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 B, Environmental (v.97, #3-4)
La0.8Sr0.2Ga0.8Fe0.2O3− δ: Influence of the preparation procedure on reactivity toward methanol and ethanol by Alessandro Galenda; Marta Maria Natile; Luca Nodari; Antonella Glisenti (pp. 307-322).
In this paper a strontium- and iron-doped lanthanum gallate (La0.8Sr0.2Ga0.8Fe0.2O3—LSGF) is prepared by Pechini process and polyacrylamide gel method. The powders are characterized by means of X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFT), Thermal Programmed Desorption (TPD), Thermal Programmed Reduction (TPR), BET specific surface area, UV–Vis and Mössbauer Spectroscopy (MS). The activity toward methanol and ethanol is investigated by Infrared (IR) spectroscopy and Quadrupolar Mass Spectrometry (QMS) under several conditions. XRD outcomes reveal the formation of the desired perovskite phase at 900°C, however, small amounts of secondary phases are also present. LSGF synthesized by Pechini process is characterized by a lower amount of secondary phases. On the other hand, LSGF from polyacrylamide gel method has a higher specific surface area. XPS data show that the two samples differ for surface cations segregation, hydroxylation degree and carbonate contamination. These results are also confirmed by DRIFT and TPD measurements. MS and TPR analyses reveal the presence of a small amount of Fe(IV), which is reduced to Fe(III) with H2 (5% in Ar) at about 450°C and with CH3OH vapours at 200°C. Catalytic tests prove that methanol is mainly decomposed into H2 and CO at 400°C, but small amounts of CO2 are also detected. Ethanol undergoes essentially dehydrogenation thus forming acetaldehyde and H2. In oxidizing conditions, both alcohols are oxidized to CO2 and H2O at 400°C, nevertheless, partially oxidized products are also observed. Acetaldehyde is an important product in ethanol oxidation. Under steam reforming conditions, methanol and ethanol give H2, CO and CO2, but acetaldehyde is also observed in ethanol steam reforming. The presence of acetaldehyde, when dealing with ethanol, suggests a difficult C–C bond break. Both the LSGF samples undergo poisoning during the reactions.
Keywords: Doped lanthanum Gallate; Perovskite; Fuel cells; Methanol; Ethanol
Impact of CO on the transformation of a model FCC gasoline over CoMoS/Al2O3 catalysts: A combined kinetic and DFT approach by F. Pelardy; C. Dupont; C. Fontaine; E. Devers; A. Daudin; F. Bertoncini; P. Raybaud; S. Brunet (pp. 323-332).
The selective hydrodesulfurization (HDS) of FCC gasoline is a key catalytic process for reducing sulfur content in gasoline. In addition, 5.75% of the European fuels used for transportation will have to incorporate biofuels, which implies that gasoline hydrotreatment will treat feeds containing various oxygenated compounds including by-products such as CO, CO2 or H2O. In the present work, we focus on the effect of CO partial pressure on the transformation of a model FCC gasoline composed of 2-methylthiophene (2MT) and 2,3-dimethylbut-2-ene (23DMB2N) molecules, over a alumina supported CoMoS catalyst. A negative and reversible impact of carbon monoxide on the conversion of 2MT and 23DMB2N is found. Moreover, the hydrodesulfurization (HDS) of 2MT alone is much more inhibited (30%) than hydrogenation (HYD) of 23DMB2N alone (10%). In contrast, when considering the model feed where 23DMB2N and 2MT are mixed together, the loss of HDS and HYD activities is comparable whatever the CO partial pressure. Density functional theory (DFT) calculations of CO adsorption on the S- and M-edge sites of the CoMoS particles show that CO adsorption is strongly favored with respect to olefin and 2MT adsorption on both types of sites, which explains its strong inhibiting effect on HYD and HDS. A rational explanation of the different inhibiting effects of CO observed on model molecules alone and model feed is proposed in correlation with the nature of the active S- and M-edge sites present on the hexagonal CoMoS particles and involved either in HDS or in HYD reactions.
Keywords: Hydrodesulfurization; Olefin hydrogenation; FCC gasoline; CO; CoMoS/γ-Al; 2; O; 3; Edge sites; Density functional theory
Vanadia supported on zeolites for SCR of NO by ammonia by Siva Sankar Reddy Putluru; Anders Riisager; Rasmus Fehrmann (pp. 333-339).
Vanadia supported on zeolites were prepared and characterized by N2 physisorption, FTIR, XRPD, and NH3-TPD methods. The influence of the Si/Al ratio on the total surface acidity of the catalysts as well as the optimum V2O5 content were studied and compared with the catalytic activity in the selective catalytic reduction (SCR) of NO with ammonia. The SCR activity was found to correlate directly with the total acidity of the catalysts and showed high poisoning resistivity after doping with potassium oxide (100μmol/g). The poisoning resistance was due to unique combination of high surface area, acidity and micropore structure of the support. Apparently the support hosted the potassium oxide on the acid sites, thereby protecting the active vanadium species from poisoning. Zeolite based catalysts might therefore prove useful for SCR of NO in alkali- containing flue gases from, e.g. biomass fired power plants.
Keywords: Zeolites; SCR with ammonia; Potassium poisoning; Deactivation; NH; 3; -TPD
Surface acidity and reactivity of β-FeOOH/Al2O3 for pharmaceuticals degradation with ozone: In situ ATR-FTIR studies by Li Yang; Chun Hu; Yulun Nie; Jiuhui Qu (pp. 340-346).
The surface acidity and reactive activity of β-FeOOH, mesoporous alumina (MA), β-FeOOH/MA were investigated in catalytic ozonation of pharmaceutically active compounds (PhACs) aqueous solution. β-FeOOH/MA showed high efficiency for the degradation and mineralization of ibuprofen and ciprofloxacin. Its surface Lewis acid sites on β-FeOOH/MA were more greatly enhanced compared with those on MA and β-FeOOH. In situ attenuated total reflection FTIR (ATR-FTIR) spectroscopy was used to investigate the interaction of D2O and O3 with the catalysts in aqueous phase under various conditions. The dissociative chemisorptions of D2O occurred at the surface Lewis acid sites of the catalyst. Furthermore, O3 interacted with the surface hydrogen-bonded –O–D and D2O to initiate reactive oxygen species (ROS). The stronger Lewis acid sites of β-FeOOH/MA caused the more chemisorbed water enhancing the interaction with ozone, resulting in higher catalytic reactivity. The observations verified that the Lewis acid sites were reactive centers for the catalytic ozonation of PhACs in water.
Keywords: ATR-FTIR; Catalytic ozonation; Mesoporous alumina; β-FeOOH; Pharmaceuticals; Surface Lewis acid sites
Oxygen reduction on Pd3Pt1 bimetallic nanoparticles highly loaded on different carbon supports by Wei He; Mei Chen; Zhiqing Zou; Zhilin Li; Xiaogang Zhang; Seon-Ah Jin; Dae Jong You; Chanho Pak; Hui Yang (pp. 347-353).
The development of new cost-effective cathode catalysts with high methanol tolerance and at a high catalyst loading is highly desirable for the direct methanol fuel cell. The Pd3Pt1 bimetallic alloy nanoparticles highly loaded on different carbon supports, including Vulcan XC-72R carbon, single and multi-walled carbon nanotubes (SWCNTs/MWCNTs) and ordered mesoporous carbon (OMC), have been prepared by a modified polyol reduction route. The activities of the catalysts for the oxygen reduction reaction (ORR) have been studied based on the rotating disk and ring-disk electrode (RDE/RRDE) techniques in pure and methanol-containing electrolytes. X-ray diffraction indicates that all the Pd3Pt1/C nanoparticles evidence a single-phase fcc disordered structure. The mean particle size of Pd3Pt1 alloy nanoparticles on different supports is ca. 4–5nm even at a metal loading of 50wt%. Among various carbons supported catalysts, the highest ORR activity, found on the OMC-supported Pd3Pt1 catalyst, even surpasses that on the commercial Pt/C catalyst. Kinetic analysis reveals that the ORR on the Pd3Pt1/OMC catalyst predominantly undergoes a four-electron process, leading to water formation. Furthermore, the Pd3Pt1/OMC catalyst exhibited a higher methanol tolerance during the ORR than the commercial Pt/C catalyst; ensuring a higher ORR performance while diminishing Pt utilization.
Keywords: Pd–Pt alloy; Carbon nanotube; Ordered mesoporous carbon; Electrocatalysis; Oxygen reduction reaction; Methanol tolerance
Effect of crystal phase composition on the reductive and oxidative abilities of TiO2 nanotubes under UV and visible light by Kevin L. Schulte; Paul A. DeSario; Kimberly A. Gray (pp. 354-360).
Titania nanotube arrays synthesized by the electrochemical oxidation of titanium foils have generated considerable interest as photocatalysts for their ordered nature and large surface area. Mixed-phase materials combining the anatase and rutile crystal phases of TiO2, however, have been much more widely studied due to their enhanced reactivity in comparison to pure phase materials. In this study, we seek to integrate these two lines of research and investigate the reductive and oxidative reactivity of TiO2 nanotube arrays (anatase phase) supported on TiO2 films of varying crystal phase composition. A series of TiO2 nanotubes 1.2μm in length was synthesized, annealed at varying temperatures to control their crystallinity, and characterized by various physical techniques (e.g. XRD, diffuse reflectance, SEM). Photocatalytic CO2 reduction and acetaldehyde oxidation reactions were performed in the gas phase under UV and visible wavelengths. For CO2 reduction, reaction rates decreased with increasing rutile phase under UV. Rates increased with rutile phase ratio under visible and near visible light. For oxidation, the mixed-phase samples showed enhanced reactivity, with a maximum acetaldehyde destruction rate achieved at a 79:21 ratio of anatase to rutile. The samples were substantially less active under visible light, except for the 620°C composite (77% rutile) which showed a slight rate increase. Nanotubes annealed at 680°C collapsed to a random porous structure, but showed comparable reductive ability to the non-collapsed samples despite the loss of surface area. This is attributed to the creation of additional anatase–rutile crystallite interfacial area leading to the formation of unique active sites. Control of crystal phase composition through anneal temperature is found to be a simple way to tune the reactivity of these materials and enhance their ability to absorb visible light.
Keywords: Titanium dioxide; Nanotubes; Carbon dioxide reduction; Acetaldehyde oxidation
Syngas production from methane and air via a redox process using Ce–Fe mixed oxides as oxygen carriers by Kongzhai Li; Hua Wang; Yonggang Wei; Dongxia Yan (pp. 361-372).
CeO2, Fe2O3, Fe2O3/Al2O3 and Ce–Fe mixed oxides with different Ce/Fe ratios were prepared and characterized using XRD, Raman, XPS, and H2–TPR techniques. The selective oxidation of methane to syngas using a gas–solid reaction was investigated at 850°C. For binary Ce–Fe oxides, only small amounts of iron ions could be incorporated into the CeO2 lattice with the superfluous Fe2O3 remaining on the surface of the molecule. Chemical interactions between surface iron sites and the Ce–Fe solid solution strongly enhanced the reducibility of materials. Methane was found to adsorb and activate on the surface iron sites as carbonaceous species and hydrogen. Carbon deposition was selectively oxidized to CO by the release of activated oxygen from the CeO2 lattice. The activation rate of methane was dependent on the quality of dispersion of surface Fe species, while the oxygen mobility of the material dominated the CO formation rate. Hydrothermally prepared Ce0.7Fe0.3O2− δ showed high activity and selectivity during the successive production of syngas using repetitive redox processes (methane reduction/air re-oxidation). Both the dispersion of surface Fe2O3 and the formation of the Ce–Fe solid solution were enhanced by the redox treatment, which made the oxygen carrier more stable.
Keywords: Methane selective oxidation; Syngas; Gas–solid reaction; Ce–Fe solid solution; Surface Fe species
Understanding the Ag/Al2O3 hydrocarbon-SCR catalyst deactivation through TG/DT analyses of different configurations by B. Sawatmongkhon; A. Tsolakis; S. Sitshebo; J. Rodríguez-Fernández; M. Ahmadinejad; J. Collier; R.R. Rajaram (pp. 373-380).
Understanding the parameters affecting the Ag/Al2O3 hydrocarbon SCR catalyst activity or the procedure by which the C-containing species are deposited on the catalyst surface, under actual diesel engine operation, can lead to design a low temperature active Ag/Al2O3 SCR catalyst. In this work we investigated the role of the Ag/Al2O3 HC-SCR catalyst configuration for NOx reduction activity and its deactivation by coking under passive and active operation. This was done by separating the powdered catalyst into two layers/partitions (front and rear). The single and double-layered catalysts were exposed to real diesel engine exhaust gas, and then thermo gravimetric (TG) and differential thermal (DT) analyses were carried out. The analysis showed that the retention of carbon-rich species (hydrocarbons and soot) in the double-layered configuration occurs mainly in the first catalyst layer (front layer), therefore resulting in a cleaner second layer (rear layer). The results confirm that the catalyst deactivation initiated at the front part of the catalyst and progressively spreads towards the back. TG/DT analyses also showed that the retention of carbon-rich species over the catalysts was strongly reduced at temperatures higher than 350°C or when hydrogen was introduced, but the deactivation pattern was similar. The reactor design (e.g. catalyst configuration) in HC-SCR with silver is an important factor, and in the presented work the space in between the beds shown to be a critical parameter as it enhanced the low temperature catalytic activity.
Keywords: Catalyst; HC-SCR; Catalyst deactivation; Reactor design
Time-resolved operando X-ray absorption study of CuO–CeO2/Al2O3 catalyst during total oxidation of propane by Konstantinos Alexopoulos; Mettu Anilkumar; Marie-Françoise Reyniers; Hilde Poelman; Sylvain Cristol; Veerle Balcaen; Philippe M. Heynderickx; Dirk Poelman; Guy B. Marin (pp. 381-388).
The local structure of the copper phase of a CuO–CeO2/Al2O3 catalyst and its activity for the total oxidation of propane have been studied under working conditions, using time-resolved X-ray absorption spectroscopy (XAS) in transmission mode at the Cu K edge coupled with on-line mass spectrometry (MS). In the temperature range of 573–723K, the copper phase of the catalyst remains oxidized (i.e. Cu2+) during total oxidation reaction conditions (1%C3H8–5%O2/He), while three species are present (i.e. Cu2+, Cu1+ and Cu0) during reduction (2%C3H8/He) and re-oxidation (10%O2/He) treatments where a two-step mechanism is found. Catalyst reduction is fully reversible, as the Cu2+ nature of the catalyst is recovered after a reduction–oxidation cycle. Re-oxidation of the catalyst is two orders of magnitude faster than its reduction and has an apparent activation energy of 24kJ/mol. On the other hand, catalyst reduction requires an apparent activation energy of 70kJ/mol, which is equal to the apparent activation energy determined under total oxidation reaction conditions. These results give support to a Mars–van-Krevelen reaction scheme with the copper phase of the catalyst being close to a fully oxidized state.
Keywords: Structure–activity investigation; Supported metal oxides; Reduction and oxidation mechanism; Propane total oxidation; Volatile organic compounds
Au-decorated Na xH2− xTi3O7 nanobelts exhibiting remarkable photocatalytic properties under visible-light illumination by Ying-Chih Pu; Yu-Chih Chen; Yung-Jung Hsu (pp. 389-397).
We demonstrated for the first time that Na-intercalated H2Ti3O7 (Na xH2− xTi3O7) NBs, prepared in the typical alkaline hydrothermal process, can effectively absorb visible light to carry out photocatalytic reactions. With the capability of effective light absorption in visible range, Na xH2− xTi3O7 NBs performed much better in the photodegradation of thionine than the other three counterpart products including H2Ti3O7, mixed Na2Ti6O13/TiO2 and anatase TiO2 under visible-light irradiations. As compared to the relevant commercial products like P-25 TiO2 and Na2Ti3O7 powders, the as-synthesized Na xH2− xTi3O7 NBs exhibited superior photocatalytic efficiency under UV illumination, demonstrating their potential as an efficient photocatalyst in relevant redox reactions. A further enhancement in the photocatalytic activity can be achieved for Na xH2− xTi3O7 NBs when Au nanoparticles of suitable amount were deposited on their surfaces. This improvement is due to the band offsets between Na xH2− xTi3O7 and Au, which may promote charge carrier separation to favor the photocatalysis. The recycling test reveals that Au-decorated Na xH2− xTi3O7 NBs could be promisingly utilized in the long-term course of photocatalysis. Furthermore, the result of performance evaluation under natural sunlight shows that the current Au-decorated Na xH2− xTi3O7 NBs can be used as highly efficient photocatalysts which may practically harvest energy from sunlight.
Keywords: Titanate; Nanobelts; Photocatalysis; Visible-light-driven; Charge separation
Flame-made MgAl2− xM xO4 (M=Mn, Fe, Co) mixed oxides: Structural properties and catalytic behavior in methane combustion by Niels van Vegten; Tinku Baidya; Frank Krumeich; Wolfgang Kleist; Alfons Baiker (pp. 398-406).
Spinel-like oxides with the general formula MgAl2− xM xO4 (M=Mn, Fe, Co) were synthesized in a single step by flame-spray pyrolysis. High surface area materials were obtained, which showed improved resistance to sintering upon increasing the Al-content. XPS showed surface enrichment of the transition metal constituent, which favorably increased the fraction of transition metal exposed to the environment. By tuning the fraction of transition metal in the mixed oxide, materials were obtained with a good balance between thermal stability and activity in the catalytic combustion of methane. The activity of the materials increased in the order Fe
Keywords: MgAl; 2−; x; M; x; O; 4; (M; =; Mn, Fe, Co) mixed oxides; Flame-spray pyrolysis; Spinel; Methane combustion
Mild oxidation of bulky organic compounds with hydrogen peroxide over mesoporous TiO2-SiO2 xerogels prepared by non-hydrolytic sol–gel by Ana Mihaela Cojocariu; P. Hubert Mutin; Emil Dumitriu; François Fajula; André Vioux; Vasile Hulea (pp. 407-413).
The oxidation of bulky organic compounds with aqueous H2O2 over a TiO2-SiO2 xerogel catalyst prepared by a simple non-hydrolytic sol–gel route is described for the first time. Anthracene, cyclooctene, styrene, α-naphtol, diphenyl sulfide, dibenzothiophene and 4,6-dimethyl-dibenzothiophene were oxidized with high activity, selectivity and H2O2 efficiency at moderate temperatures (40–60°C). Moreover, a similar catalytic behavior was observed when tert-butyl hydroperoxide (TBHP) was used as an oxidizing agent. These excellent catalytic performances were ascribed to the unique texture of the catalyst (specific surface area 1200m2g−1, pore volume 2.4cm3g−1, average pore diameter 15nm) and to the stability of Ti sites after exposure to aqueous H2O2 or TBHP.
Keywords: Non-hydrolytic sol–gel; Anthracene; Cyclooctene; Styrene; α-Naphtol; Mild oxidation; H; 2; O; 2