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.96, #3-4)
Effect of silver doping on the TiO2 for photocatalytic reduction of CO2 by K. Kočí; K. Matějů; L. Obalová; S. Krejčíková; Z. Lacný; D. Plachá; L. Čapek; A. Hospodková; O. Šolcová (pp. 239-244).
Pure TiO2 and various silver-enriched TiO2 powders were prepared by the sol–gel process controlled in the reverse micellar environment. The catalysts were tested in CO2 photocatalytic reduction and characterized by X-ray diffraction (XRD), nitrogen adsorption measurement and UV–vis. Methane and methanol were the main reduction products. The yield of methane and methanol increases when modifying the TiO2 by silver incorporation is caused by two mechanisms: up to 5% of Ag in TiO2 the Ag impurity band inside the TiO2 bandgap decreases the absorption edge and increases so the electron–hole pair generation, above 5% of Ag in TiO2 Ag metallic clusters are formed in TiO2 crystals with Shottky barrier at the metal–semiconductor interface, which spatially separates electron and holes and increases their lifetime (decreases probability of their recombination).
Keywords: Ag doping; TiO; 2; CO; 2; reduction; Photocatalysis
Tungsten-based materials for fuel cell applications by Ermete Antolini; Ernesto R. Gonzalez (pp. 245-266).
Tungsten-based materials can play different roles in fuel cell systems. They are the only compounds which can be used as catalysts, co-catalysts, catalyst supports and electrolytes in different types of fuels cells. In particular, tungsten-based materials fulfill the requirements for their use as thermally stable carbon-alternative catalyst supports and Nafion®-alternative proton conducting electrolytes in fuel cells operating at intermediate temperature. In this work an overview of the use of tungsten-containing materials in fuel cells is presented.
Keywords: Tungsten; Fuel cells; Catalysts; Nanomaterials
The high activity and stability of La0.5Ba0.5MnO3 nanocubes in the oxidation of CO and CH4 by Shuhui Liang; Tongguang Xu; Fei Teng; Ruilong Zong; Yongfa Zhu (pp. 267-275).
La0.5Ba0.5MnO3 nanocubes and nanoparticles were synthesized by hydrothermal and co-precipitation methods, respectively. The catalytic performances and thermal stabilities of the samples in the oxidation of CO and CH4 were evaluated. La0.5Ba0.5MnO3 nanocubes showed much higher catalytic activity and thermal stability in CO and CH4 oxidation compared with the nanoparticles. After running at 560°C for 50h under the reaction conditions in CH4 oxidation, the surface area of the nanoparticles decreased significantly, while the nanocubes well maintained their surface area. Jahn–Teller effect had a significant influence on the catalytic performances of La0.5Ba0.5MnO3 nanocubes and nanoparticles. The much higher catalytic activity and thermal stability of La0.5Ba0.5MnO3 nanocubes were mainly predominated by the perfect single crystal structure.
Keywords: La; 0.5; Ba; 0.5; MnO; 3; Nanocubes; Single crystal structure; Jahn–Teller distortion; CO oxidation; CH; 4; oxidation
Low-temperature purification of gas streams from phenol by steam reforming over novel supported-Rh catalysts by Domna A. Constantinou; Angelos M. Efstathiou (pp. 276-289).
The purification of gas streams from phenol at low-temperatures (350–550°C) was investigated by its reaction with steam over novel catalytic systems, namely 0.5wt% Rh supported on Ce0.15Zr0.85O2, Ce0.15Zr0.83Mg0.02O2 and Ce0.14Zr0.81Mg0.05O2 mixed metal oxides. It was found that the rate of reforming reaction was largely influenced by the support chemical composition, where catalytic activity and selectivity towards H2 formation were increased with increasing support Mg content (0–5atom%). The 0.5wt% Rh/Ce0.14Zr0.81Mg0.05O2 catalyst showed the best activity in terms of phenol conversion and H2-yield, and the lowest CO/CO2 product ratio in the 350–550°C range. In particular, at 450°C a phenol conversion of about 80% and a H2-yield of about 85% were obtained for a feed containing 0.6vol.% phenol and 40vol.% H2O at a gas hourly space velocity of 54,000h−1. The latter catalyst composition exhibited significantly better catalytic performance in the 350–450°C range when compared to a commercial Ni-based catalyst used for tar steam reforming. In particular, at 450°C the H2-yield was increased by 75% and the CO/CO2 product ratio decreased by a factor of eight compared to the commercial Ni-based catalyst. It was found that the catalytic behaviour of 0.5wt% Rh/Ce0.14Zr0.81Mg0.05O2 correlates with the presence of a larger concentration of basic sites, a larger concentration of labile oxygen species, and of very small mean Rh particle size (∼1.3nm) compared to the other supported-Rh catalysts investigated. The significantly lower CO/CO2 product ratio obtained in the Rh/Ce0.14Zr0.81Mg0.05O2 compared to the other supported-Rh catalysts was related to the presence of a large surface concentration of Rh n+ cationic sites which may promote the water–gas shift (WGS) reaction. The activity towards the WGS reaction was found to be promoted by the presence of Mg2+ in the support composition. In situ DRIFTS–WGS reaction studies revealed that the kinds and surface concentration of formate species formed, likely active reaction intermediates in the WGS reaction, depend on the chemical support composition. The Ce0.14Zr0.81Mg0.05O2 support when used to deposit the same amount of Rh metal (0.5wt%) resulted in a larger concentration of formate species than the Ce0.15Zr0.85O2 support. This result could partly explain the significantly larger phenol steam reforming activity towards H2 and CO2 observed on the Rh/Ce0.14Zr0.81Mg0.05O2 than Rh/Ce0.15Zr0.85O2 catalyst.
Keywords: Phenol steam reforming; Hydrogen production; Supported-Rh catalysts; CO; 2; –TPD; CO–TPD; CO–DRIFTS; WGS–DRIFTS
Degradation of microcystin-LR using sulfate radicals generated through photolysis, thermolysis and e− transfer mechanisms by Maria G. Antoniou; Armah A. de la Cruz; Dionysios D. Dionysiou (pp. 290-298).
This study explores the potential use of sulfate radical-based advanced oxidation technologies (SR-AOTs) for the degradation of the naturally occurring hepatotoxin, microcystin-LR (MC-LR). The generation of sulfate radicals was achieved by activation of the oxidants persulfate (PS) and peroxymonosulfate (PMS) through electrophilic transition metal cations (Ag+ and Co2+, respectively), radiation (UV 300< λ<400nm) and/or heat ( T=30°C). These systems were compared to more frequently used AOTs systems in industrial applications; the Fenton Reagent (FR) and hydrogen peroxide coupled with heat and radiation. Even though SO4− has similar redox potential to hydroxyl radical (HO), to the best of our knowledge, SR-AOTs have not been tested for the degradation of cyanotoxins. In this study, PMS was activated very efficiently with Co2+ at neutral pH and increasing catalyst concentration resulted in dramatic increase of the initial rates of degradation that reached a plateau for CCo(II)≥1mg. Based on the optimum pH conditions for each system, the efficiency order is Co2+/PMS>Fe2+/H2O2≫Ag+/PS, which we believe is associated with the energy of the lower unoccupied molecular orbital of the oxidants. When UV (300< λ<400nm) radiation was used, the PS system was more efficient than PMS and H2O2 at all different oxidant concentrations.Since, the UV lamps used in the study emit light at a range of wavelengths (300< λ<400nm), the activation of the oxidants is believed to be caused by the emission spectra and not just λmax=365nm. At acidic conditions, the PS/UV (300< λ<400nm)/pH 3 and PMS/UV/pH 3 systems were most efficient and required the least amount of energy to reduce the toxin concentration by one order of magnitude. When thermal activation was used, PMS yielded the highest degradation efficiency (∼77%) compared to 52% for the PS and less then 2.5% for H2O2.
Keywords: Cyanotoxins; e; −; transfer mechanisms; Microcystin-LR; Fenton Reagent; Hydrogen peroxide; Oxidants; Persulfate; Peroxymonosulfate; Photolysis; Sulfate radicals; Thermolysis
Roles of nano-sized Au in the reduction of NO x by propene over Au/TiO2: An in situ DRIFTS study by Long Q. Nguyen; Chris Salim; Hirofumi Hinode (pp. 299-306).
A mechanistic study of the selective catalytic reduction (SCR) of NO x by C3H6 has been investigated over nano-sized Au/TiO2 catalyst using in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). The formation and consumption of adsorbed species on the catalyst surface have been intensively studied during co-adsorption of reactants and reaction condition. The presence of nano-sized Au particles played an important role in the formation of oxygenated hydrocarbons, especially acetate species. Importantly, Au active sites were crucial to the formation of isocyanate intermediate compounds and contributed to the conversion of these intermediates to N2. The reaction mechanism of SCR over Au/TiO2 has been discussed on the basis of DRIFTS results.
Keywords: In situ DRIFTS; Nano-sized Au; Au/TiO; 2; Mechanism; SCR
Aqueous bromate reduction by catalytic hydrogenation over Pd/Al2O3 catalysts by Huan Chen; Zhaoyi Xu; Haiqin Wan; Jianzhong Zheng; Daqiang Yin; Shourong Zheng (pp. 307-313).
Bromate is recognized as an oxyhalide disinfection byproduct in drinking water. In this study, supported noble metal (Pd, Pt) catalysts with different supports of SiO2, Al2O3 and activated carbon (AC) were prepared and the catalytic hydrogenation of aqueous bromate was first investigated. Characterization results showed the isoelectric points (IEPs) of Pd/SiO2 and Pd/Al2O3 catalysts were around 2.0 and 8.0, respectively, whereas the IEP of Pd/AC was much lower than 2.0. In comparison with Pd/SiO2 and Pd/AC, Pd/Al2O3 exhibited a substantially higher catalytic activity at pH 5.6 for bromate reduction due to the electrostatic attractive interaction between the bromate ion and the catalyst. Moreover, bromate with an initial concentration of 0.39mM was removed by 80.2% over Pt/Al2O3 and nearly 100% over Pd/Al2O3 after reaction for 2h, indicative of a higher catalytic activity of Pd/Al2O3. For Pd/Al2O3, the bromate reduction followed the Langmuir–Hinshelwood model, reflecting an adsorption controlled reduction mechanism. Increasing Pd loading amount resulted in enhanced bromate reduction. In addition, the bromate reduction was found to be strongly pH-dependent and enhanced reduction rate could be achieved at low pH. In the presence of coexisting anions (Cl−, Br− and SO42−) the bromate reduction was suppressed, wherein SO42− exhibited the most marked inhibition effect, attributed to competitive adsorption for active surface sites. The present results indicate that catalytic hydrogenation can be used as a potential treatment technique for the removal of bromate in drinking water.
Keywords: Bromate reduction; Catalytic hydrogenation; Pd/Al; 2; O; 3; catalyst
Solar photoactivity of nano-N-TiO2 from tertiary amine: role of defects and paramagnetic species by Francesca Spadavecchia; Giuseppe Cappelletti; Silvia Ardizzone; Claudia L. Bianchi; Serena Cappelli; Cesare Oliva; Paolo Scardi; Matteo Leoni; Paola Fermo (pp. 314-322).
N-doped TiO2 nanocrystals were successfully synthesized by a controlled sol–gel reaction at pH 9 followed by calcinations at 400°C. Triethylamine was used to modulate the N content of the samples. The photocatalytic activity was tested using a solar irradiation source with regard to two different pollutants: NO x (in the gas phase) and methylene blue (MB), deposited onto the oxide film. In the case of MB degradation the disappearance of the (MB) blue colour was measured directly onto the solid, by means of UV–vis-NIR diffuse reflectance spectroscopy. The final mineralization of the organic molecule was assessed by COD determinations. All N-doped samples produce a better removal of both pollutants than the undoped and commercial samples. By coupling structural (by X-ray synchrotron radiation) and morphological (HRTEM, BET, granulometry) characterizations with spectroscopic analyses (EPR and XPS), the presence of paramagnetic centers, defects, edge dislocations and surface states is appreciated and found to affect the material photocatalytic behaviour.
Keywords: N-doped nanotitania; Synchrotron radiation X-ray diffraction; NO; x; degradation; Unconventional methylene blue removal; Paramagnetic sites
Pd-catalyzed hydrodechlorination of chlorinated aromatics in contaminated waters—Effects of surfactants, organic matter and catalyst protection by silicone coating by Frank-Dieter Kopinke; Dalia Angeles-Wedler; Detlev Fritsch; Katrin Mackenzie (pp. 323-328).
Many chlorinated aromatic and aliphatic hydrocarbons dissolved in water can be rapidly and selectively hydrodechlorinated by means of Pd catalysts. However, if they appear in a complex water matrix, as is common for wastewater treatment or after soil extraction, the protection of the Pd sites against catalyst poisons may become the key step for applicability of this reaction. In the present study, Pd/Al2O3 was tested as hydrodechlorination (HDC) catalyst in various soil washing effluents. As probe compounds 3-chlorobiphenyl (3-CBP), monochlorobenzene (MCB) and trichloroethene (TCE) were chosen. Specific catalyst activities up to APd=200Lg−1min−1 were measured in clean water. The influence of surfactants and co-solvents was studied. In addition, soil slurry supernatant was employed as reaction medium to appraise the influence of soil co-extractants (dissolved organic matter, DOM) on the dechlorination reaction. Results show that commercially available surfactants such as Tween 80, Triton X-100, SDBS, and CTMAOH as well as methanol as co-solvent with concentrations up to 20vol% did not strongly affect the catalyst activity. However, the catalyst performance was heavily decreased in the presence of a soil slurry supernatant (40mgL−1 DOM). Hydrophobic coating of the catalyst by silicone polymers was successful in protecting the Pd sites against ionic catalyst poisons such as DOM and bisulphite for at least 24h.
Keywords: Hydrodechlorination; Palladium; Silicone; Surfactants; Co-solvent; Soil washing; Catalyst poisoning; Catalyst coating
Tuning operational conditions for efficient NO x storage and reduction over a Pt–Ba/Al2O3 monolith catalyst by Beñat Pereda-Ayo; Divakar Duraiswami; Juan J. Delgado; Rubén López-Fonseca; José J. Calvino; Serafín Bernal; Juan R. González-Velasco (pp. 329-337).
A well-controlled homemade Pt–BaO/Al2O3 monolith catalyst has been used for tuning the operational conditions at which the NO x storage and reduction (NSR) of the lean-burn engine exhaust gases is achieved more efficiently. The following operational conditions have been analyzed: the duration of the lean (storage) period, and the reductant (H2) concentration and duration of the regeneration (rich) period. The storage pattern during the lean period is evaluated by the percentage of NO x stored or NO x trapping efficiency ( η T), and the performance during the rich period is evaluated by the NO x reduction conversion ( X R) and the selectivity to nitrogen (SN2). These three response variables have been integrated into the single parameter that we have named integral NSR efficiency ( ɛNSR) of the whole NSR process, which represents the percentage of N2 produced at the reactor exit relative to the NO x fed to the reactor. The proposed graphical map consists of a series of ɛNSR-isocurves and allows predicting the NSR efficiency for any combination of the three studied operational conditions(CH2,tR,tL). Such operational map shall also be useful to compare the global NSR behavior of commercial catalysts under real operating conditions.
Keywords: NSR; Efficiency; NO; x; Storage; Reduction; Lean-burn engines; Monolith; Platinum; Barium
Preparation of Ce0.67Zr0.33O2 mixed oxides as supports of improved Pd-only three-way catalysts by Bo Zhao; Guangfeng Li; Changhua Ge; Qiuyan Wang; Renxian Zhou (pp. 338-349).
Four types of Ce0.67Zr0.33O2 (CZCP, CZH, CZHP and CZM) mixed oxides as supports were prepared by coprecipitation, hydrothermal, homogeneous precipitation and microemulsion methods, respectively. The results show that both the preparation methods and the aging procedures have significant influences on the physicochemical properties of Ce0.67Zr0.33O2 mixed oxides. All these fresh Ce0.67Zr0.33O2 samples develop mesopore structure, especially that, CZCP obtains the largest diameter (20.87nm) and volume (0.455cm3/g). The XRD results indicate that fresh CZHP and CZCP samples contain cubic and tetragonal phases, while only cubic solid solution is found in fresh CZH and CZM samples, which show better low-temperature reducibility. Moreover, higher oxygen storage capacity complete (OSCC) values and faster O2 uptake are observed in CZH and CZM samples compared with those of fresh CZCP and CZHP. After calcination at 1100°C, it is found that the OSCC values and the kinetics of the O2 uptake for CZM and CZHP samples are deteriorated due to the coexistence of cubic and tetragonal phases as well as strong sintering of samples. On the contrary, the aged CZCP and CZH samples keep satisfactory low-temperature reducibility and oxygen storage capacity. For fresh catalysts, the pore-size distribution of mixed oxides seems to be important for catalytic activities. In contrast, for aged catalysts, their activities are related to both the redox properties and the textural properties of aged mixed oxides. Therefore, the Pd-only three-way catalyst supported on the CZCP exhibits the most promising amplified amplitude of stoichiometric window.
Keywords: CeO; 2; -ZrO; 2; mixed oxides; Synthesis; Pd-only TWC; Stoichiometric windows
Effects of Ce/Zr ratio on the reducibility, adsorption and catalytic activity of CuO/Ce xZr1− xO2/ γ-Al2O3 catalysts for NO reduction by CO by Qiang Yu; Lianjun Liu; Lihui Dong; Dan Li; Bin Liu; Fei Gao; Keqin Sun; Lin Dong; Yi Chen (pp. 350-360).
Effects of Ce/Zr ratio on the physicochemical properties of CuO/Ce xZr1− xO2/ γ-Al2O3 catalysts were investigated by BET, XRD, Raman and H2-TPR. The catalytic activity and the interaction between the reactants with these catalysts were compared by NO+CO model reaction and in situ FT-IR. The results suggested that the addition of ceria–zirconia mixed oxides significantly improved NO conversion and N2 yield due to dispersed copper species in proximity to ceria–zirconia. Especially, the ceria-rich catalysts displayed better performance in activity and reducibility than others, which would be resulted from the strong interaction among copper, ceria–zirconia and support. The IR results suggested NO reduction activity was correlated with the presence of Cu+ carbonyl species, and the catalysts with variable Ce/Zr ratios had no distinction at the adsorption type and rate of NO/CO at room temperature. However, on heating treatment would give distinct difference in CO2 intensity and the wavenumber of adsorbed nitrates. Simultaneously, the stability of these N- and C-containing intermediates contacted with alumina was influenced by the modified Ce/Zr ratio.
Keywords: CuO/Ce; x; Zr; 1−; x; O; 2; /; γ; -Al; 2; O; 3; NO; +; CO model reaction; H; 2; -TPR; In situ FT-IR; Carbonate; Nitrate
Mineralization of the drug β-blocker atenolol by electro-Fenton and photoelectro-Fenton using an air-diffusion cathode for H2O2 electrogeneration combined with a carbon-felt cathode for Fe2+ regeneration by Eloy Isarain-Chávez; Conchita Arias; Pere Lluís Cabot; Francesc Centellas; Rosa María Rodríguez; José Antonio Garrido; Enric Brillas (pp. 361-369).
Two-electrode cells with a Pt or boron-doped diamond anode and an air-diffusion cathode for H2O2 electrogeneration, and four-electrode combined cells containing the above pair of electrodes coupled in parallel to a Pt anode and a carbon-felt cathode, have been used to degrade the pharmaceutical β-blocker atenolol by electro-Fenton and photoelectro-Fenton methods. In these processes, organics are mainly oxidized with hydroxyl radical (OH) formed simultaneously at the anode surface from water oxidation and from Fenton's reaction between added catalytic Fe2+ and electrogenerated H2O2. Aromatic intermediates such as 4-hydroxyphenylacetamide and p-benzoquinone and generated carboxylic acids such as maleic, fumaric, tartaric, tartronic, glycolic, formic, oxalic and oxamic are detected and quantified by high-performance liquid chromatography. Compared with the single cells, the corresponding novel four-electrode combined systems enhance strongly the mineralization rate of atenolol in electro-Fenton because of the fast Fe2+ regeneration at the carbon-felt cathode favoring: (i) the production of more amounts ofOH from Fenton's reaction that destroy more rapidly aromatic pollutants and (ii) the formation of Fe(II) complexes with final carboxylic acids such as oxalic and oxamic, which are more quickly oxidized withOH. In photoelectro-Fenton, both single and combined cells show a quite similar oxidation power giving almost total mineralization as a result of the parallel quick photolysis of Fe(III) and/or Fe(II) complexes under UVA irradiation. The efficient regeneration of Fe2+ with largerOH production in the combined cells causes a quicker atenolol decay, which always follows a pseudo first-order reaction. NH4+ and in smaller proportion NO3− are always released to the medium.
Keywords: Pharmaceuticals; Electrochemical advanced oxidation processes; Decay kinetics; Oxidation products; Fe(II) complexes
On the importance of the catalyst redox properties in the N2O decomposition over alumina and ceria supported Rh, Pd and Pt by S. Parres-Esclapez; M.J. Illán-Gómez; C. Salinas-Martínez de Lecea; A. Bueno-López (pp. 370-378).
Rh, Pd and Pt have been supported on γ-Al2O3, pure CeO2 and La- or Pr-doped CeO2, and these catalysts have been tested for N2O decomposition. The effect of CO and O2 in the feed has been studied. The characterisation techniques used were Raman spectroscopy, XRD, N2 adsorption at −196°C, H2-TPR and TEM. The catalytic activity for N2O decomposition of the noble metals follows the trend Rh>Pd>Pt, and the support affects significantly the activity. For CeO2-containing catalyst, a relationship between N2O decomposition capacity and H2 reduction of ceria has been found, the easier is the reduction the higher is the catalytic activity. The rate-limiting step of the N2O decomposition mechanism over noble metal/ceria catalysts seems to be the reduction of the catalytic active sites. For Rh catalysts, ceria supports are involved actively in the decomposition of N2O, and all the ceria-based supports improve the catalytic activity of Rh with regard to γ-Al2O3 due to the redox properties of ceria. The Pd catalysts with pure and doped ceria support showed similar activity, this being higher than that of Pd/γ-Al2O3. Pt/CeO2 is the most active catalyst among those of Pt, but ceria doping by La or Pr has a negative effect on the activity. The most active catalyst among those prepared in this study is Rh/CeO2(Pr).
Keywords: N; 2; O decomposition; Noble metal catalyst; Ceria support; Cerium–praseodymium; Cerium–lanthanum
An efficient catalytic route for the preparation of silyl ethers using alumina-supported heteropolyoxometalates by Paula Villabrille; Gustavo Romanelli; Nancy Quaranta; Patricia Vázquez (pp. 379-386).
In the present work the phenol trimethylsilylation with hexamethyldisilazane using molybdophosphovanadates supported on commercial alumina cylinders as catalysts was studied. These catalysts were prepared by incipient wetness impregnation also including Fe and Cu as cations, which can be present as bulk heteropolyacids or in the previously impregnated support. These solids were characterized by several techniques such as diffuse reflectance spectroscopy, Fourier transformed infrared spectroscopy, optical and scanning electron microscopies, and X-ray diffraction, among others.The catalytic test was performed under different reaction conditions in order to know the performance of the synthesized catalysts. The method shows high conversion of phenol under heterogeneous conditions. Phenol trimethylsilyl ether formation was obtained using hexamethyldisilazane as acylating agent and toluene as reaction solvent, with different reuses. In addition, they are environmentally friendly materials. The H2PMo11VCuO40 supported on alumina showed higher activity in the tested reaction.Finally, various alcohols and phenols were silylated to trimethylsilyl ethers, under mild conditions, and excellent yields were obtained.
Keywords: Silyl ethers; Hexamethyldisilazane; Heteropolycompounds; Heterogeneous catalysis
New approaches to improving catalyst stability over Pt/ceria during ethanol steam reforming: Sn addition and CO2 co-feeding by Sania M. de Lima; Adriana M. da Silva; Gary Jacobs; Burtron H. Davis; Lisiane V. Mattos; Fábio B. Noronha (pp. 387-398).
To promote long-term stability of Pt/CeO2 catalyst for ethanol steam reforming, two approaches were examined. Sn was added to Pt to suppress carbon formation. Although the catalyst with high Sn content exhibited improved stability, acetaldehyde selectivity was prohibitive. DRIFTS experiments revealed that Sn inhibited the ability of Pt to facilitate steam-assisted forward acetate decomposition reaction to carbonate, the precursor to CO2 formation. However, CO2 co-feeding was more effective, not only in promoting long-term catalyst stability, but also in maintaining high H2 selectivity. DRIFTS experiments indicate that the kinetic influence of CO2 can be explained as a competition with ethanol for adsorption sites, leading to a suppression in the rate of formation of coke precursors.
Keywords: Hydrogen production; Ethanol steam reforming; Pt–Sn/CeO; 2; catalyst; Deactivation mechanism; Carbon formation; CO; 2; co-feeding
Modeling of a TiO2-coated quartz wool packed bed photocatalytic reactor by G. Vella; G.E. Imoberdorf; A. Sclafani; A.E. Cassano; O.M. Alfano; L. Rizzuti (pp. 399-407).
A fixed-bed, photocatalytic laboratory reactor aimed to degrade pollutants from water streams was designed and built. Quartz wool coated with a thin film of TiO2 was employed as the reactor filling. The photocatalyst was placed in the reactor forming a loose packing to guarantee the intimate contact among reactants, photons, and the photocatalytic surface. This reactor was employed to study the photocatalytic decomposition of a model pollutant (formic acid). A reactor–radiation–reaction model was developed, which was comprised of the reactor mass balance, radiation model, and kinetic model for the degradation of formic acid. The local superficial rate of photon absorption, which was necessary to evaluate the kinetic, was obtained from the results of a radiation model. The Monte Carlo approach was employed to solve the radiation model, where the interaction between photons and the TiO2-coated fibers of the packing was considered. The kinetic model was derived from a plausible kinetic scheme. Experimental results obtained in the packed-bed reactor, operating in a differential mode and without mass transfer limitations, were used to estimate the parameters of the kinetic model. A satisfactory agreement was observed between model simulations with the derived parameters and experimental results, with a root mean square error less than 8.3%.
Keywords: Packed-bed reactor; Quartz wool; Photocatalysis; TiO; 2; Kinetics; Formic acid
Selective catalytic reduction of NO with NH3 over iron titanate catalyst: Catalytic performance and characterization by Fudong Liu; Hong He; Changbin Zhang; Zhaochi Feng; Lirong Zheng; Yaning Xie; Tiandou Hu (pp. 408-420).
A novel iron titanate catalyst prepared by conventional co-precipitation method showed excellent activity, N2 selectivity and H2O/SO2 durability in the selective catalytic reduction (SCR) of NO with NH3. The influence of precursors and preparation methods on the catalyst structure and activity was comprehensively investigated. Iron titanate catalyst prepared using titanium sulfate as Ti precursor was favorable for the high activity and selectivity, comparing with that using titanium tetrachloride as precursor and Fe2O3/TiO2 loaded type catalyst. Especially, the best iron titanate catalyst showed good activity in a temperature window of 200–350°C with the NO x conversion above 90% in the absence of H2O, which was 50–150°C lower than those of other known Fe-based catalysts. Iron titanate crystallite with specific Fe–O–Ti structure was found to be the main active phase. The interaction between iron and titanium species in atomic scale led to an enhancement of oxidative ability of Fe3+, which was beneficial to the SCR reaction.
Keywords: Selective catalytic reduction; Iron titanate catalyst; Titanium sulfate; Titanium tetrachloride; Crystallite; Active phase
Effect of water vapor on the activity and stability of Pd/SZ and Co/ZrO2 in dual-catalyst treatment of simulated exhaust from lean-burn natural gas engines by Burcu Mirkelamoglu; Umit S. Ozkan (pp. 421-433).
A dual-catalyst system, consisting of an NO oxidation catalyst component (Co/ZrO2) and a NOx reduction catalyst component (Pd/SZ) was investigated for selective catalytic reduction of NOx under lean conditions. The integrated catalyst system is capable of performing three-distinct catalytic functions, namely, NOx reduction, combustion of unburned hydrocarbons and oxidation of carbon monoxide. The hydrothermal stability of the dual-catalyst system was investigated through steady-state and time-on-stream measurements. Water vapor was found to inhibit the NOx reduction activity of Pd/SZ, whereas it had no effect on NO oxidation over Co/ZrO2. The dual-catalyst system was capable of retaining stable catalytic activity during simulated lean exhaust treatment in the presence of 7% H2O.
Keywords: Lean NOx reduction; NO oxidation; Sulfated zirconia; Palladium; Cobalt
Relation between partial propene oxidation, sulphate content and selective catalytic reduction of NOx by propene on ceria/sulphated titania by Alexandre Baylet; Chloé Capdeillayre; Laurence Retailleau; Philippe Vernoux; François Figueras; Anne Giroir-Fendler (pp. 434-440).
The propene catalytic oxidation and the selective catalytic reduction of NO by propene (C3H6-SCR) have been studied over ceria catalysts supported on sulphated titania (ceria content of 0.9, 0.5, 0.3 and 0.04wt%). XPS analysis and Raman spectroscopy were carried out in order to obtain information on ceria (oxidation degree, surface content, and particle size) and sulphate compounds (species and surface content). The NOx reactivity was mainly linked to the sulphate content. The higher the sulphate content, the higher the NOx reactivity. The partial C3H6 oxidation has a role in the NOx activity. The lower the partial C3H6 oxidation into CO, the better the NOx reactivity. However, N2 selectivity was higher for the sample with the lowest sulphate content (i.e. the highest partial C3H6 oxidation). Sulphate compounds like SO32− and/or SO42− with reduced ceria (Ce3+) activate the C3H6 and NO compounds. Moreover, in the range of ceria content studied here, with or without NO in the gas stream, C3H6 oxidation was also related to sulphate content and not to ceria content. Nevertheless, the presence of ceria provides oxygen for NO oxidation to form nitrate, oxygen coming from Ce3+Vo species at the surface (Vo: oxygen vacancy). The key parameter between NOx reduction and N2 selectivity was observed to be the sulphate content.
Keywords: Selective catalytic reduction; Nitrogen oxide; Nitrogen selectivity; Propene; Ceria; Sulphated titania
A comparative study between Co and Rh for steam reforming of ethanol by Ayman M. Karim; Yu Su; Junming Sun; Cheng Yang; James J. Strohm; David L. King; Yong Wang (pp. 441-448).
Rh and Co-based catalyst performance was compared for steam reforming of ethanol under conditions suitable for industrial hydrogen production. The reaction conditions were varied to elucidate the differences in reaction pathways on both catalysts. On Co/ZnO, CH4 is a secondary product formed through the methanation reaction, while it is produced directly by ethanol decomposition on Rh. The difference in the reaction pathway is shown to favor Co-based catalysts for selective hydrogen production under elevated system pressures (up to 15bar) of industrial importance. The carbon deposition rate was also studied, and we show that Co is more prone to coking and catalyst failure. However, the Co/ZnO catalyst can be regenerated, by mild oxidation, despite the high carbon deposition rate. We conclude that Co/ZnO is a more suitable catalyst system for steam reforming of ethanol due to the low methane selectivity, low cost and the possibility of regeneration with mild oxidation.
Keywords: Ethanol reforming; Cobalt catalyst; Rhodium catalyst; Carbon deposition; Reaction pathway
Influence of preparation method on the catalytic activities of CuO/Ce0.67Zr0.33O2 catalysts in CO+O2 reaction by Jie Zhu; Lingling Zhang; Yu Deng; Bin Liu; Lihui Dong; Fei Gao; Keqin Sun; Lin Dong; Yi Chen (pp. 449-457).
Ce0.67Zr0.33O2 solid solutions synthesized by traditional co-precipitation method (hereafter donated as CZ-CP) and hydrothermal method (hereafter donated as CZ-HT) were used as supports for preparing a series of CuO/Ce0.67Zr0.33O2 catalysts. High resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), temperature-programmed reduction (TPR), CO adsorption in situ Fourier transform infrared spectroscopy (CO in situ FT-IR) and the activity of CO oxidation model reaction at low temperature (<200°C) were used to approach the properties of the catalysts. The results showed that the Ce0.67Zr0.33O2 prepared by hydrothermal method facilitate the formation and stabilization of Cu+ on the surface of support and thus the activity for CO+O2 reaction was improved. A tentative model was suggested that the difference in the preferentially exposed plane of CZ-CP and CZ-HT leads to the great difference in dispersion, reduction and reaction activity of the dispersed copper oxide species on these two supports.
Keywords: CeO; 2; –ZrO; 2; solid solution; Hydrothermal method; Preferentially exposed plane; “Incorporation Model”
Study on the photocatalysis of F–S co-doped TiO2 prepared using solvothermal method by Guidong Yang; Zheng Jiang; Huahong Shi; Martin O. Jones; Tiancun Xiao; Peter P. Edwards; Zifeng Yan (pp. 458-465).
Fluorine–sulfur (F–S) co-doped TiO2 materials have been prepared using low-temperature solvothermal method, and tested for catalytic activity by the visible light photocatalytic degradation of the Methylene Blue. For comparison, the mono-elemental doped samples, e.g., S- and F-doped TiO2 have also been prepared and tested under the same conditions. The characterization results showed that F–S co-doped TiO2 has a higher photocatalytic activity than that of mono-doped F- and S-doped samples under visible light irradiation. It is believed that the co-doping gives rise to a localized state in the band gap of the oxide and creates active surface oxygen vacancies, both which are responsible for visible light absorption and the promotion of electrons from the localized states to the conduction band. Characterization by electron paramagnetic resonance revealed the presence of a superoxide radical (O2−) which may be mainly responsible for photodegradation of Methylene Blue under visible light.
Keywords: Solvothermal method; F–S co-doped TiO; 2; Photocatalyst; Visible light response; Mechanism study; F-doped TiO; 2; S-doped TiO; 2
Comprehensive investigation of Pd/ZSM-5/MCM-48 composite catalysts with enhanced activity and stability for benzene oxidation by Chi He; Jinjun Li; Peng Li; Jie Cheng; Zhengping Hao; Zhi-Ping Xu (pp. 466-475).
ZSM-5/MCM-48 composite materials with various acidities have been successfully assembled on zeolite seeds via a two-step crystallization process. The characterization results reveal that the ZSM-5 seeds are present in the framework of the resulting composite materials with its content gradually increasing with the Si/Al molar ratio, and Al atoms prefer the tetrahedral coordination in composite products. The amount of strong acid sites increases as the Si/Al molar ratio decreases, while that of weak acid sites is almost unchanged. The activity tests demonstrate that the catalytic activity of Pd-loaded ZSM-5/MCM-48 composite catalysts is much higher than that of Pd/ZSM-5 and Pd/MCM-48, and all these catalysts are active and stable in the total oxidation of benzene. Both Pd0 and Pd2+ are responsible for the oxidation reaction, and the catalytic activity is closely related to the support acidity, the CO2 desorption capability and the Pd dispersion. This research thus indicates that the novel composite materials have promised as active Pd-supported catalysts in the elimination of volatile organic compound (VOCs).
Keywords: Two-step crystallization; ZSM-5/MCM-48; Acidity; Stability; VOCs
Biomass derived feedstock co-processing with vacuum gas oil for second-generation fuel production in FCC units by Gabriella Fogassy; Nicolas Thegarid; Guy Toussaint; Andre C. van Veen; Yves Schuurman; Claude Mirodatos (pp. 476-485).
Hydrodeoxygenated pyrolysis-oils (HDO-oil) are considered promising renewable liquid energy carriers. As such, it cannot be applied in in-stationary combustion engines so more “upgrading” is required. A considerable alternative is to co-process HDO-oil along with vacuum gas oil (VGO) in a Fluid Catalytic Cracking unit (FCC). This study evaluates the impact of adding 20wt.% HDO-oil to a conventional FCC feedstock. The VGO and bio-oil mixtures were co-injected into a fixed-bed reactor simulating FCC conditions using an equilibrated industrial FCC catalyst. Co-processing of 20wt.% HDO-oil with VGO gave comparable yields for the gasoline fraction to that of the pure VGO cracking. However, during co-processing oxygen removal from HDO-oil oxygenated components consumes hydrogen coming from the hydrocarbon feedstock. As a result the final product composition is poor in hydrogen and contains more coke, aromatics and olefins.
Keywords: Renewable feedstock; Refining; Catalytic cracking; Biofuels; Pyrolysis-oil
Effect of light source on the catalytic degradation of protocatechuic acid in a ferrioxalate-assisted photo-Fenton process by J.M. Monteagudo; A. Durán; I. San Martín; M. Aguirre (pp. 486-495).
The catalytic degradation of protocatechuic acid (PA) solutions in a ferrioxalate-assisted photo-Fenton process irradiated with solar or artificial ultraviolet light sources was investigated. The reactions were carried out either in a pilot plant consisting of a compound parabolic collector (CPC)-solar reactor or in a UV-A/C-lamp reactor. An optimization study was performed using a multivariate experimental design including the following variables: pH, temperature, solar power, air flow and initial concentrations of H2O2, Fe(II) and oxalic acid. The photocatalytic degradation efficiency was determined by measuring the elimination of the original PA and the removal of total organic carbon (TOC). TOC-removal rates of 97% and 96% were achieved under artificial UV-A/C and solar light, respectively, but with different optimum operating conditions. When artificial UV light was used in the presence of oxalic acid, the degradation rate was higher in the UV-C system than in the UV-A system because ferrioxalate complexes are primarily formed at 200–280nm.OH radicals were the main oxidative intermediate species in the artificial UV-A/C process while superoxide andOH radicals played the most significant roles in the solar process. Artificial UV-A/C light can be used as an alternative to solar CPC on cloudy days.
Keywords: Protocatechuic acid; Ferrioxalate; Photo-Fenton; UV light; CPC
CoMo/Al2O3-SiO2 catalysts prepared by co-equilibrium deposition filtration: Characterization and catalytic behavior for the hydrodesulphurization of thiophene by John Vakros; Alexis Lycourghiotis; G.A. Voyiatzis; A. Siokou; Christos Kordulis (pp. 496-507).
Four CoMo catalysts supported on Al2O3-SiO2 mixed materials of varying SiO2 content (1.5, 10, 20 and 30% SiO2 w/w) were prepared following the co-EDF methodology. The catalysts were characterized using various techniques (BET, potentiometric mass titrations, XRD, DRS, XPS, LRS, TPR, TPD of ammonia and NO chemisorption). Two additional catalysts were prepared and characterized on two mixed supports, which contain 1.5 and 20% SiO2 w/w, following the conventional impregnation procedure. The hydrodesulphurization (HDS) activities of the catalysts studied were determined using thiophene as a probe molecule.The co-EDF catalysts were proved to be more active than the corresponding ones prepared following the conventional impregnation procedure. This was attributed to the relatively high dispersion of the Mo supported phase achieved by applying co-EDF. The following activity trend was obtained over the co-EDF catalysts, 20Si > 30Si > 1.5Si > 10Si, which indicates that the activity is maximized over the catalyst prepared on a mixed support containing 20% SiO2 w/w. This zigzag trend was explained in terms of two parameters, the ratio “tetrahedral (monomer) /octahedral (polymer) Mo species” and the amount of cobalt aluminate formed, both regulated by changing the composition of the mixed support.
Keywords: CoMo catalysts; Hydrotreatment; Silicoaluminas; Catalyst preparation; EDF; Mo-deposition; DRS; LRS; TPR; HDS
Transesterification of tributyrin with methanol over basic Mg:Zr mixed oxide catalysts by Joseph T. Kozlowski; Matthew T. Aronson; Robert J. Davis (pp. 508-515).
Two series of Mg:Zr mixed oxides, prepared by either co-precipitation or sol–gel synthesis, were characterized and evaluated in the base catalyzed transesterification of tributyrin with methanol. A co-precipitated Mg-rich mixed oxide catalyst with Mg:Zr 11:1 was approximately 300% more active than MgO on a surface area basis, whereas pure ZrO2 was inactive for the reaction. To explore the nature of the activity enhancement, samples were characterized by X-ray diffraction, N2 adsorption, CO2 adsorption microcalorimetry and DRIFTS of adsorbed CO2 and CH3OH. Although the sol–gel synthesis method provided better atomic level mixing of Mg and Zr, the resulting catalysts were not as effective as mixed oxides prepared by co-precipitation. The most active mixed oxide (Mg:Zr 11:1) exhibited a high initial heat of CO2 adsorption and modified modes of methanol adsorption compared to MgO. However, the CO2 adsorption capacity did not correlate to catalyst activity.
Keywords: Base catalysis; Transesterification; Carbon dioxide microcalorimetry; Methanol; Tributyrin; IR spectroscopy
N-doped ZrO2/TiO2 bimetallic materials synthesized in supercritical CO2: Morphology and photocatalytic activity by Rahima A. Lucky; Paul A. Charpentier (pp. 516-523).
A series of N- and N/Zr-doped titanium nanomaterials were synthesized via an acetic acid modified sol–gel route using supercritical carbon dioxide (scCO2) as both the synthesis and drying medium. Titanium isopropoxide (TIP), and triethylamine (TEA) w/wo zirconium propoxide precursors were reacted with acetic acid in a polycondensation reaction in scCO2. The effects of N and N/Zr doping on the morphology, phase structure, mean crystallite size, textural properties, thermal and crystallization behavior, and photocatalytic degradation of methylene blue was investigated. SEM and TEM analysis showed that pure titania formed nanofibers from TIP and acetic acid whereas the doped samples gave a flake-like structure. The SEM and TEM images showed that a porous material consisting of ca. 10–15nm crystals were formed. XPS spectra indicated that the N1s peak for both N-doped titania and Ti–Zr binary metal oxide were centered at 400eV, indicating effective doping of nitrogen in the TiO2 matrix. From the XRD analysis, it was observed that a small amount of nitrogen and zirconia inhibited the crystal growth, resulting in smaller crystallite materials. The BET analysis of the N2 isotherm data revealed that small amount of zirconia and nitrogen (0.4at%) increased the surface area. All synthesized doped samples gave superior photocatalytic degradation of methylene blue compared to P25. These results show that scCO2 is a new promising route to provide N- and N/Zr-doped advanced photocatalytic nanomaterials.
Keywords: ZrO; 2; modified TiO; 2; nanostructure; Sol–gel chemistry; Supercritical carbon dioxide; Characterization; Photocatalysis
Regeneration of a model NO X storage/reduction catalyst using hydrocarbons as the reductant by Meshari AL-Harbi; David Radtke; William S. Epling (pp. 524-532).
Regeneration of a model NO X storage and reduction (NSR) catalyst using hydrocarbons, H2, or CO as reducing agents was investigated. As previously shown, at low temperature, 200°C, H2 proved best, while both CO and hydrocarbons were found to poison Pt sites. At 250°C, again H2 was better but the decreased performance with CO and hydrocarbons was also due to slow kinetics and not solely as a result of Pt site poisoning. At T≥300°C, hydrocarbons were found to regenerate the catalyst as efficiently as CO and H2. Hydrocarbon steam reforming experiments were performed to investigate the improved performance at T≥300°C. Steam reforming did not occur with either dodecane or m-xylene below 450°C. Additionally, although propylene steam reforming occurred at 375°C, the small amount of H2 formed was insufficient for steam reforming to be the sole reason for improved regeneration. TPR experiments show that propylene was activated on the catalyst at T≥217°C and, under the conditions examined, the complete reduction of NO by propylene was achieved at 287°C. Furthermore, propylene was observed to reduce surface chemisorbed NO X species at T>200°C, with high rates by 264°C, with this activity ultimately resulting in the comparable performance with either CO or H2 at similar temperatures during NO X cycling experiments.
Keywords: NO; X; trap; NO; X; storage; Steam reforming; NO; X; reduction; Vehicle emissions
Ruthenium(0) nanoclusters stabilized by zeolite framework as superb catalyst for the hydrogenation of neat benzene under mild conditions: Additional studies including cation site occupancy, catalytic activity, lifetime, reusability and poisoning by Mehmet Zahmakıran; Tetsuya Kodaira; Saim Özkar (pp. 533-540).
The hydrogenation of arenes is an ubiquitous chemical transformation used in both the petrochemical and specialty industry and important for the generation of clean diesel fuels. In a recent communication (M. Zahmakıran, S. Özkar, Langmuir 24 (2008) 7065) we have reported the preliminary results for the unprecedented catalytic activity of zeolite framework stabilized ruthenium(0) nanoclusters in the hydrogenation of neat benzene (TOF≈1040mol benzene/molRu·h) under mild conditions (22°C, 40±1psig H2). Here we report the work in full details, including (i) far-infrared spectroscopic investigation of ruthenium(III)-exchanged-zeolite and zeolite framework containing ruthenium(0) nanoclusters, which showed that ruthenium(0) nanoclusters formed inside the cavities of zeolite by retaining its framework intact, (ii) the collection of wealthy kinetic data to demonstrate the effect of ruthenium loading, temperature, and catalyst concentration on the catalytic activity of zeolite framework stabilized ruthenium(0) nanoclusters in the hydrogenation of neat benzene, (iii) probing the isolability, bottleability and reusability of zeolite framework stabilized ruthenium(0) nanoclusters; (iv) poisoning experiments performed by using tricyclohexylphosphine (P(C6H11)3) and 4-ethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane (P(OCH2)3CCH2CH3) in order to answer the most classical question whether the ruthenium(0) nanoclusters exist on the surface or inside the cavities of the host material; (v) a summary section detailing the main findings for the “green chemistry”.
Keywords: Zeolite; Ruthenium; Nanoclusters; Hydrogenation; Benzene; Green chemistry
Au NPs on anionic-exchange resin as catalyst for polyols oxidation in batch and fixed bed reactor by Alberto Villa; Carine E. Chan-Thaw; Laura Prati (pp. 541-547).
Commercial weak basic anion resin (Dowex M-43) was used as support for gold nanoparticles (Au NPs). Au NPs stabilized by tetrakishydroxypropylphosphonium chloride (THPC) were immobilized on the support (AuTHPC/Dowex M-43). In alternative, Au NPs were generated by adsorbing NaAuCl4 on the resin and then reduced by NaBH4 (Auads/Dowex M-43). These catalysts were tested in the liquid phase oxidation of glycerol in a glass batch reactor: AuTHPC/Dowex M-43 showed better activity than Auads/Dowex M-43. The higher activity can be attributed to the smaller Au nanoparticles in AuTHPC/Dowex M-43 than Auads/Dowex M-43. Moreover AuTHPC/Dowex M-43 was tested in the glycerol oxidation in a fixed bed reactor showing good stability during the reaction time. All the catalysts have been characterised by TEM, FT-IR and XPS.
Keywords: Gold; Resin; Liquid phase oxidation; Batch reactor; Fixed bed reactor
Removal of Reactive Black 5 azo dye from aqueous solutions by catalytic oxidation using CuO/Al2O3 and NiO/Al2O3 by Corina Bradu; Ligia Frunza; Nicoleta Mihalche; Sorin-Marius Avramescu; Marian Neaţă; Ion Udrea (pp. 548-556).
CuO/Al2O3 and NiO/Al2O3 catalysts prepared by incipient wetness impregnation were used for the oxidation of Reactive Black 5 (RB5) in aqueous solution. Removal of the dye was assessed by High Performance Liquid Chromatography (HPLC) and Total Organic Carbon (TOC) measurements and the generation of the hydroxyl radicals in the process was evaluated by chemiluminescence measurements. To put in evidence the interaction RB5 – catalyst and the surface species formed onto catalysts during the oxidation, Diffuse Reflectance Infrared Fourier Transform (DRIFT) analysis was performed. A different behavior of the two catalytic systems was revealed by the comparative analysis of the data obtained from the adsorption and oxidation tests. Only CuO/Al2O3 was effective in the RB5 degradation, NiO/Al2O3 acted as a simple adsorbent. In the presence of CuO/Al2O3, at H2O2 concentration of 40mM the azo dye was totally eliminated from both solution and catalyst surface after 4h, with a mineralization degree higher than 90%. However, a strong inhibition of the catalytic oxidation of RB5 was observed in the presence of phosphate ions. In the conditions of hydrogen peroxide excess, the rate equation in the case of copper catalyst was simply expressed by a pseudo-first order equation and the model was found to fit well the data. The amount of copper leached from catalyst during the oxidation process was only 1.0–1.6% per cycle leading to the conclusion that the decrease of the dye mineralization with the number of cycles has to be explained mostly by the surface covering with the reaction products, at least to a certain extent.
Keywords: Azo dye removal; Catalytic oxidation; Advanced oxidation processes; Reactive Black 5
Pivotal role of fluorine in enhanced photocatalytic activity of anatase TiO2 nanosheets with dominant (001) facets for the photocatalytic degradation of acetone in air by Quanjun Xiang; Kangle Lv; Jiaguo Yu (pp. 557-564).
Surface-fluorinated anatase TiO2 nanosheets with dominant {001} facets were fabricated by a simple hydrothermal route in a Ti(OC4H9)4-HF-H2O mixed solution. The atomic ratios of fluorine to titanium ( RF) exhibit an obvious influence on the structures and photocatalytic activity of TiO2 samples. In the presence of HF, TiO2 nanosheets can be easily obtained. With increasing RF, the relative anatase crystallinity, average crystallite size, pore size and percentage of exposed {001} facets increase, contrarily, BET specific surface areas decrease. All fluorinated TiO2 nanosheets exhibit much higher photocatalytic activity than Degussa P-25 TiO2 (P25) and pure TiO2 nanoparticles prepared in pure water due to the synergistic effect of surface fluorination and exposed {001} facets on the photoactivity of TiO2. Especially, at RF=1, the fluorinated TiO2 nanosheet exhibits the highest photocatalytic activity, and its photoactivity exceeds that of P25 by a factor of more than nine times.
Keywords: TiO; 2; nanosheets; {0; 0; 1} facets; Hydrothermal route; Surface fluorination; Photocatalytic activity
Photocatalytic reduction of CO2 using H2 as reductant over ATaO3 photocatalysts (A=Li, Na, K) by Kentaro Teramura; Shin-ichi Okuoka; Hideo Tsuneoka; Tetsuya Shishido; Tsunehiro Tanaka (pp. 565-568).
ATaO3 (A=Li, Na, K) compound oxides exhibit photocatalytic activity for the reduction of CO2 in the presence of H2. Only CO gas was generated over all samples under photoirradiation. The photocatalytic activity was higher in the order corresponding to KTaO3, NaTaO3 and LiTaO3 (LiTaO3>NaTaO3>KTaO3). The order of the photocatalytic activities was consistent with that of the E g (optical gap) values. After 24h of photoirradiation, the amount of evolved CO reached 0.42μmolg−1 over LiTaO3. TPD experiments indicated that the broad peak which is assigned to chemisorbed CO2 gas was observed at 573K in the case of LiTaO3. On the contrary, there was no peak in the spectra of NaTaO3 and KTaO3. The amount of evolved CO gas almost strongly depends on the amount of chemisorbed CO2 in the case of ATaO3 (A=Li, Na, K). In addition, the photocatalytic activity increased with increasing the calcination temperature of LiTaO3. This means that a smooth charge separation in a LiTaO3 photocatalyst and chemisorption of CO2 on the surface contribute to effective reduction of CO2 in the presence of H2.
Keywords: Photocatalysis; CO; 2; reduction; Solid base
The effect of particle shape on the activity of nanocrystalline TiO2 photocatalysts in phenol decomposition. Part 2: The key synthesis parameters influencing the particle shape and activity by Nándor Balázs; Dávid F. Srankó; András Dombi; Pál Sipos; Károly Mogyorósi (pp. 569-576).
Nanosized TiO2 photocatalysts were synthesized via hydrogen–air flame hydrolysis by using two slightly different, home made diffusion flame burners (Burners A and B). Titanium(IV) chloride vapor was introduced into the flame via bubbling dry air throughout the precursor liquid. X-ray diffraction (XRD) measurements revealed that the particles are anatase–rutile mixtures with a phase composition ranging from 98:2 to 57:43 anatase to rutile weight ratio. The hydrogen–oxygen molar ratio in the flame, as well as the precursor vapor feeding rate were found to be the key parameters which determine both particle structure and morphology. Spherical and polyhedral particles with significantly varying photocatalytic activity were produced in Burner A by increasing the precursor vapor feeding rate at a constant hydrogen–oxygen molar ratio, the photocatalytic activity increased for samples synthesized. The differences in particle size, specific surface area and anatase–rutile composition were found to be marginal but the particle shape changed from spherical to polyhedral by increasing that parameter. From this, it was concluded that particle shape plays an important role in photocatalytic activity, the faceted particles are better photocatalysts than spherical ones. With Burner B, predominantly polyhedral particles were obtained, some of them with further improved photocatalytic activity. Synthesis parameters for obtaining maximum activity have been established for both burners. Our results prove, that bare (undoped) TiO2 photocatalysts with photocatalytic activity significantly better than that of P25 can routinely be prepared and their performance optimized via the fine-tuning of the synthesis parameters employed.
Keywords: Titania; Anatase; Rutile; Nanoparticles; Phenol decomposition; Photocatalysis; Flame hydrolysis; Shape dependence
The effect of particle shape on the activity of nanocrystalline TiO2 photocatalysts in phenol decomposition. Part 3: The importance of surface quality by K. Mogyorósi; N. Balázs; D.F. Srankó; E. Tombácz; I. Dékány; A. Oszkó; P. Sipos; A. Dombi (pp. 577-585).
Bare TiO2 photocatalysts made up of polyhedral nanoparticles have been prepared by flame hydrolysis. In order to obtain deeper understanding of the interplay between the properties determining the photocatalytic performance, surface, aggregation and photocatalytic properties have been analyzed and compared. The aggregation of nanoparticles in aqueous solution of NaCl was determined by dynamic light scattering (DLS) technique. The average hydrodynamic diameters of the aggregates investigated under environmentally relevant conditions do not differ significantly in the pH range of 5–6. Zeta potential measurements were also done during DLS analysis, which revealed remarkably low pHIEP values for our flame made samples comparing to the commercial titanias. Furthermore an explicit correlation between the isoelectric points and the synthesis parameters was revealed. O 1s XP spectra for the high activity samples were also recorded and interpreted. Oxygen consumption experiments were used to test the photocatalytic activity in suspensions. The method was found to be not only rapid and inexpensive but also reasonably reproducible. Normalizing the oxygen consumption rate with the specific surface area of the sample and the concentration of the suspension, a good correlation could have been found with the traditionally determined photocatalytic activity. HPLC measurements were used to study the degradation mechanism of phenol via determining the concentration profile of various dihydroxy intermediates, i.e., hydroquinone (HQ) and pyrocatechol (PC). The quality of the photocatalyst strongly affects the maximum ratio of HQ:PC during the photocatalytic degradation process. For our catalysts higher pyrocatechol concentrations were measured than for Degussa P25. TOC measurements were used to follow the complete mineralization. Using our best photocatalysts (e.g., anatase:rutil ratio of 82:18 and mostly polyhedral particles, with 21m2/g BET surface area), phenol concentration decreased faster than for P25, however, the mineralization rate was somewhat lower. This can be attributed to the lower adsorption capacity of our polyhedral particles against PC and carboxylate containing intermediates formed during the more advanced stages of decomposition. These data elucidate, that hydrophilicity, O2-consumption properties and adsorption/complexation of the target compounds and their degradation products are equally important parameters in determining the photocatalytic performance of catalysts, which otherwise possess similar material properties.
Keywords: Titania; Anatase; Rutile; Nanoparticles; Phenol decomposition; Heterogeneous photocatalysis; Flame hydrolysis; Shape dependence; Dynamic light scattering; Isoelectric point; X-ray photoelectron spectroscopy; Oxygen consumption; Complete mineralization; Aromatic intermediates