zirconium, titanium and aluminum phthalate (PH, C8H4O4) and pyridine-2-carboxylate (Pyca, C6H4NO2) compounds were prepared by reaction of Zr, Ti and Al-alkoxides with phthalic acid (PHA) and pyridine-2-carboxylic acid (PycaH) in alcohol. All new complexes were characterized by a combination of elemental analysis, NMR and FTIR spectroscopy and used in polymerization of 3-glycidyloxypropyltrimethoxysilane (GPTS) in order to see their catalytic activity over epoxides. Especially, Al, Ti and Zr-phthalate catalysts were more effective in ring opening of GPTS when compared to Al, Ti and Zr-pyridine-2-carboxylate catalysts. Poly-GPTS were characterized by 1H, 13C NMR and gel permeation chromatography (GPC).
Keywords: Metal alkoxides; Phthalate catalysts; Ring-opening; Pyridine-2-carboxylate catalysts;
Synthesis of diethyl carbonate from ethyl carbamate and ethanol over ZnO-PbO catalyst by Hualiang An; Xinqiang Zhao; Lian Guo; Chunyao Jia; Baoguo Yuan; Yanji Wang (229-235).
Display Omitted► ZnO-PbO shows a high catalytic performance for diethyl carbonate synthesis. ► ZnO-PbO also shows an excellent reusability. ► Zn(NCO)2(NH3)2 and cubic metal Pb are the real active composition. ► The catalytic mechanism of Zn(NCO)2(NH3)2 and cubic metal Pb has been elucidated.The synthesis of diethyl carbonate (DEC) from ethyl carbamate and ethanol was investigated over a series of double metal oxides. Among the catalysts, ZnO-PbO showed the best catalytic activity and the highest DEC yield was 20.6%. Furthermore, ZnO-PbO had an excellent reusability. According to the results of XRD measurement, IR and element analysis, ZnO and PbO in ZnO-PbO catalyst were separately converted to Zn(NCO)2(NH3)2 and metal Pb during the reaction, indicating that the mixture of Zn(NCO)2(NH3)2 and metal Pb may be the real active composition for DEC synthesis and ZnO-PbO is the precursor. In addition, a possible reaction mechanism for DEC synthesis was proposed.
Keywords: Diethyl carbonate; Ethyl carbamate; Ethanol; Urea; ZnO-PbO;
Effect of reduction temperature on selective hydrogenation of crotonaldehyde over Ir/TiO2 catalysts by Ping Chen; Ji-Qing Lu; Guan-Qun Xie; Geng-Shen Hu; Lin Zhu; Liang-Feng Luo; Wei-Xin Huang; Meng-Fei Luo (236-242).
Display Omitted► The charge-deficient Ir species reduced at 100 °C favor C＝C bond hydrogenation. ► Strong Lewis acid sites are detrimental to catalytic behaviors. ► Ir/TiO2 catalysts reduced at 300 °C have the highest activity and selectivity. ► Moderate electron density and Lewis acidity are the virtues for high selectivity. ► The charge-rich Ir species reduced at 500 °C suppress activity and selectivity.Vapor-phase selective hydrogenation of crotonaldehyde was conducted over Ir/TiO2 catalysts to investigate the effect of reduction temperature on the catalytic behaviors. The catalyst reduced at 100 °C contained large amount of strong Lewis acid sites, which was detrimental to the activity because of the strong adsorption of crotonaldehyde molecules on the active sites. Also, the selectivity to crotyl alcohol was suppressed due to the interaction between C＝C bond and the charge-deficient Ir species, which favored the formation of butanal. When the catalyst was reduced at high temperature, it was found that 300 °C was appropriate for high activity and selectivity, due to the moderate interaction between the C＝O bond and the Ir species, as well as the weakened surface Lewis acid sites. However, higher reduction temperature (500 °C) led to a strong bonding of carbonyl carbon and the charge-rich Ir species and suppresses the activity, which may be related to a strong metal–support interaction (SMSI).
Keywords: Ir/TiO2 catalyst; Crotonaldehyde hydrogenation; Crotyl alcohol; Lewis acid;
Highly dispersed supported ruthenium oxide as an aerobic catalyst for acetic acid synthesis by Anders B. Laursen; Yury Y. Gorbanev; Filippo Cavalca; Paolo Malacrida; Alan Kleiman-Schwarsctein; Søren Kegnæs; Anders Riisager; Ib Chorkendorff; Søren Dahl (243-250).
Display Omitted► The RuO x are highly dispersed and narrow sized regardless the support and loading. ► The RuO x is active and selective for the aerobic oxidation of ethanol to acetic acid. ► RuO x on CeO2 is the most active catalyst for the aerobic oxidation of ethanol to acetic acid. ► The RuO x activity is attributed to the presence of high valence Ru(VI). ► The effect of heat-treatment on the catalytic activity is investigated.The increasing need for shifting to renewable feedstocks in the chemical industry has driven research toward using green aerobic, selective oxidation reactions to produce bulk chemicals. Here, we report the use of a ruthenium mixed oxide/hydroxide (RuO x ) on different support materials for the selective aerobic oxidation of ethanol to acetic acid. The RuO x was deposited onto different oxide supports using a new gas-phase reaction, which in all cases resulted in homogeneous nanoparticulate films. The RuO x particle size ranged from 0.3 to 1.5 nm. The catalytic activity was evaluated on TiO2, Mg6Al2(CO3)(OH)16 · 4(H2O), MgAl2O4, Na2Ti6O13 nanotubes, ZnO, γ-Al2O3, WO3, CeO2, and Ce0.5Zr0.5O2 supports. The CeO2 supported RuO x had the highest activity, and selectivity toward acetic acid, of all the materials when normalized with respect to Ru-loading. This high activity was independent of the surface area of the support and the loading of RuO x under the tested conditions. This was attributed to the highly uniform size of the RuO x deposits, demonstrating that the deposition is suitable for producing small nanoparticles at high loadings. To elucidate the reason for the promotional effect of CeO2, Ce0.5Zr0.5O2 was investigated as a high oxygen storage capacity support, however, this did not result in higher catalytic activity. The high activity of CeO2 supports compared to the low activity ZnO appear correlated to the presence of high valence Ru(VI) species analogous to that observed in literature.
Keywords: Heterogeneous catalysis; Ruthenium oxide; Aerobic ethanol oxidation; RuO4; Support effects; High-loading catalysts; Ru(VI) oxide;
Study of hydrodesulfurization of 4,6-DM-DBT over Pd supported on mesoporous USY zeolite by Lei Zhang; Wenqian Fu; Qingping Ke; Shuai Zhang; Huile Jin; Jianbo Hu; Shun Wang; Tian-di Tang (251-257).
Dependence of the remaining sulfur content in 4,6-DM-DBT-hydrogenation system on reaction time over (■) Pd/USY550, (▪) Pd/USY600, (▪) Pd/HY, and (▪) Pd/γ-Al2O3 catalysts at reaction temperature of 250 °C.Display Omitted► Pd/USY exhibited high activity in HDS of 4,6-DM-DBT under the mild condition. ► The 4,6-DM-DBT conversion over Pd/USY550 is nearly 100%. ► Stability experiment over Pd/USY was also performed (175 h).Two ultra-stable Y zeolites (USY550 and USY600) with mesoporous volumes of 0.15 and 0.25 cm3/g were prepared by steam dealumination at 550 and 600 °C, respectively. Pd catalysts were supported on γ-Al2O3, H-forms of zeolite Y (HY), mesoporous USY for hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DM-DBT). The 4,6-DM-DBT conversions over Pd/USY550 (85.7%) and Pd/USY600 (76.9%) are higher than over Pd/HY (43.7%) due to the facilitated mass transfer of 4,6-DM-DBT in the mesopores USY. The better HDS performance of Pd/USY than Pd/γ-Al2O3 is attributed to the stronger acidity of USY, as demonstrated by the stepwise temperature-programmed desorption of ammonia. Thermogravimetric and X-ray photoelectron spectroscopic analysis of the used catalysts showed that the poison of Pd particles over the supports by sulfur was responsible for the catalyst deactivation.
Keywords: Mesoporous USY; Pd catalyst; 4,6-DM-DBT; Hydrodesulfurization;
Heterogeneous magnetic catalyst for S-arylation reactions by Niranjan Panda; Ashis Kumar Jena; Sasmita Mohapatra (258-264).
Display Omitted► Synthesis of monodisperse, superparamagnetic CuFe2O4 nanoparticles has been described. ► CuFe2O4-mediated C―S cross-coupling reactions have been explored. ► Aryl chlorides and bromides are also used as coupling partners in cross-couplings. ► One-pot synthesis of dibenzothazepines have been exploited. ► This catalytic protocol is found to be economic and environmentally benign.A convenient method for the synthesis of monodisperse, superparamagnetic copper ferrite (CuFe2O4) nanoparticles with high surface area has been described. The synthesized material was characterized by various techniques. XRD showed the nanocrystalline nature of CuFe2O4 with a crystallite size of 6 nm. TEM analysis showed that uniform spherical CuFe2O4 particles are formed with a size of 55 ± 5 nm. N2 adsorption/desorption measurements confirmed the mesoporous nature of the sample with surface area >216 m2 g−1. The field dependent magnetization, illustrated by VSM and saturation magnetization was found to be 44 emu g−1. The catalytic applications of the synthesized CuFe2O4 nanoparticles were explored for the cross-coupling of thiols with diverse range of aryl halides. Aryl iodides and bromides result in biarylsulfides in good to excellent yields (62–98%) whereas aryl chlorides gave significant amount of diaryldisulfide. Scope of this catalytic protocol further extended to one-pot synthesis of biologically important tricyclic dibenzothiazepines. The superparamagnetic nature of CuFe2O4 nanoparticles was found to be advantageous for their easy, quick and quantitative separation from the reaction mixture. Negligible leaching of Cu and Fe in consecutive cycles makes the catalyst economical and environmentally benign.
Keywords: Superparamagnetic nanoparticles; Heterogeneous catalyst; Cross-coupling; S-arylation; Dibenzothiazepines; Dibenzothiazepinones; Aryl halides;
Atom efficient Friedel–Crafts acylation of toluene with propionic anhydride over solid mesoporous superacid UDCaT-5 by Ganapati D. Yadav; Shashikant B. Kamble (265-274).
Display Omitted► Friedel–Crafts acylation with heterogeneous catalysts. ► Mesoporous superacidic catalyst UDCaT-5. ► 4′-methylpropiophenone by propionylation of toluene with propionic anhydride. ► Water is the only co-product of the overall reaction. ► Mechanism and kinetics of reaction.Friedel–Crafts acylation is ubiquitous in industry and is typically carried out by using more than stoichiometric quantities of homogeneous catalysts. This creates pollution. In this work, acylation of toluene was studied in liquid phase with propionic anhydride with a variety of solid superacids to produce 4′-methylpropiophenone (4′-MPP). The solid superacids were modified versions of zirconia, namely, UDCaT-4, UDCaT-5 and UDCaT-6 developed in our laboratory; amongst which UDCaT-5 was the most active, selective and robust catalyst. The effects of various reaction parameters on the rate of reaction and selectivity were investigated to deduce the intrinsic kinetics of the reaction. The reaction is free from any external mass transfer as well as intraparticle diffusion limitations and is intrinsically kinetically controlled. The acylation conditions were: temperature 180 °C, toluene to propionic anhydride molar ratio 5:1, catalyst loading 0.06 g cm−3, speed of agitation 1000 rpm, under autogenous pressure in a stainless steel autoclave reactor. Propionic acid generated in situ also reacts sequentially with toluene to give 4′-MPP. A conversion of 62% of priopionic anyhydride is obtained after 3 h, with 100% mono-acylated product containing 67% 4′-MPP. Water is the only co-product of the overall reaction. A suitable kinetic model was developed. The reactions were carried out without using any solvent in order to make the process cleaner and greener.
Keywords: Friedel–Crafts acylation; Heterogeneous catalysis; Solid superacids; Kinetics; 4′-Methylpropiophenone; Green chemistry;
Esterification of lactic acid over TiO2–Al2O3 catalysts by Kuo-Tseng Li; Chih-Kai Wang (275-279).
Display Omitted► Binary oxide with a Ti/Al atomic ratio of 1/1 (TA11) had the best activity. ► TA11 catalyst had the largest surface area and maximum acidity. ► TA11 catalyst had higher ester yield than cation-exchanged resins and Ti–Zr catalysts.N-butyl lactate was synthesized with a good yield (the maximum product yield was 95.7% at 140 °C) by the reaction between lactic acid and n-butanol over TiO2–Al2O3 catalysts. These catalysts had various Ti/Al atomic ratios (ratio = 1/0, 9/1, 3/1, 1/1, 1/3, 1/9, and 0/1) and were prepared by a co-precipitation method. XRD, n-butylamine adsorption, nitrogen adsorption, and SEM were used to characterize the oxides. The maximum activity was found for the catalyst with Ti/Al atomic ratio = 1 (TA11). The superiority of TA11 was ascribed to its largest surface area and its maximum acidity. Under identical reaction conditions, TA11 catalyst exhibited significantly better activity than the TiO2–ZrO2 catalysts reported earlier, which should be due to the larger surface area of the former.
Keywords: Solid acid catalysts; Lactic acid esterification; TiO2–Al2O3 catalysts; Acid sites;
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