Applied Catalysis A, General (v.389, #1-2)
Editorial Board (CO2).
Immobilisation of titanium dioxide onto supporting materials in heterogeneous photocatalysis: A review by Ang Ying Shan; Tinia Idaty Mohd. Ghazi; Suraya Abdul Rashid (1-8).
Display Omitted▶ An overview of the evolution in the use of different supports for the immobilisation of a semiconductor photocatalyst, titanium dioxide (TiO2). ▶ The preparation procedure and the type of substrates used greatly influence the photocatalytic activity of TiO2. ▶ A good immobilisation method depends on the type of support used, on the type of pollutants that are to be degraded and consideration of the immobilisation techniques and the photoreactor design.The aim of this review is to offer an overview of the evolution in the use of different anchors (supports) for the immobilisation of a semiconductor photocatalyst, which is titanium dioxide (TiO2). Several supports and immobilisation techniques that are commonly used for the removal of contaminants in wastewater are discussed. Generally, the immobilisation of a photocatalyst onto supporting material has largely been carried out via one of two major routes; physical (the thermal treatment method) route or chemical (the sol–gel method, chemical vapour deposition, electrodeposition, etc.) route. The benefits and drawbacks of various immobilisation techniques to obtain a high surface area TiO2 support are also discussed.
Keywords: Immobilisation; Titanium dioxide; Photocatalyst;
Effect of noble metals deposition on the catalytic activity of MAPO-5 catalysts for the reduction of NO by CO by Vilas Ravat; Preeti Aghalayam (9-18).
Display Omitted▶ Molecular sieves MAPO-5 (M: Co, Ti, Cr and Fe) were prepared by the hydrothermal method. ▶ Noble metals were deposited by the hdp method. ▶ The various characterization studies show the high crystallinity of MAPO-5 molecular sieves. ▶ The PdCoAPO-5 and RhCoAPO-5 catalysts showed excellent performance for the reduction of NO by CO.Molecular sieves MAPO-5 (M: Co, Ti, Cr and Fe) with the AFI structure type were prepared by the hydrothermal method. Noble metals (Pd, Rh, Ir and Ru) were deposited on the molecular sieve supports using the homogeneous deposition precipitation method. The catalysts were characterized using XRD, TEM, DRUV-VIS, N2 sorption, SEM, TG/DTA and ICP analysis techniques. The PdO and RhO x species demonstrated small particle sizes as compared with other noble metals. The catalysts were evaluated for their performance in the reduction of NO by CO at different temperatures (150–500 °C) for a GHSV of 44,000 h−1. Among the palladium and noble metals deposited catalysts, the PdCoAPO-5 and RhCoAPO-5 showed excellent performance. For the RhCoAPO-5 (Rh loading = 2.98% and Rh particle size = 2.2 nm) catalyst, the temperature required for complete NO reduction was 210 °C, which is lower than that required for PdCoAPO-5 (Pd loading = 2.96% and Pd particle size = 4 nm) and IrCoAPO-5 (Ir loading = 2.89% and Ir particle size = 6.5 nm) under identical conditions. The Rh deposited CoAPO-5 catalyst effectively operated at lower temperatures as compared with the other noble metal deposited CoAPO-5 catalysts studied here.
Keywords: MAPO-5; Hydrothermal synthesis; Noble metals; hdp method; Characterization; NO reduction;
Continuous Henry reaction to a specific product over nanoporous silica-supported amine catalysts on fixed bed reactor by Ankush V. Biradar; Krishna K. Sharma; Tewodros Asefa (19-26).
Display Omitted▶ A method for continuously producing nitroaldol, nitrostyrene, or the Michael product was reported. ▶ The Henry reaction was performed efficiently over a fixed bed reactor for several days continuously. ▶ The fixed bed reactor was packed with primary or secondary amine-functionalized mesoporous silica. ▶ % Conversion and % selectivity were dependent on WHSV, reactant, catalyst and reaction temperature. ▶ Reactor showed the same catalytic efficiency for weeks at a given WSHV and reactor temperature.We report a method for continuously producing the nitroaldol, the nitrostyrene, or the Michael product by performing the Henry reaction over a fixed bed reactor that is packed with primary or secondary amine-functionalized nanoporous materials. The % conversion of the reactants as well as the % selectivity to the particular product were found to be strongly dependent on the residence time of the reactants in the reactor (weight hourly spatial velocity or WHSV) as well as the type of reactant, catalyst and reaction temperature used. When a 0.08 M p-hydroxybenzaldehyde solution in nitromethane was passed over the fixed bed reactor containing primary amine-functionalized mesoporous silica catalyst by postgrafting in toluene (AP-T) at 90 °C with WHSV of 0.20, the reactor continuously and selectively generated for hours the p-hydroxy-β-nitrostyrene product with 100% selectivity at 31% reactant conversion (or with 90% selectivity at 88% reactant conversion for WHSV of 0.10). The remaining 12% product in the latter case was the Michael product. The corresponding primary amine-functionalized sample prepared by postgrafting of 3-aminopropyltrimethoxysilane (APTS) in isopropanol (AP-I) also gave similar results with slightly higher efficiency and selectivity to p-hydroxy-β-nitrostyrene. When the same reactant solution was passed over the bed-reactor packed with secondary amine grafted mesoporous silica catalyst by postgrafting in toluene (MAP-T) with WHSV of 0.25 at 90 °C, the reactor also continuously produced selectively the p-hydroxy-β-nitrostyrene product but less efficiently; i.e. with 91% selectivity at 21 reactant conversion for WHSV of 0.20 (or with 85% selectivity at 34% reactant conversion for WHSV of 0.10). Here also, the remaining product was the Michael addition product. Increasing the reaction temperature of the reactor containing the primary amine catalyst to 150 °C at WHSV of 0.10 for p-hydroxybenzaldehyde reactant led to the reversal of the product type from being 90% p-hydroxy-β-nitrostyrene to >85% Michael product with ∼100% reactant conversion. Raising the reaction temperature of the reactor containing a secondary amine catalyst for p-hydroxybenzaldehyde reactant also increasingly favored the formation of the Michael product. When changing the reactant to 0.08 M p-nitrobenzaldehyde, the reactor packed with secondary amine catalyst resulted in the nitroalcohol product with 90% selectivity at 40% reactant conversion for WHSV of 0.15. These results indicate that higher WHSV lead to greater selectivity to a particular product; however, lower WHSV and higher temperatures favor greater reactant conversion reaching as high as ∼100% in all the cases although they can be accompanied by less % selectivity. By simply adjusting the WSHV's or the temperatures to optimum values, one of the products can be exclusively generated in a continuous manner. The continuous reactor and the catalysts were proven to catalyze the reactions and give the respective product(s) continuously for several days. This method can be used as a route for the mass production of industrially and pharmaceutically important p-substituted nitroalcohol, nitrostyrene, or Michael addition product with high selectivity, by simply packing mesoporous catalysts within a fixed bed reactor.
Keywords: Continuous reaction; Henry reaction; Nitroaldol condensation; Solid-base nanocatalyst; Heterogeneous catalyst;
Recent progress in catalytic technology in Japan – II (1994–2009) by Takashiro Muroi; Naohiro Nojiri; Takashi Deguchi (27-45).
Display Omitted▶ Ninety-six catalytic processes developed in Japan during 1994–2009 are reviewed. ▶ They are classified into 6 industrial areas including environmental catalysts. ▶ Most of them were commercialized and contributed to Green Sustainable Chemistry. ▶ A wide range of catalysts, from zeolites to precious metals, are used.Catalytic processes developed and commercialized in Japan during 1994–2009 are reviewed and classified into 6 industrial areas: petroleum and energy, bulk chemicals, polymers, fine chemicals, auto exhaust catalysts, and environmental catalysts. They have contributed to overcome a rise in oil price as well as to promote Green Sustainable Chemistry. While these technologies made significant contributions to respond to social issues or commercial demands, continuous efforts for development of these processes greatly promoted the catalytic science and technologies including catalytic materials, concepts, mechanism and surface science of catalysis.
Keywords: Catalytic technologies; Petroleum and energy; Bulk chemicals; Polymers; Fine chemicals; Auto exhaust catalysts; Environmental catalysts; Green sustainable chemistry;
The Co-promotion effect of Mo and Nd on the activity and stability of sulfated zirconia-based solid acids in esterification by Kanghua Jiang; Dongmei Tong; Jinqiang Tang; Ruili Song; Changwei Hu (46-51).
Display Omitted▶ An OA conversion of 96.1% over SZMN catalyst was obtained after sixth time reuse. ▶ The co-promotion of Mo and Nd led to the largest amount of acid sites on SZMN. ▶ Mo and Nd stabilized the structure of t-ZrO2 with small crystallite.SO4 2−/ZrO2–MoO3 (SZM), SO4 2−/ZrO2–Nd2O3 (SZN) and SO4 2−/ZrO2–MoO3–Nd2O3 (SZMN) solid acids catalysts were prepared and characterized by XRD, NH3-FTIR, NH3-TPD and TG–DTG. The activities and stabilities of the catalysts for the esterification of fatty acids were investigated. Experimental and characterization results show that the excellent activity and stability of SZMN are attributed to the firm combination of sulfur species with t-ZrO2. The co-addition of Mo and Nd increases the dispersion of t-ZrO2 and stabilizes the structure of small-crystallite t-ZrO2, which is favorable to increasing the acid sites amount, strengthening the acidity, and then enhancing the activity and stability of the catalyst.
Keywords: Sulfated zirconia-based solid acids; Fatty acids; Co-promotion; Esterification;
Heptane isomerization over molybdenum oxides obtained by H2 reduction of H x MoO3 with different hydrogen contents by Tomoya Ohno; Zhiou Li; Naonori Sakai; Hirotoshi Sakagami; Nobuo Takahashi; Takeshi Matsuda (52-59).
Display Omitted▶ The catalytic properties of H2-reduced MoO3, H x MoO3 with different hydrogen contents, and Pt/MoO3 were studied. ▶ The heptane isomerization activity increased in the following order: MoO3 < H0.34MoO3 < H0.93MoO3 < H1.68MoO3 < Pt/MoO3. ▶ The isomerization activity was related to the concentration of acid sites.The effects of the hydrogen content in hydrogen molybdenum bronze (H x MoO3) on the catalytic properties of its reduction product were studied. H2 reduction of H x MoO3 yielded an active and selective catalyst for heptane isomerization. The catalyst with a higher isomerization activity was obtained from H x MoO3 with a larger content of hydrogen. H2-reduced MoO3 was almost inactive for heptane isomerization, and the highest activity was obtained on H2-reduced Pt/MoO3. The isomerization activity was well related to the number of acid sites, which was determined from temperature-programmed desorption of NH3. H2-reduced H x MoO3 and Pt/MoO3 consisted of MoO x H y and Mo metal. In contrast, reduction of MoO3 yielded a mixture of MoO2 and Mo metal. We suggest from these results that the generation of acid sites is related to the formation of MoO x H y , and that the acidity of MoO x H y can be enlarged as the hydrogen content in H x MoO3 is increased.
Keywords: Heptane isomerization; Hydrogen molybdenum bronze; Acidity;
On the photocatalytic activity of the sulfur doped titania nano-porous films derived via micro-arc oxidation by M.R. Bayati; A.Z. Moshfegh; F. Golestani-Fard (60-67).
Display Omitted▶ S:TiO2 films were synthesized via MAO under direct current for the first time. ▶ Effect of MAO parameters on properties of the layers was studied. ▶ Based on our XPS results, a cationic doping was observed.Sulfur doped TiO2 layers containing nano/micro-sized pores were synthesized by micro-arc oxidation process. Effect of the applied voltage and the electrolyte composition on physical and chemical properties of the layers was investigated using SEM, AFM, XRD, XPS, and EDS techniques. A UV–vis spectrophotometer was also used to study optical properties of the layers. It was found that the doped layers were porous with a pore size of 40–170 nm. They consisted of anatase and rutile phases with varying fraction depending on the applied voltage and electrolyte concentration. Our XPS investigations revealed the existence of sulfur in the forms of S4+ and S6+ states which substituted Ti4+ in the titania lattice. The sulfur concentration in the layers also increased with the voltage and the electrolyte concentration. Furthermore, the absorption edge of the doped layers shifted significantly toward longer wavelengths as compared to the pure TiO2 layers. The band gap energy was calculated as 2.29 eV for sulfur doped TiO2 layers, respectively. Finally, photocatalytic activity of the layers was studied by measuring the degradation rate of methylene blue on their surface under UV and visible illuminations. The doped layers showed a slightly enhanced photoactivity than the pure layers under UV-irradiation, while their photocatalytic performance was much higher than that of pure layers under visible-irradiation. It was measured that about 92% and 66% of methylene blue was decomposed over doped layers under UV and visible irradiations, respectively.
Keywords: Micro-arc oxidation; TiO2; Sulfur; Photocatalysis; Doping;
Low temperature catalytic methane steam reforming over ceria–zirconia supported rhodium by M.H. Halabi; M.H.J.M. de Croon; J. van der Schaaf; P.D. Cobden; J.C. Schouten (68-79).
Display Omitted▶ CH4 steam reforming is experimentally investigated over Rh/Ce0.6Zr0.4O2. ▶ Catalyst performance and reaction mechanistic aspects are demonstrated. ▶ Catalyst application goal is for low temperature sorption enhanced H2 production. ▶ This is beneficial in terms of production rates and unit intensification.This paper presents an experimental study of the catalytic steam reforming of methane over newly developed ceria–zirconia supported rhodium as an active candidate catalyst for low temperature sorption enhanced hydrogen production from methane. The kinetic experiments are performed in a tubular fixed bed reactor over a temperature range of 475–725 °C and a total pressure of 1.5 bar in the absence of mass transport limitations. The over all reaction orders in methane and steam are determined to be less than 1 from 475 to 625 °C. At low temperature, most of the gas product is composed of CO2 and H2 due to the pronounced influence of the water–gas shift reaction. At higher temperature and low steam/carbon ratio (S/C), this influence is diminished. Inhibitory effects of H2, CO, and CO2 on the methane conversion rates are detected. Temperature-programmed steam reforming experiments over ceria–zirconia support revealed insignificant methane adsorption on the surface from 550 to 725 °C. Catalyst deactivation and steady state stability over time were examined. A molecular reaction mechanism is proposed to qualitatively explain the kinetic observations. Two distinct sites are thought to be responsible for the dissociative adsorption of methane and steam on the catalyst and the support surfaces. Methane is dissociatively adsorbed on the rhodium active metal sites and steam is dissociatively adsorbed on the support surface. Surface reactions of carbon containing methane precursors on the interface between the active metal and the support are considered to be the rate determining steps.
Keywords: Methane steam reforming; Water–gas shift; Reaction mechanism; Rhodium-based catalyst; Ceria–zirconia supported catalyst;
Intrinsic kinetics of low temperature catalytic methane–steam reforming and water–gas shift over Rh/Ce α Zr1−α O2 catalyst by M.H. Halabi; M.H.J.M. de Croon; J. van der Schaaf; P.D. Cobden; J.C. Schouten (80-91).
Display Omitted▶ The intrinsic kinetics of CH4 steam reforming is developed over Rh/Ce0.6Zr0.4O2. ▶ The model is based upon two-site adsorption surface hypothesis in a low temperature. ▶ The redox surface reactions are considered as rate determining steps. ▶ The inhibitory effect of gaseous product species is reflected in the kinetics. ▶ Rh-based steam reforming kinetics is compared to Ni-based catalyst kinetics.This paper presents the intrinsic kinetics of CH4 steam reforming developed over Rh/Ce0.6Zr0.4O2 catalyst in a relatively low temperature range of 475–575 °C and 1.5 bar pressure. The kinetic experiments are conducted in an integral fixed bed reactor with no mass and heat transport limitations and far from equilibrium conditions. Therefore, intrinsic reaction rate measurements are guaranteed. The model is based upon two-site adsorption surface hypothesis, and 14 elementary reaction steps are postulated. CH4 is dissociatively adsorbed onto the Rh active sites, and steam is dissociatively adsorbed on the ceria support active sites as an influential adsorption surface shown in the model. Therefore, no competition between CH4 and steam in adsorbing on the same site surface is observed. The kinetic rate expressions are derived according to the Langmuir–Hinshelwood formalism. The redox surface reactions between the carbon containing species and the lattice oxygen leading to CO and CO2 formation are considered as rate determining steps. The inhibitory effect of gaseous product species is also reflected in the kinetics. The model is found to be statistically accurate and thermodynamically consistent. The estimated activation energies and adsorption enthalpies are in agreement with literature for CH4 steam reforming reaction over Rh. The reaction kinetics is validated by steam reforming experiments at 550 °C and 1.5 bar using 150 mg catalyst in a diluted bed of 5 cm length. The kinetic model is implemented in a one-dimensional pseudo-homogenous plug flow reactor model and thus simulated at identical experimental conditions. The simulation results are in excellent agreement with the experimental values.
Keywords: Methane steam reforming; Intrinsic reaction kinetics; Water–gas shift; Reaction mechanism; Rhodium-based catalyst; Ceria–zirconia supported catalyst;
Reforming of methane with carbon dioxide over Pt/ZrO2/SiO2 catalysts—Effect of zirconia to silica ratio by Gunugunuri K. Reddy; Stéphane Loridant; Atsushi Takahashi; Pierre Delichère; Benjaram M. Reddy (92-100).
Display Omitted▶ High dry reforming activity was obtained with Pt supported over ZrO2/SiO2 supports. ▶ The best support contained no remaining free silica but ZrSiO4 in higher amount. ▶ The higher activity of the best catalyst was due to higher Pt dispersion. ▶ Improved thermal stability of the ZrO2/SiO2 supports compared to ZrO2 was evidenced.ZrO2/SiO2 mixed oxides with different ratios (2:1 to 4:1) were prepared by a deposition–precipitation method from zirconium hydroxide and colloidal silica and used as supports for platinum nano-particles. The synthesized catalysts along with Pt/ZrO2 reference materials were tested for CH4 reforming with CO2 at a high temperature of 1073 K and at high space velocity.Very high reforming activity was observed for the Pt/ZrO2/SiO2 (4:1) sample among all the prepared catalysts. The effect of zirconia to silica ratio on the physico-chemical properties that determine the catalytic activity has been investigated characterizing all the catalysts after calcination, reduction as well as after reaction with several techniques. From X-ray diffraction patterns, BET and H2 chemisorption measurements, X-ray photoelectron and FTIR spectra, the better catalytic properties of the Pt/ZrO2/SiO2 (4:1) sample have been explained by higher Pt dispersion due to the absence of remaining free silica and the presence of amorphous ZrSiO4 in higher amount. Additionally, a better thermal stability of the prepared ZrO2/SiO2 supports compared to ZrO2 was evidenced after ageing at 1073 K for 16 h in particular for the ratio 4:1. It also underlines the interest of the preparation method.
Keywords: Pt supported catalysts; ZrO2/SiO2 support; Dry reforming; Carbon dioxide; Methane; Syngas;
Copper–manganese oxide catalysts supported on alumina: Physicochemical features and catalytic performances in the aerobic oxidation of benzyl alcohol by Qinghu Tang; Xiaonan Gong; Peizheng Zhao; Yuanting Chen; Yanhui Yang (101-107).
Display Omitted▶ Copper–manganese bimetallic catalysts were synthesized by a facile method. ▶ Adding copper remarkably improves the catalytic activity of Mn/Al2O3. ▶ Mn1.5Cu1.5O4 microcrystalline phase is responsible for enhanced activity. ▶ High temperature calcination results in the decomposition of this mixed oxide. ▶ The Mn3O4 formed shows poor catalytic activity in benzyl alcohol oxidation.We report the facile synthesis of alumina supported copper–manganese mixed oxide catalysts by a homogeneous deposition–precipitation method and the catalytic applications of these catalysts in the oxidation of benzyl alcohol using molecular oxygen. Benzyl alcohol conversion of ca. 90.9% was achieved with benzaldehyde as the main product. The catalyst can be recycled consecutively up to seven runs without appreciable loss of its activity and selectivity. Characterizations with X-ray diffraction, transmission electron microscopy, Raman, X-ray absorption spectroscopy, and hydrogen temperature-programmed reduction suggested the formation of a mixed oxide (Mn1.5Cu1.5O4) microcrystalline phase after adding copper to the manganese supported on alumina. Such formation would account for the high catalytic performance. Calcination under high temperature decomposed this mixed oxide phase, resulting in a poor catalytic activity.
Keywords: Manganese; Copper; Alumina; Benzyl alcohol oxidation; Molecular oxygen;
Terpolymerization of propene and ethene with carbon monoxide catalyzed by [PdCl2(dppf)] in HCOOH–H2O as a solvent [dppf = 1,1′-bis(diphenylphosphino)ferrocene] by Andrea Vavasori; Lucio Ronchin; Luigi Toniolo (108-113).
Display Omitted▶ [PdCl2(dppf)] efficiently catalyzes the propene–ethene–CO terpolymerization. ▶ The Pd(II) precursor is activated by the combined effects of H2O and HCOOH. ▶ H2O/HCOOH, propene concentration and reaction time influence the productivity. ▶ Polymer chain is formed mainly by ethene–CO and in low percent by propene–CO units.The [PdCl2(dppf)] complex efficiently catalyzes the terpolymerization of propene and ethene with carbon monoxide in HCOOH–H2O as a solvent, when H2O concentration ranges between 50 and 65 molar %. The productivity, the melting temperature and the viscosity average molecular weight of the terpolymer depend on the propene concentration and on the reaction time.The NMR analysis of the polymer composition indicates the presence along the chain mainly of ethene–CO units together with a low percent of propene–CO units.A reaction mechanism is proposed and discussed.
Keywords: Ethene; Propene; Carbon monoxide; Terpolymerization; [PdCl2(dppp)] catalyst; HCOOH–H2O solvent;
Competitive reactions and mechanisms in the simultaneous HDO of phenol and methyl heptanoate over sulphided NiMo/γ-Al2O3 by Eeva-Maija Ryymin; Maija L. Honkela; Tuula-Riitta Viljava; A.Outi I. Krause (114-121).
.Display Omitted▶ Product distribution changes in the mixture compared to reactants tested separately. ▶ Reduction reactions occur on coordinatively unsaturated sites (CUS). ▶ Acid-catalysed and decarbonylation reactions occur on sulphur-saturated sites. ▶ Sulphur adsorbs on CUS and affects the reactions occurring on these sites.Hydrodeoxygenation (HDO) of phenol and methyl heptanoate separately and as mixtures was carried out over a sulphided NiMo catalyst to compare the HDO of aromatic and aliphatic reactants. Some experiments were also carried out in the presence of a sulphur additive. The conversion of phenol was suppressed in the presence of methyl heptanoate, whereas the conversion of methyl heptanoate was practically unaffected by phenol. In addition, distributions of the hydrocarbon products were different for reactants in the mixture and the reactants tested separately. Sulphur additive changed the product distribution of the separate components more than that of the mixture. The findings indicate that reduction (including hydrogenation) reactions occur on coordinatively unsaturated sites (CUS) independently of the aromatic or aliphatic character of the component. Sulphur, too, adsorbs on CUS and competes with other reactants that have an affinity to CUS. Decarbonylation and acid-catalysed reactions are, instead, proposed to occur on sulphur-saturated sites.
Keywords: Hydrodeoxygenation (HDO); Methyl heptanoate; Phenol; Sulphided NiMo; Competitive reactions;
Density functional theory study of sulfur tolerance of CO adsorption and dissociation on Rh–Ni binary metals by Kyungtae Lee; Chunshan Song; Michael J. Janik (122-130).
Display Omitted▶ Rh–Ni metals are more tolerant to S poisoning during reforming reactions. ▶ The adsorption of S is weakened on Rh–Ni surfaces in comparison to pure Rh surfaces. ▶ CO dissociation with S is faster on Rh–Ni surface than on pure metal surfaces.The effect of Ni addition to improve the sulfur tolerance of a Rh catalyst for CO dissociation was studied using density functional theory (DFT) methods. Adsorption and dissociation were considered over the (1 1 1) surfaces of binary Rh1Ni2 and Rh2Ni1 metals with comparison to pure Rh and Ni surfaces. Sulfur adsorption on the Rh1Ni2(1 1 1) surface is 0.21 eV more endothermic than on the Rh(1 1 1) surface, suggesting that a Rh1Ni2 bimetallic catalyst has a higher sulfur tolerance than pure Rh catalysts due to a lower surface coverage of the sulfur poison. To compare catalytic activity in the presence of adsorbed sulfur, the CO dissociation rates over the binary and pure metals were calculated with 1/9 sulfur coverage. CO dissociation is fastest on the pure Rh surface under sulfur-free conditions, whereas among sulfur poisoned surfaces, the Rh1Ni2 surface shows the fastest CO dissociation rate. The CO dissociation barrier on Rh1Ni2 is destabilized less by a S coadsorbate than for the other metals. The addition of Ni atoms to a Rh catalyst improves the sulfur tolerance of the catalyst for CO dissociation by minimizing the repulsion between the adsorbed S atom and the CO dissociation transition state, as evidenced through a projected density of states analysis. The Rh1Ni2(2 2 1) stepped surface also shows a lower activation barrier and higher CO dissociation rate in the presence of sulfur than the Rh(2 2 1) stepped surface.
Keywords: CO dissociation; Rh–Ni binary metals; Reforming; Methanation; Density functional theory; Sulfur poisoning;
Fischer–Tropsch synthesis: Attempt to tune FTS and WGS by alkali promoting of iron catalysts by Venkat Ramana Rao Pendyala; Gary Jacobs; Janet C. Mohandas; Mingsheng Luo; Wenping Ma; Muthu Kumaran Gnanamani; Burtron H. Davis (131-139).
Display Omitted▶ Effect of water on FT synthesis. ▶ Comparison of alkali promoters on iron catalysts. ▶ Methane selectivity increase with increase in water v.p. ▶ Hydrocarbon selectivity decreases with increase in water v.p.The effect of water on the performance of alkali-promoted, precipitated Fe catalysts was investigated during Fischer–Tropsch (FT) synthesis in a continuously stirred tank reactor. In these studies, the added water (5–25 mol%) replaced an equivalent amount of inert gas so that all other reaction conditions remained the same before, during and after water addition. The externally added water had a positive effect on the CO conversion for all the alkali-promoted, precipitated iron catalysts. The impact of the added water is to increase the rate of the water-gas shift (WGS) reaction with up to 10–15 mol% added water, and then leveling off for further increases in the amount of water added to the feed gas. Increasing the water amount in the feed gas caused the fraction of CO converted into hydrocarbons to decrease and both the WGS activity and the oxygenate selectivity to increase. Common for all the alkali promoted iron catalysts was a decrease in C5+ selectivity and an increase in the methane selectivity with increasing amounts of water up to 10–15 mol%; with further increases of water, the C5+ selectivity increases and methane selectivity decreases. Methane selectivity is directly correlated to the CO conversion and H2/CO ratio inside the reactor.
Keywords: Fischer–Tropsch synthesis; Iron catalysts; Alkali; Water effect; Lithium; Potassium; Rubidium;
Conversion of 1-tetralone over HY zeolite: An indicator of the extent of hydrogen transfer by Teerawit Prasomsri; Roberto E. Galiasso Tailleur; Walter E. Alvarez; Tawan Sooknoi; Daniel E. Resasco (140-146).
Display Omitted▶ Product distribution from tetralone conversion can be used as an indicator of hydrogen transfer ability of hydrocarbons present in FCC. ▶ The higher the rate of hydrogen transfer the higher the naphthalene-to-naphthol product ratio. ▶ Hydrogen transfer ability follows the sequence DMT > tetralin ≈ decalin > n-decane. ▶ This trend agrees with the hydride dissociation energy of individual donors calculated by DFT.The conversion of pure 1-tetralone and its mixtures with n-decane, decalin, tetralin, or 1,5-dimethyl tetralin (DMT) has been investigated over HY zeolite. The dominant reactions undergone by 1-tetralone are the dehydrogenation to 1-naphthol and the subsequent isomerization to 2-naphthol. In the presence of hydrocarbons, the hydrogen transfer/dehydration of naphthols is accelerated, and naphthalene is formed in different amounts, depending on the nature of the co-fed hydrocarbon. In this contribution, it is demonstrated how the product distribution from the tetralone conversion can be used as an indicator of the hydrogen transfer ability of a particular hydrocarbon, or mixture of hydrocarbons. The relative order of hydrogen transfer ability of the various hydrogen donating compounds, as inferred from the naphthalene-to-naphthol product ratio, is DMT > tetralin ≈ decalin > n-decane. This trend agrees well with the hydride dissociation energy of individual donors calculated by DFT.
Keywords: Oxygenated aromatics; 1-tetralone; Hydrogen transfer; HY zeolites; FCC;
Iron-alumina materials prepared by the non-hydrolytic sol–gel route: Synthesis, characterization and application in hydrocarbons oxidation using hydrogen peroxide as oxidant by Gustavo P. Ricci; Zênis N. Rocha; Shirley Nakagaki; Kelly A.D.F. Castro; A.E. Miller Crotti; Paulo S. Calefi; Eduardo J. Nassar; Katia J. Ciuffi (147-154).
Display Omitted▶ Non-hydrolytic sol–gel route led to real heterogeneous FeIII-alumina catalysts. ▶ FeAlO-1100 furnished a cyclooctene conversion of 96% after 48 h at 50–55 °C. ▶ FeAlO-1100 furnished a cyclohexane conversion of 22% after 48 h at 50–55 °C. ▶ The green oxidant H2O2 was employed in the catalytic systems.Novel alumina materials containing FeIII ions were prepared by the non-hydrolytic sol–gel route and applied as heterogeneous catalysts in the oxidation of hydrocarbons (cyclooctene and cyclohexane) by the green oxidant hydrogen peroxide. The synthetic route followed an alkyl halide elimination pathway, via etherolysis/condensation between AlCl3 and diisopropyl ether (iPr2O), in the presence of FeIII ions (FeIII:AlIII:iPr2O molar ratio ∼1:15:30). The obtained xerogel (designated FeAlO-50) was thermally treated at 400, 750, or 1100 °C (samples FeAlO-400, FeAlO-750, and FeAlO-1100, respectively), and the resulting materials were characterized by means of different techniques, such as thermal analyses (TG/DTA), ultraviolet–visible (UV–vis) and infrared (FTIR) absorption spectroscopy, X-ray powder diffraction (XRD) and electron paramagnetic resonance (EPR). The concentration of Brönsted acid sites (BAS) at the surface of the samples was also evaluated by adsorption–desorption of cyclohexylamine. The thermal treatments led to truly heterogeneous catalysts, and the FeAlO-1100 material furnished the highest substrate conversion values. The larger catalytic activity of FeAlO-1100 is probably due to the absence of BAS on its surface. Indeed, the other FeAlO samples presented high BAS concentration, and it is known that H2O2 can be non-productively decomposed in the presence of strong acid sites. The catalytic efficiency of FeAlO-1100 can be considered promising (96% cyclooctene and 22% cyclohexane conversions), while the selectivity cyclohexanone/cyclohexanol achieved in the oxidation of cyclohexane was 1.2 (molar ratio). The catalytic systems obtained here are advantageous because they involve the use of H2O2, a green oxidant, and the temperature employed for the oxidation reactions (50–55 °C) is milder than those reported in the literature for other heterogeneous catalyst/H2O2 systems.
Keywords: Iron(III); Alumina; Non-hydrolytic sol–gel; Heterogeneous catalysis; Hydrogen peroxide;
Light alkane dehydrogenation over mesoporous Cr2O3/Al2O3 catalysts by Debaprasad Shee; Abdelhamid Sayari (155-164).
Display Omitted▶ Novel mesoporous Cr2O3/Al2O3 were synthesis and tested for light alkane dehydrogenation. ▶ XPS studies revealed that surface chromium occurs in two chemical states as Cr(III) and Cr(VI). ▶ Characterization of spent and regenerated catalysts indicated that the formation of subsurface Cr(III) species during dehydrogenation may be the reason for partial irreversible loss of activity.Light alkane dehydrogenation was investigated over a series of mesoporous Cr2O3/Al2O3 catalysts containing 2–15 wt.% chromia, synthesized via the supramolecular templating technique. The catalysts were characterized by N2 adsorption, X-ray diffraction (XRD), Raman, Fourier transform infrared spectroscopy (FTIR), UV–vis (ultra violet visible), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). Depending on chromia loading, chromium was found to be present essentially as two surface species, each possessing one short terminal Cr＝O bond and polymeric species. UV–vis and XPS studies revealed that the surface chromium occurs in two chemical states as Cr(III) and Cr(VI) species. Investigation of ethane and propane adsorption by in situ diffuse reflectance FTIR spectroscopy (DRIFT) revealed the formation of adsorbed acetaldehyde, acetone, formate and acetate. During the dehydrogenation reaction, acetate/carboxylate and hydrocarbon species were detected. Under otherwise the same conditions, the alkane dehydrogenation activity increased with increasing chromia loading. The activity of regenerated catalysts was found to be lower than the corresponding fresh catalysts, suggesting that the deactivation is partly permanent. Detailed characterization studies of spent and regenerated catalysts indicated that the formation of subsurface Cr(III) species during dehydrogenation may be the reason for the permanently lost activity.
Keywords: Chromia-alumina; Alkane dehydrogenation; Catalyst deactivation; Diffuse reflectance Fourier transform infrared spectroscopy (DRIFT); Raman; X-ray photoelectron spectroscopy (XPS); UV–vis (ultra violet visible);
Direct nitrous oxide decomposition with a cobalt oxide catalyst by Ewa Wilczkowska; Krzysztof Krawczyk; Jan Petryk; Janusz W. Sobczak; Zbigniew Kaszkur (165-172).
Display Omitted▶ Feed components influence N2O decomposition on Co3O4. ▶ Nitric oxide does not affect the catalyst state, but the reaction pathway. ▶ Water blocks the surface of Co3O4 reducing the number of available active sites. ▶ Oxygen increases the active phase content in the catalyst at 850 °C.The influence of individual components of the gas mixture, which is found directly downstream of the platinum–rhodium gauze in ammonia oxidation, i.e. nitric oxide, oxygen and water vapor, on the state of Co3O4 under high-temperature nitrous oxide decomposition conditions has been determined. A variety of characterization techniques, such as: nitrogen physisorption, XRD, XPS and TG–DTA–MS, was applied. The result of the research shows that nitric oxide is not decomposed on the catalyst and it does not influence the temperature of the beginning of Co3O4 reduction. However, the addition of NO in the feed leads to slightly higher activity of the catalyst in N2O decomposition than that obtained in a stream of 5% N2O in argon. In contrast, oxygen and water vapor influence the state of the catalyst. An addition of oxygen shifts the temperature of the beginning of Co3O4 reduction to higher temperatures. Therefore, the activity of the catalyst is significantly higher at 850 °C in the presence of oxygen than without it. In the case of lower temperatures, a negative impact of oxygen on the activity of the catalyst has been observed. Water vapor in the feed causes a decrease in the activity in the studied temperature range due to competitive chemisorption.
Keywords: Nitrous oxide decomposition; Spinel catalyst; Catalyst state; Reduction; Competitive chemisorption;
Preparation and characterization of stable Ru nanoparticles embedded on the ordered mesoporous carbon material for applications in Fischer–Tropsch synthesis by Kun Xiong; Jinlin Li; Kongyong Liew; Xiaodong Zhan (173-178).
Display Omitted▶ A novel Ru–OMC catalyst was prepared by autoreduction reaction. ▶ Ru nanoparticles were embedded on the carbon walls of the ordered mesoporous carbon material. ▶ The Ru–OMC catalyst retained original ordered mesoporous structure. ▶ The Ru–OMC catalyst exhibited superior catalytic activity for Fischer–Tropsch synthesis.A novel Ru–OMC catalyst was prepared by autoreduction reaction between a ruthenium precursor and a carbon source at 1123 K. Ruthenium nanoparticles were embedded on the carbon walls of the ordered mesoporous carbon material. Characterization tools including power X-ray diffraction (XRD), nitrogen adsorption–desorption, and transmission electron microscopy (TEM) were used to scrutinize the catalysts. The catalyst activity for Fischer–Tropsch synthesis (FTS) was carried out in a fixed bed reactor. For comparison, Ru catalysts supported on ordered mesoporous carbon (OMC), active carbon (AC), and carbon nanotubes (CNT) were prepared using conventional impregnation method and evaluated at the same FTS reaction conditions. The Ru–OMC catalyst exhibited highly ordered mesoporous structure and large surface area, indistinguishable with those of the OMC material. On this catalyst, Ru nanoparticles were actually embedded on the carbon walls, forming an intimate contact with the carbon supports. It is proposed that this feature might create certain electron-deficient sheets on the interfacial contact, which facilitates the transfer of spilled-over hydrogen and improves hydrogen disassociation on the catalyst surface.
Keywords: Ordered mesoporous carbon; Ruthenium; Embedded; Fischer–Tropsch synthesis;
Supported ionic liquid phase catalysis for aerobic oxidation of primary alcohols by Anna Chrobok; Stefan Baj; Wojciech Pudło; Andrzej Jarzębski (179-185).
Display Omitted▶ Method for the oxidation of alcohols to aldehydes with high yields and selectivities. ▶ Concept of supported ionic liquid phase catalysis with dissolved CuCl2. ▶ Halogen-free ILs like [bmim]OSO3Oc as the “catalyst-philic” phase, supported on ionogel. ▶ Effective recycle of catalyst is possible.The copper-TEMPO-catalysed aerobic oxidation of primary alcohols based on the new supported ionic liquid phase (SILP) catalysts is presented. CuCl2 acts as a homogenous catalyst dissolved in the small quantity of ionic liquid dispersed in the form of film on the solid support. A bi-modal pore structure silica with a highly developed surface and an ionogel were used as solid supports. 1-Butyl-3-methylimidazolium octylsulfate as the most active “catalyst-philic” phase was found. The application of SILP catalysts for the oxidation of alcohols allows the high yields of corresponding aldehydes (92–95%). The catalysts were used in seven cycles without significant loss of activity. High recoveries of the catalysts were observed.
Keywords: Supported ionic liquid phase catalysis; Ionogel; Alcohol oxidation; Aldehydes;
Multinuclear solid-state NMR study of the coordinative nature of alkylaluminum cocatalyst on Phillips CrO x /SiO2 catalyst by Wei Xia; Boping Liu; Yuwei Fang; Tadahiro Fujitani; Toshiaki Taniike; Minoru Terano (186-194).
Display Omitted▶ Solid-state NMR was first used to investigate coordinative states of Al on Phillips catalysts. ▶ States of Al species strongly depended on the concentration of TEA and the calcination temperature. ▶ 4-Coordinated Al species seems related to the polymerization activity.Solid-state nuclear magnetic resonance (NMR) spectroscopy was used to investigate the coordinative states of surface Al species on various triethylaluminum (TEA)-modified Phillips CrO x /SiO2 catalysts under different Al/Cr molar ratios. 1H and 27Al MAS NMR spectra clearly demonstrated that the existing states of surface Al species in TEA modified catalysts strongly depended on the concentration of TEA and on the calcination temperature used during the catalyst preparation process. 1H MAS NMR spectra of TEA-modified Phillips CrO x /SiO2 catalysts calcined at three different temperatures exhibited similar trends in peak shifts with increasing Al/Cr molar ratios, but the sensitivity dependence of variation in chemical shift of the main peaks on Al/Cr molar ratios increases with increasing of calcinations temperature. This increased sensitivity might have been due to the relatively low amount of residual hydroxyl groups present on the silica support after catalyst calcination. 27Al MAS NMR spectra showed the presence of three different coordination states (6-, 5-, and 4-coordinated Al species) in the TEA-modified Phillips catalysts. At relatively low Al/Cr molar ratios, the 6-coordinated Al species was the dominant species observed in the catalysts. However, the 4-coordinated Al species became dominant at relatively high Al/Cr ratios for TEA-modified catalysts calcined at 600 and 800 °C, because the increase in TEA concentration might have decreased the amount of oxygen atoms surrounding each Al species. After a saturation state of Al species directly coordinated on the catalyst or silica surface reached, residual TEA coordinated with the Al species already coordinated on the catalyst or silica surface, thus increasing the coordination number of the Al species. Consequently, the 6-coordinated Al species became predominant again for the TEA-modified catalysts calcined at 600 and 800 °C.
Keywords: Phillips catalyst; Al–alkyl cocatalyst; Ethylene polymerization; Solid-state NMR;
Reaction mechanism for hydrodenitrogenation of carbazole on molybdenum nitride based on DFT study by Hiroyuki Tominaga; Masatoshi Nagai (195-204).
Display Omitted▶ We find the best solutions to the following four questions. ▶ Where are the active sites of hydrogenation and C–N bonds scission. ▶ What is the driving force of the hydrogenation and C–N bond scission. ▶ Why the nitrogen atom was not directly removed from the nitrogen compounds.The hydrodenitrogenation of carbazole on the γ-Mo2N(1 1 0) slab was investigated based on density functional theory calculations. In one of the four adsorption models, carbazole was located with an η5-configuration of the pyrrole ring on the Mo atom of the γ-Mo2N(1 1 0) slab before optimization. However, after optimization, the nitrogen atom of the carbazole migrated to the top position of the Mo atom with two benzene rings along the x axis in a boat configuration. This model was energetically the most stable. The hydrogenation steps of carbazole, 1,2,3,4-tetrahydrocarbazole and 1,2,3,4,5,6,7,8-octahydrocarbazole required higher activation energies than the C–N bond scission of tetrahydrocarbazole and the denitrogenation to cyclohexylbenzene. The hydrogenation of tetrahydrocarbazole to octahydrocarbazole preceded the C–N bonds scission of 1-cyclohexyl-2-iminobenzene to bicyclohexyl via cyclohexylcyclohexene. The direct C–N bond cleavage of carbazole to biphenyl did not occur on the γ-Mo2N(1 1 0) slab, while the C–N bond cleavages of tetrahydrocarbazole to cyclohexylbenzene and of octahydrocarbazole to cyclohexylcyclohexene and bicyclohexyl occurred. The Mo atom was responsible for the hydrogenation and one C–N bond scission of tetrahydrocarbazole and octahydrocarbazole, and the bridge position of the two molybdenum atoms is active site for the removal of the nitrogen atom of the hydrogenated carbazole and the dissociative adsorption of hydrogen. The mechanism for the C–N scission during the carbazole HDN was discussed with respect to the activation energy, the configuration characteristics, the bond order and the Mulliken charge analysis.
Keywords: Molybdenum nitride; DFT; Hydrodenitrogenation; Carbazole;