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.69, #1-2)
Solar water disinfection by photocatalytic singlet oxygen production in heterogeneous medium by Laura Villén; Francisco Manjón; David García-Fresnadillo; Guillermo Orellana (pp. 1-9).
Water disinfection in isolated rural areas of less-developed countries poses specific problems since operational expenses must be low, chemicals are not easily deployable and qualification of operators is scarce. Therefore, alternative technologies to the widespread chlorination have been considered for household use. We have evaluated the viability of a photocatalytic process for bacteria inactivation with sunlight, affordable 0.8m2 compound parabolic collectors (CPC) and an UV–vis absorbing ruthenium (II) tris–chelate complex immobilised (2gm−2) onto porous silicone as singlet molecular oxygen generator. We have tested the efficiency of two CPC prototypes with different configuration of the photosensitising material, namely, a coaxial- and a fin-type one. Mineral water flowing at 2Lmin−1 and spiked with Escherichia coli or Enterococcus faecalis was subject to the photocatalytic treatment for 5h (a 0.6–0.8MJm−2L−1 dose of 360–700nm sunlight radiation at 40°N latitude). Using the fin-type reactor under these conditions, the bacterial survival for 104 to 102CFUmL−1 initial concentrations drop to ca. 1% and 0.1% for E. coli and E. faecalis, respectively. The average disinfection rates are similar with both photoreactor designs, regardless the bacteria used (ca. 2×104 and 2×106CFUL−1h−1 for the low and the high initial levels of bacteria, respectively). The novel systems are comparable to or better than solid-supported TiO2 photocatalysts at inactivating waterborne bacteria.
Keywords: Solar water disinfection; Ruthenium catalyst; Solar collector; Singlet oxygen
Characterization and regeneration of Pt-catalysts deactivated in municipal waste flue gas by Søren Birk Rasmussen; Arkady Kustov; Johannes Due-Hansen; Bernard Siret; Frank Tabaries; Rasmus Fehrmann (pp. 10-16).
Severe deactivation was observed for industrially aged catalysts used in waste incineration plants and tested in lab-scale. Possible compounds that cause deactivation of these Pt-based CO oxidation catalysts have been studied. Kinetic observations of industrial and model catalysts showed that siloxanes were the most severe catalyst poisons, although acidic sulfur compounds also caused deactivation. Furthermore, a method for on-site regeneration without shutdown of the catalytic flue gas cleaning system has been developed, i.e. an addition of H2/N2 gas to the off-gas can completely restore the activity of the deactivated catalysts.
Keywords: Platinum; CO oxidation; Poisoning; IR spectroscopy; Regeneration; Hexamethyldisiloxane; Catalytic oxidation; Hydrogen
Photocatalytic decomposition of acetaldehyde and Escherichia coli using NiO/SrBi2O4 under visible light irradiation by Xuexiang Hu; Chun Hu; Jiuhui Qu (pp. 17-23).
A monoclinic structure SrBi2O4 was prepared by coprecipitation method and characterized using X-ray diffraction (XRD), scanning electron microscope (SEM) and diffuse reflection UV–vis spectra (DRS). Photocatalytic activity of the catalysts was evaluated through the degradation of acetaldehyde and Escherichia coli ( E. coli) under visible light irradiation ( λ>420nm). The results indicated that monoclinic structure SrBi2O4 shows visible light activity and its photocatalytic activity was greatly enhanced when further loaded with NiO by the impregnation method. This is attributed to NiO promoting the electron–hole separation and interfacial charge transfer. The FT-IR spectra of the used NiO/SrBi2O4 indicated that some intermediates such as acetic acid, H2O, CO2 were formed for the degradation of acetaldehyde. The determination of intracellular K+ leakage with the inactivation of E. coli verified that the outer membrane of the cell is destroyed, causing the cell to die under visible light excitation of NiO/SrBi2O4. ESR studies revealed thatOH, O2− were involved as the active species in the photocatalytic reaction. A possible visible light photocatalytic mechanism was proposed.
Keywords: Bacteria; Monoclinic structure; NiO/SrBi; 2; O; 4; Toxic organic pollutant; Visible light photocatalyst
Correlation of structural properties and film thickness to photocatalytic activity of thick TiO2 films coated on stainless steel by Yongjun Chen; Dionysios D. Dionysiou (pp. 24-33).
A transparent, relatively dense and thick TiO2 film with good mechanical properties and enhanced photocatalytic activity has been successfully immobilized on 304 stainless steel. The study included optimization of structural properties and film thickness. Experiments on the photocatalytic degradation of 4-chlorobenzoic acid (4-CBA) as a model organic contaminant showed that the photocatalytic activity of this kind of thick film can be significantly improved by decreasing calcination temperature (i.e. from 600 to 500°C), which is due to an increase in BET surface area and porosity, decrease in crystal size, and decrease in foreign metal diffusion from stainless steel support to the surface of the film. The observed apparent rate constant of TiO2-500 (500°C, two dip coating layers) was found to be approximately 5.2 times that of TiO2-600 (600°C, two dip coating layers). The results showed that increasing film thickness within a certain range (up to 10μm) could significantly improve the photocatalytic activity without causing crack formation for the thick TiO2-500 film (500°C). The optimum film thickness is 10μm (four dip coating cycles), under which the observed apparent rate constant of TiO2-500 is approximately 2.3 times higher than that of TiO2-500 with 2.5μm film thickness (one dip coating layer). Based on several advantages of TiO2-500 film (500°C, four dip coating layers), including high photocatalytic activity, absence of foreign metal ions at the film surface, optimum film thickness, good structural integrity, and excellent adhesion on the stainless steel support, this kind of sol–gel-derived thick film immobilized on stainless steel support is a promising potential photocatalyst for water treatment applications.
Keywords: Thick film; Optical clarity; Photocatalytic activity; Photocatalysis; Structural properties; Stainless steel; 4-Chlorobenzoic acid; TiO; 2; Water treatment; Water purification
Substrate development for surface-enhanced Raman study of photocatalytic degradation processes: Congo red over silver modified titanium dioxide films by Carlos E. Bonancêa; Gustavo M. do Nascimento; Michele L. de Souza; Marcia L.A. Temperini; Paola Corio (pp. 34-42).
A methodology for the investigation of photocatalytic degradation processes of organic molecules involving surface-enhanced Raman spectroscopy (SERS) is developed and applied to the investigation of an azo dye. Initially, the development of substrates to enable SERS to be used for sensitive in situ characterization of photochemical processes in thin-films materials was focused. An optimized method for the preparation of a surface that is altogether photocatalytic (by the presence of semiconducting TiO2) and SERS-active (by the presence of nanostructured silver) was developed. The optimized SERS-active substrate was then employed to study the photodegradation reaction of Congo red. Considering that photocatalytic degradation process of organic molecules adsorbed on TiO2 might involve either their oxidation or reduction reaction, the spectroelectrochemical study of the dye was also performed, in order to clarify the transformations involved in initial steps of its photochemical decomposition. The approach here described involves combination of data relative to the photochemical behavior of dye and its electrochemical study – using enhanced spectroscopic techniques for identification and characterization of products – and proved to be very promising, in the sense of offering relevant information about the complex mechanisms that are involved in photodegradation processes of organic molecules.
Keywords: Environmental photochemistry; Photocatalytic degradation; TiO; 2; Raman spectroscopy; Congo red; Azo dyes
In/Co-ferrierite: A highly active catalyst for the CH4-SCR NO process under presence of steam by A. Kubacka; J. Janas; B. Sulikowski (pp. 43-48).
A series of monometallic (In, Co) and bimetallic (In/Co and Co/In) catalysts supported on ferrierite type zeolite were tested in the selective catalytic reduction of nitric oxide, in the presence of methane and excess of oxygen. All the catalysts were prepared by contact-induced ion exchange. A strong synergistic effect was observed for the catalysts containing both indium and cobalt, in comparison with the monometallic samples. For these bimetallic catalysts, a very high selectivity to nitrogen and rather efficient fuel economy were observed under the standard reaction conditions (NO=1000ppm, CH4=2000ppm, O2=4%, H2O=2500ppm). Moreover, the In/Co-ferrierite catalyst displays significant stability under a prolonged test (∼200h) in the presence of 2.5% of steam: the activity dropped rather moderately but was completely restored if steam supply was cut off, while the selectivity of the reaction was not affected in the whole temperature range scanned (300–500°C). The study suggests that a redox-type promotional effect of Co species on NO oxidation may be responsible of the strong synergistic effect detected in bimetallic In–Co formulations.
Keywords: Selective catalytic reduction; Nitric oxide; Ferrierite; Methane; Cobalt; Indium; Contact-induced ion exchange
Nonhydrolytic vanadia-titania xerogels: Synthesis, characterization, and behavior in the selective catalytic reduction of NO by NH3 by P. Hubert Mutin; Aurelian F. Popa; André Vioux; Gérard Delahay; Bernard Coq (pp. 49-57).
V2O5-TiO2 catalysts with V2O5 contents ranging from 6 to 18wt% were obtained by calcination at 773K of xerogels prepared by a nonhydrolytic sol–gel route from VOCl3, TiCl4, and iPr2O. These materials were characterized by X-ray diffraction, micro-FT-Raman spectroscopy, static51V NMR, SEM, N2 physisorption, temperature-programmed desorption of ammonia (NH3-TPD), and temperature-programmed reduction by H2 (H2-TPR). In all cases mesoporous solids were obtained with specific surface areas up to 87m2g−1. Raman spectroscopy indicated the presence of the same vanadia species as in conventional vanadia-titania catalysts. Up to a critical V2O5 loading (between 10 and 12wt%), all the vanadium was highly dispersed in the form of monomeric vanadyl and polymeric vanadate species, whereas for higher loadings V2O5 crystallites also formed. Most of the vanadium species (80–90%) were accessible to reduction by H2. The catalytic properties of these materials were evaluated in the selective catalytic reduction of NO by NH3. The estimated turnover frequency ‘TOF’ at 473K (mole of NO converted per mole of V per hour) went through a maximum value (16.6h−1) at a V loading of 8wt%, corresponding to an estimated surface vanadia loading of about 10μmolm−2. The N2O selectivity increased upon V loading as expected. A compromise between activity and high N2 selectivity (98% at 623K) could be found with the material containing 6wt% V2O5.
Keywords: Nonhydrolytic sol–gel; deNO; x; SCR; V; 2; O; 5; -TiO; 2
Effect of Mg, Ca and Ba on the Pt-catalyst for NO x storage reduction by F. Basile; G. Fornasari; A. Grimandi; M. Livi; A. Vaccari (pp. 58-64).
A set of catalysts was prepared to improve the activity of the Ba-Pt/γAl2O3 catalyst in the NO x storage reduction (NSR), by replacing Ba with Mg or Ca, but maintaining constant the moles of alkaline–earth element in order to keep the number of storage sites constant. The catalysts were prepared by impregnating first 1.0wt.% Pt and then the alkaline–earth cations (Ca, Mg and/or Ba) on a commercial γAl2O3 (Sasol, D). Tests were carried out in a wide temperature range (100–500°C), thus evidencing the specific role of each different alkaline–earth element. Both the activity and the resistance to SO2 poisoning in the catalysts were different and the alkaline–earth cation with lower electronegativity registered the strongest deactivation. A new catalyst with high activity and resistance to deactivation by SO2 was obtained by co-impregnating Ba and Mg on γAl2O3 (1.5Mg8.5Ba-1Pt/γAl2O3).
Keywords: NO; x; storage reduction; NSR; Ba; Ca; Mg; Pt; γAl; 2; O; 3; SO; 2; poisoning
Surface characterization of nanostructured TiO2 and carbon blacks composites by dye adsorption and photoelectrochemical studies by M.E. Rincón; M.E. Trujillo-Camacho; A.K. Cuentas-Gallegos; N. Casillas (pp. 65-74).
Photocatalysts based on nanostructured TiO2 and carbon blacks (CB) particles were obtained by chemical (sol–gel) and physical (mechanical grinding) preparation techniques. Characterization of these samples by XRD, FT-IR and dye adsorption studies was combined with optical and scanning photoelectrochemical analysis in an attempt to explain the photodegradation efficiency of these materials. The superior adsorption of sol–gel materials in the aqueous dye solutions did not account for the differences observed in photocatalytic activity, where the sol–gel composite outperforms the physical mixture or TiO2 alone by one digit. Data on the photoelectrochemical activity of these composites showed the abundance of inactive sites in the mixtures, while the sol–gel composite showed a uniform active surface. Rectification properties brought up by carbon in sol–gel composites and plus the abundance of hydroxyl groups on the oxide surface are proposed to be responsible for the long-term activity of these photocatalysts.
Keywords: Titanium oxide; Carbon black; Nanostructures; Sol–gel; Photocatalysts; Photoelectrochemical; Adsorption; Methyl violet
Effect of Ni addition over PtRu/C based electrocatalysts for fuel cell applications by M.V. Martínez-Huerta; S. Rojas; J.L. Gómez de la Fuente; P. Terreros; M.A. Peña; J.L.G. Fierro (pp. 75-84).
The electrocatalytic behaviour of PtRu/C is modified by the addition of nickel. Results from X-ray photoelectron spectroscopy reveal that the amount of surface Ni is less than the expected from the bulk stoichiometry, especially in the used samples where Ni was not detected. The oxidation state of Ni plays a key role on the catalytic performance of PtRuNi/C electrocatalysts, particularly in the CO oxidation reaction due to the development of Pt–Ni electronic interaction. The influence of the nature of the carbon support was also evaluated. Electrocatalysts prepared on a carbon-modified substrate displayed higher activities in the methanol oxidation reaction than those prepared over non-treated carbon. For the Ni-containing samples, the preparation route determines the degree of interaction between Pt and Ni of the different samples and hence their catalytic performance.
Keywords: Fuel cells; Electrocatalyst; Methanol electrooxidation; Nickel
High catalytic activity of SCS-synthesized ceria towards diesel soot combustion by Pietro Palmisano; Nunzio Russo; Paolo Fino; Debora Fino; Claudio Badini (pp. 85-92).
Nano-sized particles of ceria with high surface area were processed by solution combustion synthesis (SCS) and their catalytic activity towards combustion of carbonaceous materials was compared with that obtained by simple thermal decomposition of cerium nitrate, exhibiting the same specific surface area. These two kinds of ceria powders were tested by DTA and temperature-programmed combustion of diesel soot and a commercial carbon.Ceria processed by SCS was found to be more active than its counter part since it could decrease significantly both the combustion activation energy (from 115 to 111kcal/mol) and the TPC-plot peak temperature of diesel soot (from 466 to 405°C).The mechanism of the catalytic reaction of combustion was investigated by TPD/R experiments. Likewise other combustion catalysts acting as oxygen pumps, ceria can exchange limited amounts of oxygen even below 300°C, the SCS-synthesized one showing a superior O2 release at low temperatures (≤450°C). Moreover, the SCS-ceria exhibited a microstructure (i.e. a foam of nano-sized crystals) particularly suitable for maximizing the number of contact points between catalyst and carbon. Finally, the effect of specific aging protocols (thermal treatment at 600°C for 96h) in the presence of potentially deactivating species present in diesel exhaust gases (SO2 and water) was also studied showing that the here proposed material suffers from less significant ageing than Ce(NO3)3-derived ceria.
Keywords: Ceria; Solution combustion synthesis; Catalytic combustion; Soot; Diesel engine
Photooxidation of naphthalenesulphonic acids in presence of transition metal-doped carbon aerogels by M. Sánchez-Polo; J. Rivera-Utrilla (pp. 93-100).
The aim of the present study was to analyse the activity of carbon aerogels doped with transition metals (Co(II), Mn(II) and Ti(IV)) in the photooxidation process of naphthalenesulphonic acids (1-naphthalenesulphonic (NS), 1,5-naphthalenedisulphonic (NDS) and 1,3,6-naphthalenetrisulphonic (NTS)) from aqueous medium. Results derived from the textural characterization of the aerogels showed that there is no significant influence of the metal added during preparation process (Co(II), Mn(II) or Ti(IV)) on the textural properties of the aerogels. Determination of pH of point of zero charge (pHPZC) and X-ray photoelectron emission spectroscopy (XPS) analyses of the different samples showed them to have highly acidic surfaces (pHPZC≈3–4) with considerably high surface oxygen concentrations (Os≈20%) regardless of the metal present in the aerogel. XPS analysis showed an oxidation state of +2 for Co and Mn, and +4 for Ti. Results obtained demonstrated that photodegradation of naphthalenesulphonic acids with UV radiation (254nm) is not effective. Quantum yield ( Φ) values at a wavelength of 254nm were close to zero, showing the low reactivity of these compounds in the photodegradation process. In experiments using a medium-pressure lamp, it was detected that the photodegradation rate of these acids decreased as the number of sulphonic groups present in the aromatic rings increased. Thus, quantum yield values ( Φ) for NS, NDS and NTS were 0.019, 0.008 and 0.002, respectively. Presence of Ti(IV) or Co(II) aerogels or of the aerogel prepared without transition metal addition did not affect the photooxidation rate of naphthalenesulphonic acids. However, the addition of Mn(II)-doped carbon aerogel accelerated the elimination rate of these contaminants. These results could indicate that Mn(II)-doped carbon aerogel may act as photocatalyst in NTS photooxidation process. A rise in the surface concentration of Mn increased the NTS photooxidation rate. Activation of Mn aerogel with CO2 markedly increased its microporosity whereas its photocatalytic activity was not enhanced. Presence of tert-butanol (OH radical scavenger) decreased the NTS photodegradation rate, in presence of the Mn aerogel, confirming that oxidation byOH radicals is the main photooxidation pathway. Moreover, the addition of hydrogen peroxide accelerated the NTS photodegradation rate; however, in order to maintain the efficiency of the added hydrogen peroxide, the appropriate dose must be used. Comparison of the results obtained from the photocatalytic activity of the Mn(II) aerogel with TiO2 during photodegradation of naphthalenesulphonic acids showed that TiO2 was more efficient.
Keywords: Naphthalenesulphonic acids; Photolysis; Photocatalysis; Transition metal-doped carbon aerogels
An investigation of the thermal stability and performance of wet-incipient WO3/V2O5/TiO2 catalysts and a comparison with flame aerosol catalysts of similar composition for the gas-phase oxidation of methanol by Vipul Kumar; Nathan Lee; Catherine Bothe Almquist (pp. 101-114).
WO3/V2O5/TiO2 catalysts prepared using the wet-incipient and the flame aerosol methods are compared. The wet-incipient catalysts were dried and calcined; the flame aerosol catalysts were used as prepared. The key conclusion of this study is that surface V coverage on anatase TiO2 is the most important factor regarding both thermal stability and performance, and the synthesis method did not have significant effects on observed trends.For the wet-incipient catalysts, this study represents a systematic investigation on the effects of V and W loading on anatase TiO2 with respect to sintering, crystal structure changes, and catalyst performance. Both sintering and crystal phase conversion were promoted by surface V loadings greater than one monolayer. However, a high degree of sintering did not necessarily correspond with crystal phase conversion from anatase to rutile TiO2. The presence of W on the surface inhibits sintering, strongly inhibits crystal structure changes in the TiO2 support, and has very little effect on the performance of the catalysts. An optimum catalyst performance was observed at approximately one monolayer of surface V coverage on anatase TiO2. At sub-monolayer surface V loadings, the flame aerosol catalysts performed better than the wet-incipient catalysts. The better dispersion of V over the surface of TiO2 at low V loadings in the flame aerosol catalysts is likely the reason for this observation. Overall, the performance of the flame aerosol catalysts was comparable to the best wet-incipient catalysts with similar composition for the oxidation of methanol.
Keywords: WO; 3; /V; 2; O; 5; /TiO; 2; catalyst; Methanol; Sintering; Crystal phase; Flame aerosol; Wet-incipient
Improved Pd-on-Au bimetallic nanoparticle catalysts for aqueous-phase trichloroethene hydrodechlorination by Michael O. Nutt; Kimberly N. Heck; Pedro Alvarez; Michael S. Wong (pp. 115-125).
Groundwater remediation through the catalytic breakdown of the undesired contaminants is a more effective and desirable approach than the conventional physical displacement methods of air-stripping and carbon adsorption. Palladium-on-gold nanoparticles (Pd/Au NPs) have recently been shown to catalyze the hydrodechlorination of trichloroethene in water, at room temperature, and in the presence of hydrogen, with the most active Pd/Au material found to be >70 times more active than Pd supported on alumina on a per-Pd atom basis. The potential of this catalyst as a groundwater remediation technology could be improved by synthesizing Pd/Au NPs with smaller diameters and immobilizing them on a solid support. For this study, we synthesized Pd/Au NPs with a core diameter of 4nm and with different Pd loadings and studied them in colloidal form for aqueous-phase trichloroethene hydrodechlorination. The most active catalysts were considerably more active (>1900L/gPd/min) than Pd NPs (55L/gPd/min) and conventionally synthesized Pd/Al2O3 (47L/gPd/min). Accounting for a gas–liquid mass transfer effect and converting the Pd loading to Pd surface coverage using a magic cluster model for the Pd/Au NPs, the reaction rates in terms of initial turnover frequencies were >1.4, 4.35×10−2, and 3.76×10−2s−1, respectively. These materials exhibited volcano-like catalytic activity, in which hydrodechlorination rate was maximum near 70% Pd surface coverage. Au appeared to promote catalysis through geometric and electronic effects. Immobilization of the NPs on alumina, magnesia, and silica supports yielded active oxide-supported catalysts.
Keywords: Palladium; Gold; Nanoparticles; Groundwater; Trichloroethene; Remediation