Applied Catalysis A, General (v.307, #2)
Editorial Board (CO2).
Catalytic polymeric membranes: Preparation and application by Sibel Sain Ozdemir; Maria Giovanna Buonomenna; E. Drioli (167-183).
The study of catalytic membranes is a multidisciplinary activity, which in recent years has attracted the attention of scientists in a number of disciplines, including material science, chemistry and chemical engineering. Membrane based reactive separation processes, which seek to combine two distinct functions, i.e. reaction and separation, have been around as a concept since the early stages of the membrane field, itself, but have only attracted substantial technical interest the last decade or so. According to the literature, most studies combining membranes and catalysts concern gas phase reactions at relatively high temperature. In most of these applications inorganic membrane made from ceramic or metals are applied. Polymeric membranes (porous or dense) are used when the reaction temperatures are lower, i.e. in the field of fine chemicals or when biocatalysts are present. Dense polymeric membranes in use to separate gases or liquids from mixtures by a sorption–diffusion mechanism can be coupled to catalytic reaction and then be used to separate and react in one step. The polymeric membrane should be not only highly selective, but it should also be permeable enough to give a sufficient separation.Liquid phase catalytic reactions are involved in numerous industrial processes ranging from fine to bulk chemical synthesis; polymeric membranes may also play a significant role in this field.In this paper, a review on the preparation and application of polymeric membranes in the field of fine chemicals with adequate performance in catalysis both in gas phase and liquid phase reactions is presented and discussed.
Keywords: Polymeric membranes; Heterogeneous catalysis; Fine chemicals;
Autothermal steam reforming of higher hydrocarbons: n-Decane, n-hexadecane, and JP-8 by B.J. Dreyer; I.C. Lee; J.J. Krummenacher; L.D. Schmidt (184-194).
Steam addition to the catalytic partial oxidation of n-decane and n-hexadecane with air over Rh-coated monoliths at millisecond contact times produces considerably higher H2 and CO2 and lower olefin and CO selectivities than without steam addition. For steam to carbon feed ratios from 0.0 to 4.0, the reactor operated autothermally, and the H2 to CO product ratio increased from ∼1.0 to ∼4.0, which is essentially the equilibrium product composition near synthesis gas stoichiometry (C/O ∼1) at contact times of ∼7 ms. In fuel-rich feeds exceeding the synthesis gas ratio (C/O > 1), steam addition suppressed olefins and promoted synthesis gas and water–gas shift products. Steam addition also reduced catalyst surface carbon. Furthermore, steam addition to the catalytic partial oxidation of the military fuel JP-8 was performed successfully, also increasing H2 and suppressing olefins.
Keywords: Autothermal reforming; JP-8; Higher hydrocarbons; Millisecond reactors; Rhodium reactor;
Highly reactive species formed by interface reaction between Fe0–iron oxides particles: An efficient electron transfer system for environmental applications by Flávia C.C. Moura; Grazielli C. Oliveira; Maria Helena Araujo; José D. Ardisson; Waldemar A.A. Macedo; Rochel M. Lago (195-204).
This work studied the formation of highly reactive species in the interface of Fe0/iron oxides mixtures, i.e. Fe3O4 (magnetite), γ-Fe2O3 (maghemite) or α-Fe2O3 (hematite) prepared by mechanical grinding and thermal treatment at 200, 400, 600 or 800 °C under argon atmosphere. Mössbauer spectroscopy, powder X-ray diffraction, scanning electron microscopy, BET surface area and magnetization measurements suggest a strong interaction between the metal and the oxide surfaces at temperature as low as 200 °C, producing highly reactive surface species. These reactive species are readily oxidized when exposed to air at room temperature to form large quantities of Fe2O3. The treatment at 600 and 800 °C leads to an extensive solid state reaction of Fe0 with Fe3O4 to produce the phase wüstite, FeO, with a strong decrease in BET surface area and reactivity. These thermally treated mixtures Fe0/iron oxides were also studied as heterogeneous catalysts to promote the decomposition of H2O2. The mixtures Fe0/Fe3O4 treated at 200 and 400 °C showed a remarkable increase in activity for the H2O2 decomposition. The high reactivity of these samples is discussed in terms of Fesurf 2+ species formed by electron transfer from Fe0 to Fe3+ at the interface metal/oxide which are active to initiate the H2O2 decomposition via a Haber–Weiss mechanism. The mixtures Fe0/γ-Fe2O3 and Fe0/α-Fe2O3 ground and thermally treated were also studied, however much lower activities for the H2O2 decomposition were observed.
Keywords: Iron metal; Iron oxides; Interface reaction; Oxidation; Hydrogen peroxide decomposition;
Nanocrystalline NbC formation from mesostructured niobium oxide studied by HRTEM, SAED and in situ XRD by S. Witkowski; M. Ruszak; C. Sayag; J. Pielaszek; G. Djéga-Mariadassou (205-211).
Mechanism of the nanometric size niobium carbide synthesis from mesostructured niobium oxide precursor is proposed. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) combined with in situ X-ray diffraction (XRD) were successfully used to study phase transitions during formation of niobium carbide. The results showed the importance of oxygen diffusion during the entire carburization process; it was evidenced that oxygen diffusion may be a rate-determining step. The proposed model involves the dynamic balance between processes of carbon diffusion into the bulk of the precursor and oxygen diffusion towards the gas phase (both running in spatially separated areas) and rationalizes the observed differences between nano- and micro-crystalline niobium carbide formation.
Keywords: Carbides; Synthesis; Carburization model; Carbide layer;
In situ synthesis and characterization of Ru promoted Co/Al2O3 Fischer–Tropsch catalysts by P. Li; J. Liu; N. Nag; P.A. Crozier (212-221).
We have conducted a detailed investigation of the initial stages of the formation of metal nanoparticles during the incipient wetness synthesis process for both Co on γ-Al2O3 and Ru-promoted Co on γ-Al2O3 catalysts. The synthesis was performed in the reaction cell of an environmental transmission electron microscope so that the processes can be followed using in situ atomic resolution imaging, Z-contrast imaging and nanospectroscopy. The metal precursors were found to have a highly non-uniform distribution on the alumina support, which leads to a non-uniform distribution of metal particles in the final catalysts. In situ atomic resolution images and electron energy-loss nano-analyses showed that during the reduction process, the metal precursor material transformed into an intermediate phase of cubic CoO. With the addition of Ru, however, in addition to the presence of large CoO particles, small particles of either CoRu or pure Ru were also formed. Our experimental results directly show that the addition of Ru promotes the formation of individual CoRu bimetallic nanoparticles and enhanced the reducibility of small Co particles in the Co(Ru)/γ-Al2O3 systems.
Keywords: Cobalt; Alumina; Promoters; Fischer–Tropsch synthesis; Environmental TEM;
Coke deposition and characterization on titanium silicalite-1 catalyst in cyclohexanone ammoximation by Xiangjing Zhang; Yan Wang; Feng Xin (222-230).
In this work, the changes of catalytic activity, as well as the main deactivation mode were investigated on a commercial titanium silicalite-1 (TS-1) catalyst under simulated industrial conditions in continuous tank slurry reactor. The conclusions about deactivation behavior have been achieved based on the changes of activity, conversion and selectivity. XRD and FTIR analyses indicate the MFI framework structure of zeolite cannot be changed evidently during the reaction. It is found by comparative experiments that the main reason for catalyst deactivation is coke formation on the surface of TS-1. Results from TGA-DTA, N2 adsorption and pyridine TPD analyses of used catalysts demonstrate there are two types of coke deposited mainly on micropores. Soft coke is located near Ti sites and can be removed by oxidation under 350 °C, while refractory coke can be oxidized by air until 700 °C. Analysis results of GC–MS for soluble coke and NMR, FTIR spectra for insoluble coke indicate that N-containing polycyclic aromatic and/or polyalkene species are the main components of coke deposits.
Keywords: Coking deactivation; Titanium silicalite; Ammoximation; Cyclohexanone oxime;
A hydrotalcite-based catalyst system for the single-stage liquid-phase synthesis of MIBK by Ferry Winter; Mariska Wolters; A. Jos van Dillen; Krijn P. de Jong (231-238).
A comparative study was performed between Pd supported on activated hydrotalcites bi-functional catalysts and physical mixtures of activated hydrotalcites with Pd supported on carbon nanofibers for the single-stage liquid-phase synthesis of methyl isobutyl ketone from acetone and H2. Since it was found earlier that the dehydration reaction of diacetone alcohol over activated hydrotalcites is the rate-determining step in this process, Mg–Al hydrotalcites were investigated in the condensation of acetone to diacetone alcohol and its dehydration to mesityl oxide to enhance the activity. A correlation between the number of active base sites, as determined by volumetric CO2 adsorption measurements at low pressures, and the activity in the dehydration reaction could be derived. A dependency on the Pd-loading (0–1 wt%) of Pd supported on activated hydrotalcites catalysts was found in the single-stage synthesis of methyl isobutyl ketone, whereas no such an effect was found when using physical mixtures of activated hydrotalcites with Pd on carbon nanofibers. Results from TEM, CO2 chemisorption and N2 physisorption as well as catalytic experiments in the hydrogenation of mesityl oxide and of cyclohexene indicate that this dependency is largely accounted for by entrapment of Pd particles in the agglomerates of the irregular stacks of hydrotalcite platelets, making these sites inaccessible for the reactants.
Keywords: Hydrotalcite; Layered double hydroxide; LDH; Solid base catalyst; Palladium; Methyl isobutyl ketone; MIBK; Hydrogenation; Bi-functional catalyst;
1H MAS NMR study of the coordination of hydroxyl groups generated upon adsorption of H2O and CD3OH on clean MgO surfaces by Céline Chizallet; Guylène Costentin; Hélène Lauron-Pernot; Jocelyne Maquet; Michel Che (239-244).
The coordination of OH groups on MgO has been characterized by 1H MAS NMR after appropriate pre-treatment conditions to obtain surfaces free from carbonates and with a controlled degree of hydroxylation. On MgO-sol–gel sample treated at 1023 K under flowing nitrogen, hydroxylated with water and evacuated at 673 K for 2 h, at least six lines have been identified at 1.2, 0.7, 0.0, −0.4, −0.7 and −1.8 ppm. Upon dehydroxylation at higher temperature, the signals become sharper and a relative decrease of intensity of the lines at δ ≥ −0.4 and at −1.8 ppm is observed. After adsorption of CD3OH and further desorption at 473 K, an OH signal with two main lines at 0.4 and 0.0 ppm and a broad contribution around 1.0 ppm are observed. Thus deuterated methanol dissociation generates only OH groups at high chemical shift. These observations are related to the coordination of the oxygen atom of the OH groups. It is thus suggested that, when water dissociates on the surface, the OH groups coming from protonation of O2− ions and being the more coordinated, give a signal at a higher chemical shift than the OH groups formed by coordination of a hydroxide ion to a Mg2+. The link with the acido-basic properties is then discussed on the basis of literature data.
Keywords: 1H MAS NMR; MgO; Surface; Hydroxyl groups; Basicity;
Synthesis of commercial important diethyl phthalate over Al-, Fe- and Al,Zn-MCM-41 molecular sieves by Seshachalam Udayakumar; Samikannu Ajaikumar; Arumugam Pandurangan (245-256).
The synthesis of diethyl phthalate (DEP) from phthalic anhydride (PAH) and ethanol (EtOH) has been carried out successfully on aluminum-, iron- and zinc- containing MCM-41 molecular sieves. These catalysts were prepared by the hydrothermal method. The catalysts have been characterized by the XRD, BET (surface area) and 29Si and, 27Al MAS-NMR techniques. The catalytic activity of these molecular sieves has been tested by the above-mentioned reaction, by the batch processes at 135, 150 and 175 °C. Both conversion and selectivity increased with an increase in temperature and mole ratio (EtOH/PAH). The activity of these catalysts followed the order: Al-MCM-41 (Si/Al = 112) > Fe-MCM-41 (Si/Fe = 115) > Al-MCM-41 (Si/Al = 70) > Al-MCM-41 (Si/Al = 52) > Fe-MCM-41 (Si/Fe = 61) > Al, Zn-MCM-41 (Si/Al + Zn = 104) > Al-MCM-41 (Si/Al = 30). The reaction yielded both monoethyl phthalate (MEP) and diethyl phthalate (DEP). The nature of the catalyst sites has been clarified using water as an impurity. The weight of the catalyst was optimized at 0.06 g. Some times hydrophilic and some times hydrophobic nature of the catalyst been explained by the influence of water; the external surface acidity also facilitates the reaction. This has been confirmed by the addition test reaction.
Keywords: MCM-41; Conversion; Selectivity; Hydrophobicity; Hydrophilicity; Diethyl phthalate;
A novel photocatalyst BiSbO4 for degradation of methylene blue by Xin P. Lin; Fu Q. Huang; Wen D. Wang; Ke L. Zhang (257-262).
BiSbO4 powder was synthesized by a solid state reaction method. The sample was characterized by X-ray diffraction and UV–vis diffuse reflectance spectra. BiSbO4 is an indirect gap material with the intrinsic band gap of 2.75 eV. It possesses a fair activity for visible-light-driven photocatalysis. The results concerning methylene blue photodecomposition generally show that the catalytic efficiency of BiSbO4 is slightly higher than that of rutile-type TiO2 under UV light irradiation. The 3–5 wt% RuO2 sensitization causes about three-time increase in catalytic efficiency. The photocatalytic activity is discussed in close connection with calculated band structure and crystal structure. In this article, the effects of powder concentration and pH value in suspending aqueous solution are also presented.
Keywords: Photocatalyst; BiSbO4; MB;
Fe-ZSM-11 magnetic properties: Its relation with the catalytic activity for NO x SCR with iso-butane and O2 by Oscar A. Anunziata; Marcos Gómez Costa; Andrea R. Beltramone (263-269).
Fe n+-ZSM-11 zeolites, with Fe2+ and/or Fe3+ as active sites prepared by us by reproducible post-synthesis methods showed magnetic properties. Otherwise, they are very important in environmental catalysis for the reduction of NO x to N2 with hydrocarbons. The magnetic and catalytic properties of Fe-ZSM-11 samples with different contents of Fe2+ and Fe3+ were compared. The Fe2+-ZSM-11 sample (with 1.8 Fe2+ per unit cell) showed the best catalytic activity and greater saturation magnetization than the other samples. The proportion of Fe2+ per unit cell allows having higher amount of active sites for the reduction of NO when Fe2+ is bonded to the zeolite structure. These Fe2+ species bonded to the framework could generate ferromagnetic couples conferring the ferromagnetic behavior to the samples. The saturation magnetization of the other samples is smaller due to the lower amount of couples Fe2+–Fe2+. When the amount of Fe3+ increases, the Fe bonded to the structure as counter ion decreases, forming α-Fe2O3 as isolated clusters inactive for the reduction of NO. Mössbauer characterization of Fe2+-ZSM-11 showed that the Fe is forming couples (ferromagnetic) in an important amount. XANES studies of Fe n+-ZSM-11 samples were performed in order to obtain the Fe2,3+composition.
Keywords: Fe-ZSM-11; Fe2,3+; Magnetization; Catalytic activity; NO x SCR;
The kinetics of homogeneous catalytic methane oxidation by Beata Michalkiewicz (270-274).
Selective, direct oxidation of methane into useful chemicals remains a big challenge in catalysis in the 21st century. The study presents a new and efficient method based on methane esterification and further hydrolysis to methanol. A platinum-catalyzed system using oleum as the reaction medium for the oxidation of methane to methyl bisulfate in the temperature range between 140 and 180 °C at methane pressure 3.0–6.8 MPa has been studied. Analyzing the relationship between the ester concentration and the methane partial pressure, the sulfur trioxide concentration and the temperature, leads to a well-defined equation describing the reaction rate. This equation is applicable for the estimation of the reaction rate and the ester concentration in any moment up to a process time of 22 h. An apparent activation energy is also calculated.
Keywords: Methane; Methanol; Methyl bisulfate; Kinetics equation; Reaction rate;
High catalytic performance of Pt-Fe alloy nanoparticles supported in mordenite pores for preferential CO oxidation in H2-rich gas by Masashi Kotobuki; Akiko Watanabe; Hiroyuki Uchida; Hisao Yamashita; Masahiro Watanabe (275-283).
Catalytic performance of Pt-Fe/mordenite for preferential CO oxidation (PROX) was tested in comparison with that of Pt-Fe/Al2O3. The former catalyst pretreated at 300 °C (Pt-Fe/M-300) showed extremely high reactivity and selectivity for the PROX reaction but the catalyst treated at 500 °C (Pt-Fe/M-500) showed the inferior performances as well as Pt-Fe/Al2O3. Characterization of the catalysts indicated that most of metallic particles at Pt-Fe/M-300 were supported in the mordenite cages, whereas the particles at Pt-Fe/M-500 were supported outside. It was also found that the catalyst particles in the cages of the Pt-Fe/M-300 have ca. 10 times higher surface area than that of outside and can adsorb CO selectively, compared with H2, but not at Pt-Fe/M-500. Such a difference in the above specific properties of Pt-Fe/M-300 from the others is presumably the reason why it exhibits the superior PROX performance. Complete CO elimination was demonstrated at 150 °C in a synthesized gas mixture of 1% CO, 1% O2, 20% CO2, 20% H2O and H2 balance on Pt-Fe/M-300 and no noticeable degradation of the performances was done for 24 h, indicating the potential of practical application of the catalyst to a fuel processor for polymer electrolyte fuel cells.
Keywords: Preferential oxidation; Selective oxidation; Carbon monoxide; Zeolite catalyst; Hydrogen purification; Fuel cell;