Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Applied Catalysis A, General (v.280, #2)
The decomposition of dimethyl carbonate over copper zeolite catalysts by Steven A. Anderson; Sefenyiwe Manthata; Thatcher W. Root (pp. 117-124).
Direct synthesis of dimethyl carbonate offers prospects for a “green chemistry� replacement to eliminate use of phosgene for polymer production and other processes. Dimethyl carbonate (DMC) production over copper zeolite catalysts has shown high selectivity, however the rate of DMC decomposition becomes significant as the product concentration in the reactor increases, thus limiting the yield of DMC. DMC decomposition occurs over the residual Brønsted sites of the copper zeolite catalyst, which are present as a result of incomplete copper exchange. Several strategies were investigated to block acid sites during reaction or remove them during catalyst preparation. Pyridine adsorption on acid sites decreased the rate of DMC decomposition. Aqueous-phase exchange of Li+ ions with ammonium or acid zeolites prior to copper loading greatly decreased residual acidity of the catalyst, resulting in a greatly reduced rate of DMC decomposition. Aqueous-phase exchange of Li+ ions after copper loading reduced the rate of decomposition by 30% without affecting copper performance or copper loading, resulting in higher observed activity of DMC production compared to the conventional Cu+Y catalyst.
Keywords: Dimethyl carbonate; Methanol; Copper; Zeolite Y; Oxidative carbonylation
Palladium nanoparticles stabilized in block-copolymer micelles for highly selective 2-butyne-1,4-diol partial hydrogenation by Natalia Semagina; Eric Joannet; Sandra Parra; Esther Sulman; Albert Renken; Lioubov Kiwi-Minsker (pp. 141-147).
Pd nanoparticles (2nm) stabilized in the micelle core of poly(ethylene oxide)-block-poly-2-vinylpyridine were studied in 2-butyne-1,4-diol partial hydrogenation. Both unsupported micelles (0.6kgPd/m3) and supported ones on γ-Al2O3 (0.042wt.% Pd) showed nearly 100% selectivity to 2-butene-1,4-diol up to 94% conversion. The only side product observed was 2-butane-1,4-diol. The catalysis was ascribed to Pd nanoparticles’ surface modified by pyridine units of micelles and alkali reaction medium (pH of 13.4). TOFs over the unsupported and supported catalysts were found to be 0.56 and 0.91s−1 (at 323K, 0.6MPa H2 pressure, solvent 2-propanol/water=7:3), respectively. Reaction kinetics fit the Langmuir–Hinshelwood model assuming weak hydrogen adsorption. The experiments on the catalyst reuse showed that Pd nanoparticles remain inside the micelle core, but the micelles slightly desorbed (less then 5%) during the catalytic run.
Keywords: Palladium; Nanoparticle; Alkyne alcohol hydrogenation; Micelle catalysis
Electro-catalysis of the Cu/carbon cathode for the reduction of O2 during fuel-cell reactions by Yuta Nabae; Ichiro Yamanaka; Kiyoshi Otsuka (pp. 149-155).
To develop a new cathode without using Pt for a H2/O2 polymer-electrolyte-membrane-fuel-cell, we studied the possibility of using a Cu/carbon cathode for the reduction of O2. The plan for development of the Cu/carbon cathode is: (i) formation of redox functional groups on carbon to promote electron-transfer reaction, (ii) deposition of phosphorous groups on carbon to promote proton diffusion and (iii) loading Cu on the modified carbon support. The electro-catalytic activity of the Cu/carbon cathode was not so excellent as that of the Pt/carbon cathode, but it was fairly good at lowerP(O2). To clarify the Cu function for the acceleration of the O2 reduction, we characterized the Cu/carbon electro-catalyst with XRD, SEM and CV measurements. When the oxidation state of Cu was 2+ at higher cell voltages, the reduction of O2 was accelerated. On the other hand, when metallic Cu was formed at lower cell voltages, the enhancing effect of Cu disappeared. The CV data strongly suggested that Cu2+ species functioned as an adsorption site of O2, not as a redox mediator. On the basis of the experimental results, a suitable model of the reduction mechanism of O2 over the Cu/carbon cathode was proposed.
Keywords: Oxygen reduction; Cu/carbon cathode; Electro-catalysis; Fuel cell
Titanium-based solid catalysts for transesterification of methyl-methacrylate by 1-butanol: the homogeneous catalysis contribution by Maria Concetta Gaudino; Romain Valentin; Daniel Brunel; François Fajula; Françoise Quignard; Alain Riondel (pp. 157-164).
Titanium-based solid catalysts were prepared according to two different procedures. In order to improve the stability of the SiOTi bond in the titanium grafted silica catalysts, the surface remaining hydroxyl groups were passivated to prevent the titanium leaching by SiOTi bond solvolysis. This was performed by grafting trimethoxy-silane groups on isolated silanols of silica, after or before metal grafting. The synthesised materials were characterised by FT-IR spectroscopy, and their catalytic properties evaluated in the reaction of transesterification of methyl-methacrylate (MMA) with 1-butanol (BuOH) in liquid phase to produce butyl-methacrylate (BuMA). An important titanium leaching (18–35%) was always detected with all the solid catalysts.Investigation of the behaviour of Ti(OBu)4 as homogeneous catalyst for very small concentrations of titanium was carried out in order to evaluate the catalytic contribution of the active dissolved species. We demonstrate here that the catalytic activity is mainly due to the homogeneous catalysis.
Keywords: Heterogeneous transesterification; Titanium-grafted catalysts; Titanium leaching
Synthesis, characterization and olefin polymerization studies of iron(II) and cobalt(II) catalysts bearing 2,6-bis(pyrazol-1-yl)pyridines and 2,6-bis(pyrazol-1-ylmethyl)pyridines ligands by Arquímedes R. Karam; Edgar L. Catarí; Francisco López-Linares; Giuseppe Agrifoglio; Carmen L. Albano; Antonio Díaz-Barrios; Teresa E. Lehmann; Sara V. Pekerar; Luis A. Albornoz; Reinaldo Atencio; Teresa González; Heriberto B. Ortega; Pablo Joskowics (pp. 165-173).
The complexes Py(PzR3)2MCl2 (R=H, Me; M=Fe, Co) and Py(CH2PzR3)2MCl2 (R=H, Me; M=Fe, Co) have been synthesized, characterized and used in the ethylene polymerization. Treatment of these iron and cobalt complexes with methylaluminoxane (MAO) as cocatalyst leads to active ethylene polymerization catalysts that produced linear polyethylene. In general, iron catalysts were more active than cobalt analogs. The steric and electronic effects of the ligands were study over the catalytic activity toward ethylene polymerization. Complexes with small substituents groups (R=H) on the pyrazolyl ring, increase the catalytic activity in comparison to complexes with bigger substituents groups (R=CH3). Additionally, complexes with methylene groups placed between pyridine and pyrazole rings of ligands have less catalytic activity than complexes without the methylene group (CH2). The presence of methyl groups (R=CH3) in iron and cobalt complexes allow to obtain polyethylene with molecular weights higher than the one obtained with complexes without these methyl groups. Additionally, complexes with methylene groups present between pyridine and pyrazole rings generate polyethylenes with molecular weight higher than the ones produced with complexes without these methylene groups.
Keywords: Iron(II); Cobalt(II); 2,6-Bis(pyrazol-1-yl)pyridine; 2,6-Bis(pyrazol-1-ylmethyl)pyridine; Ethylene polymerization catalysts
Gold nanoparticles in mesoporous materials showing catalytic selective oxidation cyclohexane using oxygen by Gaomeng Lü; Dong Ji; Guang Qian; Yanxing Qi; Xiaolai Wang; Jishuan Suo (pp. 175-180).
The nano-Au supported mesoporous materials were prepared and characterized by XRD, N2 adsorption/desorption, UV–vis, XPS, and ICP-AES. The liquid-phase selective oxidation cyclohexane to cyclohexanol and cyclohexanone over nano-Au in mesoporous materials catalyst was carried out in a solvent-free system, in which oxygen was the only oxidant and the reaction conditions are very moderate.
Keywords: Gold; Mesoporous materials; Selective oxidation; Cyclohexane
Production of hydrogen over bimetallic Pt–Ni/δ-Al2O3 by Burcu Selen Çağlayan; Ahmet K. Avcı; Z. İlsen Önsan; A. Erhan Aksoylu (pp. 181-188).
Indirect partial oxidation (IPOX) of propane was studied over bimetallic 0.2wt.% Pt–15wt.% Ni/δ-Al2O3 catalyst in the 623–743K temperature range. The unreduced and reduced forms of the catalyst were characterized by ESEM–EDAX and X-ray diffraction (XRD). In the IPOX tests, the effects of steam to carbon ratio (S/C), carbon to oxygen ratio (C/O2) and residence time ( W/ F (gcath/mol HC)) on the hydrogen production activity, selectivity and product distribution were studied in detail. The effect of temperature program applied (increasing from 623 to 743K, ITP; decreasing from 743 to 623K, DTP) during reaction was also tested. The results showed that the Pt–Ni bimetallic system has superior performance characteristics compared to the monometallic catalysts reported in literature. The reason is thought to be the utilization of the catalyst particles as micro heat exchangers during IPOX; the heat generated by Pt sites during exothermic total oxidation (TOX) being readily transferred through the catalyst particles acting as micro heat exchangers to the Ni sites, which promote endothermic steam reforming (SR). The optimal conditions were found as S/C=3, C/O2=2.70 and W/ F=0.51gcath/mol HC for IPOX of propane on the basis of high hydrogen productivity and selectivity between 623 and 748K for the experimental conditions tested. The thermo-neutral points obtained showed the sustainability of reaction in terms of energy.
Keywords: Autothermal reforming; Indirect partial oxidation; Hydrogen production; Pt–Ni catalysts; Propane
Surface and catalytic properties of Cr2O3/MgO system doped with manganese and cobalt oxides by Sahar A. El-Molla (pp. 189-197).
The effects of cobalt and manganese oxides-doping on surface and catalytic properties of Cr2O3/MgO system have been investigated. The dopant concentration was changed between 1 and 5mol% cobalt and manganese oxides. Pure and variously doped solids were subjected to heat treatment at 400 and 700°C. The techniques employed were X-ray diffraction (XRD), nitrogen adsorption at –196°C, catalytic conversion of iso-propanol at 200–400°C using flow technique and catalytic decomposition of H2O2 at 20–40°C. The results revealed that the doping process of the system investigated followed by calcinations at 400 or 700°C, enhanced the solid–solid interactions between catalyst constituents yielding (α-MgCrO4, β-MgCrO4) and MgCr2O4, respectively. Furthermore, manganese and cobalt oxide-doping for Cr2O3/MgO system increased its catalytic activity much towards H2O2-decomposition. The increase was, however, more pronounced in the case of manganese-doping. Opposite results have been observed in the case of iso-propanol conversion, which proceeds via dehydrogenation and dehydration reaction. The SBET of the investigated system was found to decrease by increasing the dopant concentration. The doping process did not modify the activation energy of the catalyzed reaction, but rather changed the concentration of the catalytically active constituents without changing their energetic nature.
Keywords: Cr; 2; O; 3; /MgO catalyst; Cobalt oxide-doping; Manganese oxide-doping; H; 2; O; 2; -decomposition; iso; -Propanol conversion
Influence of feed components on the activity and stability of cobalt molybdenum alumina metathesis catalyst by Miranda N. Kwini; Jan M. Botha (pp. 199-208).
Alkene metathesis plays a vital role industrially in the upgrading of low value alkenes to higher value alkenes such as linear internal alkenes in the C10–C18 range. These in turn find application as feedstock for manufacturing of surfactants and detergents. Industrial alkene cuts contain component(s) that might be detrimental to the catalyst active sites during the metathesis reaction leading to catalyst deactivation. The focus of this study was to investigate the effect of some of the components present in typical low value feed streams on the activity and stability of a CoO/MoO3/Al2O3 catalyst. The results indicated that the feed composition does have a major influence on the metathesis reactivity of the catalyst. Pure 1-octene (98%), which was used as a reference feed was spiked with various components that had a concentration of 100ppm. Results revealed a trend in terms of the severity of the component that deactivated the catalyst to be water>methylcyclopentadiene dimer>methylcyclopentane>toluene>2-pentanone>2-methyl-1,5-hexadiene>2-methyl-1-hexene>butanol.A study was also undertaken to examine whether the component (methylcyclopentadiene dimer as an example) that deactivates the catalyst is a temporary or permanent poison. Results showed that methylcyclopentadiene dimer is a temporary poison. The carbonaceous deposits (oligomers) formed during the reaction seem to be the primary cause of catalyst deactivation. However, the catalyst deactivation mechanism in the presence of water in 1-octene feed is mostly linked to the molecular structural change of the catalyst rather than accumulation of carbonaceous deposits on the surface of the catalyst.
Keywords: Metathesis; Deactivation; Feed components; Cobalt molybdenum alumina catalyst
Effect of carbon black composite (CBC) support properties on hydrodesulfurization performance of sulfided Mo and Co, and carburized Mo, catalysts by S. Suppan; J. Trawczyński; J. Kaczmarczyk; G. Djéga-Mariadassou; A. Hynaux; C. Sayag (pp. 209-214).
Carbon black composites (CBCs) have been prepared by pyrolyzing mixture of a carbon black with polyfurfuryl alcohol and then pretreated by oxidation with nitric acid, gasification with water steam or ammoxidation. The effects of the chemical character of the carrier surface, nature of the active metal phase and pH value of the impregnation solution on the catalytic activity towards the hydrodesulfurization (HDS) of thiophene of the CBC supported Mo (Co) catalysts were determined. It was stated that the catalytic properties of the CBC supported sulfides of Mo or Co and of Mo carbides are affected by the chemical character of the carrier surface. Generally, catalysts supported over basic surface CBC exhibit higher activity than those ones supported over CBC possessing acidic surface character. Co catalysts supported on acidic surface show lower activity (per mol of active metal) than Mo based ones supported on the same carrier. In the case of catalysts supported on basic CBC, Co exhibits distinctly higher activity than Mo. At the experimental conditions adopted for this study, CBC surface properties, active phase nature, and catalyst impregnation pH were found to exert a relatively small influence on both HDS and hydrogenation activities.
Keywords: Carbon composites; Catalyst support; Catalytic properties
A comparative study of supported MoO3 catalysts prepared by the new “slurry� impregnation method and by the conventional method: their activity in transesterification of dimethyl oxalate and phenol by Xinbin Ma; Jinlong Gong; Xia Yang; Shengping Wang (pp. 215-223).
A new preparation method for supported MoO3 catalyst, slurry impregnation, has been described and compared with the conventional impregnation method. Slurry MoO3/water is used instead of the solution ammonium heptamolybdate, AHM [(NH4)6Mo7O24]. The MoO3/γ-alumina, MoO3/active carbon, and MoO3/silica catalysts with different Mo loadings were prepared by slurry and by conventional method. The low solubility of MoO3 was sufficient to transport molybdenum species from solid MoO3 to the adsorbed phase. The equilibrium was achieved after several hours at 95°C based on the loading amount of molybdenum. Only the process of drying was needed; calcination was not necessary and was left out. This is an important advantage for active carbon support because oxidative degradation of active carbon impregnated by molybdena starts at a relatively low temperature of about 250°C during calcination on air. The activity was tested in the transesterification of dimethyl oxalate (DMO) and phenol at 180°C. The dependences of catalytic activity on Mo loadings for the slurry prepared catalysts were similar to the dependences for the samples prepared by the conventional impregnation method with AHM. The activities of the slurry impregnation MoO3/γ-Al2O3 catalysts were almost the same as those of catalysts prepared conventionally. Although the performances of slurry impregnation MoO3/SiO2 catalysts for transesterification of DMO were slightly better than those of the corresponding catalysts prepared by conventional impregnation, no waste solution and no calcining nitrogenous gases were produced. Therefore, we conclude that the new slurry impregnation method for preparation of supported molybdenum catalysts is an environmentally friendly process and a simple, clean alternative to the conventional preparation using solutions of (NH4)6Mo7O24. The present work will lead to a remarkable improvement in the catalyst preparation for the transesterification reaction.
Keywords: Supported Mo catalysts; Slurry impregnation; Transesterification; Diphenyl carbonate; Diphenyl oxalate; Methyl phenyl oxalate; Dimethyl oxalate
Catalyst based on BaZrO3 with different elements incorporated in the structure by P. Viparelli; P. Villa; F. Basile; F. Trifirò; A. Vaccari; P. Nanni; M. Viviani (pp. 225-232).
New catalytic systems, synthesised by a variant of the citrate route, are proposed for the partial oxidation of methane. They consist of solid solutions – barium, zirconium, rhodium and oxygen – with a perovskite structure of formula BaZr(1− x)Rh xO3. Detailed analysis of the XRD diffractograms and the TGA cycles show that Rh is randomly distributed as RhIV among the B sites of the perovskite, together with Zr. The activities of the catalysts have been tested for the catalytic partial oxidation of methane at short contact times to evaluate the potential of materials giving promising results in terms of syngas yield at low Rh loading.
Keywords: Catalytic partial oxidation; Methane; Syngas; Perovskite; Hydrogen
Reforming of methane with carbon dioxide over supported bimetallic catalysts containing Ni and noble metal by W.K. Jóźwiak; M. Nowosielska; J. Rynkowski (pp. 233-244).
The activity and stability of silica supported monometallic Ni, Rh and bimetallic Ni–Rh catalysts have been studied towards the carbon dioxide reforming of methane. The catalysts were prepared by incipient wetness impregnation with different contents of Rh and Ni and they were characterized by H2 chemisorption,TPRH2, XRD and FT-IR methods. SiO2 supported monometallic Ni, Rh and bimetallic Ni–Rh catalysts are comparably good catalysts for carbon dioxide reforming of methane and Rh-rich catalysts are resistant to deactivation and carbon formation. Temperature-programmed hydrogen assisted decomposition of bimetallic Ni–Rh/SiO2 catalyst precursors leads to formation of Ni–Rh alloys. Segregation of metals leads to the formation of Ni-rich surface alloy. TG-DTA-MS,TPSRH2, TPO,TPSRCO2, TOC and SEM methods were used in order to characterize the carbonaceous deposits. At least two types of carbon deposit with different reactivity have been detected on the surface of bimetallic catalysts. The results suggest a significant metal–metal interaction in the bimetallic systems.
Keywords: Dry reforming of methane; Ni–Rh; SiO; 2; TP techniques; XRD; FT-IR; Carbon deposit
Study of the conversion of aromatic hydrocarbons on EMT-type zeolite by Ioana Fechete; Philippe Caullet; Emil Dumitriu; Vasile Hulea; Henri Kessler (pp. 245-254).
(Al,Ga)EMT-type zeolites (Al:Ga=1:0, 0.75:0.25 and 0.5:0.5) were prepared and tested as catalysts in the gas-phase toluene–methanol alkylation and toluene–trimethylbenzene transalkylation. Various techniques including XRD, N2 sorption, MAS NMR and SEM were used to monitor the physico-chemical properties of these solids. The results revealed a high purity and crystallinity of the materials, and that the Ga atoms are entirely incorporated into the framework. The ammonia TPD measurements indicated that the isomorphous substitution of aluminium by gallium leads to a decrease of both acidic strength and acid sites concentration. The catalytic performances of the EMT-type solids in the conversion of methylaromatic hydrocarbons were correlated with their acid properties. Thus, the less acidic (Al,Ga)EMT samples exhibited a lower activity, but a higher selectivity towards the xylenes formation by comparison with (Al)EMT.
Keywords: (Al,Ga)EMT-type zeolite; Toluene; Trimethylbenzene; Xylene; Methanol; Alkylation; Transalkylation
Supported Co-based perovskites as catalysts for total oxidation of methane by M. Alifanti; N. Blangenois; M. Florea; B. Delmon (pp. 255-265).
Supported LaCoO3 perovskites with 2, 5, 10, 15, 20 and 30wt.% loading were prepared by impregnation of a Ce0.8Zr0.2O2 support (40m2g−1) with: (i) a solution of La and Co nitrates and (ii) a “citrate� solution, namely containing La and Co nitrates, and citric acid. All precursors were decomposed and calcined at 700°C for 5h. XRD investigations indicated the formation of a pure perovskite phase only if citrates were used. These materials were tested as catalysts for methane combustion in the temperature range 300–700°C. All catalysts showed a lower T50 (the temperature at which the conversion level of methane is 50%) than the Ce0.8Zr0.2O2 support or non-supported LaCoO3. The activity increased continuously with the perovskite loading. The samples prepared from citrates were slightly more active than from nitrates. This is due to a more homogeneous surface, as indicated by XPS measurements. The presence of a well-characterized perovskite phase (as opposed to highly dispersed elements) seems necessary for good activity. A higher reaction rate per perovskite weight is observed for low loadings when compared to bulk LaCoO3, but the variation with perovskite loading presents a breakpoint, suggesting complex interactions in the catalysts or in the oxidation mechanism.In spite of the experimental impossibility to evaluate the area developed by the supported perovskite, an approximative approach strongly suggests a synergy between the support and supported species.
Keywords: Supported perovskite; Catalytic methane combustion