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Applied Catalysis A, General (v.321, #2)
Structural properties and catalytic oxidation of benzene to phenol over CuO-impregnated mesoporous silica by K.M. Parida; Dharitri Rath (pp. 101-108).
Cu/MCM-41 is an efficient catalyst for one-step benzene oxidation to phenol. H2O2 reacts with Cu/MCM-41 to give hydroxyl radical through a redox mechanism, which attacks benzene ring to give phenol. Phenol again oxidized in presence of hydroxyl radical to give hydroquinone and benzoquinone. ▪A series of copper catalysts supported on mesoporous molecular sieves MCM-41 with copper loading varying from 2wt% to 10wt% were synthesized by impregnation method using aqueous copper nitrate solution as the precursor. The samples were characterized by nitrogen adsorption–desorption, X-ray powder diffraction, FT-IR, UV-diffuse reflectance spectra and temperature programmed reduction. X-ray diffraction patterns indicate the presence of crystalline CuO phase above 4wt% copper loading. TPR patterns at low temperatures reveal the presence of highly dispersed copper oxide on the surface of the support and the profiles at high temperatures indicates bulk copper oxide. The catalytic activity of the samples was evaluated towards benzene oxidation using H2O2 as the oxidant in acetic acid solvent at room temperature. The effect of reaction parameters, i.e. time, temperature, catalyst amount, amount of H2O2, solvent and alkyl substitution on the substrate, were also investigated. Among the catalysts studied, 4wt% copper loaded MCM-41 showed maximum conversion (21%) and selectivity (94%) towards phenol.
Keywords: CuO-impregnated MCM-41; Benzene oxidation; Phenol
Synthesis of nano-sized porous γ-alumina powder via a precipitation/digestion route by H.S. Potdar; Ki-Won Jun; Jong Wook Bae; Seung-Moon Kim; Yun-Jo Lee (pp. 109-116).
Synthesis of spherical nano-sized porous γ-alumina powder via a boehmite precursor possessing controlled physical and chemical characteristics obtained through controlled precipitation/digestion reaction at 70°C in aqueous medium which give comparable catalytic activity in dehydration reaction of methanol to DME as that of γ-alumina powder derived from Catapal-B boehmite. ▪As a part of a study for the preparation of nano-sized γ-Al2O3 powder with controlled porosity and pore size distribution, a precipitation/digestion route was exploited to generate a boehmite precursor having a narrow size distribution of spherical nano-sized particles: size 3.5nm with surface area ∼261m2/g, average pore diameter of 4.86nm, and pore volume ∼0.377cm3/g. In this route, aqueous solution of aluminum nitrate and sodium carbonate were added simultaneously drop by drop to a well-stirred 200ml volume of deionized water (taken in a round-bottom flask) at 70°C to precipitate boehmite precursor in the pH range of 7.5–8.5 after digestion at the same temperature for 3h. The boehmite precursor thus obtained is further washed with deionized water first to avoid ‘Na’ contamination and then by ethanol/acetone. The digested precipitate was finally air dried at room temperature. The calcinations of as-dried boehmite precursor at 550°C/5h in air produced porous nano-sized γ-Al2O3 powder particles having spherical shape with size of 4.5nm. These powder particles showed BET surface surface area ∼220m2/g with average pore diameter of 7.0nm and pore volume ∼0.487cm3/g. However, room temperature precipitation/digestion produces non-crystalline boehmite that gave poorly crystallized γ-Al2O3 powder particles with lower surface area ∼133.90m2/g; these had higher average pore diameter of 26.67nm with pore volume of 1.02cm3/g. In methanol conversion to DME reaction, γ-Al2O3 catalyst made from precipitation/digestion at 70°C gave a similar yield of DME when compared with the yield for γ-Al2O3 prepared from commercial Catapal-B boehmite sample.
Keywords: Precipitation; Digestion; Boehmite; Nanocrystals; γ-Al; 2; O; 3
Structural and thermal study of carbon-modified molybdenum sub-oxide catalysts by G. Rodríguez-Gattorno; A. Martínez-Hernández; L.O. Aleman-Vázquez; E. Torres-García (pp. 117-124).
The formation of molybdenum sub-oxides during the reduction of the MoO3 catalyst has been extensively studied. However, the nature of the surface species during isomerization processes is not yet fully understood. The purpose of this work is to show a more realistic chemical approach to the complexity of this system and to raise a novel understanding of its catalytic behavior during isomerization reactions.▪The phase composition and the physico-chemical nature of the “carbon-modified molybdenum sub-oxide” catalyst during the isomerization of n-heptane were studied. It was found that different phases of molybdenum sub-oxides coexist, MoO2, MoO, besides MoO3− x. Our results indicate that MoO is present as dispersed nano-structures inside the bulk catalysts. The thermal oxidation study revealed that the O2 is consumed to oxidize part of the reduced oxide as well as carbonaceous deposits simultaneously, giving an additional evidence of the mixture of oxide phases during reaction. A thermo-kinetic study of the different oxidation process is included and the results are discussed in terms of the activation energy for the oxidation of each phase. The structural and thermal characterization has revealed the complexity of the system, but has also opened a window to a new insight into the understanding of MoO3 catalyst.
Keywords: Molybdenum oxide; Raman spectroscopy; Surface structure; Carbon-modified molybdenum sub-oxide; Thermal analysis; Heterogeneous catalysis
Study on ethylbenzene and xylene conversion over modified ZSM-5 by Tseng-Chang Tsai; Ikai Wang; Chung-Kan Huang; Sheng-De Liu (pp. 125-134).
A multiple modification technique of H-ZSM-5, by combing silica chemical vapor deposition, 5,6-benzoquinoline adsorption and platinum impregnation, was developed having higher p-xylene yield and lower xylene loss than the existing commercial catalysts in the conversion of ethylbenzene (EB) and m-xylene.▪The effects of modification of H-ZSM-5 on its catalytic performance in the conversion of ethylbenzene (EB) and m-xylene were studied. The methods of silica chemical vapor deposition and 5,6-benzoquinoline adsorption can inactivate the external surface of ZSM-5, thus suppressing disproportionation and transalkylation side reactions with which isomerization selectivity and xylene yield increase at the expense of EB conversion and p-xylene yield. In contrast, platinum impregnation cannot only retard the side reactions but can also enhance EB conversion, p-xylene yield and catalyst stability. Combining those simple techniques into a multiple modification procedure provoked a synergistic effect enabling optimum design of a Pt/Si/ZSM-5 catalyst. According to reaction mechanisms, the present paper also briefly reviews different generations of commercial isomerization processes.
Keywords: Xylene isomerization; Ethylbenzene dealkylation; Surface modification; Aromatics interconversion; Selectivity
Aerobic oxidation of cyclohexane with γ-alumina supported metallophthalocyanines in the gas phase by Amin Ebadi; Nasser Safari; Mohammad Hassan Peyrovi (pp. 135-139).
Unsubstituted phthalocyanines of Co, Fe and Mn supported on γ-alumina were synthesized and characterized with UV–vis and IR spectroscopic techniques. Catalytic activities of the supported phthalocyanines for oxidation of cyclohexane to cyclohexanol and cyclohexanone by air were studied in the gas phase in the absence of solvents and reducing agents. These metallophthalocyanines (MPc) supported on γ-alumina were effective catalysts in a temperature range of 300–400°C at 1atm of air. Under these reaction conditions, the order of catalytic activities is as follows: CoPc/γ-alumina>FePc/γ-alumina>MnPc/γ-alumina. When the reaction was catalyzed with γ-alumina without any phthalocyanines, the reaction yield and conversion were reduced considerably compared to those of supported γ-alumina. With 10% CoPc supported on γ-alumina and under our experimental conditions, the conversion percent of cyclohexane is 32.6% with 37.3% selectivity of cyclohexanol+cyclohexanone and 17.4% cyclohexene at 340°C. To achieve higher conversion of cyclohexane and better selectivity toward cyclohexanone+cyclohexanol, factors such as type and percentage of the metallophthalocyanine, reaction temperature and space velocity were studied, and optimized conditions were investigated.Metallophthalocyanines supported on γ-alumina were effective catalysts of cyclohexane oxidation accompanied to cyclohexene formation in a temperature range of 300–400°C under atmospheric pressure of air and under these reaction conditions, the order of catalytic activities are as follows: CoPc/γ-alumina>FePc/γ-alumina>MnPc/γ-alumina.▪
Keywords: Aerobic oxidation; γ-Alumina support; Metallophthalocyanines; Cyclohexane; Cyclohexanol; Cyclohexanone
The role of SiO2 barrier layers in determining the structure and photocatalytic activity of TiO2 films deposited on stainless steel by P. Evans; T. English; D. Hammond; M.E. Pemble; D.W. Sheel (pp. 140-146).
TiO2 thin films were deposited using two different precursor systems, and their photocatalytic activities studied in the context of the feasibility of self-cleaning added value steel products. SiO2 layers deposited using flame-assisted CVD were investigated as possible barrier layers to prevent diffusion of substrate components in to the TiO2 films. The films were characterized by X-ray photoelectron spectroscopy (XPS), sputtered neutral mass spectrometry (SNMS), Raman spectroscopy and scanning electron microscopy (SEM). Photo-activity was characterised by the UV-induced destruction of stearic acid layers.On bare steel growth using titanium tetraisopropoxide yielded anatase, while growth with titanium tetrachloride (with ethyl acetate) yielded rutile. In contrast, on silica coated steels both precursor systems yielded anatase exclusively.The diffusion of components originating from the steel substrates was shown to have a deleterious effect on the photoactivities of the TiO2 thin films, with this effect being more influential at higher deposition temperatures. However, the presence of the SiO2 barrier layers significantly reduced ion diffusion into the TiO2 film and consequently also improved the photocatalytic activity of the samples. While the SiO2 coated samples gave rise to anatase growth, there is evidence that the thickness of the SiO2 coating has a direct effect on TiO2 morphology.This paper describes the deposition of TiO2 thin films using two different precursor systems, and their photocatalytic activities studied in the context of the feasibility of self-cleaning added value steel products. SiO2 layers deposited using flame-assisted CVD were investigated as possible barrier layers to prevent diffusion of substrate components in to the TiO2 films. ▪
Keywords: Titania; Silica; Steel; APCVD; TTIP; TiCl; 4
meta-Stannic acid as an effective support for the preparation of sulfated and tungstated stannias by Makoto Hino; Satoshi Takasaki; Satoshi Furuta; Hiromi Matsuhashi; Kazushi Arata (pp. 147-154).
Sulfated and tungstated stannias were prepared from commercial Sn-gels of meta-stannic acids; the former showed catalytic activities higher than those of the materials obtained from conventional gels and of sulfated zirconias. The latter led to the synthesis of a ceramics acid, calcined at >1000°C, whose catalytic activity and acidity were intermediate between mordenite and silica–alumina. ▪Sulfated stannia (SO4/SnO2) obtained by drying meta-stannic acids (supplied by Koujundo Kagaku and Yamanaka) at 200°C, followed by exposing to 3M H2SO4 and calcining at 300°C showed catalytic activities higher than those of the materials obtained from conventional gels (preparation of stannia gels from SnCl4 and calcination at 500°C) for the dehydration of methanol and the isomerization of butane. The catalytic activities were much higher than those of sulfated zirconias. The high activity for the reaction of methanol was kept beyond 8h of time on stream under flow conditions. The highest activity for the reactions of methanol and butane was brought out by the sulfation with 3–9M H2SO4. The thermal analysis determined the sulfur value in the catalyst to be 1.7, 2.6, 5.7, and 5.6wt.% S for the materials prepared by sulfation with 0.5, 1.5, 3, and 6M concentrations of H2SO4, followed by calcination at 300°C, respectively. Those quantities of S were coincident with their catalytic activities for the reactions of methanol and butane. Tungstated stannia (WO3/SnO2) was obtained by impregnating meta-stannic acid (Koujundo Kagaku Ltd.) with aqueous ammonium metatungstate (1–80wt.% W) followed by calcining in air; the materials were examined in the dehydrations of methanol and ethanol and the isomerization of cycloheptane to methylcyclohexane. The materials with small quantities of W gave their highest activities in the high temperature range of calcination, indicating the following tendency; the lower the quantity, the higher was the temperature showing the highest activity: 900, 1000, 1100, 1150, and 1250°C for the materials with 20, 10, 5, 2, and 1wt.% W, respectively. The results led to the synthesis of a ceramic acid, calcined at temperatures above 1000°C, by impregnating with 5 and 10%W followed by calcining at 1000 or 1100°C in air. The surface acidity determined by the adsorption heat of Ar and the catalytic activity for decompositions of toluene and ethylbenzene were intermediate between the values for mordenite and for silica–alumina, and the stability to water was high.
Keywords: meta; -Stannic acid; SO; 4; /SnO; 2; Ceramic acid; WO; 3; /SnO; 2; Dehydration; Methanol; Ethanol; Butane; Cracking; Ethylbenzene; Toluene; Ar adsorption
Partial oxidation of propane over Ru promoted Ni/Mg(Al)O catalysts by Dalin Li; Masato Shiraga; Ikuo Atake; Tetsuya Shishido; Yasunori Oumi; Tsuneji Sano; Katsuomi Takehira (pp. 155-164).
Ru–Ni0.5/Mg2.5(Al)O bimetallic catalysts prepared by adopting “memory effect” of hydrotalcite showed activity in the partial oxidation of propane to synthesis gas without pre-reduction treatment; the activity was enhanced by the reduction–oxidation treatment due to the formation of finely dispersed Ni–Ru bimetallic species. ▪Ru (0.1–0.5wt%) loaded Ni/Mg(Al)O catalysts have been prepared by adopting the “memory effect,” i.e., the reconstitution of Mg(Ni)–Al hydrotalcite from the Mg(Ni, Al)O periclase after the heat-treatment, and their catalytic activities have been tested in the partial oxidation of propane. The Ru–Ni0.5/Mg2.5(Al)O catalysts were prepared by dipping Mg2.5(Al,Ni0.5)O periclase derived from Mg2.5(Ni0.5)–Al hydrotalcite in an aqueous solution of Ru(III) nitrate. The reconstitution of hydrotalcite took place by the “memory effect” and was simultaneously accompanied by Ru incorporation in the hydrotalcite layer, leading to the formation of the active Ni–Ru bimetal loaded catalyst after the calcination followed by the reduction. Upon O2 purging at 700°C during the propane partial oxidation at 600°C, the Ru–Ni0.5/Mg2.5(Al)O catalyst showed no deactivation, while the Ni0.5/Mg2.5(Al)O catalyst was totally deactivated by the Ni oxidation. Moreover, the Ru–Ni0.5/Mg2.5(Al)O catalysts were self-activated under the reaction conditions without reduction pre-treatment with H2. The activity of the Ru–Ni0.5/Mg2.5(Al)O catalysts was enhanced with increasing the Ru loading after the reduction–oxidation pretreatment. After the treatment, two types of Ni reduction peak were observed in the TPR of the catalysts: the 1st peak observed around 550°C was weakened, whereas the 2nd peak observed around 750°C was enhanced, with increasing the Ru loading. The 1st is assigned to non-active Ni2+ ions having square-pyramidal coordination in the outermost layer of the Mg(Al)O structure, while the 2nd is probably of active Ni–Ru bimetallic species composed of finely dispersed Ni metal particles combined with Ru.
Keywords: Propane partial oxidation; H; 2; production; Ru–Ni/Mg(Al)O catalyst; Hydrotalcite; Self-activation; Reduction–oxidation treatment
Production of CO-free hydrogen through the decomposition of LPG and kerosene over Ni-based catalysts by Sakae Takenaka; Kenji Kawashima; Hideki Matsune; Masahiro Kishida (pp. 165-174).
Ni–Pd/SiO2 showed a higher activity and a longer life for the decomposition of hydrocarbons of C3–C8 into CO-free hydrogen, compared to Ni/SiO2 and Ni–Cu/SiO2 catalysts. These results suggested that Ni–Pd/SiO2 can produce CO-free hydrogen as a fuel for PEFC through the decomposition of LPG and kerosene.▪The catalytic performance of Ni-based catalysts for the decomposition of hydrocarbons of C3–C8 into CO-free hydrogen and carbon fibers was investigated in order to produce CO-free hydrogen as a fuel for PEFC from liquefied petroleum gas (LPG) and kerosene. The addition of Cu or Pd into Ni/SiO2 catalyst elongated its catalytic life for the propane decomposition. Especially, Ni–Pd/SiO2 catalyst showed higher activity and longer life for the decomposition of propane at 823 and 873K, compared to Ni/SiO2 and Ni–Cu/SiO2 catalysts. Ni–Pd/SiO2 catalyst was deactivated gradually with time on stream during the decomposition of propane due to the deposition of large amounts of carbon. However, the activity of the catalyst for the propane decomposition was recovered completely by the gasification of deposited carbon with CO2 into CO. This result suggested that CO-free hydrogen and CO could be produced successively through the decomposition of hydrocarbons and the subsequent gasification of deposited carbon with CO2. Ni–Pd/SiO2 showed high catalytic activity for the decomposition of hydrocarbons of C6–C8 to form CO-free hydrogen. Thus, CO-free hydrogen was produced through the decomposition of commercial kerosene over Ni–Pd/SiO2 catalyst.
Keywords: Ni-based catalysts; Ni–Pd/SiO; 2; catalyst; Decomposition of hydrocarbons; CO-free hydrogen; Carbon fiber; LPG; Kerosene
Synthesis of dialkyl peroxides in the presence of polyethylene glycol or its derivatives as phase-transfer catalyst in liquid–liquid–liquid system by Stefan Baj; Agnieszka Siewniak (pp. 175-179).
Synthesis of dialkyl peroxides in the presence of polyethylene glycol or its derivatives (PEG) as phase-transfer catalyst in liquid–liquid–liquid system was investigated. Conditions for forming a third-liquid phase, rich in phase-transfer catalyst were determined and included the amount and concentration of NaOH in the aqueous phase and the kind of organic solvent. The effect of chain length of PEG and possibility of catalyst recycling was also examined. Selected dialkyl peroxides were obtained in high yields (68–96%). ▪Synthesis of dialkyl peroxides in the presence of polyethylene glycol or its derivatives (PEG) as phase-transfer catalyst in liquid–liquid–liquid system was investigated. Conditions for forming a third-liquid phase, rich in phase-transfer catalyst were determined and included the amount and concentration of NaOH in the aqueous phase and the kind of organic solvent. The effect of chain length of PEG and possibility of catalyst recycling was also examined. Selected dialkyl peroxides were obtained in high yields.
Keywords: Dialkyl peroxides; Hydroperoxides; Phase-transfer catalysts
Autonomous and forced oscillations during methane oxidation over cobalt catalysts by V.Yu. Bychkov; Yu.P. Tyulenin; M.M. Slinko; V.N. Korchak (pp. 180-189).
Oscillatory behaviour during methane oxidation over a Co foil has been studied using on-line mass-spectrometry and video recording of the colour of the catalyst surface. It was demonstrated that during oscillatory behaviour, periodic transitions of the catalyst surface from an oxidised state (dark colour) to a reduced state (light colour) occurred together with the variation of the catalyst temperature. Oscillations over the Co foil appeared at higher temperatures (860–950°C), and had longer periods, in comparison with oscillatory behaviour which was observed earlier over a nickel foil. The application of TGA in combination with TPR experiments revealed the differences in nickel and cobalt redox properties which are responsible for the variation in the properties of the oscillations. Forced oscillations could be obtained in a low temperature region (700–860°C), if bare chromel and alumel wires were spot-welded separately to the cobalt foil. ▪Oscillatory behaviour during methane oxidation over a cobalt foil has been studied using on-line mass-spectrometry and video recording of the colour of the catalyst surface. It was demonstrated that during oscillatory behaviour, periodic transitions of the catalyst surface from an oxidised state (dark colour) to a reduced state (light colour) occurred together with the variation of the catalyst temperature. Oscillations over the cobalt foil appeared at higher temperatures (860–950°C), and had longer periods, in comparison with oscillatory behaviour which was observed earlier over a nickel foil. The application of TGA in combination with TPR experiments revealed the differences in nickel and cobalt redox properties which are responsible for the variation in the properties of the oscillations. Forced oscillations could be obtained in a low temperature region (700–860°C), if bare chromel and alumel wires were spot-welded separately to the cobalt foil. It was shown that in this case the chromel wire induced oscillatory behaviour of the whole cobalt foil. Complicated mixed mode oscillations detected at higher temperatures were shown to be the result of the coupling of high frequency oscillations produced by the unshielded chromel–alumel thermocouple and low frequency oscillations appearing over the cobalt foil.
Keywords: Oscillations; Forced oscillations; Methane oxidation; Cobalt catalysts; Nickel catalysts; Synchronization
Facile preparation of RuO2/CNT catalyst by a homogenous oxidation precipitation method and its catalytic performance by Xiaobo Fu; Hao Yu; Feng Peng; Hongjuan Wang; Yu Qian (pp. 190-197).
CNT-supported highly dispersed hydrous RuO2 nanoparticles can be facilely prepared by a homogenous oxidation precipitation method using hydrogen peroxide as both oxidant and precipitant at room temperature. This new method provides an effective way to prepare new catalysts for aerobic oxidation of alcohols and demonstrates the great potential of CNTs as catalyst supports. ▪Ruthenium(IV) oxide (RuO2) nanoparticles supported by herringbone carbon nanotubes (CNTs) were synthesized by a homogenous-oxidation-precipitation (HOP) method with H2O2. The morphology and composition of the resulting composite were characterized by TEM, XPS, XRD, TG and TPR. CNTs exhibited the better ability to induce the formation of highly dispersed nanoparticles, compared with common used supports, such as γ-Al2O3 and activated carbon. Amorphous hydrous RuO2 nanoparticles uniformly dispersed on the surface of CNTs. The average size of RuO2 was significantly reduced to 1.35nm. This result leads to the high activity and excellent selectivity, which has been demonstrated in the aerobic oxidation of alcohols to aldehydes or ketones. The new preparation technique of CNT-supported oxide nanoparticles reported in this paper has great potential for various catalytic applications.
Keywords: Carbon nanotubes; Ruthenium oxide catalyst; Nanoparticles; Aerobic oxidation; Alcohols