Applied Catalysis A, General (v.478, #C)
Editorial Board (CO2).
Carbon nanotubes as catalyst for the aerobic oxidation of cumene to cumene hydroperoxide by Shixia Liao; Feng Peng; Hao Yu; Hongjuan Wang (1-8).
The commercial carbon nanotubes (CNTs) exhibited high activity and good stability for the liquid aerobic oxidation of cumene to cumene hydroperoxide (CHP) under low temperature.The effective oxidation reaction system using the commercial carbon nanotubes (CNTs) as catalysts for the liquid aerobic oxidation of cumene to cumene hydroperoxide (CHP) under low temperature is reported in this paper. Several reaction parameters, including the temperature, catalyst content, oxygen flow rate and reaction time were carefully studied. Under optimal conditions, cumene conversion of 24.1% with CHP selectivity of 88.4%, close to that of metal catalyst, was obtained. Cumene oxidation catalyzed by CNTs was proved a radical-involved reaction, and the outstanding catalytic performance was attributed to CHP decomposition catalyzed by CNTs to produce free radicals. Oxygenated functional groups on the surface of catalyst showed a negative effect on cumene oxidation due to the localization of electrons after the introducing of defects and oxygenated functional groups. CNTs as catalysts also showed desirable recyclability after five cycling tests. This study not only provides an applicable method for selective oxidation of cumene to CHP, but also gives some useful information on catalytic role of CNTs-catalyzed liquid-phase oxidation reactions of aromatic hydrocarbons.
Keywords: Cumene; Catalytic oxidation; Carbon nanotubes; Cumene hydroperoxide;
Conversion of biomass tar containing sulphur to syngas by Gd―CeO2 coated Ni―Fe bimetallic-based catalysts by N. Laosiripojana; W. Sutthisripok; S. Charojrochkul; S. Assabumrungrat (9-14).
Catalytic activities of pellet-shape Ni―Fe/MgO―Al2O3 with and without Gd―CeO2 (CGO) coating toward steam reforming of naphthalene (as tar model compound) and biomass tar from pyrolysis of eucalyptus in the presence of H2S was studied under various conditions including different temperatures (between 700 and 900 °C), inlet H2S (from 100 to 1000 ppm) and inlet H2O concentrations. It was found that under sufficient conditions CGO coating can efficiently promote sulfur tolerant and resistance toward carbon deposition of Ni―Fe/MgO―Al2O3, from which less deactivation occurs after prolong testing (18 h) compared to the catalyst without CGO coating. In addition, the catalyst activity can be completely regenerated by purging air at 800 °C, from which almost the same level of H2 yield can be enhanced after regeneration. It was revealed from the study that in the presence of sufficient H2O concentration, the phase of CeO2 potentially transforms to Ce(SO4)2, which helps Ni―Fe/MgO―Al2O3 promote high tar reforming activity. In contrast, with less H2O presenting, Ce2O2S is formed and consequently results in low sulfur tolerant activity. Nevertheless, by purging Ce2O2S with air, the phases of CeO2 and Ce(SO4)2 can be effectively recovered. This study therefore highlights the great benefit of CGO coating over Ni―Fe/MgO―Al2O3 for tar reforming in terms of sulphur tolerant promotion and achievable catalyst regeneration.
Keywords: Tar conversion; H2S; Catalyst deactivation; CeO2;
Hydrogen generation from hydrolysis of ammonia borane in the presence of highly efficient poly(N-vinyl-2-pyrrolidone)-protected platinum-ruthenium nanoparticles by Murat Rakap (15-20).
Herein, the employment of PVP-protected Pt–Ru bimetallic nanoparticles (3.2 ± 1.4 nm) as highly efficient catalysts in the hydrolysis of ammonia borane for hydrogen generation is reported. They were prepared by co-reduction of two metal ions in ethanol/water mixture by an alcohol reduction method and characterized by TEM–EDX analysis, UV–vis spectroscopy, and X-ray photoelectron spectroscopy. They are recyclable and highly active for hydrogen generation from the hydrolysis of ammonia borane even at very low concentrations and temperature, providing a record numbers of average TOF value (308 mol H2 molcat −1 min−1) and maximum hydrogen generation rate (9884 L H2 min−1 (molcat)−1) for ammonia borane. PVP-protected Pt–Ru bimetallic nanoparticles provide activation energy of 56.3 ± 2 kJ mol−1 for the hydrolysis of ammonia borane.
Keywords: Platinum; Ruthenium; Nanoparticles; Ammonia borane; Hydrogen;
Crystalline structure refinements and properties of Ni/TiO2 and Ni/TiO2-Ce catalysts and application to catalytic reaction of “CO + NO” by Adolfo Romero-Galarza; Kevin A. Dahlberg; Xiaoyin Chen; Johannes W. Schwank (21-29).
Catalysts containing 7 wt% Ni were prepared by impregnation of anatase-phase TiO2 and Ce-doped TiO2 that were synthesized by sol–gel techniques. The catalysts were extensively characterized by a variety of methods including BET surface area measurements, temperature programmed H2 reduction (H2-TPR), scanning transmission electron microscopy (STEM), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) for CO adsorption. The crystallography, crystallite size, microstrain in the crystalline structure and concentration of all phases in the catalysts were determined by X-ray diffraction and refinement of the crystalline structure with the Rietveld method. As catalytic probe reaction, the stoichiometric oxidation of CO by NO was used. Doping with ceria affected the crystallography of the anatase-phase titania, increased the structural defects, and decreased the anatase crystallite size. This, in turn, led to more extensive contact of nickel particles with the support facilitating the reduction of nickel and of the surface of the Ce-doped TiO2. Among the various catalysts investigated, the Ce-doped Ni/TiO2 catalyst with a Ce/(Ce + Ti) ratio of 0.1 was found to be the most active for CO oxidation by NO.
Keywords: Anatase; Nickel; Ceria; Rietveld refinement; Structural defects; CO + NO reaction;
Imidazolium functionalized NT-Im-Au-Ag hybrids for surface-enhanced Raman scattering and catalytic reduction of 4-nitrophenol by Xiao Wu; Lihua Qiu; Zhenzhong Yang; Feng Yan (30-37).
A facile and effective procedure for the preparation of poly(divinybenzene-co-chloromethylstyrene) (poly(DVB-co-VBC)) nanotube/Au-Ag nanoparticle composite (NT-Im-Au-Ag) via using covalently attached imidazolium as linkers was reported. The approach involves the surface functionalization of poly(DVB-co-VBC) NTs with imidazolium cation, anion-exchange with Au precursor (HAuCl4) and followed by the reduction of metal ions. The obtained NT-Im-Au nanoparticle composite was further used as the seeds to produce NT-Im-Au-Ag nanoparticle composite. The morphology and optical properties of the produced nanohybrids were characterized by transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy. The as-prepared NT-Im-Au-Ag nanohybrids show an extremely suitable substrate for surface-enhanced Raman spectroscopy (SERS) with a high enhancement factor of 6.7 × 107, enabling the detection of 10−12 M Rhodamine 6G solution. The catalytic performance of NT-Im-Au-Ag nanohybrids was studied by the reduction of 4-nitrophenol with NaBH4 as a reducing agent. Their reaction rate constant was calculated according to the pseudo-ﬁrst-order reaction equation.
Keywords: Au-Ag nanoparticles; SERS; 4-Nitrophenol; Oxygen reduction;
Palladium nanoparticle's surface structure and morphology effect on the catalytic activity for dry reforming of methane by Ignacio O. Costilla; Miguel D. Sánchez; Carlos E. Gigola (38-44).
Low loaded Pd/α-Al2O3 catalysts (<0.5 wt% Pd) were characterized and tested for CH4 reforming with CO2 at 650 °C. The catalysts were prepared by a recharging procedure, using an organometallic precursor, followed by intermediate washing and calcination steps. FTIR spectra of adsorbed CO showed that the Pd surface structure and the particle size were dependent on the number of post-impregnation washing steps. A catalyst sample with a metal dispersion of 33% showing well defined low-index planes (by FTIR) and nearly spherical particles (by TEM) was obtained using two-washing steps. In the reaction, it exhibited a high initial activity followed by a pronounced deactivation due to carbon nanofiber's formation and sintering. TEM analysis of the used catalyst revealed the presence of spherical Pd particles at the end of the fibers that were not attached to the support surface. On the other hand, a high dispersion sample (78%) with a large fraction of Pd atoms with low coordination was obtained by applying three washing steps after impregnation. The presence of small hemispherical particles and larger nearly-flat ones attached to the support were found by TEM. In this case, the catalyst initially showed a very low activity that increased slowly up to a steady value. Although sintering also occurred and the surface structure of the used catalyst resembled the one of the low dispersion catalyst, the amount of carbon formed was quite low. The observed activation under reaction conditions was associated with the slow development of a surface structure that exhibited mainly the (1 0 0) plane favoring methane dissociation. However, the initial interaction of the particles with the support suggested by TEM micrographs seems to remain unaltered despite the particle size increase. Consequently, the process of nanofiber formation and particle separation was inhibited.
Keywords: Pd (palladium); Catalyst preparation; Dry reforming; Particle's morphology; Carbon formation;
Metallic structured catalysts: Influence of the substrate on the catalytic activity by M.I. Domínguez; A. Pérez; M.A. Centeno; J.A. Odriozola (45-57).
In order to study the influence of the metallic substrate on the catalytic activity of structured micromonolithic catalysts, a CuO x /CeO2 catalyst was deposited on different oxidized or enameled metallic micromonoliths and tested in the PROX reaction under ideal and realistic conditions. The obtained results show as both activity and selectivity depend on the nature of the alloy and the nature of the interphase between the metal substrate and the catalyst layer. In oxidized micromonoliths, diffusion of Cr and Fe has been observed. For enameled micromonoliths, together with that diffusion, the interaction of the glass–ceramic interphase with the reactive gas streams resulted in the partial hydrolysis of this layer leading to diffusion toward the catalyst surface of the hydrolysis products, namely Na, Ca and Si cations. In some cases, the alteration of the surface composition favors the spreading of the copper active phase. As a result, it must be concluded that the metallic substrates are not spectators, at least in the PROX reaction, playing a fundamental role in the performances of the catalytic devices.
Keywords: Enamel; Structured reactors; Metallic micromonolith; Diffusion barrier; PROX;
Preparation of amorphous silica-alumina using polyethylene glycol and its role for matrix in catalytic cracking of n-dodecane by Atsushi Ishihara; Takanori Wakamatsu; Hiroyuki Nasu; Tadanori Hashimoto (58-65).
MP plots measured by N2 adsorption for amorphous silica-alumina and zeolite-silica-alumina catalysts of P183 series. P183: silica-alumina, MAT: mixed catalyst with zeolite, sp: small particles, 6000: average molecular weight of PEG, average molecular weight of other catalysts was 400.For catalytic cracking, mixed catalysts of zeolite as a main catalyst and matrix with large pore capable of reacting large molecules, which cannot enter into the tiny pore of zeolite, are used. Hence the selection of matrix is quite important for the activity and product selectivity of catalytic cracking. Therefore, this paper reports the preparation and the analysis of reactivity of amorphous silica-alumina as a matrix, which has not been studied in catalytic cracking extensively and academically.Amorphous silica-alumina matrices were prepared by the sol–gel method using polyethylene glycol (PEG) as an organic template. Further, catalytic cracking of n-dodecane was performed in order to explore their reactivity as matrices. Silica-aluminas prepared had only moderate amounts of mesopore and larger amounts of micropore, of which the pore size was larger than that of zeolite. The surface area and the pore volume of prepared silica-aluminas increased with increasing the amount of PEG added. The amounts of NH3 desorbed and the conversions of n-dodecane using mixed catalysts with zeolite also increased with increasing the amount of PEG added. The results suggested that larger amounts of micropores as well as moderate amounts of mesopores would affect the higher conversions. The conversion increased, gasoline fraction decreased and gas fraction increased with decreasing particle size of silica-aluminas. The ratio of multi-branched products to single-branched products (multi/single ratio) decreased when the conversion increased by increasing PEG content. The result indicates that although the addition of PEG increased the surface area and the activity, sizes and amounts of mesopores prepared using PEG were not enough large to increase multi-branched products improving the selectivity.
Keywords: Amorphous silica-alumina; Polyethylene glycol; Catalytic cracking; n-Dodecane; β zeolite; Matrix;
XAFS and HAADF STEM combined characterization for size regulated Ni nanocluster catalyst and its unique size dependence for water gas shift reaction by Hirotake Kitagawa; Nobuyuki Ichikuni; Hanako Okuno; Takayoshi Hara; Shogo Shimazu (66-70).
X-ray absorption fine structure (XAFS) and high angle annular dark field scanning transmission electron microscopy (HAADF STEM) were both applied to a characterization of the size regulated Ni nanocluster catalyst on alumina. XAFS analysis showed that NiAl2O4 was not formed in our colloid derived catalyst. The wide variety of coordination number (CN) for Ni–Ni indicated the achievement of the size regulated Ni nanocluster catalyst preparation. HAADF STEM analysis showed narrow size distribution of Ni nanocluster catalyst even after H2 reduction at 673 K. Distorted particles were observed and the ratio of distorted particles increased with decrease in the cluster size. Water gas shift reaction was carried out to investigate the catalysis. Volcano-shaped size dependence was observed for the activity of supported Ni nanocluster catalyst.
Keywords: Ni nanocluster catalyst; XAFS; HAADF STEM; Water gas shift reaction;
Promoting mechanism of sulfur addition in catalytic dehydrogenation of isobutane over Mo/MgAl2O4 catalysts by Guowei Wang; Nannan Sun; Chuancheng Gao; Xiaolin Zhu; Yanan Sun; Chunyi Li; Honghong Shan (71-80).
Mo/MgAl2O4 catalysts with sulfur addition were verified to exhibit excellent performance in catalytic dehydrogenation of isobutane, which could yield up to 56.3 wt% isobutene at 560 °C. Catalyst characterization and activity test results jointly revealed that MoS2 formed during the induction period probably constituted the active phase for dehydrogenation. As to the formation of MoS2, treatment with appropriate reducing gases (e.g., CO) was required. However, in the atmosphere of H2, molybdate species were partially reduced to MoO2, which inhibited the formation of MoS2. Furthermore, Mo/MgAl2O4 catalysts sulfided by H2S/N2 exhibited a high initial activity, further confirming that MoS2 species were indispensable to dehydrogenation reaction. Stability evaluation of the Mo/MgAl2O4-S catalyst indicated that the catalytic activity decreased slightly within six reaction-regeneration cycles. The irreversible deactivation probably resulted from the obvious sulfur loss. Therefore, appropriate measures to replenish sulfur should be carried out in future commercial application.
Keywords: Isobutane; Dehydrogenation; Mo/MgAl2O4; Sulfur; MoS2;
Molecular size- and shape-selective Knoevenagel condensation over microporous Cu3(BTC)2 immobilized amino-functionalized basic ionic liquid catalyst by Qun-xing Luo; Xue-dan Song; Min Ji; Sang-Eon Park; Ce Hao; Yan-qin Li (81-90).
A novel molecular size- and shape-selective catalyst, microporous metal-organic framework HKUST-1 immobilized amino-functionalized basic ionic liquid (ABIL-OH), was synthesized by facile impregnation and activation. Characterizations and catalytic results revealed that the catalytically active species ABIL-OH could be confined in well-defined HKUST-1 nanocavities via Cu―NH2 coordination bond. The resulting ABIL-OH/HKUST-1 heterogeneous catalyst showed comparable catalytic activity and enhanced selectivity in liquid phase Knoevenagel condensation, and it could be recovered conveniently and reused at least 5 times without significant loss of its catalytic efficiency. Moreover, ABIL-OH/HKUST-1 catalyst demonstrated distinct size- and shape-selective properties for discrimination of reactants in Knoevenagel condensation. It was supposed that diffusion kinetics of reactants might be controlling step and play a more important role than the nature of the substituents in the confined microenvironment.
Keywords: Size and shape-selective catalysis; Metal-organic framework; Cu3(BTC)2 nanocavities; Amino-functionalized basic ionic liquid; Immobilization;
Methane oxidation hysteresis over Pt/Al2O3 by Ashraf Amin; Ali Abedi; Robert Hayes; Martin Votsmeier; William Epling (91-97).
With growing, accessible natural gas reserves, there is renewed interest in natural gas engines for the wider automotive market. A potential issue, if legislated, is controlling (reducing) the un-combusted CH4 emissions. The key challenge in catalytic CH4 oxidation is the high temperature required, relative to other hydrocarbon species. In this context, a monolith-supported Pt/Al2O3 catalyst was evaluated for CH4 combustion under fuel lean and fuel rich mixtures using temperature programmed reaction (TPRxn) and step-change temperature and oxygen level experiments. The experiments included performance evaluation during both ignition (increasing temperature) and extinction (decreasing temperature after ignition). Conversion hysteresis was observed, with the conversions during extinction higher than those during ignition under fuel lean or stoichiometric combustion reaction conditions. Results obtained demonstrate that this hysteresis effect can be used to achieve high CH4 oxidation conversions at temperatures lower than that required for ignition, admittedly first through using high temperatures to obtain ignition, then lowering the temperature to take advantage of the hysteresis. Results also suggest that changing O2 levels can lead to similar benefits. With the assumption that lean conditions and lower exhaust temperatures are associated with improved fuel economy, while higher exhaust temperatures and fuel rich conditions lead to higher CH4 oxidation rates over the catalyst, the findings presented clearly demonstrate the potential to achieve both via a cyclic operating approach, with the frequency on the order of 10 s of minutes. Data obtained when cycling between temperatures above and below the ignition point and between excess O2 and stoichiometric O2 levels proved this hypothesis.
Keywords: Methane oxidation; Low temperature oxidation; Hysteresis;
Sulfonated niobia and pillared clay as catalysts in etherification reaction of glycerol by Patrícia A. Celdeira; Maraisa Gonçalves; Flávia C.A. Figueiredo; Sandra Maria Dal Bosco; Dalmo Mandelli; Wagner A. Carvalho (98-106).
Sulfonated niobia (HY-340 CBMM) and pillared clay (Fluka) were tested in the catalytic conversion of glycerol by etherification reactions. The solids were treated with concentrated fuming sulfuric acid (AS100 and NS100), and a 30% aqueous solution of this acid (AS30 and NS30). Both the presence of sulfur and the increase in the acidity of the solids demonstrate the suitability of the sulfonation process, especially in samples treated with concentrated fuming sulfuric acid. The best catalyst for the reaction of etherification with tert-butyl alcohol was AS100, with a glycerol conversion of 95% after 5 h at 393 K and yield of 60.3, 33.2 and 5.4%, respectively for mono-tert-butyl-glycerol (MTBG), di-tert-butyl-glycerol (DTBG) and tri-tert-butyl-glycerol (TTBG).
Keywords: Glycerol; Etherification; Sulfonation; Niobia; Pillared clay;
Influence of support on the aerobic oxidation of HMF into FDCA over preformed Pd nanoparticle based materials by Baraa Siyo; Matthias Schneider; Jörg Radnik; Marga-Martina Pohl; Peter Langer; Norbert Steinfeldt (107-116).
Here, the preparation and evaluation of supported nanoparticle based catalytic material is reported. Polyvinylpyrrolidone (PVP) stabilized palladium nanoparticles with a mean particle size of 1.8 nm were synthesized in ethylene glycol and subsequently deposited onto different metal oxide supports (TiO2, γ-Al2O3, KF/Al2O3, and ZrO2/La2O3). The prepared catalysts were applied to the aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) in aqueous solution at atmospheric pressure (T = 90 °C, pO2 = 1 bar) and compared regarding their catalytic performance and stability. The highest FDCA yield (>90%) was obtained for the Pd/ZrO2/La2O3 catalysts which additionally showed a relatively stable catalytic performance when the material was reused. Various characterization methods including XRD, TEM, XPS, and AAS were applied to obtain information about the Pd NP before and after utilization in HMF oxidation. For the Pd/TiO2 the least changes in Pd NP structure were observed after using the material in HMF oxidation. This was attributed to a stronger interaction between the Pd NP and the TiO2 support compared to other supports used in the studies.
Keywords: Pd; Nanoparticles; Supported catalysts; 5-Hydroxymethylfurfural; 2 ;5-Furandicarboxylic acid; Oxidation;
Mechanistic insights into the effects of support on the reaction pathway for aqueous-phase hydrogenation of carboxylic acid over the supported Ru catalysts by Lungang Chen; YuPing Li; Xinghua Zhang; Qi Zhang; Tiejun Wang; Longlong Ma (117-128).
The presence of enough acid sites and SMSI are indispensable for the formation of metal–acid bifunctional sites, which improve the C＝O hydrogenation of acyl species—the intermediate species dissociated from the adsorbed carboxylic acid molecules. However, the decarbonylation of acyl species are favored on the bare Ru sites, which requiring the available metal sites with weaker metal–support interaction and few of acid sites.Several supported Ru catalysts, Ru/TiO2, Ru/ZrO2, Ru/SiO2, Ru/γ-Al2O3 and Ru/SiO2-Al2O3, were prepared and investigated for propanoic acid aqueous-phase hydrogenation. H2-TPR, NH3-TPD, pyridine-FTIR and propanoic acid-DRIFTS techniques were performed to explore the metal–support interaction, acid sites and key adsorption species. The effect of support on the reaction pathway of C＝O hydrogenation and decarbonylation of acyl species was discussed. Compared with Ru/ZrO2 and Ru/SiO2 catalysts, high selectivity of C＝O hydrogenation was obtained over the catalysts with more Lewis acid sites, such as Ru/γ-Al2O3 and Ru/SiO2-Al2O3 catalysts. The DRIFTS results suggest that the formation of adsorption species (acyl, carboxylate and carboxylic acid) is strongly depended on the nature of support. The metal–acid bifunctional sites are indispensable for the C＝O hydrogenation of acyl. However, the decarbonylation of acyl on the metal sites requires the relatively weak metal–support interaction and few of Lewis acid sites.
Keywords: Aqueous-phase; Hydrogenation; Ru catalyst; Effect of support; Acyl; Decarbonylation; DRIFTS;
Effect of chemical composition of Sr x Ca1 − x Fe2O4 (0.0 ≤ x ≤ 1.0) catalyst and alkali towards efficient and selective epoxidation of styrene by Ravindra Y. Pawar; Parag V. Adhyapak; Satish K. Pardeshi (129-137).
Spinel type strontium substituted calcium (SSC) ferrite Sr x Ca1 − x Fe2O4 (0.0 ≤ x ≤ 1.0) catalyst synthesized by citrate-gel combustion method are well characterized by various techniques such as TG–DTG, FT-IR, X-ray diffraction, SEM, EDS and BET. The crystallization temperature of the spinel particle prepared by citrate gel is 600 °C, which is lower in comparison to ferrite prepared by other methods. Among this series of catalysts, Sr0.2Ca0.8Fe2O4 which has highest surface area shows the best catalytic efficiency. GCMS analysis revealed that, during the course of reaction the insertion of oxygen takes place selectively than the oxidative cleavage of C＝C bonds; to give epoxide as major product, while addition of NaOH suppresses further isomerization of the styrene epoxide, thereby increasing the selectivity remarkably to give epoxide as major product. The catalyst containing both Sr2+ and Ca2+ ions are more active than pure SrFe2O4 and CaFe2O4. The synergistic effect of Sr2+, Ca2+ ions and greater site preference energy of Sr2+ than Fe3+ favour the selective epoxidation of styrene in presence of 30% H2O2 as oxidant. The optimization and the effect of various reaction conditions on the conversion of styrene and product distribution were also studied.
Keywords: Strontium substituted calcium ferrite; Styrene epoxidation; Ring opening prevention; Synergistic effect; Site preference energy;
Metathesis of cardanol over Ru catalysts supported on mesoporous molecular sieve SBA-15 by Tushar Shinde; Vojtech Varga; Miroslav Polášek; Michal Horáček; Naděžda Žilková; Hynek Balcar (138-145).
The Hoveyda–Grubbs type Zhan catalysts (ZC) and Grubbs second generation catalyst (GII) were immobilized on SBA-15 mesoporous molecular sieve by non-covalent interactions and phosphine linkers, respectively. Both hybrid catalysts proved to be highly active and selective in cardanol metathesis and cardanol cross-metathesis with ethene and cis-1,4-diacetoxy-2-butene (DAB). GII/SBA-15 was less active than ZC/SBA-15, however, Ru leaching was significantly lower for GII/SBA-15 (0.5%) than for ZC/SBA-15 (2.5%). In ethenolysis of cardanol, 3-(non-8-enyl)phenol was isolated as a major product. In cross-metathesis with DAB 9-(3-hydroxyphenyl)non-2-enyl acetate and non-2-enyl acetate were formed with high selectivity. Easy catalyst–product separation and low Ru leaching provide the products (applicable as detergent precursors and fragrance and flavor agents) free from the catalyst residue.
Keywords: Cardanol; Metathesis; Supported catalysts; Ru carbenes; SBA-15;
Stable surface terminations of orthorhombic Mo2C catalysts and their CO activation mechanisms by Tao Wang; Qiquan Luo; Yong-Wang Li; Jianguo Wang; Matthias Beller; Haijun Jiao (146-156).
The structure and stability of all twenty-two terminations of the seven low-Miller index orthorhombic Mo2C surfaces have been systematically investigated on the basis of the computed surface energies from periodic density functional theory. With the increase of the carbon chemical potential (μ C), the most stable surface structure and composition change from the metallic (1 1 0)-Mo and (1 0 0)-Mo terminations to the mixed (1 1 1)-Mo/C and strongly reconstructed (1 1 0)-Mo/C terminations. The calculated stability order and surface area proportions of the (1 0 0), (1 1 0) and (1 1 1) surfaces agree very well with the available X-ray diffraction data. In addition, CO adsorption and dissociation on these surfaces have been computed and micro-kinetic analysis reveals that CO dissociation is rate-determining on the metallic termination, and CO adsorption is rate-determining on the mixed Mo/C-termination. This might explain the observed catalytic differences of orthorhombic Mo2C catalysts prepared from different ways.
Keywords: DFT; Orthorhombic Mo2C; Surface energy; Morphology; CO activation;
Green, selective and swift oxidation of cyclic alcohols to corresponding ketones by Gregory Chatel; Camille Monnier; Nathalie Kardos; Celine Voiron; Bruno Andrioletti; Micheline Draye (157-164).
Cyclohexanol oxidation to cyclohexanone is an important reaction in both organic chemistry and industry. We propose here an efficient, eco-friendly, and general method for oxidizing five- to eight-membered cyclanols used as model substrates, with aqueous hydrogen peroxide (H2O2) in the presence of tungstic acid (H2WO4) as a catalyst and an ammonium-based ionic liquid (IL) as a co-catalyst under organic solvent-free conditions. Cyclohexanol was found to be the most reactive of the four tested cyclanols. In addition, the role of the IL as a phase transfer catalyst was confirmed by the use of Aliquat 336 and the kinetic of the reaction was significantly improved under microwave or ultrasonic activation, leading to excellent yields in only a few minutes.
Keywords: Oxidation; Tungsten; Microwave; Ultrasound; Ionic liquids; Hydrogen peroxide; Phase transfer catalysis;
Fabrication of Ni–Al nanoparticles via vacuum arc plasma evaporation and their catalytic properties for CO oxidation by Ya Xu; Junyou Yang; Masahiko Demura; Toru Hara; Toshiyuki Hirano; Yoshitaka Matsushita; Masahiko Tanaka; Yoshio Katsuya (165-174).
Ni–Al nanoparticles were fabricated from Ni3Al-based alloys using vacuum arc plasma evaporation, and their catalytic activities for carbon monoxide (CO) oxidation were examined. The synthesized nanoparticles were characterized in detail using synchrotron radiation X-ray diffraction analyses, scanning transmission electron microscopy, and surface area measurements based on nitrogen adsorption. The as-fabricated nanoparticles were composed of Ni, Ni3Al, and a small amount of NiAl, with Al2O3 and NiO phases formed on their surfaces. The nanoparticles exhibited a much higher activity than that of a conventional atomized Ni3Al powder. It was found that the Ni phase is oxidized to NiO during CO oxidation, while the Ni3Al phase remains unchanged. It is likely that the NiO phase serves as the active species for CO oxidation, and the Ni3Al and Al2O3 phases serve as supports for the NiO phase.
Keywords: Nanoparticles; Ni–Al intermetallic compounds; CO oxidation catalysts; Arc plasma evaporation;
Rationally designed Fe-MCM-41 by protein size to enhance lipase immobilization, catalytic efficiency and performance by Jiafu Lin; Bohan Zhao; Yu Cao; Hui Xu; Shuhan Ma; Mingyue Guo; Dairong Qiao; Yi Cao (175-185).
A three-dimensional structure of lipase protein was constructed by using homology modeling. Six different Fe-MCM-41 carriers were synthesized with different pore size based on the properties of the lipase examined. The relative activity of lipase from Yarrowia lipolytica (YYL) immobilized on Fe-MCM-41 with a pore size of 4.27 nm (FM-4-YYL) reached 197% when compared with free lipase. This result was notably higher than that of YYL encapsulated in other forms of Fe-MCM-41. Moreover, FM-4-YYL has excellent thermal stability in that it can preserve nearly 80% of the initial activity after incubation at 60 °C for 1 h. In addition, immobilized lipases were used as catalysts for the transesterification of olive oil with methanol. The highest conversion yield (98%) was observed when FM-4-YYL was used as a biocatalyst for biodiesel (10 mL olive oil, 1.66 mL methanol, and 1.5 mL water at 30 °C for 4 h). FM-4-YYL can be reused for nine cycles without significant loss in activity. The work demonstrates that the selection and modification of adsorbents based on enzyme protein properties is a very promising strategy for increasing stability and enhancing active the performance of biocatalysts for industrial production.
Keywords: Lipase; Immobilization; Catalytic efficiency; Fe-MCM-41; Biodiesel;
How to increase the selectivity of Pd-based catalyst in alkynol hydrogenation: Effect of second metal by Artur Yarulin; Igor Yuranov; Fernando Cárdenas-Lizana; Duncan T.L. Alexander; Lioubov Kiwi-Minsker (186-193).
The development of selective Pd-based catalyst for semi-hydrogenation of dehydroisophytol (DIP), a C20-alkynol, is reported. A series of unsupported mono- (Pd) and bimetallic (Pd-M) nanoparticles (NPs) with Pd/M molar ratios of 1.5 - 5.0 (M = Ag or Cu) were examined as model systems. The Pd-Ag and Pd-Cu NPs with controlled crystal sizes of ∼3.3 nm were prepared by Ag (Cu) electroless deposition on pre-formed poly(N-vinyl-2-pyrrolidone)-stabilized Pd0 colloids. Bimetallic Pd-Ag NPs adopted a core (Pd)-shell (Ag) structure whereas a mixed alloy was attained in the Pd-Cu nanocrystals. A (partial) Pd surface segregation induced by reaction with H2 was in evidence for the Pd-Ag NPs. A significant increase in selectivity up to 97% (at X DIP = 99%) to the target alkenol was demonstrated following the incorporation of a second metal. This result is attributed to the dilution of the surface Pd-sites by Ag (Cu) and a modification of the Pd electronic properties. Pd-Ag NPs, having shown the highest selectivity, were further deposited on a structured support based on sintered metal fibers (SMF) coated with ZnO. The improved selectivity achieved over the unsupported Pd-Ag colloidal NPs was retained over the structured catalytic system. The bimetallic Pd5.0Ag/ZnO/SMF (S IP = 93%) demonstrated a drastic increase in IP selectivity relative to the monometallic Pd/ZnO/SMF (S IP = 78%) and state-of-the-art Lindlar catalyst (S IP = 62%) at DIP conversion ≥99% with the stable activity during 50 h, suggesting catalyst feasibility for selective semi-hydrogenation of long chain alkynols with important applications in the manufacture of vitamins and fine chemicals.
Keywords: Partial hydrogenation; Dehydroisophytol; Isophytol; Pd nanoparticles; Sintered metal fibers; ZnO; Pd-Cu; Pd-Ag;
Non-covalent immobilization of RhDuphos on carbon nanotubes and carbon xerogels by C.C. Gheorghiu; C. Salinas-Martínez de Lecea; M.C. Román-Martínez (194-203).
The immobilization of the chiral complex RhDuphos, by electrostatic or π–π (adsorption) interactions, on carbon nanotubes and carbon xerogels is investigated. To promote such interactions, the supports were either oxidized or heat treated to create carboxylic type surface groups or an apolar surface, respectively. The catalysts were tested in the hydrogenation of methyl 2-acetamidoacrylate.The prepared hybrid catalysts are less active than the homogeneous RhDuphos, but most of them show a high enantioselectivity and the one prepared with the oxidized carbon xerogel is also reusable, being able to give a high substrate conversion, keeping as well a high enantioselectivity. The anchorage by electrostatic interactions is more interesting than the anchorage by π–π interactions, as the π–π adsorption method produces a modification of the metal complex structure leading to an active hybrid catalyst but without enantioselectivity.The creation of carboxylic groups on the support surface has led to some hindering of the complex leaching.
Keywords: Hybrid catalysts; Rhodium chiral complex; Carbon xerogels; Carbon nanotubes; Hydrogenation;
Origin of superior photocatalytic activity in rutile TiO2 hierarchical microspheres: The dominate role of “microcavity” structure by Tingjiang Yan; Rusheng Yuan; Wenjuan Li; Jinmao You (204-210).
This paper aims to investigate the role that hierarchical structure plays in photocatalytic process. Hierarchical rutile TiO2 microspheres assembled by nanowires bundles were initially synthesized and then treated by thermal annealing or ultrasonic irradiation. Various technologies including SEM, XRD, DRS, and N2 sorption were employed to investigate the effect of post-treatments on the microstructures of TiO2 samples. The results revealed that annealing treatment caused obvious growth of particle size, decreased surface area and pore volume, and weakened optical absorbance, while ultrasonic irradiation had little influence on these properties. However, both annealing treatment and ultrasonic irradiation seriously destroyed the microcavity structure which existed in between the roughly parallel nanowires of hierarchical TiO2 microspheres. The existence of microcavity in these TiO2 hierarchical microspheres was proved to be crucial to the photoactivity toward degradation of methyl orange (MO). It has been proposed that the microcavities could act as microcapacitors for electronic storage and therefore contribute to a high separation efficiency of photogenerated electron–hole pairs. On the basis of ESR and active species scavenger experiments, h+ was found to be the primary active species in MO degradation while •O2 − slightly promoted the degradation efficiency via the formation of •OH. This finding is of great significance for the design of efficient photocatalytic materials with potential applications in solving worldwide energy crisis and environmental pollution.
Keywords: Hierarchical; Rutile; TiO2; Microcavity; Photocatalysis;
Molybdenum complex tethered to the surface of activated carbon as a new recoverable catalyst for the epoxidation of olefins by M. Masteri-Farahani; S. Abednatanzi (211-218).
A new recoverable catalyst for the epoxidation of olefins was developed by covalent attachment of aminopropyl groups on the surface of oxidized activated carbon (AC) and next reaction with bis(acetylacetonato)dioxomolybdenum(VI). Characterization of the prepared catalyst was performed with different physicochemical methods such as Fourier transform infrared and atomic absorption spectroscopies, scanning electron microscopy, energy-dispersive X-ray and nitrogen sorption analyses. Nitrogen adsorption–desorption analysis revealed that the textural characteristics of the support were changed during the grafting experiments but the channels remained relatively accessible despite sequential reduction in surface area, pore volume and pore size. Elemental analysis showed the presence of 0.06 mmol g−1 molybdenum in the catalyst. The prepared catalyst catalyzed the epoxidation of olefins and allyl alcohols with tert-butyl hydroperoxide (TBHP) and cumene hydroperoxide (CHP) quantitatively with excellent selectivity toward the corresponding epoxides under mild reaction conditions. The results indicated that the hydrophobicity of the AC support promoted the catalytic efficiency of the catalyst in the epoxidation of olefins.
Keywords: Molybdenum; Activated carbon; Tethering; Heterogeneous catalysis; Epoxidation;
Neodymium tris-diarylphosphates: Systematic study of the structure–reactivity relationship in butadiene and isoprene polymerisation by Ilya E. Nifant’ev; Alexander N. Tavtorkin; Sof’ya A. Korchagina; Inna F. Gavrilenko; Nataliya N. Glebova; Nataliya N. Kostitsyna; Vladimir A. Yakovlev; Galina N. Bondarenko; Marina P. Filatova (219-227).
The catalytic properties of neodymium tris-phosphates with various diarylphosphate ligands in the stereoregular 1,4-cis-polymerisation of butadiene and isoprene were studied. The considerable variability of the diaryl phosphate structure allowed for the systematic investigation of the dependence of the catalytic properties of neodymium tris-diarylphosphates on the electronic and steric properties of the ligand. Electron-withdrawing substituents (F, Cl, Br) in the aryl moiety increased the catalyst activity of tris-diarylphosphate. Neodymium aryl phosphates containing lipophilic bulky ligands provided the synthesis of polydienes with a monomodal molecular-weight distribution. The optimal catalytic properties demonstrated that the neodymium aryl phosphate prepared from bis(2,6-dimethyl-4-tert-butylphenyl)-phosphoric acid showed high activity and ensured a monomodal MWD of polydienes (M w/M n ∼ 2 for polybutadiene and M w/M n ∼ 3 for polyisoprene) in various conditions.
Keywords: Neodymium polymerisation; Structure–activity relationship; Aryl phosphate; Structurally rigid ligand; 1,3-Butadiene; Polybutadiene; Isoprene; Polyisoprene;
n-Hexane cracking at high pressures on H-ZSM-5, H-BEA, H-MOR, and USY for endothermic reforming by Jing Luo; Balaaji V. Bhaskar; Yu-Hao Yeh; Raymond J. Gorte (228-233).
Catalytic cracking of n-hexane was studied over H-ZSM-5, H-BEA, H-MOR, and USY zeolites at pressures between 1 and 137 bar and temperatures between 573 and 673 K, for application to endothermic reforming for cooling of aircraft engines. While the product distributions over each zeolite exhibited characteristics of a bimolecular mechanism, the product distributions were distinctly different on H-ZSM-5, exhibiting much less isomerization and more C-4 and C-5 products. Furthermore, in contrast to results on the larger pore zeolites, the reaction rates on H-ZSM-5 followed a simple Langmuir–Hinshelwood rate expression over the entire range of pressures and were stable for at least several hours at all pressures. Reaction rates on H-BEA, H-MOR, and USY were only weakly dependent on pressure and also exhibited an induction period at 137 bar before decreasing with time. Implications of these results for endothermic reforming are discussed.
Keywords: n-Hexane cracking; Zeolites; Endothermic fuel reforming; Monomolecular reaction; Bimolecular reaction;
Steam reforming of tar using toluene as a model compound with nickel catalysts supported on hexaaluminates by Cristina P.B. Quitete; Roberto Carlos P. Bittencourt; Mariana M.V.M. Souza (234-240).
Hexaaluminates of lanthanum, lanthanum/cerium and calcium were prepared by coprecipitation method and used as supports for nickel catalysts, with 6 and 14 wt% of NiO. After calcination at 1200 °C the hexaaluminate supports consisted of different crystalline phases, including α-alumina, perovskites and oxides, with specific surface areas of 14–18 m2 g−1. All the catalysts exhibited nickel reduction peaks in the range of 360–500 °C. Coking rates measured in thermogravimetric experiments using a synthetic mixture were directly correlated with Ni particle sizes. Catalysts with lower Ni dispersion exhibited lower initial toluene conversion at 650 °C. Ce-containing catalysts presented higher stability during 16 h of toluene steam reforming, which is coherent with their higher resistance to coke formation.
Keywords: Tar; Steam reforming; Nickel; Hexaaluminates;
Reinvestigating Raney nickel mediated selective alkylation of amines with alcohols via hydrogen autotransfer methodology by Astha Mehta; A. Thaker; V. Londhe; Santosh R. Nandan (241-251).
An efficient, cost-effective use of Raney nickel (R-Ni) a widely used industrial catalyst for N-alkylation using alcohols is highlighted here. The work describes the scope and capability of R-Ni in hydrogen autotransfer reactions enabling its widespread use in the Chemical and Pharmaceutical industry. R-Ni of W4, T4, and W7 grades were prepared and evaluated for alkylation of amines. The best activity and selectivity for mono alkylation of amines were obtained using W4 R-Ni at 1:4 moles of amine to alcohol in xylene at reflux. T4 R-Ni also showed ability to form stable imines. The prepared R-Ni was also recycled and reused for N-alkylation reaction. The optimized methodology was applied for synthesis of Active Pharmaceutical ingredients Piribedil and Mepyramine. The simplicity and wide substrate scope makes this method a preferred Hydrogen Auto-transfer protocol for the alkylation of amines.
Keywords: Amines; Heterogenous catalyst; Hydrogen autotransfer; N-alkylation; Raney nickel;
Pt nanoparticles over TiO2–ZrO2 mixed oxide as multifunctional catalysts for an integrated conversion of furfural to 1,4-butanediol by Fengbo Li; Tao Lu; Bingfeng Chen; Zhijun Huang; Guoqing Yuan (252-258).
1,4-butanediol (BDO) is an important commodity chemical for manufacturing many basic chemicals and valuable polymers. Its current manufacturing processes are exclusively based on feedstocks derived from oil and natural gas. The biomass-to-BDO chemical transformation is via furfural, a key platform molecule from glucose and xylose. The integrated conversion involves two sequent reaction steps: selective oxidation of furfural to furanones and hydrogenation of the mixture of furanones to BDO. Platinum nanoparticles supported over TiO2–ZrO2 perform well for both oxidation and hydrogenation steps and the total yield of BDO reaches 85.2%. The chemical composition and crystallinity of the mixed oxide support significantly affect the catalytic performance. The best catalyst is platinum supported over TiO2–ZrO2 mixed oxide (Ti/Zr, 1:1) calcined at 823 K, which also exhibits good recoverability and recyclability in the five-run test.
Keywords: Biomass conversion; Heterogeneous catalysis; Integrated process; Furfural; BDO;
Copper-immobilized platinum electrocatalyst for the effective reduction of nitrate in a low conductive medium: Mechanism, adsorption thermodynamics and stability by M.A. Hasnat; S. Ben Aoun; S.M. Nizam Uddin; M.M. Alam; P.P. Koay; S. Amertharaj; M.A. Rashed; Mohammed M. Rahman; N. Mohamed (259-266).
The electrocatalytic reduction of NO3 − and its intermediate NO2 − in neutral medium was performed at a Cu-immobilized Pt surface. The voltammetric investigations showed that the bare Cu electrode has little effect on nitrate reduction reactions (NRR) whereas an enhanced catalytic effect (i.e. a positive shift of the peak potential and an increased reduction current) was observed when Cu particles were immobilized onto Pt surface. At the Cu–Pt electrode surface, the NRR process was observed to occur via a two-step reduction mechanism with a transfer of 2 and 6 electrons in the first and second steps, respectively. Similar results were obtained by chronoamperometric (CA) studies. Closer NRR mechanistic studies at the as prepared Cu–Pt electrode revealed concentration-dependent kinetics with a “critical” nitrate ion concentration of ca. 0.02 M. Moreover, NRR proceeded via a simple adsorption–desorption mechanism following a Langmuir isotherm with an adsorption Gibbs free-energy of ca. −10.16 kJ mol−1 (1st step) and ca. −10.05 kJ mol−1 (2nd step). By means of a Pt|Nafion|Cu–Pt type reactor without any supporting electrolyte, bulk electrolysis was performed to identify nitrate reduction products. It was found that after 180 min of electrolysis, 51% of NO3 − was converted into NO2 − intermediate. This percentage decreased to 30% in CO2 buffered conditions. However, when a tri-metallic Pt–Pd–Cu electrode was employed as a cathode, all of the NO2 − produced could be successfully converted into NH3 and N2. The electrocatalysis of nitrate ion on Cu–Pt electrode surface showed no apparent surface poisoning as confirmed by its stability after excessive CV runs. This was further supported by surface analysis and morphology of the as-prepared catalyst with scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis.
Keywords: Nitrate reduction reaction; Cu–Pt electrode surface; Electrocatalysis; Adsorption; Electrocatalysis; Surface stability;
An efficient eco-sustainable oxidative desulfurization process using μ-oxo-bridged Fe(III) complex of meso-tetrakis(pentafluorophenyl)porphyrin by António Aguiar; Susana Ribeiro; André M.N. Silva; Luís Cunha-Silva; Baltazar de Castro; Ana M.G. Silva; Salete S. Balula (267-274).
The present work is the first report of using a FeIII dimeric porphyrin as an active and efficient catalyst for the oxidative desulfurization of a multicomponent oil formed by the most refractory sulfur compounds in fuels (dibenzothiophene, DBT, 1-benzothiophene, 1-BT, and 4,6-dimethyldibenzothiophene, 4,6-DMDBT), using the biphasic system model oil/extraction solvent. The binuclear μ-oxodiiron(III) complex of meso-tetrakis(pentafluorophenyl)porphyrin μ-O(FeTPFPP)2, was synthesized and characterized by UV/Vis spectroscopy, mass spectrometry and single-crystal X-ray diffraction. μ-O(FeTPFPP)2 was shown to achieve a complete desulfurization after 2 h when acetonitrile and methanol were used as extraction solvents, in the presence of a residual amount of H2O2 as oxidant, at room temperature. The catalytic efficiency of the porphyrin was evaluated for each refractory sulfur compound following the order 1-BT > DBT > 4,6-DMDBT. Surprisingly, the porphyrin presents a remarkable catalytic performance for the desulfurization of 1-BT when compared with other catalysts already reported in the literature. Furthermore, the extracting phase containing the porphyrin could be reused in consecutive desulfurization cycles.
Keywords: μ-Oxodimeric iron(III) porphyrin; Hydrogen peroxide; Oxidative desulfurization; Homogeneous catalysis; Benzothiophene derivatives;
Visible light-promoted selective oxidation of sulfides to sulfoxides catalyzed by ruthenium porphyrins with iodobenzene diacetate by Tse-Hong Chen; Zhibo Yuan; Aaron Carver; Rui Zhang (275-282).
Under visible light irradiation, the carbonyl ruthenium(II) porphyrin complexes efficiently catalyze the selective oxidation of sulfides to sulfoxides with iodobenzene diacetate [PhI(OAc)2] as the oxygen source. Various thioanisoles and allylic sulfides were oxidized to the corresponding sulfoxides without overoxidation to sulfones. The high selectivity of this unprecedented oxygen-transfer process is mechanistically rationalized by a low-reactivity ruthenium(IV)-oxo species which can be detected in the reaction of carbonyl ruthenium(II) porphyrin with iodobenzene diacetate. To the best of our knowledge, this is the first demonstration of a mild and high-yield method for the highly selective sulfoxidations by ruthenium porphyrins and PhI(OAc)2.
Keywords: Ruthenium porphyrin; Oxidation; Sulfide; Iodobenzene diacetate; Visible light;