Applied Catalysis B, Environmental (v.88, #3-4)
Editorial Board (i).
Contents Continued (I-II).
IFC Editorial Board (CO2).
Simultaneous oxidation of carbon black and volatile organic compounds over Ru/CeO2 catalysts by Samer Aouad; Edmond Abi-Aad; Antoine Aboukaïs (249-256).
Ru/CeO2 catalysts with Ru loading of 1–5 wt.% were prepared by wet impregnation from aqueous ruthenium (III) nitrosyl nitrate solution and activation with an air flow at 600 °C for 4 h. This activation resulted in a considerable reactivity for the catalytic oxidation of carbon black (CB) (T 50% ∼350 °C “tight contact” mixtures and T 50% ∼515 °C “loose contact” mixtures) and volatile organic compounds (VOCs) (T 50% = 175 °C for propene, T 50% = 215 °C for toluene). When carbon black oxidation was conducted under “propene (6000 ppm) + air” or “toluene (2000 ppm) + air” flow, the elimination of an important part of CB was observed at relatively low temperatures comparing to its elimination under pure air flow. These temperatures correspond to the total oxidation of the VOC present in the reactant gases. Carbon black total elimination was also investigated under isotherm conditions in the presence and in the absence of propene. Total elimination occurred during shorter times when combustion was performed under propene. TPR study showed that ruthenium species present in the catalysts after activation reduces at relatively low temperatures (<100 °C) and that from a Ru loading of 1.5 wt.%, agglomerated ruthenium oxide was formed and that this latter is more difficult to reduce (>100 °C).
Keywords: Carbon black; Catalysts; Ruthenium; TPR; XRD; VOC;
Impregnated carbon based catalyst for protection against carbon monoxide gas by Beer Singh; Amit Saxena; Avanish Kumar Srivastava; R. Vijayaraghavan (257-262).
Activated carbon based palladium impregnated catalyst (Pd/C) was prepared for the reactive removal of carbon monoxide (CO) gas under ambient air conditions. For this, active carbon of 1250 m2/g surface area was impregnated with palladium salt to get Pd/C catalyst, containing palladium from 4.0 to 8.0% (w/w). Catalytic efficiency of the catalyst against CO gas was determined under dynamic conditions by passing CO–air mixture to the fixed bed of the Pd/C catalyst. Results indicated that Pd/C catalyst was continuously adsorbing and actively removing CO gas during the course of the palladium catalyzed reaction, i.e., CO + 1/2 O2 → CO2 and was found capable of providing excellent protection against CO gas. Moisture content (humidity) of inlet CO–air mixture indicated it to be an important factor affecting the CO removal efficiency of the catalyst, as an increase in humidity after the CO breakthrough resulted in to the activation of the catalyst due to the generation of hydroxyl groups and enhanced protection by the regeneration of the catalyst. Study indicated that Pd/C catalyst works as a catalytic converter, i.e., the continuous conversion of CO to CO2 using atmospheric oxygen and moisture. In order to determine the shelf life, the Pd/C catalyst was also evaluated for its performance after accelerated ageing at 70 °C and 50% relative humidity (RH) for 3.75 and 7.5 months. The catalyst was found to be working efficiently for 3.75 months but after 7.5 months it could not provide 100% protection against CO gas, however, the same catalyst started giving 100% protection after regeneration. Hence, studies indicated the Pd/C catalyst to be a promising catalyst for the reactive removal of CO gas in enclosed spaces/compartments, coal mines, fire accidents and for getting the protection for longer duration under ambient air conditions.
Keywords: Palladium; Catalyst; Carbon monoxide; Oxidation; Impregnation; Reproducibility;
Application of NO X storage/release materials based on alkali-earth oxides supported on Al2O3 for high-temperature diesel soot oxidation by A.L. Kustov; M. Makkee (263-271).
Alkali-earth oxides and nitrates supported on alumina were studied as model systems for NO X storage/release. Their impact on the high-temperature soot oxidation has been investigated. The stability of surface nitrates and temperature of NO X release increase parallel to the basicity of the cation. The presence of soot decreases the temperature of NO X release. The storage capacity depends on the several factors, such as basicity, dispersion of the cation, and pre-treating conditions. Adsorption of NO with O2 at 200 °C leads to the formation of surface nitrates that mainly exist as ionic nitrates. Stored nitrates contribute to the soot oxidation and assist to lower the temperature of soot oxidation up to almost 100 °C. In the presence of only NO X storage material the efficiency of NO X utilization is, however, quite low, around 30%. Therefore, the presence of an oxidation catalyst is essential to increase the efficiency of NO X utilization for soot oxidation up to 140% and selectivity towards CO2. A combination of oxidation catalyst with NO X storage materials enables to lower the temperature of soot oxidation more than 100 °C for the Sr- and Ca-based systems.
Keywords: Soot oxidation; Diesel particulate filter; NO X storage/release; Alkali-earth catalysts;
A comparative study of water gas shift reaction over gold and platinum supported on ZrO2 and CeO2–ZrO2 by Marta Boaro; Michela Vicario; Jordi Llorca; Carla de Leitenburg; Giuliano Dolcetti; Alessandro Trovarelli (272-282).
In this study platinum- and gold-based catalysts supported on ZrO2 and ceria–zirconia solid solution have been characterized by several techniques (TPR, XRD, BET, HRTEM) and tested in the water gas shift (WGS) reaction under feed conditions typical of an autothermal reformer outlet. Platinum and gold catalysts behave differently especially in the range of 423–513 K, with gold being superior than platinum. The possibility of modifying the redox and structural characteristics of zirconia with the insertion of ceria allowed us to conclude that the bulk redox properties of the support play a secondary role, while the key parameter for an active WGS catalyst is the nature of metal support interface. This, in turn, depends on the metal particle distribution and on the structural and morphological properties of support. It has been found that the synergism between precious metals and support can be designed with an appropriate choice of the parameters of synthesis and the characteristics of support.
Keywords: Gold; Platinum; Zirconia; Ceria–zirconia; WGSR; Hydrogen;
Inactivation of Bacteria E. coli and photodegradation of humic acids using natural sunlight by Ana I. Gomes; João C. Santos; Vítor J.P. Vilar; Rui A.R. Boaventura (283-291).
In this work, the disinfection of bacteria Escherichia coli and degradation of humic acids, using sunlight, sunlight + TiO2 (Degussa P25) in suspension or TiO2 supported on Ahlstrom paper (NW10) fixed around concentric tubes inside the photoreactor, were investigated in a pilot plant. The inactivation of bacteria E. coli proved to be more efficient (only 1 kJUV/L for 5-log decrease in concentration) when using sunlight and TiO2 in suspension. However, true disinfection was not achieved under the conditions reported in this work. A first-order model was able to fit the photocatalytic deactivation of E. coli ([TiO2] = 50 mg/L) with an inactivation rate constant of 8.21 L/kJ. A Langmuir–Hinshelwood-like model was successfully applied for modelling photolysis and supported-TiO2 photocatalysis of bacteria E. coli, considering an initial latency period, a classical log-linear behaviour and a tail region. The effect of the flow rate between 5 and 15 L/min was negligible in the inactivation of E. coli in the presence of sunlight and supported TiO2. The inactivation rate constant increased with the initial concentration of E. coli. Almost no bacterial regrowth was observed in dark conditions during 24 h after illumination of E. coli suspension until complete deactivation. The humic acids (HA) degradation was also investigated by solar photocatalysis with suspended and supported TiO2 and exposure to sunlight-only, in a CPC photoreactor. Supported-TiO2 photocatalysis of HA originated 70% concentration reduction after Q UV ≈ 14 kJ/L, whereas only 20% reduction was obtained by photolysis and slurry photocatalysis. First-order kinetic constants of 0.088 and 0.010 L/kJ were obtained, respectively, for suspended and supported TiO2.
Keywords: Solar disinfection; Photocatalysis; Escherichia coli; Humic acids;
Performance of a catalytically activated ceramic hot gas filter for catalytic tar removal from biomass gasification gas by Manfred Nacken; Lina Ma; Steffen Heidenreich; Gino V. Baron (292-298).
Silicon carbide-based filter elements were catalytically activated to provide filter elements for catalytic tar removal from biomass-derived syngas. The filter element support was coated with CeO2, CaO–Al2O3 and MgO with a specific surface of 7.4, 15.9 and 21.9 m2/g synthesized by exo-templating with activated carbon. Doping of a MgO coated filter element with 60 wt% NiO has led to an increase of the specific surface from 0.15 to 0.21 m2/g, whereas in case of a MgO–Al2O3 coated filter element a decrease from 1.18 to 0.91 m2/g was found. An increase of the NiO loading from 6 to 60 wt% on a MgO coated filter element resulted in an increase of the naphthalene conversion from 91 to 100% at 800 °C and a face velocity of 2.5 cm/s at a naphthalene concentration of 5 g/Nm3 in model biomass gasification gas. In case of a MgO–Al2O3 coated filter element with 60 wt% NiO in addition to complete naphthalene conversion in the absence of H2S, a higher conversion of 66% was found in the presence of 100 ppmv H2S compared to 49% of the MgO–NiO coated filter element. After scaling up of the catalytic activation procedure to a 1520 mm long filter candle, which shows an acceptable differential pressure of 54.9 mbar, 58 and 97% naphthalene conversion was achieved in the presence and absence of H2S, respectively. The calculated WHSV value of 209.6 Nm3 h−1 kg−1 indicates the technical feasibility of a further increase of the catalytic performance by an increase of the NiO loading.
Keywords: Catalytic filter; MgO; NiO; Tar reforming catalyst; Biomass gasification;
Screening of Fe–BEA catalysts for wet hydrogen peroxide oxidation of crude olive mill wastewater under mild conditions by Wahiba Najjar; Samia Azabou; Sami Sayadi; Abdelhamid Ghorbel (299-304).
A series of Fe–BEA catalysts, differing in the amount of iron have been characterized by XRD, BET surface area, UV–vis spectroscopy and chemical analysis. The zeolite samples have been tested as heterogeneous catalysts for the wet hydrogen peroxide oxidation of crude olive mill wastewaters (OMW) under very mild conditions (at 28 °C and atmospheric pressure). All experiments were performed on a laboratory scale set-up.BSE-1/3 catalyst with a moderate Fe content (Fe/Al = 1.19) showed the best results in terms of catalytic activity and loss of active species into the aqueous solutions. The stability of Fe species has been shown to be strongly dependent on the Fe environment into the zeolite framework.Over the selected catalyst, application of catalytic procedure on diluted OMW solution permitted high removal efficiencies of pollutants. The process produces a removal capacity of 28% of total organic carbon (TOC), 40% of total phenols, 30% of chemical oxygen demand (COD) and 59% of colour, just after 12 h. 5-Day biochemical oxygen demand (BOD5), and toxicity towards the bioluminescent bacteria Vibrio fischeri were selected to follow the performance of this process in terms of reducing the ecotoxicity of OMW. Results showed an increase in the biodegradability of the treated sample and a decrease of the microtoxicity from 100% to 70% load towards V. fischeri.Occurrence of small catalyst deactivation by carbonaeous during the oxidation reaction was observed through scanning electron microscopy (SEM) and elemental analysis.
Keywords: BEA zeolite; Catalytic wet hydrogen peroxide oxidation; Iron; Olive mill wastewater;
Effects of iron and cerium in La1−y Ce y Co1−x Fe x O3 perovskites as catalysts for VOC oxidation by B. Levasseur; S. Kaliaguine (305-314).
Perovskite-type mixed oxides La1−y Ce y Co1−x Fe x O3 with high specific surface area were prepared by reactive grinding. These catalysts were characterized by N2 adsorption, X-ray diffraction, oxygen storage capacity (OSC), H2-temperature-programmed reduction (TPR-H2), O2-, and CH3OH-temperature-programmed desorption (TPD). The catalytic performance of the samples for volatile organic compounds (VOC), CH3OH, CO and CH4 oxidation was evaluated. Cerium allows an enhancement of the reducibility of the B-site cations in perovskite structure during OSC and TPR-H2 and an increase in the amount of β-O2 desorbed during TPD-O2. As opposed to cerium, the addition of iron in the perovskite structure causes a drop in B-site cations reducibility and a decrease of the oxygen mobility in the bulk. As a consequence, the catalytic activity in VOC oxidation is enhanced by introduction of cerium and weakened by iron in the lattice.
Keywords: Perovskite; Iron; Cerium; VOC oxidation; Thermodesorption experiments; Electronegativity; Carbonates;
Carbon nanotube-supported Pd–ZnO catalyst for hydrogenation of CO2 to methanol by Xue-Lian Liang; Xin Dong; Guo-Dong Lin; Hong-Bin Zhang (315-322).
A type of Pd–ZnO catalysts supported on multi-walled carbon nanotubes (MWCNTs) were developed, with excellent performance for CO2 hydrogenation to methanol. Under reaction conditions of 3.0 MPa and 523 K, the observed turnover-frequency of CO2 hydrogenation reached 1.15 × 10−2 s−1 over the 16%Pd0.1Zn1/CNTs(h-type). This value was 1.17 and 1.18 times that (0.98 × 10−2 and 0.97 × 10−2 s−1) of the 35%Pd0.1Zn1/AC and 20%Pd0.1Zn1/γ-Al2O3 catalysts with the respective optimal Pd0.1Zn1-loading. Using the MWCNTs in place of AC or γ-Al2O3 as the catalyst support displayed little change in the apparent activation energy for the CO2 hydrogenation, but led to an increase of surface concentration of the Pd0-species in the form of PdZn alloys, a kind of catalytically active Pd0-species closely associated with the methanol generation. On the other hand, the MWCNT-supported Pd–ZnO catalyst could reversibly adsorb a greater amount of hydrogen at temperatures ranging from room temperature to 623 K. This unique feature would help to generate a micro-environment with higher concentration of active H-adspecies at the surface of the functioning catalyst, thus increasing the rate of surface hydrogenation reactions. In comparison with the “Parallel-type (p-type)” MWCNTs, the “Herringbone-type (h-type)” MWCNTs possess more active surface (with more dangling bonds), and thus, higher capacity for adsorbing H2, which make their promoting action more remarkable.
Keywords: Carbon nanotubes; CNT-supported Pd–ZnO catalyst; CO2 hydrogenation; Methanol synthesis;
Immobilization of hydrothermally produced TiO2 with different phase composition for photocatalytic degradation of phenol by Roberto Scotti; Massimiliano D’Arienzo; Franca Morazzoni; Ignazio Renato Bellobono (323-330).
Hydrothermally produced TiO2 powders with different phase composition (anatase, rutile and mixed phase) were immobilized on glass fibers and tested in the phenol mineralization process. Both H2O2 and O2 were used as oxygen donors, and their performances were compared with those of the same TiO2 samples as slurries.The catalytic properties of the immobilized different crystalline phases, rutile and anatase, show the same trend as the slurry samples: pure rutile displays the highest catalytic efficiency in the presence of H2O2, while samples containing anatase improve the photodegradation efficacy with O2. It was suggested that the stability of the photogenerated electron–hole couple allows high activity of rutile in the presence of H2O2, while the relevant oxygen chemisorption on anatase causes high catalytic activity in the presence of O2. A four parameters kinetics model shows that both reaction steps, the phenol degradation and the mineralization of the intermediates, are photoactivated by TiO2.Photoactivity of the coated glass fibers is generally lower than that of slurries, even if their efficiencies are almost comparable when the oxidation is performed by H2O2, while much lower when the oxygen donor is O2. As a matter of fact, the morphology of immobilized catalysts shows the presence of chestnut burr aggregates of large rutile crystalline rods on the glass fiber, which are much less compact than the aggregates of small anatase particles. This preserves rutile surface area from the coarsening effects; thus, when rutile is the more active species, as in the presence of H2O2, the photocatalytic activity is less affected by immobilization.
Keywords: Photocatalysis; Rutile; Anatase; Hydrothermal; Phenol mineralization;
Montmorillonite, vermiculite and saponite based porous clay heterostructures modified with transition metals as catalysts for the DeNOx process by Lucjan Chmielarz; Piotr Kuśtrowski; Zofia Piwowarska; Barbara Dudek; Barbara Gil; Marek Michalik (331-340).
Porous clay heterostructures (PCHs) were synthesized from natural montmorillonite and vermiculite as well as synthetic saponite using the surfactant directed method. The direct synthesis of PCHs from saponite and montmorillonite was possible, while the pre-treatment of parent vermiculite with acids was necessary prior to the intercalation step. The PCH samples were characterized with respect to their composition (EPMA), structure (XRD, UV–vis-DRS), texture (BET), surface acidity (FT-IR) and chemical nature of the deposited transition metal species (UV–vis-DRS). Porous clay heterostructures as well as their derivatives modified by deposition of transition metal (Cu, Fe) oxides were tested as catalysts for the DeNOx process. The transition metal containing PCH samples were found to be active, selective and stable catalysts of this process. Their catalytic performance depended on the kind of the parent clay used for the PCH synthesis as well as deposited transition metals.
Keywords: Porous clay heterostructures (PCHs); Montmorillonite; Vermiculite; Saponite; DeNOx; Ammonia;
Activated carbon and ceria catalysts applied to the catalytic ozonation of dyes and textile effluents by P.C.C. Faria; J.J.M. Órfão; M.F.R. Pereira (341-350).
The application of catalytic ozonation processes for the decolourisation and mineralisation of coloured aqueous solutions was studied. One acid azo dye, CI Acid Blue 113, and two reactive dyes, CI Reactive Yellow 3 and CI Reactive Blue 5, with azo and anthraquinone chromophores, respectively, were used as representative textile dyes. The catalytic activities of activated carbon, cerium oxide and a ceria-activated carbon composite were evaluated in the removal of the selected dyes. In all cases, with an initial dye concentration of 50 mg/L, a complete decolourisation was achieved by single ozonation in short reaction times (less than 10 min). The ceria-activated carbon composite allowed the highest removal of total organic carbon. For dye concentrations of 50 mg/L, mineralisation degrees of 100%, 98% and 97% were achieved with the composite after 2 h of reaction, respectively for CI Reactive Blue 5, CI Acid Blue 113 and CI Reactive Yellow 3. The activity of the catalyst containing cerium was affected by the presence of carbonate and bicarbonate ions due to their scavenging effect towards hydroxyl radicals; for example the mineralisation degree of CI Reactive Blue 5 (C 0 = 300 mg/L) after 120 min of reaction was only 63%, contrasting with the value of 85% obtained in the absence of carbonates. All the catalytic systems were evaluated in the treatment of textile effluents, collected before or after conventional biological treatment. Catalytic ozonation was proven to be effective when used as tertiary treatment for bio-treated effluents.
Keywords: Catalytic ozonation; Activated carbon; Mineralisation; Cerium oxide; Dyes; Textile wastewater;
A crucial role of O2 − and O2 2− on mayenite structure for biomass tar steam reforming over Ni/Ca12Al14O33 by Chunshan Li; Daisuke Hirabayashi; Kenzi Suzuki (351-360).
Newly synthesized nickel calcium aluminum catalysts (Ni/Ca12Al14O33) were tested in a fixed bed reactor for biomass tar steam reforming, toluene as tar destruction model compound. Four catalysts (Ni/Ca12Al14O33) were prepared with Ni loading amount from 1, 3, 5 to 7 wt%, even 1% loading catalyst also showed excellent performance. Catalysts aged experiments in the absence (60 h on stream) and presence of H2S were characterized by BET, X-ray diffraction (XRD), and Raman spectra. It was observed that Ni/Ca12Al14O33 showed excellent sustainability against coke formation due to the “free oxygen” in the catalysts. It also exhibited higher H2S-poisoning resistance property compared to the commercial catalysts Ni/Al2O3 (5%) and Ni/CaO0.5/MgO0.5. Raman spectra revealed that “free oxygen O2 − and O2 2−” in the structure of the catalysts could be substituted by sulfur then protected Ni poisoning on some degree, but reactivation experiments by O2 flowing showed that the sulfide Ni/Ca12Al14O33 was difficult to completely restore, incorporation of sulfur in the structure only partly regain by O2. The kinetic model proposes, as generally accepted, a first-order reaction for toluene with activation energy of 82.06 kJ mol−1 was coincident with the literature data. The Ni/Ca12Al14O33 catalyst was effective and relative cheap, which may be lead to reduction in the cost of hot gas cleaning process.
Keywords: Biomass tar; Toluene steam reforming; Ni/Ca12Al14O33; Coke-resistance; Sulfur poisoning;
Steam reforming of methane under water deficient conditions over gadolinium-doped ceria by Bertha Mosqueda; Jamil Toyir; Akim Kaddouri; Patrick Gélin (361-367).
The catalytic properties of gadolinium-doped ceria (CGO) in methane steam reforming were studied. Catalytic tests were carried out between 750 and 900 °C, for H2O/CH4 ratios varying between 0.1 and 1, pretreated in H2O/N2, N2 and H2/N2. Above 800 °C, slight deactivation with time on stream was observed except for the H2-pretreated sample. Surface area measurements, O2 adsorption at room temperature and O2-temperature programmed oxidation experiments were performed after catalytic testing. Changes in both surface area and redox properties of CGO were observed and related to catalytic deactivation. Hydrogen is thought to play a key role in catalytic activity and deactivation process.
Keywords: Gadolinium-doped ceria; SOFC; Methane; Gradual internal steam reforming; Carbon deposition; Deactivation;
Hollow core/mesoporous shell carbon capsule as an unique cathode catalyst support in direct methanol fuel cell by Jung Ho Kim; Baizeng Fang; Suk Bon Yoon; Jong-Sung Yu (368-375).
Hollow core mesoporous shell (HCMS) carbon has been explored for the first time as a cathode catalyst support in direct methanol fuel cells (DMFCs). The HCMS carbon consisting of discrete spherical particles possesses unique structural characteristics including large specific surface area and mesoporous volume and well-developed interconnected void structure, which are highly desired for a cathode catalyst support in low temperature fuel cells. Significant enhancement in the electrocatalytic activity toward oxygen reduction reaction has been achieved by the HCMS carbon-supported Pt nanoparticles compared with carbon black Vulcan XC-72-supported ones in the DMFC. In addition, much higher power was delivered by the Pt/HCMS catalysts (i.e., corresponding to an enhancement of ca. 91–128% in power density compared with that of Pt/Vulcan), suggesting that HCMS carbon is a unique cathode catalyst support in direct methanol fuel cell.
Keywords: Hollow core mesoporous shell carbon; Electrocatalyst; Catalyst support; Oxygen reduction reaction; Direct methanol fuel cell;
Investigation of the steam reforming of a series of model compounds derived from bio-oil for hydrogen production by Xun Hu; Gongxuan Lu (376-385).
In this study, steam reforming of acetic acid, ethylene glycol, acetone, ethyl acetate, m-xylene, and glucose, which were representative of the main components in bio-oil, were performed to investigate the feasibility of these feedstocks for hydrogen production. The effects of reaction temperature and steam to carbon ratios (S/C) on steam reforming as well as coke formation tendency of the bio-oil components in the presence and absence of steam were investigated in a detailed manner. Low reaction temperature and S/C led to low steam reforming efficiency, and consequently decomposition or degradation of the feedstocks dominated, resulting in large amounts of by-products. Increasing reaction temperature and S/C increased the steam reforming rates and the partial pressure of steam on catalyst surface, favoring conversion of the feedstocks and removal of the by-products. Coke formation rates of the feedstocks during the long-term experiments decreased in the following orders: glucose ≫ m-xylene > acetone > ethyl acetate > ethylene glycol > acetic acid. Decomposition or polymerization of the feedstocks to carbonaceous deposit was the main route for coke formation in glucose, m-xylene, and acetone reforming, while the large amounts of by-products such as ethylene, CO, or acetone were main sources of coke in the steam reforming of ethyl acetate, ethylene glycol, and acetic acid.
Keywords: Steam reforming; Hydrogen; Bio-oil; Coke formation;
Synthetic gas bench study of a natural gas vehicle commercial catalyst in monolithic form: On the effect of gas composition by Marc Salaün; Anita Kouakou; Stéphanie Da Costa; Patrick Da Costa (386-397).
With growing concerns about global environmental and increased focus on population health is renewed interest in transportation sector. The challenge is to find and develop cost effective ways to improve urban air quality without scarifying economy. The natural gas, as fuel, constitutes an alternative to the traditional fuels because its impact on the reduction of the global warming impact is consequent compared to the traditional fuels such as gasoline. This study deals with a study of NGV’s catalysts. Natural gas vehicles’ catalysts were characterized by XPS, STEM in order to determine the various active phases. The results of characterization showed that the palladium oxidized Pd2+ was the principal active site. The experimental runs were carried out close to the real operating conditions using a sample of monolith. Numerous reactions were identified, such as NO reduction by hydrogen, carbon monoxide at low temperature and methane at high temperature. Moreover, methane reforming and water-gas shift were clearly found on commercial system. The influence of each reaction on the kinetics behaviour of the whole mixture makes difficult to uncouple the different reactions of oxidations and reductions, because the rate of these reactions was highly dependant on the reactant present in the automobile exhaust gases as well as their relative concentration. To identify each involved reaction in NGV TWC process, we remove alternatively reducing agents or oxidizing agents.
Keywords: NGV; TWC; Commercial catalyst; Palladium; rhodium;
Abatement of organics and Escherichia coli by N, S co-doped TiO2 under UV and visible light. Implications of the formation of singlet oxygen (1O2) under visible light by J.A. Rengifo-Herrera; K. Pierzchała; A. Sienkiewicz; L. Forró; J. Kiwi; C. Pulgarin (398-406).
Nitrogen and sulfur co-doping has been achieved in the commercial TiO2 nanoparticles of anatase TKP 102 (Tayca) by grinding it with thiourea and calcinating at 400 °C. The successful substitutional N-doping and cationic/anionic S-doping were validated by XPS measurements. Diffuse reflectance spectroscopy (DRS) showed a marked broadening of the absorption spectrum of the doped material towards the visible range.Phenol and dichloroacetate (DCA) oxidation and Escherichia coli inactivation were achieved under UV illumination using the N, S co-doped TiO2 powders. Electron spin resonance (ESR) spin-trapping experiments showed that under UV light irradiation, the •OH radicals were the main species responsible for photo-degradation of phenol and E. coli abatement. Photo-degradation of DCA was found to be due a direct interaction of the TiO2 valence band holes ( h VB + ) with the DCA molecules.Moreover, under visible light (400–500 nm) illumination of N, S co-doped TiO2 a complete inactivation of E. coli bacteria was observed. In contrast, under such conditions, phenol was only partially degraded, whereas DCA was not at all affected. ESR experiments performed with N, S co-doped TiO2 powders illuminated with visible light and in the presence of singlet oxygen (1O2) quencher, TMP-OH, showed the formation of 1O2. This suggests that superoxide radical (•O2 −) and its oxidation product, 1O2, were responsible for E. coli inactivation by N, S co-doped TiO2 nanoparticles under visible light.
Keywords: Heterogeneous photocatalysis; Visible light response; Nitrogen doped TiO2; Sulfur doped TiO2;
Photodegradation of lauric acid at an anatase single crystal surface studied by atomic force microscopy by A. Zaleska; J. Nalaskowski; J. Hupka; J.D. Miller (407-412).
The photodegradation of lauric acid at an anatase single crystal surface was visualized using atomic force microscopy (AFM). Photooxidation was performed for lauric acid thin films with thickness about 80–90 nm to simulate more realistic processing conditions rather than using submonolayer films. It was noticed that lauric acid deposited by spin coating technique formed domain structure at the TiO2 surface. The phenomenon of domain surface decrease without change in the film thickness was observed. This suggests that only molecules at the crystal–air–lauric acid contact line and extended therefrom were degraded.
Keywords: Anatase; Rutile; Single crystal; Photooxidation; AFM;
Screening of doped MnO x –CeO2 catalysts for low-temperature NO-SCR by Maria Casapu; Oliver Kröcher; Martin Elsener (413-419).
The effect of different dopants including niobium, iron, tungsten and zirconium oxide on the low-temperature activity of MnO x –CeO2 catalysts for the selective catalytic reduction (SCR) of NO x with ammonia has been studied with coated cordierite monoliths in model gas experiments. A clearly higher activity and particularly superior nitrogen selectivity was obtained with the niobium-doped catalyst in comparison with the MnO x –CeO2 reference system. At 200 °C, the DeNO x was 80% while the N2 selectivity reached more than 96%. In contrast, a decrease of the SCR activity was observed when iron, zirconium or tungsten oxides were added to MnO x –CeO2. However, the addition of niobium oxide did not improve the resistance of the catalyst against SO2 poisoning. A strong and irreversible deactivation occurred after exposure to SO2.
Keywords: Selective catalytic reduction; NO-SCR; NO/NO2-SCR; Manganese oxide; Cerium oxide; Niobium oxide; SO2 poisoning;
A study of copper-exchanged mordenite natural and ZSM-5 zeolites as SCR–NOx catalysts for diesel road vehicles: Simulation by neural networks approach by Mona Lisa Moura de Oliveira; Carla Monteiro Silva; Ramon Moreno-Tost; Tiago Lopes Farias; Antonio Jiménez-López; Enrique Rodríguez-Castellón (420-429).
Copper-catalysts, based on the ZSM-5 (CuZSM5) and Cuban natural Mordenite (CuMORD) zeolites have been prepared by a conventional ion-exchange method and their catalytic activity in the selective catalytic reduction (SCR) of NO was studied using ammonia in presence of H2O and SO2. A commercial catalyst SCR (CATCO) based on V2O5–WO3–TiO2, was also studied as reference. This paper presents experimental results using catalysts without the toxic vanadium and exploits a neural network based approach to predict NOx conversion efficiency of three SCR catalysts. The derived mathematical functions are integrated in a numerical model for diesel road vehicle simulation to simulate diesel vehicles equipped with such SCR catalysts. The main results indicate that despite of toxic vanadium and N2O formation, CATCO shows the better NOx conversion efficiencies. However, CuMORD does not form N2O and have better performance than the CuZSM5. The simulation results show lower level of NOx for heavy-duty and light-duty diesel vehicles compared with homologation load cycles.
Keywords: SCR; NOx; Diesel road vehicle; Zeolites; Neural-networks; Road vehicle simulator;
Oxidation of CH4 over Pd supported on TiO2-doped SiO2: Effect of Ti(IV) loading and influence of SO2 by A.M. Venezia; G. Di Carlo; G. Pantaleo; L.F. Liotta; G. Melaet; N. Kruse (430-437).
Titania-modified silicas with different weight% of TiO2 were prepared by sol–gel method and used as supports for Pd (1 wt%) catalysts. The obtained materials were tested in the oxidation of methane under lean conditions in absence and in presence of SO2. Test reactions were consecutively performed in order to evaluate the thermal stability and poisoning reversibility. Increasing amounts of TiO2 improved the catalytic activity, with an optimum of the performance for 10 wt% TiO2 loading. Moreover, the titania-containing catalysts exhibited a superior tolerance towards SO2 by either adding it to the reactants or feeding it as a pure pretreatment atmosphere at 350 °C. Catalysts were characterized by XPS, XRD, FT-IR and BET measurements. According to the structural and surface analyses, the mixed oxides contained Si–O–Ti linkages which were interpreted as being responsible for the enhanced intrinsic activity of supported PdO with respect to PdO on either pure SiO2 or pure TiO2. Moreover, the preferential interaction of the sulfur molecule with TiO2 and the easy SO x desorption from high surface area silica were the determining factors for the superior SO2 tolerance of the TiO2-doped catalysts.
Keywords: Methane combustion; TiO2/SiO2 supports; PdO catalyst; SO2 effect;
La(1−x)Sr x Co1−y Fe y O3 perovskites prepared by sol–gel method: Characterization and relationships with catalytic properties for total oxidation of toluene by S. Rousseau; S. Loridant; P. Delichere; A. Boreave; J.P. Deloume; P. Vernoux (438-447).
La(1−x)Sr x Co(1−y)Fe y O3 samples have been prepared by sol–gel method using EDTA and citric acid as complexing agents. For the first time, Raman mappings were achieved on this type of samples especially to look for traces of Co3O4 that can be present as additional phase and not detect by XRD. The prepared samples were pure perovskites with good structural homogeneity. All these perovskites were very active for total oxidation of toluene above 200 °C. The ageing procedure used indicated good thermal stability of the samples. A strong improvement of catalytic properties was obtained substituting 30% of La3+ by Sr2+ cations and a slight additional improvement was observed substituting 20% of cobalt by iron. Hence, the optimized composition was La0.7Sr0.3Co0.8Fe0.2O3. The samples were also characterized by BET measurements, SEM and XRD techniques. Iron oxidation states were determined by Mössbauer spectroscopy. Cobalt oxidation states and the amount of O− electrophilic species were analyzed from XPS achieved after treatment without re-exposition to ambient air. Textural characterization revealed a strong increase in the specific surface area and a complete change of the shape of primary particles substituting La3+ by Sr2+. The strong lowering of the temperature at conversion 20% for the La0.7Sr0.3Co(1−y)Fe y O3 samples can be explained by these changes. X photoelectron spectra obtained with our procedure evidenced very high amount of O− electrophilic species for the La0.7Sr0.3Co(1−y)Fe y O3 samples. These species able to activate hydrocarbons could be the active sites. The partial substitution of cobalt by iron has only a limited effect on the textural properties and the amount of O− species. However, Raman spectroscopy revealed a strong dynamic structural distortion by Jahn–Teller effect and Mössbauer spectroscopy evidenced the presence of Fe4+ cations in the iron containing samples. These structural modifications could improve the reactivity of the active sites explaining the better specific activity rate of the La0.7Sr0.3Co0.8Fe0.2O3 sample. Finally, an additional improvement of catalytic properties was obtained by the addition of 5% of cobalt cations in the solution of preparation. As evidenced by Raman mappings and TEM images, this method of preparation allowed to well-dispersed small Co3O4 particles that are very efficient for total oxidation of toluene with good thermal stability contrary to bulk Co3O4.
Keywords: La(1−x)Sr x Co(1−y)Fe y O3; Perovskite; Sol–gel method; Toluene total oxidation; VOC abatement; Raman mappings; XPS; Mössbauer spectroscopy; O− species; Co3O4;
Solar photo-Fenton treatment of pesticides in water: Effect of iron concentration on degradation and assessment of ecotoxicity and biodegradability by A. Zapata; T. Velegraki; J.A. Sánchez-Pérez; D. Mantzavinos; M.I. Maldonado; S. Malato (448-454).
A combined solar photo-Fenton and biological treatment is proposed for the decontamination of a mixture of five commercial pesticides commonly used in intensive agriculture Vydate (10% Oxamyl), Metomur (20% Methomyl), Couraze (20% Imidacloprid), Ditimur-40 (40% Dimethoate) and Scala (40% Pyrimethanil). Photo-Fenton experiments were conducted in a solar pilot reactor consisting of four compound parabolic collectors in which the pesticide mixture was treated at an original dissolved organic carbon (DOC) concentration of 200 mg/L in the presence of Fe2+ or Fe3+ concentration of 5, 20 and 55 mg/L. Ferrous ions were marginally more active than ferric in terms of active ingredient degradation, which followed zero order kinetics, more so in the early reaction stages. Photo-Fenton was also far more effective (by at least two orders of magnitude) than the respective dark reaction under identical experimental conditions.Irradiation for 50–100 min (normalized at 30 W/m2 light intensity) at 20 mg/L Fe2+ was able to completely eliminate the active ingredients, and reduce DOC by about 15–50% and COD by 40–70%, respectively. At these conditions, ecotoxicity to the marine bacteria V. fischeri was substantially lessened, while aerobic biodegradability in tests with activated sludge was enhanced.
Keywords: Biodegradability; Detoxification; Pesticides treatment; Photocatalysis; Solar photo-Fenton;
Removal of aqueous organic pollutants by adsorption-catalytic process using mesoporous carbon beads loaded with metal oxides by Takuji Yamamoto; Seong-Ick Kim; Jintawat Chaichanawong; Eiad-ua Apiluck; Takao Ohmori (455-461).
Removal of aqueous organic pollutants using an adsorption-catalytic process was examined using metal-loaded carbon cryogel beads (CCBs) which possess numerous mesopores of controlled size. Adsorption isotherms of phenol, as a model organic pollutant, on CCBs could be interpreted based on the Langmuir model, indicating the preferable adsorption of phenol on micropores rather than on mesopores. Removal of aqueous phenol was examined using metal oxide-loaded CCBs in the presence of ozone. Due to the adsorptive-concentration effect of CCBs, it proved possible to increase the phenol removal efficiency by the simultaneous use of ozone with CCBs as compared with ozone only. Of the support materials for loading metal oxides, CCBs showed the highest removal efficiency. The enhancement effect of CCBs in the removal of aqueous phenol was examined with regard to the metal species loaded, the amount of loaded metal, the size of the mesopores, and the carbonization temperature used in the preparation of CCBs.
Keywords: Adsorption-catalytic process; Aqueous phenol; Carbon cryogel beads; Degradation; Ozone;
Iron–cobalt mixed oxide nanocatalysts: Heterogeneous peroxymonosulfate activation, cobalt leaching, and ferromagnetic properties for environmental applications by Qiujing Yang; Hyeok Choi; Souhail R. Al-Abed; Dionysios D. Dionysiou (462-469).
Sulfate radical-based advanced oxidation technologies (SR-AOTs) are attracting considerable attention due to the high oxidizing ability of SRs to degrade organic pollutants in aqueous environments. This study was carried out to respond to current concerns and challenges in SR-AOTs, including (i) need of heterogeneous activation of sulfate salts using transition metal oxides, (ii) nanoscaling of the metal oxide catalysts for high catalytic activity and promising properties with respect to leaching, and (iii) easy removal and recovery of the catalytic materials after their applications for water and wastewater treatments. In this study, we report a novel approach of using Fe–Co mixed oxide nanocatalysts for the heterogeneous activation of peroxymonosulfate (PMS) to generate SRs targeting the decomposition of 2,4-dichlorophenol, and especially focus on some synthesis parameters such as calcination temperature, Fe/Co contents, and TiO2 support. The physicochemical properties of the catalysts were investigated using porosimetry, XRD, HR-TEM, H2-TPR, and XPS. Ferromagnetic CoFe2O4 composites formed by thermal oxidation of a mixed phase of Fe and Co exhibited significant implications for the efficient and environmentally friendly activation of PMS, including (i) the cobalt species in CoFe2O4 are of Co(II), unlike Co3O4 showing some detrimental effects of Co(III) on the PMS activation, (ii) CoFe2O4 possesses suppressed Co leaching properties due to strong Fe–Co interactions (i.e. Fe–Co linkages), and (iii) Fe–Co catalysts in form of CoFe2O4 are easier to recover due to the unique ferromagnetic nature of CoFe2O4. In addition, the presence of Fe was found to be beneficial for enriching hydroxyl group content on the Fe–Co catalyst surface, which is believed to facilitate the formation of Co(II)-OH complexes that are vital for heterogeneous PMS activation.
Keywords: 2,4-Dichlorophenol; Advanced oxidation processes (AOPs); Advanced oxidation technologies (AOTs); Cobalt; Fe–Co; Ferromagnetic properties; Heterogeneous reaction; Iron; Iron–cobalt; Leaching; Mixed oxide; Nanoparticles; Oxone; Peroxymonosulfate; Support materials; Sulfate radicals; Titanium dioxide; Titania; TiO2; Water treatment; Water purification;
Selective methanation of CO over supported Ru catalysts by Paraskevi Panagiotopoulou; Dimitris I. Kondarides; Xenophon. E. Verykios (470-478).
The catalytic performance of supported ruthenium catalysts for the selective methanation of CO in the presence of excess CO2 has been investigated with respect to the loading (0.5–5.0 wt.%) and mean crystallite size (1.3–13.6 nm) of the metallic phase as well as with respect to the nature of the support (Al2O3, TiO2, YSZ, CeO2 and SiO2). Experiments were conducted in the temperature range of 170–470 °C using a feed composition consisting of 1%CO, 50% H2 15% CO2 and 0–30% H2O (balance He). It has been found that, for all catalysts investigated, conversion of CO2 is completely suppressed until conversion of CO reaches its maximum value. Selectivity toward methane, which is typically higher than 70%, increases with increasing temperature and becomes 100% when the CO2 methanation reaction is initiated. Increasing metal loading results in a significant shift of the CO conversion curve toward lower temperatures, where the undesired reverse water–gas shift reaction becomes less significant. Results of kinetic measurements show that CO/CO2 hydrogenation reactions over Ru catalysts are structure sensitive, i.e., the reaction rate per surface metal atom (turnover frequency, TOF) depends on metal crystallite size. In particular, for Ru/TiO2 catalysts, TOFs of both CO (at 215 °C) and CO2 (at 330 °C) increase by a factor of 40 and 25, respectively, with increasing mean crystallite size of Ru from 2.1 to 4.5 nm, which is accompanied by an increase of selectivity to methane. Qualitatively similar results were obtained from Ru catalysts supported on Al2O3. Experiments conducted with the use of Ru catalyst of the same metal loading (5 wt.%) and comparable crystallite size show that the nature of the metal oxide support affects significantly catalytic performance. In particular, the turnover frequency of CO is 1–2 orders of magnitude higher when Ru is supported on TiO2, compared to YSZ or SiO2, whereas CeO2- and Al2O3-supported catalysts exhibit intermediate performance. Optimal results were obtained over the 5%Ru/TiO2 catalyst, which is able to completely and selectively convert CO at temperatures around 230 °C. Addition of water vapor in the feed does not affect CO hydrogenation but shifts the CO2 conversion curve toward higher temperatures, thereby further improving the performance of this catalyst for the title reaction. In addition, long-term stability tests conducted under realistic reaction conditions show that the 5%Ru/TiO2 catalyst is very stable and, therefore, is a promising candidate for use in the selective methanation of CO for fuel cell applications.
Keywords: Selective methanation; CO; CO2; Structure sensitivity; Ru; Titanium dioxide; Support effects; CO removal; Fuel cell applications;
Electrochemical hydrodehalogenation of polychloromethanes at silver and carbon electrodes by Christian Durante; Abdirisak Ahmed Isse; Giancarlo Sandonà; Armando Gennaro (479-489).
The reductive dehalogenation of CCl4, CHCl3, CH2Cl2 and CH3Cl has been investigated by cyclic voltammetry and controlled-potential electrolysis at Ag, glassy carbon (GC) and graphite electrodes in dimethylformamide (DMF) + 0.1 M Et4NClO4 in the absence and presence of a proton donor. In particular, the study was focused in the evaluation of the intermediates and final products of the reduction process and how their distribution could be affected by tuning relevant chemical and electrochemical parameters. In general, depending on the value of the applied potential, all polychloromethanes (PCMs) can be partially or completely dechlorinated, methane being exclusively formed in the latter case. The nature of the electrode material and the proton availability of the medium affect drastically the distribution of reduction products. The results point out that at both types of electrode, reduction of PCMs takes place through two competing reaction pathways both leading to methane. One reaction route involves a sequence of reductive dehalogenation steps, with the removal of one chlorine atom at a time, whereas the other is based on hydrogenolysis of carbenes and bypasses the intermediacy of partially dechlorinated PCMs. The presence of a proton source affects substantially the hydrodehalogenation efficiency, enhancing the concentration of intermediate PCMs and the final yield of methane. The silver electrode exhibits an extraordinary electrocatalytic effect resulting in remarkable positive shifts of the reduction potentials of all PCMs with respect to GC. The Ag surface strongly affects the kinetics of the dissociative electron transfer to CH n Cl(4−n) (n = 0–3) as well as the reactivity of the intermediate radicals, carbanions and carbenes.
Keywords: Polychlormethanes; Electrocatalytic reduction; Hydrodechlorination; Silver cathode;
Steady-state isotopic transient kinetic analysis of steam reforming of methanol over Cu-based catalysts by Joan Papavasiliou; George Avgouropoulos; Theophilos Ioannides (490-496).
Mechanistic aspects of steam reforming of methanol were studied via steady-state isotopic transient kinetic analysis over three copper-based catalysts, namely combustion-synthesized Cu-Ce-O and Cu-Mn-O, and commercial Cu-ZnO-Al2O3. The “C-path” and “O-path” for the production of CO2 via steam reforming of methanol was analysed with the following step changes in the feed: 12CH3OH/H2O/Ar/He → 13CH3OH/H2O/He and CH3OH/H2 16O/Ar/He → CH3OH/H2 16O/H2 18O/He. The presence of CH3 18OH in the products after the switch to 18O-labeled water indicates that a major path of the reaction is the one involving a methyl formate intermediate. This appears to be the main path over the Cu-Mn-O catalyst, while parallel paths via dioxomethylene and methyl formate intermediates appear to be operative over Cu-Ce-O and Cu-ZnO-Al2O3 catalysts.
Keywords: SSITKA; Steam reforming; Methanol; Copper; Ceria; Manganese;
Photocatalytic mineralization of phenol catalyzed by pure and mixed phase hydrothermal titanium dioxide by Roberto Scotti; Massimiliano D’Arienzo; Andrea Testino; Franca Morazzoni (497-504).
The photocatalytic mineralization of phenol catalyzed by pure (anatase, rutile) and mixed phase hydrothermal TiO2 was studied in aqueous solution employing different oxidative agents, H2O2 and O2. In the case of H2O2, rutile particles, having large dimensions and high aspect ratio (size: 30–70 nm × 150–350 nm), display the highest catalytic activity due to their low tendency to recombine electrons and holes generated by UV irradiation. By using water dissolved gaseous O2, the catalytic TiO2 activity generally decreases and rutile displays the lowest efficacy. In fact, oxygen preferentially chemisorbs at the surface of the nanosized particles of anatase (5–15 nm) and acts as effective electron scavenger, inhibiting the electron-hole recombination. The number of electron and hole traps (Ti3+, O2 − and O−) and the rate of formation of the short-lived hydroxyl radicals OH• under UV irradiation, were evaluated by electron paramagnetic resonance (EPR). A correlation was suggested among the amount of the charge carrier centers, the rate of formation of OH• radicals and the catalyst photoactivity. This confirms that the photocatalytic properties depend on the possibility that electrons and holes separately interact with the oxidative agents at the TiO2 surface, inducing the formation of OH• radicals.
Keywords: Electron paramagnetic resonance; Spin-trap; Hydroxyl radicals; Ti3+; O−; Rutile; Anatase; Photocatalysis;
Tailoring and structure of PtRu nanoparticles supported on functionalized carbon for DMFC applications: New evidence of the hydrous ruthenium oxide phase by J.L. Gómez de la Fuente; M.V. Martínez-Huerta; S. Rojas; P. Hernández-Fernández; P. Terreros; J.L.G. Fierro; M.A. Peña (505-514).
The influence of the structure and morphology of PtRu nanoparticles supported on functionalized carbon black has been investigated for CO and methanol electrooxidation in a half-cell and in a DMFC single cell. Carbon black was treated with HNO3 to obtain an oxidized surface (Vulcan-N), and PtRu nanoparticles supported on Vulcan-N were prepared via impregnation, Bönnemann's method and the sulfito-complex route. Temperature programmed reduction (TPR) measurements evidence the presence of RuO2·xH2O phase in the catalyst obtained by the sulfito-complex route. This phase was stabilized by metal–support interaction, whereas alloy characteristics were estimated for PtRu catalyst obtained by impregnation and Bönnemann's method. The nature of the precursor–support interaction, induced by the nature of the functional groups on the carbon surface, affects the structure of the electrocatalyst and subsequent behavior in electroactivity. When synthesized through Bönnemann's method, the surface oxygen-containing groups of the support seem to be unable to stabilize the anhydrous precursors of platinum and ruthenium, yielding crystalline RuO2. Methanol electrooxidation performance was clearly different in the three catalysts, whereas only a few negligible differences were observed in CO oxidation. The superior performance in DMFC of the catalysts obtained by the sulfito-complex route accounts for both the presence of RuO2·xH2O species and the functionalization of carbon black.
Keywords: Electrocatalyst; Methanol; PtRu; Functionalized support; RuO2·xH2O; Hydrous ruthenium oxide; Fuel cell;
Combined TiO2/SiO2 mesoporous photocatalysts with location and phase controllable TiO2 nanoparticles by E. Beyers; E. Biermans; S. Ribbens; K. De Witte; M. Mertens; V. Meynen; S. Bals; G. Van Tendeloo; E.F. Vansant; P. Cool (515-524).
Combined TiO2/SiO2 mesoporous materials were prepared by deposition of TiO2 nanoparticles synthesised via the acid-catalysed sol–gel method. In the first synthesis step a titania solution is prepared, by dissolving titaniumtetraisopropoxide in nitric acid. The influences of the initial titaniumtetraisopropoxide concentration and the temperature of dissolving on the final structural properties were investigated. In the second step of the synthesis, the titania nanoparticles were deposited on a silica support. Here, the influence of the temperature during deposition was studied. The depositions were carried out on two different mesoporous silica supports, SBA-15 and MCF, leading to substantial differences in the catalytic and structural properties. The samples were analysed with N2-sorption, X-ray diffraction (XRD), electron probe microanalysis (EPMA) and transmission electron microscopy (TEM) to obtain structural information, determining the amount of titania, the crystal phase and the location of the titania particles on the mesoporous material (inside or outside the mesoporous channels). The structural differences of the support strongly determine the location of the nanoparticles and the subsequent photocatalytic activity towards the degradation of rhodamine 6G in aqueous solution under UV irradiation.
Keywords: Location; Crystalline phase; Mesoporous SiO2 support; TiO2 photocatalyst;
Preparation and characterization of TiO2 photocatalysts by Fe3+ doping together with Au deposition for the degradation of organic pollutants by Yongmei Wu; Jinlong Zhang; Ling Xiao; Feng Chen (525-532).
Fe3+ doped TiO2 deposited with Au (Au/Fe–TiO2) was successfully prepared with an attempt to extend light absorption of TiO2 into the visible region and reduce the rapid recombination of electrons and holes. The samples were characterized by X-ray diffraction (XRD), N2 physical adsorption, Raman spectroscopy, atomic absorption flame emission spectroscopy (AAS), UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra. The photocatalytic activities of the samples were evaluated for the degradation of 2,4-chlorophenol in aqueous solutions under visible light (λ > 420 nm) and UV light irradiation. The results of XRD, XPS and high-resolution transmission electron microscopy (HRTEM) analysis indicated that Fe3+ substituted for Ti4+ in the lattice of TiO2, Au existed as Au0 on the surface of the photocatalyst and the mean particle size of Au was 8 nm. Diffuse reflectance measurements showed an extension of light absorption into the visible region for Au/Fe–TiO2, and PL analysis indicated that the electron–hole recombination rate has been effectively inhibited when Au deposited on the surface of Fe-doped TiO2. Compared with Fe doped TiO2 sample and Au deposited TiO2 sample, the Au/Fe–TiO2 photocatalyst exhibited excellent visible light and UV light activity and the synergistic effects of Fe3+ and Au was responsible for improving the photocatalytic activity.
Keywords: Titania; Fe3+ doped; Au deposited; Photodegradation; Synergistic effect;
Stability of protonic zeolites in the catalytic oxidation of chlorinated VOCs (1,2-dichloroethane) by A. Aranzabal; J.A. González-Marcos; M. Romero-Sáez; J.R. González-Velasco; M. Guillemot; P. Magnoux (533-541).
The deactivation of protonic zeolites in the catalytic oxidation of 1,2-dichloroethane (DCA) was evaluated. DCA oxidation reactions were carried out in a conventional fixed-bed reactor at atmospheric pressure under conditions of lean DCA concentration in air (1000 ppm). The outlet composition was analysed by a gas chromatograph, an IR spectroscopy-based analyser and another UV analyser. The effect of the zeolite crystalline structure was examined in order to track the catalytic stability of H-ZSM-5, H-MOR and H-BEA under typical reaction environment and conditions (1000 ppm DCA, 300 °C, 13,500 h−1). With the aim of a better understanding of the deactivation pathway, the influence of the space velocity and temperature on the durability of protonic zeolites was analysed. Since some products formed during reaction could also cause deactivation, H2O and HCl were introduced in the feed stream along with the DCA itself, so as to evaluate their effect. In general terms, coke formation was concluded to be the main reason for zeolite catalyst deactivation. Coke was formed from the intermediate vinyl chloride (VC), which resulted from a first dehydrochlorination step of DCA.
Keywords: Catalytic oxidation; 1,2-Dichloroethane; H-zeolite catalysts; Deactivation; Space velocity; Temperature; H2O; HCl;
Enhancement of oxygen storage capacity by reductive treatment of Al2O3 and CeO2–ZrO2 solid solution nanocomposite by Akira Morikawa; Koichi Kikuta; Akihiko Suda; Hirofumi Shinjo (542-549).
Oxygen storage capacity (OSC) of CeO2–ZrO2 solid solution, Ce x Zr(1−x)O4, is one of the most contributing factors to control the performance of an automotive catalyst. To improve the OSC, heat treatments were employed on a nanoscaled composite of Al2O3 and CeZrO4 (ACZ). Reductive treatments from 700 to 1000 °C significantly improved the complete oxygen storage capacity (OSC-c) of ACZ. In particular, the OSC-c measured at 300 °C reached the theoretical maximum with a sufficient specific surface area (SSA) (35 m2/g) after reductive treatment at 1000 °C. The introduced Al2O3 facilitated the regular rearrangement of Ce and Zr ions in CeZrO4 as well as helped in maintaining the sufficient SSA. Reductive treatments also enhanced the oxygen release rate (OSC-r); however, the OSC-r variation against the evaluation temperature and the reduction temperature differed from that of OSC-c. OSC-r measured below 200 °C reached its maximum against the reduction temperature at 800 °C, while those evaluated at 300 °C increased with the reduction temperature in the same manner as OSC-c.
Keywords: Al2O3; CeO2; ZrO2; Oxygen storage capacity; Reduction;
Catalytic oxidation of ethyl acetate over a cesium modified cryptomelane catalyst by V.P. Santos; M.F.R. Pereira; J.J.M. Órfão; J.L. Figueiredo (550-556).
Cryptomelane-type manganese oxide was synthesized by redox reaction under acid and reflux conditions. Cesium was incorporated into the tunnel structure by the ion-exchange technique. The catalytic oxidation of ethyl acetate in low concentration (1600 ppmv) was used to test the performance of the catalysts prepared. The presence of small amounts of cesium was found to improve the catalytic performance of cryptomelane. This behaviour was correlated with the basic properties of the catalyst. Temperature programmed experiments, and tests without oxygen in the feed, suggest that lattice oxygen atoms can react with ethyl acetate at low temperatures and are involved in the mechanism of ethyl acetate oxidation.
Keywords: Ethyl acetate; Oxidation; Cryptomelane; Cesium; Basicity;
Preparation of catalytic films of platinum on Au substrates modified by self-assembled PAMAM dendrimer monolayers by Sheela Berchmans; Paulraj Arunkumar; Shrikanth Lalitha; Venkatraman Yegnaraman; Santanu Bera (557-563).
In this work we demonstrate the preparation of highly catalytically active Pt formed by the galvanic replacement of the copper adlayer on Au substrates, modified by the self-assembly of fourth generation amine terminated PAMAM dendrimer (G4NH2). The copper adlayer was formed on the dendrimer-modified gold substrate by chemical preconcentration of copper ions followed by electrochemical reduction. The Pt overlayer was characterized by SEM, XPS and by cyclic voltammetry. The catalytic efficiency of the modified film thus prepared through soft route was evaluated by the electro catalytic oxidation of methanol using cyclic voltammetry, chronoamperometry and AC impedance techniques. This work also demonstrates that the copper adlayer formed on the dendrimer-modified electrode can undergo galvanic replacement by nobler metals like Au and Ag, besides Pt. An elegant soft route involving a new three-step protocol to build the concentration of active Pt on the Au surface has been developed. Concentration of the same metal (Pt) or two different metals (Pt–Au) can be built at the interface in a stepwise manner at ambient temperature.
Keywords: Pt overlayers; Galvanic replacement; Electro catalysis; Methanol oxidation; PAMAM dendrimers;
Effect of ethyleneglycol addition on the properties of P-doped NiMo/Al2O3 HDS catalysts: Part I. Materials preparation and characterization by José Escobar; María C. Barrera; José A. Toledo; María A. Cortés-Jácome; Carlos Angeles-Chávez; Sara Núñez; Víctor Santes; Elizabeth Gómez; Leonardo Díaz; Eduardo Romero; José G. Pacheco (564-575).
Phosphorous-doped NiMo/Al2O3 hydrodesulfurization (HDS) catalysts (nominal Mo, Ni and P loadings of 12, 3, and 1.6 wt%, respectively) were prepared using ethyleneglycol (EG) as additive. The organic agent was diluted in aqueous impregnating solutions obtained by MoO3 digestion in presence of H3PO4, followed by 2NiCO3·3Ni(OH)2·4H2O addition. EG/Ni molar ratio was varied (1, 2.5 and 7) to determine the influence of this parameter on the surface and structural properties of synthesized materials. As determined by temperature-programmed reduction, ethyleneglycol addition during impregnation resulted in decreased interaction between deposited phases (Mo and Ni) and the alumina carrier. Dispersion and sulfidability (as observed by X-ray photoelectron microscopy) of molybdenum and nickel showed opposite trends when incremental amounts of the organic were added during catalysts preparation. Meanwhile Mo sulfidation was progressively decreased by augmenting EG concentration in the impregnating solution, more dispersed sulfidic nickel was evidenced in materials synthesized at higher EG/Ni ratios. Also, enhanced formation of the so-called “NiMoS phase” was registered by increasing the amount of added ethyleneglycol during simultaneous Ni–Mo–P–EG deposition over the alumina carrier. That fact was reflected in enhanced activity in liquid-phase dibenzothiophene HDS (batch reactor, T = 320 °C, P = 70 kg/cm2) and straight-run gas oil desulfurization (steady-state flow reactor), the latter test carried out at conditions similar to those used in industrial hydrotreaters for the production of ultra-low sulfur diesel (T = 350 °C, P = 70 kg/cm2, LHSV = 1.5 h−1 and H2/oil = 2500 ft3/bbl).
Keywords: Ethyleneglycol; Phosphomolybdates; Hydrodesulfurization; NiMo/Al2O3 catalyst; NiMoS phase; ULSD;
Visible-light-induced photocatalytic inactivation of bacteria by composite photocatalysts of palladium oxide and nitrogen-doped titanium oxide by Pinggui Wu; Rongcai Xie; James A. Imlay; Jian Ku Shang (576-581).
Composite photocatalysts of palladium oxide and nitrogen-doped titanium oxide (PdO/TiON) were synthesized by a sol–gel process, as convenient forms of nanopowder or immobilized powder on nanofiber. The PdO/TiON catalysts were tested for visible-light-activated photocatalysis using different bacterial indicators, including gram-negative cells of Escherichia coli and Pseudomonas aeruginosa, and gram-positive cells of Staphylococcus aureus. Disinfection data indicated that PdO/TiON composite photocatalysts have a much better photocatalytic activity than either palladium-doped (PdO/TiO2) or nitrogen-doped titanium oxide (TiON) under visible-light illumination. The roles of Pd and N were discussed in terms of the production and separation of the charge carriers under visible-light illumination. The photocatalytic activity was thus dependent on dopants and light intensity. Microscopic characterization demonstrated that visible-light photocatalysis on PdO/TiON caused drastic damage on the bacteria cell wall and the cell membrane.
Keywords: Titanium oxide; Photocatalyst; Photocatalysis; Composite; Water; Disinfection;
Corrigendum to “Kinetics of the photocatalytic disinfection of Escherichia coli suspensions” [Appl. Catal. B: Environ. 82 (2008) 27–36] by Javier Marugán; Rafael van Grieken; Carlos Sordo; Cristina Cruz (582-583).