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Applied Catalysis A, General (v.306, #1-198)
Evaluation of vanadium traps occluded in resid fluidized catalytic cracking (RFCC) catalyst for high gasoline yield by Hee Jung Jeon; Sang Ku Park; Seong Ihl Woo (pp. 1-7).
As crude oil becomes heavier, it contains more poisonous metals such as Ni, Fe and V and more Conradson carbon residue (CCR). More efficient metal traps are required to increase the gasoline yield. MgO, CaO, CeO2, MgTiO3, CaTiO3, Li2Ti2O7 and ZnTiO3 were evaluated for their capabilities to passivate vanadium compounds into non-poisonous compounds in the n-hexadecane and vacuum gas oil cracking reactions by measuring the yield for H2, dry gas, gasoline and coke. These vanadium traps were incorporated during the preparation of resid fluidized catalytic cracking (RFCC) catalyst. Mitchell deactivation method gave more reliable results because of its more uniform distribution of metals on the surface of RFCC catalysts. It was found that mixtures of CeO2 and MgO are best as a vanadium trap. The number of acid site, BET surface area, pore size distribution and pore volumes of prepared RFCC catalyst are dependent on the structure, amount and morphology of vanadium traps incorporated into the RFCC catalyst.
Keywords: Metal trap; Magnesium oxide; Perovskite; RFCC catalyst; MAT; n; -Hexadecane cracking test
A comparison study on the partial oxidation of n-butane and propane over VPO catalysts supported on SBA-15, MCM-41, and fumed SiO2 by Xiu-Kai Li; Wei-Jie Ji; Jing Zhao; Zhibing Zhang; Chak-Tong Au (pp. 8-16).
A desorption–precipitation method was used to prepare VPO catalysts supported on SBA-15, MCM-41, and fumed SiO2 for the partial oxidation of n-butane and propane. Techniques such as N2 adsorption–desorption measurements, XRD, XPS, Raman, and H2-TPR were adopted to explore the nature of the catalysts as well as the characters of the supported VPO species. For all the samples, the VPO components were present predominantly in the form of well-crystallized (VO)2P2O7 phase, and the VOPO4-like phases were absent. The interaction between VPO and support was significant for the samples activated under n-butane/air but not so much for those activated in the atmosphere of water vapor/propane/air. Hence, the key factors that influenced the catalytic activity in n-butane and propane oxidation should be VPO-support interaction and VPO dispersion. Generally speaking, the VPO catalysts supported on the three silica-based materials showed fairly good performance for n-butane oxidation (i.e. high in butane conversion and MA selectivity). The three catalysts are less active for propane oxidation but show fairly good selectivity to propylene and acid products at low propane conversion. The discrepancies in the reaction behavior suggest that VPO-type catalysts are rather structure specific towards the reactant molecules.
Keywords: Supported VPO; Partial oxidation; n; -Butane; Propane; SBA-15; MCM-41; Fumed SiO; 2
Discovery of new catalytic materials for the water–gas shift reaction by high-throughput experimentation by G. Grubert; S. Kolf; M. Baerns; I. Vauthey; D. Farrusseng; A.C. van Veen; C. Mirodatos; E.R. Stobbe; P.D. Cobden (pp. 17-21).
New Cu-free non-pyrophoric catalytic materials have been discovered for the water–gas shift reaction (WGSR) by high-throughput experimentation applying an evolutionary search strategy. Two approaches were applied for the design of experiments: (1) the amount of Cu in the composition was not restricted; as expected from common knowledge Cu containing catalysts were superior within the given parameter space. (2) By allowing only a maximum Cu content of 1wt.% in the second approach new Cu-free materials were discovered. The new compositions contained mainly oxides of Cr or Fe along with Mn and Pt on ZrO2 as support material. A maximal activity for WGSR was achieved at 250°C (CO conversion of 55%); the feed composition amounted to 3% CO, 37% H2, 14% CO2, 23% H2O, Ar balance and the GSHV to 3000h−1.
Keywords: Water–gas shift reaction; Cu catalysts; Zirconia-supported catalysts; Oxides of Cr; Fe; Mn and Pt as compounds for WGSR catalysts; Genetic algorithm-based experimental design; High-throughput experimentation
Production of hydrogen by steam reforming of methanol over copper-based catalysts: The effect of cesium doping by A. Houteit; H. Mahzoul; P. Ehrburger; P. Bernhardt; P. Légaré; F. Garin (pp. 22-28).
The catalytic production of hydrogen by steam reforming of methanol was investigated using samples of copper oxide supported on alumina (Cu/Al2O3) and promoted with cesium (Cu-Cs/Al2O3). The effects of cesium content and reaction temperature on the catalytic activity were investigated. The Cu-Cs/Al2O3 catalysts exhibited higher activity and stability as compared to the undoped ones. The catalyst containing 2wt% of cesium was the most active and at 300°C the methanol conversion reached 94mol% and the hydrogen selectivity 97mol% with no detectable formation of CO. After an ageing treatment at 400°C, methanol conversion was still close to 100% with the cesium-doped catalyst, while the undoped catalyst drastically deactivated. X-ray powder diffraction (XRD) and XPS measurements indicate that cesium prevents the reduction of copper oxide into metallic Cu, by the hydrogen produced, and inhibits the formation of CuAl2O4 spinel upon thermal treatment.
Keywords: Methanol reforming; Steam reforming; Hydrogen production; Copper; Cesium
Methane partial oxidation to syngas in YBa2Cu3O7− x membrane reactor by Jie Hu; Tianlai Xing; Qingchao Jia; Haoshan Hao; Delin Yang; Yiqun Guo; Xing Hu (pp. 29-33).
We investigated the performance of YBa2Cu3O7− x (YBCO) membrane reactor in the process of partial oxidation of methane (POM) to syngas. When Ni/ZrO2 catalyst was used the CH4 conversion and CO selectivity could reach almost 100% and 95%, respectively, and the oxygen permeation fluxes could reach 1.5mlmin−1cm−2 at 900°C. The YBCO membranes reactor also showed self-catalytic properties; without any catalysts the CH4 conversion and CO selectivity could reach about 28% and 90% at 900°C, respectively. However, the stability of YBCO membrane was not desirable because of the reduction of copper from the YBCO membrane. The reaction mechanism of POM in YBCO reactor was also discussed based on the influence of space velocity (SV) on CO selectivity. The indirect partial oxidation mechanism may be the dominant mechanism of POM process in the YBCO membrane reactor.
Keywords: Methane; Partial oxidation; Syngas; YBa; 2; Cu; 3; O; 7−; x; Membrane reactor
Effect of H2S partial pressure on the HDS of dibenzothiophene and 4,6-dimethyldibenzothiophene over sulfided NiMoP/Al2O3 and CoMoP/Al2O3 catalysts by V. Rabarihoela-Rakotovao; S. Brunet; G. Perot; F. Diehl (pp. 34-44).
The effect of hydrogen sulfide (H2S) partial pressure on the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (46DMDBT) was studied over commercial NiMoP/Al2O3 and CoMoP/Al2O3 catalysts under conditions close to those commonly used in the hydrotreating of diesel fuels (280 or 340°C; total pressure between 2.5 and 5.5MPa). The sulfur compounds diluted in n-heptane were in proportions representative of those found in diesel fuels (0.0014MPa of DBT or 46DMDBT, 0.0058–0.1MPa of H2S generated from dimethyldisulfide).A significant negative effect of H2S on the HDS of the dibenzothiophenes (DBT and 46DMDBT) was observed whatever the total pressure (2.5–5.5MPa) and the catalyst used. However, the reactivity of DBT was more reduced than that of 46DMDBT. Moreover, the “direct desulfurization pathway� (DDS) of both reactants was more inhibited by H2S than the so-called “hydrogenation pathway� (HYD) over the two catalysts. It was also found that the NiMoP/Al2O3 catalyst was more sensitive to H2S than its CoMoP/Al2O3 counterpart whatever the experimental conditions.Several hypotheses were considered and discussed to explain these findings: specific centres for each of the two reactions (DDS and HYD) or centres being similar in nature (sulfur vacancies associated to sulfur anions) but which would differ in their acid–base properties. It was also suggested that the centres could be identical but that DDS and HYD could have different rate-limiting steps which would not involve the same part of the dual site so that their sensitivity to H2S would be different.
Keywords: Deep hydrodesulfurization; Dibenzothiophene; 4,6-Dimethyldibenzothiophene; NiMoP/Al; 2; O; 3; CoMoP/Al; 2; O; 3; H; 2; S effect; H; 2; S/H; 2; ratio
Partial oxidation of methane to syngas with or without simultaneous steam or CO2 reforming over a high-temperature stable-NiCoMgCeO x supported on zirconia–hafnia catalyst by V.R. Choudhary; K.C. Mondal; T.V. Choudhary (pp. 45-50).
A NiCoMgCeO x (Ni/Co/Mg/Ce:1:0.2:1.2:1.2)/zirconia–hafnia catalyst with unusually high thermal stability has been investigated for syngas generation via a process that includes the catalytic partial oxidation of methane (CPOM), the oxidative steam reforming of methane (OSRM) and the oxidative CO2 reforming of methane (OCRM). The catalyst calcined at 1400°C (for 4h) showed excellent activity/selectivity for the CPOM, OSRM and the OCRM reactions; furthermore no catalyst deactivation was observed for a period of 20h. For the CPOM process, the selectivity for H2 was >95% at reaction temperatures ≥650°C; however temperatures above 800°C were required to achieve >95% CO selectivity. While the reaction temperature had a considerable influence on the CPOM product H2/CO ratio, the space velocity (at 850°C) did not affect it to any significant extent. For the OSRM process, the H2O/CH4 ratio and the reaction temperature had a strong effect on the product H2/CO ratio and the heat of the reaction; depending on the H2O/CH4 ratio and reaction temperature, the OSRM process could be operated in a mildly exothermic, thermoneutral or mildly endothermic mode. The CO2 conversion was very strongly affected by the reaction temperature in the OCRM process; reasonably high CO2 conversion (>40%) could only be obtained at high OCRM reaction temperatures (>850°C). The exothermicity of the OCRM reaction was found to decrease with increasing reaction temperature.
Keywords: Methane; Partial oxidation; Syngas; Steam reforming; Dry (CO; 2; ) reforming; Oxy-steam reforming; High-temperature stable
An investigation on the use of liquid phase photo-deposition for the preparation of supported Pt catalysts by C. Crisafulli; S. Scirè; S. Giuffrida; G. Ventimiglia; R. Lo Nigro (pp. 51-57).
The preparation of alumina supported Pt catalysts through a photochemical approach, namely the liquid phase photo-deposition (LPPD) technique, was here investigated. LPPD Pt/γ-Al2O3 catalysts were prepared irradiating at 25°C and different wavelengths (254, 350 and 400nm) an ethanol suspension of Pt(acac)2 containing γ-Al2O3. Catalytic activity of so prepared samples was evaluated in the combustion of volatile organic compounds (VOC) and in the hydrogenation of propene, comparing the results with those of a conventionally impregnated Pt/γ-Al2O3 sample. LPPD catalysts exhibited better performance, in particular in the VOC combustion, compared to the reference Pt sample. The activity was found to be substantially independent from the wavelength irradiation employed during catalysts preparation. On the basis of characterization results (TEM, H2 chemisorption and FT-IR of chemisorbed CO) the higher activity of LPPD samples was related to the narrower particle size distribution of Pt clusters observed on these samples with respect to that of the impregnated Pt catalyst.
Keywords: Catalyst preparation; Platinum; Alumina; Photo-deposition; LPPD; Combustion; Volatile organic compounds
Photocatalytic activities of a novel ZnWO4 catalyst prepared by a hydrothermal process by Hongbo Fu; Jie Lin; Liwu Zhang; Yongfa Zhu (pp. 58-67).
ZnWO4 catalysts have been successfully synthesized by a hydrothermal crystallization process. ZnWO4 catalyst synthesized at 180°C for 24h exhibited relatively high photochemical activity for the decomposition of rhodamine-B, and showed better activity for the degradation of formaldehyde than that of TiO2 (P-25). The generations of the photocurrent and H2 evolution from pure water were also realized. UV bands observed in the catalyst were assigned to the band transition from the occupied O 2p orbitals to the empty W 5d orbitals. On the basis of the analysis of the energy levels and the band structures, the photocatalytic mechanism of the catalyst was also discussed.
Keywords: ZnWO; 4; Photocatalyst; Nanorod; Rhodamine-B; Formaldehyde
Performance of Pt/CeO2 catalyst for propane oxidative steam reforming by Lidia Pino; Antonio Vita; Francesco Cipitì; Massimo Laganà ; Vincenzo Recupero (pp. 68-77).
Catalytic autothermal reforming of hydrocarbons to hydrogen rich reformate represents an important step in fuel processor development for fuel cell systems. As a part of a larger research program aimed at developing and testing of such system based on autothermal reforming of light hydrocarbons, like liquefied petroleum gas (LPG), to be integrated with polymer electrolyte fuel cells (PEM), we investigated the C3H8 oxidative steam reforming (OSR) over a Pt/CeO2 catalyst prepared by combustion synthesis technique. The catalytic activity, as a function of O2/C3H8, H2O/C3H8 molar ratios in the feed, reaction temperature and gas hourly space velocity, was evaluated. The experimental tests were used to define the operating parameters that can assure total fuel conversion and high H2 selectivity, basic elements for the realization of a fuel processor.
Keywords: Propane oxidative steam reforming; Hydrogen production; Ceria-supported platinum catalyst
Effects of crystal size and Si/Al ratio on the surface properties of H-ZSM-5 zeolites by T. Armaroli; L.J. Simon; M. Digne; T. Montanari; M. Bevilacqua; V. Valtchev; J. Patarin; G. Busca (pp. 78-84).
Highly crystalline H-ZSM-5 zeolite samples with crystal sizes from 0.5 to 5μm and Si/Al ratios ranging from 20 to 70 have been prepared and characterized by IR spectroscopy, SEM and XRD techniques. The surface properties of these materials have been compared with those of conventional small crystal size materials by using FT-IR spectroscopy of the surface hydroxyl groups and of adsorbed carbon monoxide. The external surface has been investigated using pivalonitrile (2,2-dimethyl-propionitrile) as an adsorption probe. Data show that the basic structure of the zeolite active sites do not depend significantly on the crystal size. Brønsted acid sites of high acid strength are constituted by bridging OH groups located inside the zeolite channels, while Lewis acid sites and weakly acidic silanol groups are found on the external surface in all cases.
Keywords: ZSM5 zeolite; Lewis acidity; Brønsted acidity; External surface; Crystal size; Morphology; IR spectroscopy; CO adsorption; Nitrile adsorption
Non-oxidative propane dehydrogenation over Pt–Zn-containing zeolites by Patrizia Laura De Cola; Roger Gläser; Jens Weitkamp (pp. 85-97).
Starting from the zeolites Na-ZSM-5 (MFI), Na-ZSM-11 (MEL), Na-Beta (*BEA), Na-mordenite (MOR), K-L (LTL) and Na-Y (FAU), Pt–Zn-containing catalysts with a zinc content between 0.6 and 13.4wt.% and a platinum content of 0.5wt.% were prepared. Zinc was introduced by impregnation or aqueous ion exchange, platinum by subsequent impregnation with H2PtCl6. The catalysts were characterized by chemical analysis (AES/ICP), X-ray diffraction (XRD), FT IR spectroscopy of adsorbed pyridine, nitrogen adsorption and temperature-programmed reduction (TPR). After the aqueous ion exchange of the zeolites with nSi/ nAl-ratios≥26, the zinc content in the catalysts was higher than that expected from their ion exchange capacity. This over-exchange with zinc was explained by the formation of oxidic zinc species. The Pt–Zn-containing zeolites were tested in the non-oxidative dehydrogenation of propane at 555°C. Aromatization occurred over the 10-membered-ring zeolites Na-ZSM-5 and Na-ZSM-11, whereas propane dehydrogenation was the major reaction over the 12-membered-ring zeolites Na-Beta, Na-mordenite, K-L and Na-Y. The different procedures used for the incorporation of zinc did not significantly affect the catalytic behavior of the large-pore zeolites with lower nSi/ nAl-ratios (≤3.4). The highest and most stable conversion levels were obtained on zeolites Beta and mordenite with nSi/ nAl-ratios≥8.7 and zinc contents close to 2.5wt.%. Over the zeolite 0.5Pt/2.6Zn-Beta, a stable conversion close to the thermodynamic equilibrium for the dehydrogenation of propane to propene ( XPr≈29%, T=555°C and p=0.1MPa) was observed for at least 63h time-on-stream. The propene selectivity over this zeolite was >90%.
Keywords: Pt–Zn-zeolites; Propane dehydrogenation; Zinc ion exchange; Zinc over-exchange
Effect of preparation conditions on the catalytic performance of cobalt manganese oxide catalysts for conversion of synthesis gas to light olefins by Ali A. Mirzaei; Mostafa Faizi; Razieh Habibpour (pp. 98-107).
Cobalt manganese oxides are prepared using a co-precipitation procedure and studied for the conversion of synthesis gas to light olefins. In particular, the effect of a range of preparation variables is investigated in detail. The variables investigated include the precipitate ageing time, pH and temperature of precipitation, the [Co]/[Mn] ratio of the precipitation solution and also reactor conditions such as reaction temperature and H2/CO molar feed ratio. The effect of different supports on the activity and selectivity of catalysts are also studied. The optimum preparation conditions are identified with respect to catalytic performance for the conversion of synthesis gas to ethylene and propylene. The results are interpreted in terms of the structure of the active catalyst. Generally it has been concluded that catalysts containing cobalt manganese mixed phases are found to be the most active.
Keywords: Catalyst preparation condition; Co-precipitation; Effect of ageing; Cobalt manganese oxide catalyst; Fischer–Tropsch synthesis; Light olefins
In situ characterization of the genesis of cobalt metal particles in silica-supported Fischer-Tropsch catalysts using Foner magnetic method by P.A. Chernavskii; A.Y. Khodakov; G.V. Pankina; J.-S. Girardon; E. Quinet (pp. 108-119).
The genesis of cobalt metal particles in silica-supported Fischer-Tropsch catalysts was studied using in situ Foner vibrating-sample magnetic method. The cobalt promoted and unpromoted catalysts were prepared by aqueous (co)-impregnation using cobalt nitrate or acetate, ruthenium nitrosyl nitrate or perrhenic acid followed by oxidative pre-treatment in air and reduction in hydrogen. In several catalyst preparations, sucrose was added to the impregnating solutions.The genesis of cobalt metal phases in these catalysts was monitored in situ by the magnetic method during the temperature-programmed reduction in pure hydrogen. A considerably higher extent of cobalt reduction was found in the catalysts prepared from cobalt nitrate than in those prepared from cobalt acetate. Promotion with ruthenium and rhenium results in a considerable decrease in the temperature of the emergence of cobalt metal phases.Small superparamagnetic, single-domain and multi-domain ferromagnetic cobalt metal particles were observed in the reduced catalysts by the magnetic method. It was found that lower temperature calcination of the cobalt catalysts prepared from cobalt nitrate and addition of sucrose to the impregnating solution lead to a decrease in the concentration of multi-domain cobalt ferromagnetic metal particles and to an increase in the fraction of superparamagnetic cobalt particles. Superparamagnetic cobalt particles smaller than 6–7nm were detected in the reduced catalysts prepared from cobalt nitrate with sucrose addition and in the catalysts prepared from cobalt acetate. Catalyst characterization using X-ray diffraction and X-ray photoelectron spectroscopy has confirmed the results about cobalt dispersion and reducibility in the cobalt silica-supported catalysts obtained by the Foner magnetic method.
Keywords: In situ; Catalyst characterization; Dynamic magnetic method; Foner vibrating-sample magnetometer; Fischer-Tropsch synthesis; Cobalt catalyst; Nanoparticles
Synthesis, characterization and photocatalytic activity of different metal-doped titania systems by J.C. Colmenares; M.A. AramendÃa; A. Marinas; J.M. Marinas; F.J. Urbano (pp. 120-127).
Different titania-based systems doped with diverse transition metals (Ag, Fe, Pd, Pt, Zn and Zr) were synthesized by the sol–gel method. Samples were characterized by a wide range of physical techniques (ICP-MS, N2-isotherms, TGA–DTA, TEM, XRD, FT-Raman and UV–vis spectroscopies). The effect of aging of the gel either under magnetic stirring (ST) or ultrasonic irradiation (US) on the characteristics of the resulting solids was studied. Sonication ensured the obtention of pure anatase nanoparticles and generally led to an increase in surface area. All the solids were tested for gas phase selective photooxidation of 2-propanol. Irrespective of the aging method, doping with Pd, Pt or Ag resulted in an increase in molar conversion as compared to bare-TiO2, whereas the presence of Fe and Zr had a detrimental effect. Those solids for which sonication had the greatest impact on textural and structural characteristics (bare-TiO2 and Zn-containing samples) exhibited the greatest difference in molar conversion. Moreover, high selectivities to acetone were achieved in most of the cases.
Keywords: Photocatalysis; Selective photooxidation; Titania-based catalysts; Metal-doped catalysts; Sonication; Isopropanol; Sol–gel synthesis
New biocomponents from glycerol by R.S. Karinen; A.O.I. Krause (pp. 128-133).
Glycerol is a by-product of biodiesel production, for which new uses are being sought. Etherification of glycerol with isobutene in liquid phase with acidic ion exchange resin catalyst gave five product ethers and, as a side reaction, isobutene reacted to C8–C16 hydrocarbons. The effect of the reaction conditions on the system was studied and conditions for optimal selectivity toward ethers were discovered near with isobutene/glycerol molar ratio of 3 at 80°C. The conditions controlling the distribution of the product ethers were studied and it was found that the extent of the etherification reaction and thus the main ether products can be changed by varying the reaction conditions.
Keywords: Etherification; Glycerol; Isobutene; tert; -Butyl ether of glycerol
Production of hydrogen by steam reforming of ethanol over Ni/Al2O3 spherical catalysts by Humberto Vieira Fajardo; Luiz Fernando Dias Probst (pp. 134-141).
A new and simple method to prepare Al2O3 and Ni/Al2O3 spherical catalysts for hydrogen production by steam reforming of ethanol is proposed. The present method was developed using a biopolymer (chitosan) and Al solution. A hybrid spherical compound of aluminum hydroxide and the biopolymer is formed. Through polymer elimination by thermal treatment, porous spheres with a high specific surface area and large pore volume are obtained. The Ni/Al2O3 spheres showed a high catalytic activity in ethanol steam reforming and hydrogen selectivity at temperatures between 450 and 650°C. In all cases no CO was detected indicating that the Ni/Al2O3 spheres could be considered as a good choice for hydrogen production from ethanol steam reforming for fuel-cell applications.
Keywords: Hydrogen; Alumina; Catalysts; Steam reforming
The role of support and promoter on the oxidation of sulfur dioxide using platinum based catalysts by Sotirios Koutsopoulos; Søren B. Rasmussen; K. Michael Eriksen; Rasmus Fehrmann (pp. 142-148).
The catalytic oxidation of SO2 to SO3 was studied over platinum based catalysts in the absence and the presence of dopants. The active metal was supported on silica gel or titania (anatase) by impregnation. The activities of the silica supported catalysts were found to follow the order Pt–Rh/SiO2>Pt/SiO2>Pt–Al/SiO2. For the samples supported on titania the respective order was Pt/TiO2>Pt–Rh/TiO2>Pt–Al/TiO2. The size of the particles of the active phase, the presence of dopants and the purity of the catalyst were found to affect the catalytic performance. A careful selection of the pH of the impregnation solution and of the reduction temperature of the precursor salts resulted in a very active catalyst with average particle size of 1.7nm.
Keywords: Silica; Titania; Platinum; Palladium; Rhodium; Catalyst; Sulphur dioxide oxidation
n-Octane aromatization on Mo2C-containing catalysts by Aleksandar Széchenyi; Frigyes Solymosi (pp. 149-158).
The reaction pathways of n-octane were studied on various Mo2C-containing catalysts. On unsupported Mo2C prepared by C2H6/H2 gas mixture the reaction of octane started at 573K, and the conversion reached an initial value of ∼38% at 873K. At lower temperature, 573–623K, the main process is the dehydrogenation with some cracking. At 673–873K, however, aromatics, xylene, toluene, benzene and ethylbenzene also formed with 58–30% selectivity. On Mo2C/Al2O3 the product distribution was different. At 773–823K the main aromatics were ethylbenzene and o-xylene, they formed with ∼62–51% selectivity at 23–50% conversion. In contrast, on Mo2C/ZSM-5(80), which was found to be the most effective catalyst in the present work, toluene and benzene were the dominant aromatics. This suggests that the occurrence of the hydrogenolysis of C8 aromatics on the acidic sites of ZSM-5. This catalyst exhibited a very stable activity: the conversion decayed only with few percent even after 10h, and the aromatizing capability also remained high. The results are interpreted by the monofunctional (pure Mo2C) and bifunctional mechanism (supported Mo2C) of the aromatization of n-octane.
Keywords: Dehydrogenation of octane; Aromatization of octane; Reaction of octene; Mo; 2; C catalyst; Mo; 2; C/Al; 2; O; 3; Mo; 2; C/SiO; 2; Mo; 2; C/ZSM-5
Acylation of 2-methoxynaphthalene with acetic anhydride over silica-embedded triflate catalysts by A.N. Pârvulescu; B.C. Gagea; V.I. Pârvulescu; D. De Vos; P.A. Jacobs (pp. 159-164).
Silica sol–gel immobilized triflate compounds like La(OTf)3, tert-butyldimethylsilyl trifluoromethanesulfonate (BDMST) and triflic acid (HOTf) were tested in the acylation of 2-methoxynaphthalene with acetic anhydride, leading to 1-acetyl-2-methoxynaphthalene as the major product. The reaction only proceeded with good yields on BDMST and HOTf catalysts, while La(OTf)3 presented a low activity. For BDMST in solvent-free conditions, the resulting TOF was superior to that reported in literature for other heterogeneous catalysts and even for homogeneous triflates. The rates of reactions in various solvents strongly depend on the donor number of these solvents.
Keywords: La(OTf); 3; tert; -Butyldimethyl silyltrifluoromethanesulfonate; Triflic acid; Acylation of 2-methoxynaphthalene
Preparation and characterization of molybdenum sulfide supported on β-zeolites obtained from [Mo3S4(H2O)9]4+ precursor by Claude-Emmanuel Hédoire; Emmanuel Cadot; Françoise Villain; Anne Davidson; Catherine Louis; Michèle Breysse (pp. 165-174).
In this paper, we report an alternative procedure of cation exchange to introduce higher amount of [Mo3S4(H2O)9]4+ in β-zeolites than as reported for various zeolites (∼2wt.%). The parent β-zeolite (Si/Al=13.8) was partially dealuminated with a nitric acid treatment (Si/Al=15.0 and 18.7). The three zeolites of various acidities were used as supports. The addition of ammonia during the cation exchange procedure allowed us to double the Mo loadings (4.5wt.%) even with the most dealuminated zeolite. The acidity of the zeolitic host was restored after exchange through a thermal treatment at 350°C under Ar. Characterizations of the Mo/β catalysts by XRD, BET and EXAFS revealed that the structures of the zeolites and that of [Mo3S4(H2O)9]4+ were preserved during ion-exchange procedure. After the thermal treatment at 350°C, UV–visible spectroscopy, EXAFS and TEM showed that the [Mo3IVS4(H2O)9]4+ was decomposed leading to MoIVS2 and a MoVIO x species probably grafted onto the zeolite surface. Whatever the exchange conditions, in presence or in absence of ammonia, molybdenum was mainly located on the external surface of the zeolite grains and a small fraction was inside the porosity as indicated by the TEM study.
Keywords: Catalyst preparation; Cation exchange; [Mo; 3; S; 4; (H; 2; O); 9; ]; 4+; Thiocomplex; Cubane; β-Zeolites; Hydrodesulfurization; Hydrotreatment; Acidity; EXAFS; XANES; TEM; UV–visible
A CO-TAP study of the reducibility of La1− xSr xFe(Pd)O3± δ perovskites by Zhaoxia Song; Hiroyasu Nishiguchi; Wei Liu (pp. 175-183).
In order to obtain useful information about the effect of Sr, Pd promotion and calcination temperature on the reducibility of La1− xSr xFe(Pd)O3± δ perovskites, CO-TAP in combination with XRD, BET, TG-DTA, and SEM were employed to characterise the perovskite oxides prepared by the method of sol–gel auto-combustion. Reducibility of the perovskites was studied by means of the oxygen release capacity measurement in which a TAP reactor system was used to perform the CO pulse or alternate CO–O2 pulse experiments. Partial substitution of La3+ by Sr2+ in LaFeO3 significantly enhanced the reducibility and La0.6Sr0.4FeO3± δ showed the highest reducibility among the La1− xSr xFeO3± δ perovskites. An incorporation of Pd in replacement of 5mol% of Fe into La0.6Sr0.4FeO3± δ caused a significant decrease of reduction temperature and an enhancement of reducibility. Moreover, the thermal stability was improved in the presence of Pd. It was found that the reducibility was strongly affected by the calcination temperatures. Extremely high reducibility (ca. 650μmol-CO2 g−1 of OSC and ca. 800μmol-CO2 g−1 of OSCC) was observed on the 1000°C calcined La0.6Sr0.4Fe0.95Pd0.05O3± δ although its BET specific surface area was very low. We concluded that calcination of La0.6Sr0.4Fe0.95Pd0.05O3± δ at relatively high temperatures was favourable of creating more lattice defects and the lattice defects instead of surface area were mainly responsible for the reducibility.
Keywords: Temporal analysis of products (TAP); Perovskite; Reducibility; Sol–gel auto-combustion method
Reaction kinetics of an ethylene tetramerisation catalyst by Richard Walsh; David H. Morgan; Annette Bollmann; John T. Dixon (pp. 184-191).
This paper describes a study on the reaction kinetics of an ethylene tetramerisation catalyst comprising Cr(acac)3, a bis(diphenylphosphino)isopropylamine ligand and MAO as catalyst activator. The reaction rate was found to be dependent on temperature as well as on ethylene concentration to the order of 1.57. The catalyst deactivation rate was found to be a function of temperature. A reaction rate model was developed providing good description of reaction performance in the temperature range of 35–45°C and pressure range of 30–45bar. Selectivity data is provided which illustrates the effects of pressure, temperature and time on stream. Increased temperature and decreased pressure result in increased 1-hexene and decreased 1-octene selectivity, while time on stream data indicates the occurrence of secondary incorporation reactions of 1-hexene and 1-octene.
Keywords: Tetramerisation; Trimerisation; Aluminoxane; Chromium; Bis(diphenylphosphino)isopropylamine; Selective oligomerisation; Reaction kinetics
Sulphamic acid: An efficient, cost-effective and recyclable solid acid catalyst for highly chemoselective allylation of aldehydes by J.S. Yadav; P. Purushothama Rao; R. Srinivasa Rao; P.S.R. Reddy; K. Nagaiah; A.R. Prasad (pp. 192-196).
Aldehydes undergo smooth nucleophilic addition with allyl- n-tributylstannane in the presence of sulphamic acid (5mol%, SA) under extremely mild reaction conditions to afford the corresponding homoallylic alcohols in excellent yields with high chemoselectivity. The catalyst can be recovered by simple filtration and can be recycled in subsequent reactions. The method is simple, cost-effective and environmentally benign.
Keywords: Sulphamic acid (SA); Allyl-; n; -tributylstannane; Homoallylic alcohols; Chemoselectivity