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Applied Catalysis B, Environmental (v.93, #3-4)
Effect of applied potential on photocatalytic phenol degradation using nanocrystalline TiO2 electrodes by Haroldo G. Oliveira; Daiane C. Nery; Claudia Longo (pp. 205-211).
The activity of transparent and highly porous nanocrystalline TiO2 electrodes for phenol degradation by heterogeneous photocatalysis was investigated. Electrochemical characterization, performed for electrodes with areas=1.0cm2, revealed that the capacitance values increased under irradiation. Electrodes with areas=9.0cm2 were used for remediation of 10mL of an aqueous solution containing 50mgL−1 of phenol. Irradiated by a solar simulator, removal of 48% of total organic carbon was achieved after 3h. The efficiency was significantly enhanced for electrochemically assisted photocatalysis; the average mineralization was 78% after 3h and was almost complete after 6h for a TiO2 electrode externally connected to a Pt counter-electrode and biased at +0.7 or +1.1V with a potentiostat, or by a series connection to a solar cell. Phenol degradation exhibited pseudo-first-order kinetics, and application of the bias potential increased the rate constant from 0.21 to 0.47h−1. Applying a potential bias to the TiO2 electrode minimizes the recombination of photogenerated charge carriers and enhances the photocatalytic activity towards organic pollutant degradation.
Keywords: TiO; 2; Photocatalysis; Photoelectrocatalysis; Phenol
Enhanced inactivation of bacterial spores by atmospheric pressure plasma with catalyst TiO2 by Heesoo Jung; D.B. Kim; B. Gweon; S.Y. Moon; W. Choe (pp. 212-216).
Both atmospheric pressure plasma and photo-catalyst metal oxide titanium dioxide (TiO2) are well known for their microorganism inactivation and chemical material decomposition abilities. In this work, radio-frequency atmospheric pressure plasma and TiO2 are used together to inactivate Bacillus subtilis spores that have a very high degree of environmental resistance to ultra-violet (UV) photons and heat. The combinational use of the plasma and TiO2 demonstrates an enhanced performance of B. subtilis spore inactivation by showing a decrease in the decimal reduction time of as large as 40% compared with the use of plasma alone. A significant increase of hydroxyl (OH) and excited oxygen atomic emission line (O I) intensities in the presence of TiO2 suggests that the atmospheric pressure plasma assisted by TiO2 is very effective at generating reactive oxygen radicals, which is known to be a dominant factor in bacterial spore inactivation. Possible TiO2 activation mechanism by the plasma is investigated.
Keywords: TiO; 2; Atomspheric pressure plasma; Bacterial spore; Sterilization; Bacillus subtilis; Plasma catalysis; Oxygen vacancy
Photocatalysis and surface doping states of N-doped TiO x films prepared by reactive sputtering with dry air by Seon-Hong Lee; Eiji Yamasue; Keiichi N. Ishihara; Hideyuki Okumura (pp. 217-226).
Complex N (NO)-doped TiO x films on the glass substrate were prepared by radio-frequency (RF) magnetron reactive sputtering of Ti target in a mixed gas of argon and dry air with low oxygen concentrations. The surface doping states and energy band gap properties were studied by XPS and density-functional theory (DFT) applied to a 2×2×1 supercell of N-doped TiO2 with oxygen deficiency. Although all the films exhibit an anatase structure, the photocatalytic properties as well as other film properties (lattice parameters, grain sizes, introduced nitrogen contents, and optical properties) largely depend on the air flow ratios. The electronic bonding configurations at the nanoscale film surface are extremely important for photocatalysis, and there appears an optimal surface nitrogen amount incorporated in the anatase TiO2 lattice. Reduced Ti ions (and regions) at the nanoscale surface are proposed to play an important role by providing a local charge imbalance through the Schottky-barrier-like mechanism. Our DFT calculation shows the modified band calculation, especially for the film surface, involving both oxygen deficiency and N (NO) doping is important, due to the variation in the number and location of the impurity levels in the energy band gap. It is suggested that interstitial NO x (or substitutional NO) doping states with oxygen vacancy involving N–Ti–O or Ti–N–O bondings (linkages) are more effective on photocatalysis than the substitutional N doping states with oxygen vacancy. The seemingly desired impurity energy level(s) introduced in the electronic band gap does not necessarily improve photocatalysis, despite the desired optical properties observed, due to the active recombination sites newly produced and the complexity of the nanoscale surface science.
Keywords: Photocatalysis; Nitrogen doping; Titanium dioxide; Radio-frequency magnetron sputtering; Density-functional theory
Efficient visible light induced degradation of organic contaminants by Bi2WO6 film on SiO2 modified reticular substrate by Jiehui Xu; Wenzhong Wang; Meng Shang; Songmei Sun; Jia Ren; Ling Zhang (pp. 227-232).
Bi2WO6 film has been successfully immobilized on reticular stainless steel substrate by a simple dip-coating method. The as-prepared film exhibited excellent photocatalytic activity induced by visible light ( λ>420nm) in decomposing textile dye and toxic gas. It possesses notable advantages in gaseous contamination decomposition especially in static system due to its large specific surface area which makes the catalysts and contaminants sufficiently contacted with each other. The advantages of the SiO2 coating on the iron substrates were discussed. It effectively prevented the diffuseness of charge carriers from the substrate to the Bi2WO6, which resulted in the enhanced photocatalytic activity. Moreover, the stability of the photocatalytic film is also good which makes it potential for practical application.
Keywords: Bi; 2; WO; 6; film; Photocatalysis; Visible light; High activity
A highly stable catalyst for PEM fuel cell based on durable titanium diboride support and polymer stabilization by Shibin Yin; Shichun Mu; Haifeng Lv; Niancai Cheng; Mu Pan; Zhengyi Fu (pp. 233-240).
Titanium diboride (TiB2) is an electrically conducting ceramic with good conductivity, excellent thermal stability and corrosion resistance in acid medium. Here we report for the first time its application as a new catalyst support in proton exchange membrane (PEM) fuel cells. This novel catalyst (Pt/TiB2) was formed by a colloid route, in which the highly dispersed Pt nanoparticles were stabilized by Nafion functional polymers. This significantly facilitates the dispersion of Pt nanoparticles on TiB2. The electrochemical stability of TiB2 was investigated and showed almost no changes in redox region after oxidation during 48h at 1.20V. Further, it was found that the electrochemical stability of Pt/TiB2 catalyst is about four times higher than that of the commercial Pt/C under electrochemical oxidation cycles in the potential range of 0.6–1.2V. The excellent stability of Pt/TiB2 could be attributed to the stability of TiB2 support as well as the introduction of Nafion as stabilizer, which enhance both the metal–support interaction and the steric hindrance effect of the surface of Pt nanoparticles.
Keywords: Catalyst; Conducting ceramic; Titanium diboride; Stability; Proton exchange membrane fuel cells
Catalytic performance of platinum doped tungsten carbide in simultaneous hydrodenitrogenation and hydrodesulphurization by M. Lewandowski; P. Da Costa; D. Benichou; C. Sayag (pp. 241-249).
The simultaneous hydrodesulphurization (HDS) and hydrodenitrogenation (HDN) reactions of refractory model compounds were performed for the first time over tungsten carbide doped with platinum before and after preparation (0.3wt%). It was then compared to that of a pure non-modified W2C. The model compounds were 4,6-dimethyldibenzothiophene (4,6-DMDBT) and carbazole. The catalysts were characterized by X-ray diffraction (XRD). The surface properties were determined by N2 BET specific surface area and chemisorption of CO. Addition of platinum before synthesis of carbide decreased the uptake of CO chemisorption, but did not change significantly the specific surface area and the crystallographic structure of tungsten carbide—β-W2C. Addition of platinum after preparation of carbide did not decreased significantly the specific surface area of W2C but extremely increased the uptake of chemisorption of CO. No influence of platinum on the HDS activity was observed for contact times between 0.08 and 0.31s. At longer contact time ( tc>0.31s) the highest activity was observed over W2C–Pt catalyst (platinum doped after preparation) for the HDS of 4,6-DMDBT. The main products were 3,3-DMBPh (along DDS route) and MCHT (along HYD route).A strong influence of platinum, added after preparation (W2C–Pt), was observed for the HDN of carbazole. Indeed, this catalyst was found to be more active in the whole range of applied contact times than W2C and Pt–W2C. It was also more active in the consecutive reaction of isomerization of the main product of the HDN reaction, i.e. bicyclohexyl (BCH) transformed into methylcyclopenthylcyclohexane (MCPCH). Furthermore the activity in HDN over the W2C–Pt catalyst was shown to be highly dependent on the amount of metallic sites introduced by platinum.
Keywords: Tungsten carbide (W; 2; C); Platinum; Hydrodesulphurization (HDS); Hydrodenitrogenation (HDN); 4,6-Dimethyldibenzothiophene; Carbazole; Hydrogenation
Discussing the use of modified ceria as support for Pt catalysts on water–gas shift reaction by Andréa M. Duarte de Farias; Danh Nguyen-Thanh; Marco A. Fraga (pp. 250-258).
CeO2 was doped with 25wt.% of MeO x (Me=Zr, Sm, or La) and Ce75Me25 mixed oxides were obtained. Pt (1wt.%) was then deposited on these oxides and CeO2. The resulting catalysts were tested for the water–gas shift (WGS) reaction in a mixture whose composition was 5.49% CO, 4.10% CO2, 9.71% H2, 30.75% H2O. Subsequently, CeO2 was loaded with various levels of ZrO2 ( y wt.%), which gave another set of Ce100− yZr y ( y=25, 40, 50, and 75) supports and the respective catalysts were also tested for the WGS. While XRD analysis showed that all the mixed oxides had retained the cubic structure of CeO2, Raman analysis suggested that the doped ceria supports contain more oxygen vacancies resulting in higher oxygen mobility than CeO2, which were corroborated by the TPR analyses of all modified catalysts. However, only catalysts of the Pt/CeZr family produced larger CO conversions than Pt/CeO2 (except for Pt/Ce25Zr75) indicating that reducibility is not a crucial factor to improve WGS activity. The chemical composition, on the other hand, revealed to be quite decisive. Long-term experiments indicated that deactivation occurs independently of the lanthanide introduced into the ceria lattice and therefore oxygen mobility/reducibility of the catalysts does not play any role in improving the catalyst stability either. Catalyst reactivation was also investigated by applying different thermal treatments aiming at removing superficial deposits of carbonate complexes. The results led to the conclusion that the carbonate species play only a minor role in catalysts deactivation, suggesting that another factor, acting simultaneously as soon as reactant flux is started, determines the catalytic stability of such systems based on mixed oxides of ceria.
Keywords: Deactivation; Mixed oxides; Fuel cell; Ceria–zirconia; Lanthanum; Samarium
Catalytic oxidation of NO over TiO2 supported platinum clusters I. Preparation, characterization and catalytic properties by Landong Li; Qun Shen; Jie Cheng; Zhengping Hao (pp. 259-266).
The oxidation of NO to NO2 was studied on Pt/TiO2 catalysts prepared by wet impregnation and photo-deposition method. Pt/TiO2 prepared by photo-deposition exhibited quite higher activity for NO oxidation to NO2 than that prepared by wet impregnation and over 90% NO conversion could be achieved at below 250°C at a high GHSV of 180,000h−1. The effects of catalysts pretreatment conditions and feed gas composition, i.e. SO2 and H2O in the stream, on NO oxidation were investigated in details. The different Pt/TiO2 samples were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques. The Pt-TiO2 electron-interaction was studied based on the characterization results and the role of Pt-TiO2 electron-interaction on the catalytic performance of Pt/TiO2 was further discussed.
Keywords: Electron-interaction; Nitric oxide; Oxidation; Photo-deposition; Pt/TiO; 2
Catalytic activity for soot combustion of birnessite and cryptomelane by I. Atribak; A. Bueno-López; A. García-García; P. Navarro; D. Frías; M. Montes (pp. 267-273).
Birnessite and cryptomelane samples have been prepared and characterised by N2 adsorption at −196°C, XRD, XRF, XPS and H2-TPR. The activity of birnessite and cryptomelane for catalysed combustion of soot under NO x/O2 gas mixtures has been studied and compared with that of some other commercially available pure manganese oxides, namely MnO, MnO2, Mn2O3, Mn3O4, and natural MnO2. Birnessite and cryptomelane are more active for soot combustion than all the commercial oxides tested. Among the manganese oxides studied, birnessite shows the highest catalytic activity, lowering the soot combustion temperature by 150°C regarding the uncatalysed reaction, and cryptomelane lowers this temperature by 120°C. The NO x removal profiles suggest that birnessite chemisorbs NO x and forms potassium nitrate, which melts and reacts with soot. On the contrary, the main soot combustion pathway for cryptomelane and for the commercial manganese oxide tested is based on the catalytic oxidation of NO to NO2. Birnessite and cryptomelane only yield CO2 as carbon-containing soot combustion product.
Keywords: Birnessite; Cryptomelane; Manganese oxide; Soot combustion; Diesel pollution control
Doping level effect on sunlight-driven W,N-co-doped TiO2-anatase photo-catalysts for aromatic hydrocarbon partial oxidation by Anna Kubacka; Belén Bachiller-Baeza; Gerardo Colón; Marcos Fernández-García (pp. 274-281).
A series of nanosized W,N-co-doped anatase TiO2 catalysts with different dopant contents has been prepared by a microemulsion method and examined in the sunlight selective photo-oxidation of toluene and styrene. The activity results have been correlated with structural, electronic, and surface examinations of the catalysts done with the help of XRD–Rietveld, N2 physisorption and NH3 chemisorption–calorimetry, XPS, Infrared, and UV–visible spectroscopies. Irrespective of the reaction, a consistent reaction rate enhancement with respect to titania (nano-TiO2, P25) references and W-doped TiO2 systems is observed for single-phase anatase W,N-co-doped samples. This is likely linked with the decrease of the band gap energy decrease and results from a combined W–N cooperative effect on structural properties of the anatase network. W,N simultaneous presence also makes a drastic effect on selectivity, maximizing the yield to partial oxidation products. This appears related with surface properties of the materials.
Keywords: Photo-catalysis; Titania; Anatase; Doping; Nanostructured mixed oxide; Nitrogen; Tungsten; Visible and sunlight absorption; Selective partial oxidation; Toluene; Styrene
Viral templated palladium nanocatalysts for dichromate reduction by Cuixian Yang; Amy K. Manocchi; Byeongdu Lee; Hyunmin Yi (pp. 282-291).
Despite recent progress on environmental catalysis, there exist several critical challenges in simple and readily controllable nanocatalyst synthesis including the unpredictable particle growth, deactivation of catalytic activity, cumbersome catalyst recovery and lack of in situ reaction monitoring. We demonstrate viral template-based bottom-up assembly approach for nanostructured palladium (Pd) catalyst synthesis for dichromate reduction. Specifically, genetically displayed cysteine residues on each coat protein of Tobacco Mosaic Virus (TMV) templates provide precisely spaced thiol functionalities for readily controllable surface assembly and catalytically active Pd nanoparticle formation. Reaction kinetics studies via in situ monitoring by UV–vis spectroscopy revealed catalytic activity, stability and first-order batch reaction kinetics, and allowed rapid examination of reaction parameters (pH, reducer and temperature). Further, in-depth characterization via AFM, GISAXS and XPS show preferential Pd nanoparticle formation on TMV templates, particle size and stability that correlate well with the reaction kinetics results. We envision that our approach for simple high density surface assembly of catalytically active Pd nanoparticles under mild aqueous conditions would provide a facile route to catalyst synthesis in a wide range of applications.
Keywords: Tobacco Mosaic Virus (TMV); Palladium nanocatalyst; Dichromate reduction; GISAXS
Visible light-induced photosensitized decomposition of organic pollutants with polymer nanocapsules encapsulating Fe(bpy)32+ complex by Yasuhiro Shiraishi; Kenji Manabe; Takayuki Hirai (pp. 292-298).
Fe(bpy)32+ complex encapsulated within polymer nanocapsule, Fe(bpy)32+@PC, shows high photosensitization activity for decomposition of organic pollutant in water under visible light irradiation.Cross-linked polymer nanocapsules (PC) encapsulating an iron tris(bipyridine) complex, Fe(bpy)32+@PC, have been synthesized by a ship-in-a-bottle method. This was used as a photosensitizer for the decomposition of organic pollutant in water under visible light irradiation with molecular oxygen. The Fe(bpy)32+@PC promotes efficient decomposition of organic pollutant, whereas noncapsulated Fe(bpy)32+ is inactive. The enhanced sensitization activity of Fe(bpy)32+ within PC is due to the interaction with the PC wall. This lengthens the lifetime of the excited state Fe(bpy)32+ and promotes efficient production of hydroxyl radicals. The sensitization activity of Fe(bpy)32+@PC depends on the thickness of the PC wall. The Fe(bpy)32+@PC with an appropriate PC wall thickness allows accumulation of pollutant within the PC and, hence, promotes efficient decomposition of pollutant.
Keywords: Polymer nanocapsule; Iron tris(bipyridine) complex; Photodecomposition; Hydroxyl radicals; Visible light
Enhanced visible-light photocatalytic activity in K0.81Ti1.73Li0.27O4/TiO2− xN y sandwich-like composite by Peilin Zhang; Xiangwen Liu; Shu Yin; Tsugio Sato (pp. 299-303).
A sandwich-like composite was obtained by incorporating TiO2− xN y nanoparticles into the cracks of K0.81Ti1.73Li0.27O4 plate-like particles. The specific surface area together with the porosity were increased, and the photocatalytic activity in deNO x reaction was significantly enhanced especially under irradiation of visible-light with the wavelength λ>510nm.A lepidocrocite-type tianate, K0.81Ti1.73Li0.27O4, was coupled with TiO2− xN y by a hydrothermal method in order to give the visible-light responsiveness. After treating K0.81Ti1.73Li0.27O4 in a HCl aqueous solution to peel off and/or split the titanate plates, nano-sized nitrogen doped titania particles were added to form a sandwich-like bridging structure possessing high specific surface area and porosity. The prepared K0.81Ti1.73Li0.27O4/TiO2− xN y sandwich-like composite showed excellent photocatalytic activity for the decomposition of NO x gas under both visible-light and UV light irradiation ( λ>510, 400, 290nm), being superior to that of TiO2− xN y or commercial TiO2 (AEROXIDE® TiO2 P 25) powders.
Keywords: Photocatalyst; Titanate; Nitrogen doped titania; Coupled catalyst; DeNO; x
Effect of Fe/Co-ratio on the phase composition of Pd-integrated perovskites and its H2-SCR of NO x performance by G.C. Mondragón Rodríguez; B. Saruhan (pp. 304-313).
La-based perovskites doped with palladium were synthesized by a modified citrate route and calcined at high temperature. The Fe/Co-ratio at the B-site of the perovskite (LaFe0.95− xCo xPd0.05O3, x=0.475, 0.4, 0.3) was intentionally varied in order to produce a single phase catalyst and to correlate the phase(s) variations with its catalytic performance during the H2-SCR of NO x. A mixture of crystal phases containing orthorhombic and cubic perovskites, cobalt oxide and strongly bonded palladium oxide were observed in the sample with Fe/Co=1. Single orthorhombic perovskite phase with traces of iron oxide and weak bonded palladium oxide was obtained with Fe/Co≈2.2. The perovskite with Fe/Co=1 displayed better NO x-reductions and N2-selectivities than the perovskite with Fe/Co=2.2 ratio during dry H2-SCR of NO x. The same was observed with H2O+CO2 and in the presence of CO in the feed. The observed catalytic behaviour of both perovskites is discussed in association with the state of palladium in each investigated composition since the Pd-free perovskite displayed an extremely low NO x-reduction (below 4%).
Keywords: Perovskite; Pd-state; NO; x; -reduction; Lean conditions
Low-temperature catalytic decomposition of ethylene into H2 and secondary carbon nanotubes over Ni/CNTs by P.G. Savva; K. Polychronopoulou; V.A. Ryzkov; A.M. Efstathiou (pp. 314-324).
The present work reports on the production of H2 and secondary carbon nanotubes (CNTs) during catalytic decomposition of ethylene over a novel catalytic system, namely, nickel supported on carbon nanotubes (Ni/CNTs) at remarkably low-temperatures, e.g. 400°C. A number of catalyst parameters were investigated, namely the chemical nature of support, the Ni metal loading (0.1–10wt%), the nature of nickel metal precursor (organometallic vs. inorganic) used during catalyst synthesis, and the nature of transition metal used (e.g. Co, Fe, Cu, Ni). Among the different Ni/CNT supported catalysts investigated, 0.5wt% Ni/Ros1-B1 (Ros1-B1 a commercial CNT) presented the highest activity in terms of H2 production (296molH2/gNi) and carbon capacity (3552gC/gNi). In terms of transition metal used as active catalytic phase, the activity (moles H2 per gram of metal) was found to decrease in the order Co≫Fe>Cu. The activity of supported Ni and Co catalysts was found to strongly depend on the metal loading. The structural and morphological features of primary (catalytic support) and secondary carbon nanotubes produced during ethylene decomposition at 400°C were studied using X-ray Diffraction (XRD), scanning electron microscopy (SEM), High-resolution Transmission Electron Microscopy (HRTEM), and X-ray Photoelectron Spectroscopy (XPS). The production of secondary carbon nanotubes at 400°C was confirmed after using HRTEM and after a comparison with the primary carbon nanotubes of catalyst support was made. Different regeneration conditions (use of oxygen or steam) were investigated in order to remove by gasification the amorphous carbon deposited under reaction conditions. Oxygen appeared to be a better regeneration reagent than steam, where after ten consecutive reaction/regeneration cycles the 0.5wt% Ni/Ros1-B1 catalyst showed high and stable activity with time on stream.
Keywords: Carbon nanotubes; Ethylene decomposition; H; 2; production; XPS; HRTEM
Evidencing three distinct FeII sites in Fe–FER zeolites by using CO and NO as complementary IR probes by Elena Ivanova; Mihail Mihaylov; Konstantin Hadjiivanov; Vanessa Blasin-Aubé; Olivier Marie; Anna Plesniar; Marco Daturi (pp. 325-338).
Fe–FER zeolites were characterized by FTIR spectroscopy of adsorbed CO and NO. Two aged samples (Fe–FER-1 and Fe–FER-4 with Fe content of 1.1 and 3.7wt%, respectively) and one freshly prepared57Fe rich sample (57Fe–FER, designed for Mössbauer studies and containing 1.5wt% Fe) were studied. Both CO and NO are adsorbed onto Fe2+ cations and have different sensitivities to their location and/or coordination state. CO adsorption on Fe–FER-1 reveals two kinds of Fe2+ sites with the respective complexes observed at 2195 and 2189cm−1. The principal carbonyls (2195cm−1) are easily converted into dicarbonyls (2188cm−1) at low temperature and high CO equilibrium pressure. NO is less sensitive than CO to the environment of Fe2+ ions and NO adsorption gives rise to a single band at 1878cm−1. However, careful analysis reveals that this band consists of two closely located components. With the Fe–FER-4 sample a third family of iron sites was detected by CO at 2196cm−1. These carbonyl species are stepwise converted to di- (∼2188cm−1) and tricarbonyls (∼2180cm−1). With these sites NO forms another nitrosyls clearly detected at 1895cm−1. The latter are converted with time into polynitrosyls. These new sites are very sensitive to the preliminary treatment and easily change their oxidation state, forming Fe2+/Fe3+ redox couples. The sample preliminary treated with oxygen at 673K is characterized by Fe3+–OH groups (3674cm−1) and reactive oxygen that produces carbonates when reacting with CO, and NO+ when interacting with NO. Adsorption of NO on a freshly prepared57Fe–FER sample confirms the presence of the three distinct Fe2+ sites which is consistent with Mössbauer data. Finally, summarizing all the data, location of the different sites inside the FER structure is proposed. The results obtained are discussed in relation with the catalytic performance of Fe–FER.
Keywords: Adsorption; NO; CO; Ferrierite; Iron; FTIR spectroscopy; Mössbauer spectroscopy; Zeolite
Hydrogen peroxide-promoted-CWAO of phenol with activated carbon by A. Quintanilla; J.A. Casas; J.J. Rodriguez (pp. 339-345).
The effect of hydrogen peroxide as radical promoter in the wet air oxidation of phenol with activated carbon catalysts is studied in a trickle-bed reactor at 127°C, 8atm and 20–320gACh/gPhenol. The modifications that hydrogen peroxide induces on the radical reaction mechanism and the consequences on the effluent ecotoxicity are analyzed. The synergistic effect between oxygen and hydrogen peroxide in the initiation step of the reaction is verified. Hydroperoxy radicals, produced by the reaction between hydrogen peroxide and adsorbed oxygen, initiate the reaction on the carbon and in the liquid phase. They are responsible for the increased initial activity which provokes a faster removal of phenol and aromatic intermediates and, therefore, of the toxicity. The adsorbed oxygen on the carbon is crucial for the efficient consumption of hydrogen peroxide.
Keywords: Promoted oxidation; Ecotoxicity; Catalytic wet air oxidation; Hydrogen peroxide; Activated carbon; Phenol
Synthesis and characterization of a LaNiO3 perovskite as precursor for methane reforming reactions catalysts by Rosa Pereñíguez; Víctor M. González-DelaCruz; Juan P. Holgado; Alfonso Caballero (pp. 346-353).
The objective of the present work has been the study of the physicochemical and catalytic properties of a Ni/La2O3 catalyst obtained by reduction of a lanthanum nickelite, LaNiO3, with perovskite structure. The perovskite, obtained by means of a spray pyrolysis method, provides a Ni/La2O3 system active in different methane reforming reactions. The catalyst was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), X-Ray photoemission spectroscopy (XPS), temperature-programmed reduction and oxidation (TPR, TPO) and catalytic activity tests. Although not evidenced by XRD data, XAS and TPR measurements show the presence of an amorphous NiO phase in the original sample, together with the crystalline LaNiO3 phase. Upon reoxidation treatment of the reduced Ni/La2O3 catalyst, the LaNiO3 structure is partly recovered which provides a convenient way to regenerate a waste catalyst (reoxidation and new reduction in hydrogen). The catalyst is active in several reactions of methane with oxygen, water and CO2, showing a remarkable stability specially under dry reforming of methane (DRM) reaction conditions. This quite great catalytic performance has been explained by the high resistance of the nickel particles to be oxidized, as detected by in situ XAS. In the presence of water, as in steam reforming of methane (SRM) reaction conditions, these metallic particles are gradually oxidized, which explains the linear decreasing of the catalytic performance observed for the SRM reaction.
Keywords: Methane reforming; LaNiO; 3; catalysts; In situ XAS; Nickel perovskite; Partial oxidation of methane
Electro-oxidation of glycerol at Pd based nano-catalysts for an application in alkaline fuel cells for chemicals and energy cogeneration by Mário Simões; Stève Baranton; Christophe Coutanceau (pp. 354-362).
Carbon supported Pd, Pt, Au and bimetallic PdAu and PdNi nano-catalysts with different compositions were synthesized. Their catalytic activity toward glycerol electro-oxidation was evaluated in alkaline medium. Physical and electrochemical methods where used to characterize the structure and the surface of the catalysts. It was shown that the Pd xAu1− x/C catalysts were alloys, which present an increase of crystallite (XRD) and particle (TEM) sizes with increasing Au atomic fraction. Their surfaces were palladium rich whatever the Pd atomic ratio. The structure of the Pd0.5Ni0.5/C catalyst is much more difficult to understand, but it seems to be composed of a palladium phase in interaction with a Ni(OH)2 phase.The onset potential of glycerol oxidation is ca. 0.15V lower on Pt/C than on Pd/C and Au/C. All Pd xMe1− x/C catalysts presented lower onset potential than monometallic Au/C and Pd/C ones, but higher than Pt/C. For bimetallic catalysts, the order of activity at low potentials is: Pd0.3Au0.7/C>Pd0.5Au0.5/C>Pd0.5Ni0.5/C. Electrochemical experiments and in situ infrared spectroscopy measurements have shown that glycerol electro-oxidation mechanism is dependent on the catalyst, leading to different reaction products. Adsorbed CO species are detected on monometallic Pt and on Pd rich catalysts, but not on Au and Pd0.3Au0.7 catalysts, indicating that they are not able to break the C–C bond. The formation of hydroxypyruvate ion, which is a costly chemical product, is detected on pure gold catalyst.
Keywords: Alkaline fuel cell; Glycerol; In situ; infrared spectroscopy; Oxidation; Gold; Nickel; Palladium
Removal of dimethylsulfide by adsorption on ion-exchanged zeolites by Chien-Liang Hwang; Nyan-Hwa Tai (pp. 363-367).
Removal of low-concentration sulfide in clean rooms is important in the semiconductor industry. In dry conditions, silver–manganese exchanged Y zeolite (Ag–Mn/Na-Y) has high removal efficiency and high saturation adsorption capacity towards dimethylsulfide (DMS). However, the removal efficiency of DMS on Ag–Mn/Na-Y decreases with increasing water concentration in inlet gas at room temperature and normal pressure. In high humidity conditions, the removal efficiency and saturation adsorption capacity of DMS is high for silver–manganese exchanged ZSM zeolite (Ag–Mn/ZSM-5). In this paper, the influence of water concentration on the removal efficiency of DMS on Ag–Mn/zeolites was examined. The variations of functional group detected in FT-IR spectroscopy and temperature programmed desorption (TPD) confirm that water molecules influence the ability of DMS adsorption by Ag–Mn/zeolites.
Keywords: Dimethylsulfide; Desulfurization; Relative humidity; Adsorption; Ion-exchanged zeolite
Formation of highly crystallized TiO2(B) and its photocatalytic behavior by Ashok Kumar Chakraborty; Zhang Qi; Seung Yong Chai; Chongmu Lee; Sun-Young Park; Du-Jeon Jang; Wan In Lee (pp. 368-375).
Highly crystallized TiO2(B) in a flat-whiskered morphology, with a width of ∼300nm, thickness of 50–100nm, and length of several microns, was successfully synthesized by three-step reactions employing Degussa P25 and CsCO3 as starting materials. The synthesized TiO2(B) with a crystallite size of 30.2nm demonstrated an extended thermal stability up to 650°C and an unexpectedly high photocatalytic activity in decomposing 4-chlorophenol (4-CP), and several other organic compounds in aqueous solution. The photocatalytic activity of TiO2(B) heat-treated at 600°C was 1.26–1.43 and 1.95–2.32 times, respectively, compared to that of Degussa P25 and 25nm-sized anatase nanoparticle. Kinetic parameters in decomposing dilute 4-CP were also determined by applying the Langmuir–Hinshelwood equation. The equilibrium binding constant ( K) of the prepared TiO2(B) was 1.6 times that of Degussa P25, even though its surface area was less than a third, whereas the reaction rate constants ( k) were similar. Exceptionally high K is attributable to the unique crystallographic structure of TiO2(B) constructed by stacking of the negatively charged titania blocks, which enhances the adsorption affinity toward organic compounds.
Keywords: TiO; 2; (B); Crystallinity; Thermal stability; Photocatalyst; Photocatalysis; Decomposition; 4-Chlorophenol; Kinetic parameter
Capillary microchannel-based microreactors with highly durable ZnO/TiO2 nanorod arrays for rapid, high efficiency and continuous-flow photocatalysis by Zhongyuan He; Yaogang Li; Qinghong Zhang; Hongzhi Wang (pp. 376-382).
A novel, highly durable capillary-based photocatalytic microreactor containing TiO2 nanoparticle-coated ZnO nanorod arrays grown on the inner wall of the capillaries (IWC) was successfully constructed simply by pumping a TiO2 sol into capillaries containing preformed ZnO nanorod arrays. Methylene blue was used as a model organic compound to evaluate the photocatalytic performance of the capillary microreactors (CMs). The CMs containing ZnO/TiO2 nanorod arrays showed higher photocatalytic performance than a CM containing only ZnO nanorods at the same residence time. The effect of the number of TiO2 sol coatings and the recyclable properties of the CM were investigated. These CMs showed rapid and highly efficient photocatalytic activities and the ZnO/TiO2 nanorod arrays displayed high durability during continuous recycling. The superior photocatalytic activity of the ZnO/TiO2 nanorod-modified CMs was attributed to the topographical morphology induced by the nanorod arrays, and the combination of two semiconductors decreasing the recombination rate of photoinduced electrons and holes. These CMs show the promising application of the photodegradation of organic pollutants.
Keywords: ZnO/TiO; 2; nanorod; Capillary microreactor; Photocatalytic; Continuous-flow system
Soot trapping and combustion on nanofibrous perovskite LaMnO3 catalysts under a continuous flow of soot by Shanxia Li; Reina Kato; Qi Wang; Toshiro Yamanaka; Tatsuya Takeguchi; Wataru Ueda (pp. 383-386).
Catalytic activity for soot combustion and efficiency of soot trapping of fibrous perovskite-oxide LaMnO3 and powder perovskite-oxide LaMnO3 were investigated. We have developed a new apparatus to produce a drizzly mixture of soot/O2/N2 to imitate actual exhaust gas from diesel engines. By using this apparatus, it is possible to feed the mixture of soot, O2 and N2 continuously on catalysts at constant rates. It was found that the activities for soot combustion of powder and fibrous LaMnO3 were similar but that the efficiency for trapping soot by fibrous oxide was higher than that for trapping soot by powder oxide. Our method demonstrates a new possibility for the study of soot reduction under conditions close to those of an actual catalyst and filter placed after a diesel engine.
Keywords: Soot combustion; Nanofibrous LaMnO; 3; Loose contact; Soot trapping; Flow reactor
Zeolite confined rhodium(0) nanoclusters as highly active, reusable, and long-lived catalyst in the methanolysis of ammonia-borane by Salim Çalışkan; Mehmet Zahmakıran; Saim Özkar (pp. 387-394).
Addressed herein is the preparation, characterization and the catalytic use of zeolite confined rhodium(0) nanoclusters in the methanolysis of ammonia-borane. Rhodium(0) nanoclusters could be generated in zeolite-Y by a two-step procedure: (i) incorporation of rhodium(III) cations into the zeolite-Y by ion-exchange and (ii) reduction of rhodium(III) ions within the zeolite cages by sodium borohydride in aqueous solution, followed by filtration and dehydration by heating to 550°C under 10−4Torr. Zeolite confined rhodium(0) nanoclusters are stable enough to be isolated as solid materials and characterized by ICP-OES, XRD, SEM, EDX, HR-TEM, XPS and N2 adsorption–desorption technique. The zeolite confined rhodium(0) nanoclusters are isolable, bottleable, redispersible and reusable as an active catalyst in the methanolysis of ammonia-borane even at low temperatures. They provide exceptional catalytic activity with an average value of TOF=380h−1 and unprecedented lifetime with 74,300 turnovers in the methanolysis of ammonia-borane at 25±0.1°C. The work reported here also includes the full experimental details of the collection of a wealth of previously unavailable kinetic data to determine the rate law, and activation parameters ( Ea, Δ H≠ and Δ S≠) for the catalytic methanolysis of ammonia-borane.
Keywords: Rhodium; Nanocluster; Zeolite; Methanolysis; Catalysis; Ammonia-borane
The catalytic performance of mesoporous cerium oxides prepared through a nanocasting route for the total oxidation of naphthalene by Begoña Puertolas; Benjamín Solsona; Said Agouram; Ramón Murillo; Ana María Mastral; Asunción Aranda; Stuart H. Taylor; Tomas Garcia (pp. 395-405).
Cerium oxides have been prepared by nanocasting of a mesoporous siliceous KIT-6. Through this synthesis method a partially ordered mesoporous structure, as demonstrated by several characterization techniques (N2 adsorption, XRD and HRTEM) has been obtained. Accordingly, very high surface areas have been achieved (up to 163m2/g), despite using high calcination temperatures (550°C). We have demonstrated that the aging temperature of the siliceous template is of outstanding importance, as this parameter is directly responsible for both the pore size and the surface area of the catalysts. In addition, whilst a low preparation temperature (40°C) makes the further removal of the silica template difficult, higher temperatures lead to more compact frameworks with a higher interconnectivity among the networks. These cerium oxide materials have been tested as catalysts for the total oxidation of naphthalene, and display excellent activity, remarkably higher than commercial CeO2. The mesoporous ceria catalysts also demonstrate a high degree of stability with extended time-on-stream and most importantly using high reaction temperatures.
Keywords: Catalytic combustion; Nanocasting; Mesoporous CeO; 2; KIT-6; Naphthalene