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Applied Catalysis B, Environmental (v.105, #1-2)
DeNOx performance of Ag/Al2O3 catalyst using simulated diesel fuel–ethanol mixture as reductant by Mun Kyu Kim; Pyung Soon Kim; Joon Hyun Baik; In-Sik Nam; Byong K. Cho; Se H. Oh (pp. 1-14).
Display Omitted► When C1/NOx and E/SD ratios were 4, the highest NOx-to-N2 conversion, 70% over Ag(3.8)/Al2O3 was achieved at 300°C. ► A proper combination of the ionic and metallic Ag on the catalyst surface, 1.4–1.7 is critical for the high deNOx performance. ► The CuZSM5 in the dual-bed system improved the deNOx performance of Ag/Al2O3, mainly due to the NH3 oxidation to N2.The NOx reduction activity of Ag/Al2O3 catalyst has been investigated systematically, using a mixture of simulated diesel fuel (SD) and ethanol (E) as the reductant with special interest in the low temperature deNOx performance below 350°C. The Ag loading and catalyst operating conditions such as C1/NOx and ethanol/simulated diesel fuel (E/SD) ratios have been optimized in order to achieve the maximum deNOx performance of the Ag/Al2O3 catalyst. Ammonia has been identified as the most abundant reaction intermediate over the Ag/Al2O3 catalyst under the optimized operating conditions. To further enhance the deNOx performance by utilizing the NH3 formed over the Ag/Al2O3 catalyst, a dual-bed reactor system has been employed with CuZSM5 catalyst in the rear bed consecutively following the front bed containing the Ag/Al2O3. The NOx-to-N2 conversion in this dual-bed system increased up to 85% from 275 to 450°C, mainly due to the NH3 oxidation to N2 by the CuZSM5 in the rear bed. Physicochemical characterization of the Ag/Al2O3 catalysts by UV–vis, TEM and EELS has indicated that both ionic and metallic Ag formed on the catalyst surface play important roles for the high deNOx performance of the present catalytic system; the ionic Ag including Ag+ and Agδ+ is the active reaction site for the reduction of NOx to N2, while the metallic Ag is responsible for the partial oxidation of hydrocarbons (HCs) which promotes the initiation of the HC/SCR process in the low temperature range. The optimum ionic/metallic (I/M) ratio of Ag species on Al2O3 support surface appears to be in the range of 1.4–1.7, depending upon the catalyst temperature range of interest.
Keywords: Hydrocarbon/selective catalytic reduction (HC/SCR); Ag/Al; 2; O; 3; Ionic Ag; Metallic Ag; Dual-bed reactor system
FT-IR study of the surface redox states on platinum-potassium-alumina catalysts by Tania Montanari; Roberto Matarrese; Nancy Artioli; Guido Busca (pp. 15-23).
.Display Omitted► The paper reports a detailed characterization of a catalyst constituted by platinum supported on heavily potassium doped γ-Al2O3 which is active in the so called NO x-trap technology and for the simultaneous Diesel particulate oxidation and NO x reduction. ► The characterization is made in comparison with a corresponding K-free Pt/Al2O3 catalyst. ► IR spectra of adsorbed CO at −140°C and at room temperature allowed the detection of oxidized Pt centers and of their very strong oxidizing ability. ► TPD and IR spectra of adsorbed CO2 allowed to characterize the basicity of the samples. ► The data indicate that Pt centers lie in close proximity of potassium oxide species generating basicity.Pt-K/Al2O3 (Pt 1%; K 5.4% wt/wt) catalyst active for the simultaneous Diesel particulate oxidation and NO x reduction have been characterized in comparison with 1% Pt/Al2O3 catalyst. IR spectra of adsorbed CO at −140°C and at room temperature allowed the detection of oxidized Pt centers and of their very strong oxidizing ability. TPD and IR spectra of adsorbed CO2 allowed to characterize the basicity of the samples. The data indicate that Pt centers lie in close proximity of potassium oxide species generating basicity.
Keywords: Platinum; Nanoparticles; IR spectroscopy; Adsorbed CO; Supported Pt catalysts; Potassium alumina; NO; x; adsorption and reduction; Catalytic combustion
Pentachlorophenol reduction by Pd/Fe bimetallic nanoparticles: Effects of copper, nickel, and ferric cations by Yang-hsin Shih; Meng-Yi Chen; Yuh-Fan Su (pp. 24-29).
Display Omitted► Pd/Fe bimetallic nanoparticles effectively degrade PCP. ► Sulfate ions inhibit on degradation of PCP with Pd/Fe nanoparticles. ► Cu2+, Ni2+, and Fe3+ ions enhance the degradation of PCP by Pd/Fe nanoparticles. ► The reduced form of copper and nickel on Pd/Fe surfaces facilitates the degradation.Bimetallic nanoparticles have been used for effective reduction of chlorinated compounds; however, the study of cation effect on degradation is limited. This study examined the effect of three selected cations normally co-present in soil and groundwater contamination sites on the degradation kinetics and removal efficiency of pentachlorophenol (PCP) by Pd/Fe nanoparticles. Degradation of PCP by Pd/Fe nanoparticles was carried out in aqueous solutions containing different cations in sulfate form, Na2SO4, CuSO4, NiSO4, and Fe2(SO4)3, respectively. The observed inhibitory effect of Na2SO4 on degradation of PCP was contributed to the existence of SO42− ions. Overcoming the inhibitory effect of SO42− ions, Cu2+, Ni2+, and Fe3+ could facilitate the degradation kinetics and efficiencies of PCP by Pd/Fe nanoparticles. XANES absorption spectra were performed to characterize their valences. The enhancement effect of Cu2+ and Ni2+ ions result from the presence of reduced forms of copper and nickel on Pd/Fe surfaces. The presence of reduced forms of copper and nickel on Pd/Fe nanoparticles were confirmed by ICP–MS analysis. The addition of Fe3+ ions caused a decrease in pH and can reasonably account for the enhancement seen in the PCP degradation process. These observations lead to a better understanding of PCP degradation with Pd/Fe nanoparticles and can facilitate the remediation design and prediction of treatment efficiency of PCP at remediation sites.
Keywords: Pentachlorophenol; Pd/Fe nanoparticles; Degradation; Cations; Sulfate
Kinetics of hydrogen iodide decomposition over activated carbon catalysts in pellets by P. Favuzza; C. Felici; L. Nardi; P. Tarquini; A. Tito (pp. 30-40).
Display Omitted► Three commercial carbons in pellets tested for HI decomposition reaction. ► Both pure HI and azeotropic HI solution used as reactant to compare the results. ► New kinetic mechanism and new equations derived for the reaction. ► Atomic iodine, once formed at the catalyst surface, behaves in an auto-catalytic way. ► Rate may increase with pressure but only at low pressure and high temperature.Three commercial carbons in pellets have been tested as catalysts for HI decomposition reaction in the range of temperature 240–500°C. A preliminary screening, conducted under identical conditions, permitted to correlate conversion values to carbons characterization data. The most active carbon was deeply investigated, showing no deactivation for the entire testing time (140h) and no secondary reaction with H2O (of the HI solution). Comparing the results obtained at different temperatures, contact times, feedings (pure HI and liquid HI–H2O solution) and I2 impurities, it was possible to derive a new kinetic mechanism and find out reliable values for I2 and HI adsorption heats, as well as for the activation energy of the reaction; H2O adsorption resulted greater than HI's. The mechanism proposed entails that atomic iodine, once formed on the catalyst surface, behaves in an auto-catalytic way for the HI molecules decomposition. This translates into a particular dependence of the reaction rate on HI pressure: at rather low pressure and/or high temperatures, rate grows with pressure; when pressure is high and/or temperature is low, rate may decrease with pressure.
Keywords: Hydrogen production; Iodine–sulfur thermochemical cycle; HI decomposition reaction; Carbon catalysts; Langmuir–Hinshelwood
Operando X-ray absorption spectroscopy study of supported Pt catalysts during NO reduction by hydrocarbons by Toshitaka Tanabe; Yasutaka Nagai; Kazuhiko Dohmae; Nobuyuki Takagi; Naoki Takahashi; Shin’inch Matsumoto; Hirohumi Shinjoh (pp. 41-49).
Display Omitted► Appropriate Pt reduction temperature exists to lower catalytic start-up temperature. ► The creation of the metallic Pt active site determines the catalytic start-up. ► Poisoning effect of adsorbed species on Pt also important for catalytic start-up. ► The active oxygen in support oxide should contribute catalytic start-up behavior. ► Control of Pt-support interaction is important for efficient automotive catalyst.To investigate the support effect on the hydrocarbon-NO-O2 reaction in automotive three-way catalytic reactions, operando X-ray absorption near edge structure (XANES) experiments were performed for reactions of C3H6 (or C3H8)-NO-O2 over Pt supported catalysts under reducing conditions. γ-Al2O3, ZrO2, CeO2-ZrO2 and La2O3 were used as the support oxides in this study. After oxidation pre-treatment, the oxidation state of the supported Pt was monitored by in situ Pt L3-edge XANES spectra while the temperature in the reaction mixture was ramped up and the catalytic reaction was followed by measuring the concentrations of C3H6 or C3H8, NO and O2. The operando experimental results were analyzed in terms of the catalytic reaction start-up temperature (20% HC conversion temperature) and the 50% Pt reduction temperature. A V-shape correlation was found between these two temperatures showing that an appropriate Pt reduction temperature should exist to lower the catalytic reaction start-up temperature. This result suggests that the creation of active metallic Pt sites together with the self-poisoning effect of adsorbed carbonaceous species on metallic Pt should determine the catalytic reaction start-up behavior of supported Pt catalysts. Besides the suitable Pt reduction temperature, the oxygen reactivity in the support oxide is also important for lowering the catalytic start-up temperature. The control of the Pt–support interactions to provide suitable Pt reducibility and also oxygen reactivity in oxide support are both important to achieve a lower catalytic reaction start-up temperature.
Keywords: Operando spectroscopy; Automotive catalyst; Pt; NO reduction; Support effect
Cobalt–polypyrrole–carbon black (Co–PPY–CB) electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells: Composition and kinetic activity by Danh Nguyen-Thanh; Anatoly I. Frenkel; Jianqiang Wang; Stephen O’Brien; Daniel L. Akins (pp. 50-60).
Display Omitted► The ORR activity of Co–PPY–CB electrocatalysts significantly varies with composition. ► A CB:PPY ratio (wt.) of 2 maximizes N presence on CB while preserving the porosity. ► A pyrrole:Co ratio (mol.) of 4 leads to complexes with Co coordinated to 3–4 N. ► Calcination of those complexes yields CoN x−2 sites that are ORR active and selective. ► A catalyst with such ratios compares favorably to a Pt one, with a 200mV loss.Electrocatalysts consisting of polypyrrole (PPY) and Co deposited on carbon black (CB) at several compositions were prepared and tested for the oxygen reduction reaction (ORR) in a HClO4 buffer (pH=1) using a rotating ring-disk electrode (RRDE). It was determined that the most favorable catalyst composition (prior to calcination) had a CB:PPY weight ratio of 2 and a pyrrole:Co (i.e., PY:Co) molar ratio of 4. This catalyst had an onset potential of 0.785V (vs. RHE) and a mass activity of ca. 1A/gcata at the fuel cell relevant voltage of 0.65V. Furthermore, it was found that the number of electrons exchanged during the ORR with the catalyst was ca. 3.5 and resulted in 28% yield of H2O2 at 0.65V, which hints to an indirect 4 e− reduction of O2 to H2O, with H2O2 as an intermediate. From energy dispersive spectroscopy (EDS) and extended X-ray absorption fine structure (EXAFS) analysis, it is proposed that a PY:Co ratio of 4 favors the formation, prior to calcination, in the catalyst precursor of Co–N complexes in which Co is coordinated to 3 or 4 N atoms, resulting in strong Co–N interactions that limit the formation upon calcination of low ORR activity Co nanoparticles. These Co–N complexes give rise upon calcination to CoN x−2 sites in which the coordination of Co could favor the adsorption on them of O2, which would make those sites particularly active and selective. At the same mass activity of 1A/gcata, the voltage yielded by the catalyst was 200mV lower than that for a state-of-the-art Pt (10wt.%) catalyst, whose H2O2 output at 0.85V was 39% and involves the exchange of 3.2 e−, overall making our material an attractive substitute to noble metal ORR electrocatalysts.
Keywords: Oxygen reduction reaction; EXAFS; Nonprecious metal electrocatalysts; Polypyrrole; PEMFCs
Sulfur poisoning of molybdenum dioxide during the partial oxidation of a Jet-A fuel surrogate by Oscar Marin-Flores; Timothy Turba; Caleb Ellefson; Louis Scudiero; Joe Breit; M. Grant Norton; Su Ha (pp. 61-68).
Display Omitted► Influence of sulfur compounds on MoO2 under partial oxidation of dodecane studied. ► MoO2 displays stable performance at benzothiophene concentrations of 1000ppmw. ► TEM and XPS show the deactivation process of MoO2 under 5wt% benzothiophene. ► Formation of surface MoS2 promotes coke formation under 5wt% benzothiophene.The aim of the present work is to investigate the effect that organic sulfur compounds have on the catalytic performance of molybdenum dioxide (MoO2) during the partial oxidation reaction of aviation fuels. N-dodecane and benzothiophene were used as surrogates for Jet-A fuel and as a model sulfur compound, respectively. Activity tests of commercial MoO2 toward the partial oxidation reaction of this model Jet-A fuel were performed at 850°C. Our studies indicate that MoO2 displays a remarkable tolerance to deactivation by organic sulfur compounds even at concentrations as high as 1000ppmw, a typical sulfur concentration found in aviation fuels. However, commercial MoO2 catalysts show a significant catalytic performance deactivation as the concentration of organic sulfur compounds increases to 3000ppmw. TEM and XPS data indicate that the deactivation process starts with the formation of Mo sulfide on the catalyst surface. The sulfide phase appears to reduce the ability of the catalyst to activate hydrocarbon molecules as well as impeding the ability to deliver lattice oxygen to the active surface sites, which leads to the enhancement of side reactions that promote the formation of coking. The catalyst deactivation resulting from the exposure to such high concentrations of organic sulfur compounds appears to be reversible with an air treatment at 850°C. The catalyst activity of MoO2 recovers approximately 80% of its initial performance as demonstrated by the H2 yield and TEM data.
Keywords: Molybdenum dioxide; Molybdenum sulfide; Organic sulfur compounds; Hydrogen production; Partial oxidation; Jet fuels
Delaminated titanate and peroxotitanate photocatalysts by Tom A. Stewart; May Nyman; Maarten P. deBoer (pp. 69-76).
Display Omitted► We compare photocatalytic activity of delaminated Cs-titanate and Na-titanate. ► They are comparably effective, yet Na-titanate is cheaper and easier to produce. ► Chemical modifications, peroxide and phosphate both enhance photocatalytic activity. ► Titanates electrostatically sorbed to a surface retain their photocatalytic activity.Delaminated layered titanates are effective, versatile, robust and practical photocatalytic materials for degradation of organic and microbiological contaminants. In prior studies, these have generally been obtained from Cs-titanate lepidocrocite-analogue parent materials. In this study we show that delaminated sodium nonatitanate (SNT) is equally effective as the delaminated Cs-titanate; yet it is cheaper to synthesize and is obtained in about one-third as many processing steps. Two chemical modifications; ligation with peroxide and treatment with phosphate resulted in improved photodegradation of common dyes; bromophenol-blue and methyl-orange. Together these two dyes provided experimental conditions ranging from pH ∼4.5–9. All layered titanate materials proved to be more effective colloidal suspension photocatalysts than standard TiO2. Although most common characterization techniques could not distinguish significant differences between the different delaminated titanates (from different parent materials, with chemical modifications), band-gap measurement via UV–vis spectroscopy proved informative. Generally the closer the match between the band-gap and the UV-light source, the more effective the catalyst. Finally, these layered titanates were electrostatically adhered to a surface, and photocatalytic activity was retained in this form. Furthermore, in this surface-adsorbed form we could see clear morphological differences between the Cs-titanate and SNT derived materials, as well as measure the height of the adsorbed layers. All observations by Atomic Force Microscopy indicated that the titanates layers that adhere to mica have a thickness of 1–10 layers thick (∼1–4nm). These materials in their surface-fixed forms are very promising for water treatment technologies.
Keywords: Photocatalysis; Layered-titanates; Peroxide; Sodium nonatitanate; Cs-titanate lepidocrocite
Photocatalytic hybrid nanocomposites of metal oxide nanoparticles enhanced towards the visible spectral range by Nihan Kosku Perkgoz; Refik Sina Toru; Emre Unal; Mustafa Akin Sefunc; Sumeyra Tek; Evren Mutlugun; Ibrahim Murat Soganci; Huseyin Celiker; Gulsen Celiker; Hilmi Volkan Demir (pp. 77-85).
Display Omitted► Hybrid nanocomposites exhibit enhanced photocatalytic activity in the visible spectral range. ► The synergy is promising for large area decontamination applications that use outdoor sunlight. ► Thin films of integrated TiO2 (ca. 6nm) and ZnO (ca. 40nm) are optically characterized at different wavelengths. ► The structure of hybrid nanocomposite films is shown by SEM, XRD, and HRTEM.We propose and demonstrate photocatalytic hybrid nanocomposites that co-integrate TiO2 and ZnO nanoparticles in the same host resin to substantially enhance their combined photocatalytic activity in the near-UV and visible spectral ranges, where the intrinsic photocatalytic activity of TiO2 nanoparticles or that of ZnO nanoparticles is individually considerably weak. For a comparative study, by embedding TiO2 nanoparticles of ca. 6nm and ZnO nanoparticles of ca. 40nm in the sol–gel matrix of acrylic resin, we make thin film coatings of TiO2–ZnO nanoparticles (combination of TiO2 and ZnO, each with a mass ratio of 8.5%), as well as the composite films of TiO2 nanoparticles alone (17.0%), and ZnO nanoparticles alone (17.0%), and a negative control group with no nanoparticles. For all of these thin films coated on polyvinyl chloride (PVC) polyester, we experimentally study photocatalytic activity and systematically measure spectral degradation (recovery obtained by photocatalytic reactions). This spectral characterization exhibits photodegradation levels of the contaminant at different excitation wavelengths (in the range of 310–469nm) to distinguish different parts of optical spectrum where TiO2 and ZnO nanoparticles are individually and concurrently active. We observe that the photocatalytic activity is significantly improved towards the visible range with the use of TiO2–ZnO combination compared to the individual cases. Particularly for the excitation wavelengths of photochemical reactions longer than 400nm, where the negative control group and ZnO nanoparticles alone yield no observable photodegradation level and TiO2 nanoparticles alone lead to a low photodegradation level of 14%, the synergic combination of TiO2–ZnO nanoparticles achieves a photodegradation level as high as 30%. Investigating their scanning electron microscopy (SEM), X-ray diffraction (XRD), and high resolution transmission electron microscopy (HRTEM), we present evidence of the heterostructure, crystallography, and chemical bonding states for the hybrid TiO2–ZnO nanocomposite films, in comparison to the films of only TiO2 nanoparticles, only ZnO nanoparticles, and no nanoparticles.
Keywords: Immobilized nanoparticles; Nanocomposite films; Titanium dioxide; Zinc oxide; Photocatalytic activity; Optical characterization
Pt-catalysts supported on activated carbons for catalytic wet air oxidation of aniline: Activity and stability by Sergio Morales-Torres; Adrián M.T. Silva; Francisco J. Maldonado-Hódar; Bruno F. Machado; Agustín F. Pérez-Cadenas; Joaquim L. Faria; José L. Figueiredo; Francisco Carrasco-Marín (pp. 86-94).
.Display Omitted► Preparation of highly porous activated carbons (ACs) from bioresidues. ► Relation of metal phase dispersion (Pt) and support porosity (ACs). ► Catalysts activity increases with Pt dispersion. ► Pt/ACs are highly active for the degradation of aniline in aqueous solutions. ► The activity of the Pt-catalysts is preserved during various cycles.Three activated carbons (ACs) were prepared from olive stones using KOH as activation agent at different temperatures. These materials present similar surface chemistry, but a larger porosity (mainly microporosity) is developed by increasing the activation temperature. The ACs were used as supports for Pt-catalysts and those with a larger porosity led to the highest Pt dispersion. The ACs and the supported Pt-catalysts were tested in the degradation of aniline by catalytic wet air oxidation. Aniline conversion and mineralization was found to depend on the porosity and Pt dispersion of the catalysts. The materials were characterized before and after reaction by different techniques (N2 and CO2 adsorption, elemental analysis, TPD and XPS). Analysis of the catalysts after reaction indicated some loss of microporosity, accompanied by an increase of the oxygenated surface groups and changes in the Pt oxidation state. In addition, no Pt leaching was detected. The performance of the catalysts was evaluated during three consecutive cycles without any reactivation treatment. The activity decreased after the first cycle, which is due to the saturation of the adsorption capacity; however, the catalytic performance was constant during the second and third cycles, showing the high stability of the tested catalysts.
Keywords: Activated carbons; Pt-catalysts; CWAO; Aniline; Catalytic performance
Solar/lamp-irradiated tubular photoreactor for air treatment with transparent supported photocatalysts by R. Portela; S. Suárez; R.F. Tessinari; M.D. Hernández-Alonso; M.C. Canela; B. Sánchez (pp. 95-102).
Display Omitted► Novel versatile annular photoreactor for solar and/or artificial radiation. ► TiO2-coated transparent monoliths – based on PET or glass – as photocatalytic units. ► Efficiency to oxidize H2S in both synthetic air and the real air of a wastewater treatment plant. ► Simultaneous elimination of other volatile organic compounds, such as mercaptanes or aromatic or aliphatic hydrocarbons. ► Adsorption–desorption phenomena are responsible for activity and selectivity hysteresis in daily cycles.A novel versatile tubular reactor that may use both types of radiation, solar and/or artificial, and different types of suspended or immobilized photocatalysts is proposed. The photocatalytic reactor was evaluated for air treatment at laboratory scale and semi-pilot-plant scale. UV-A transparent immobilized photocatalysts were employed, which allowed an efficient use of radiation. Two different types of photocatalytic modules were tested: (a) TiO2-coated PET monoliths and (b) TiO2-coated glass slides, arranged in monolith-like units with the help of especially designed star-shaped polygonal structures. Both types of units were easy to handle and assured the adequate distribution of the photocatalyst inside the tubular reactor. The efficiency of the photocatalytic system with both solar and artificial radiation to oxidize the H2S contained in an air stream was demonstrated at the laboratory roof and in the treatment of real air of a wastewater treatment plant located in Madrid (Spain). As a consequence of the chemical nature of the pollutant, the photocatalytic activity decayed over time due to the accumulation of sulfate on the surface, but easy regeneration of the exhausted photocatalyst was achieved by washing with water.
Keywords: Photoreactor; Pilot-plant; Solar; UV-lamp; Supported photocatalyst; Monolith; H; 2; S
Highly effective CuO/Fe(OH) x catalysts for selective oxidation of CO in H2-rich stream by Botao Qiao; Aiqin Wang; Jian Lin; Lin Li; Dangsheng Su; Tao Zhang (pp. 103-110).
Display Omitted► CuO/Fe(OH) x catalyst was prepared with a simple co-precipitation method. ► It is highly active and selective for PROX reaction with a wide temperature window. ► It shows good activity and stability even with the presence of CO2 and H2O. ► The significant reducibility might contribute to the high activity of the catalyst.Ferric hydroxide supported copper oxide (CuO/Fe(OH) x) catalysts were prepared with a simple co-precipitation method and used for selective oxidation of CO in H2-rich gas. The effect of calcination temperatures and Cu loadings on the activity as well as the durability of the catalyst was investigated. When the calcination temperature was 200°C and the Cu loading was ranging from 7.2 to 17.3wt%, the catalyst gave the best performance with total conversion of CO achievable in a wide temperature window from 110°C to 150°C. To reveal the reason for the high activity of the catalysts, a variety of characterization techniques were employed. The results of XRD and TG–DTA indicated that the catalysts were amorphous even after being calcined at 400°C, which gave rise to large surface areas. HRTEM and XPS examinations indicated that the surface copper species were Cu2O with particle size of smaller than 5nm. In situ DRIFT and FT-IR results showed that the reduction of Cu2+ in the composite occurred even below room temperature when exposed to CO. The significant reducibility might contribute to the high activity of the catalysts.
Keywords: CuO; Fe(OH); x; CuO–Fe; 2; O; 3; CO oxidation; PROX; Hydrogen purification
Photocatalytic degradation of ethylene: An FTIR in situ study under atmospheric conditions by Birger Hauchecorne; Tom Tytgat; Sammy W. Verbruggen; Dieter Hauchecorne; Dieter Terrens; Marianne Smits; Katrien Vinken; Silvia Lenaerts (pp. 111-116).
Display Omitted► FTIR in situ reactor used for real time study of photocatalytic ethylene removal. ► Backdonation as hypothesis on how the oxidation reaction is initiated. ► Formaldehyde and formic acid are found as reaction intermediates.In this paper, the reaction mechanism of the photocatalytic oxidation of ethylene is elucidated by means of an in-house developed FTIR in situ reactor. This reactor allowed us to look at the catalytic surface at the moment the reactions actually occur. This new approach gave some exciting new insights in how ethylene is photocatalytically oxidised. It was found that there is a change in dipole moment of the ethylene molecule when it is brought in the neighbourhood of the catalyst. From this finding, a hypothesis was formulated on how the CC-bond from ethylene will break. It was found that the aforementioned interaction between the catalyst and the molecule, allows the excited electrons from the UV irradiated catalyst to occupy the lowest unoccupied molecular orbital (LUMO) of the ethylene molecule through a process known as backdonation. Following this hypothesis, it was found that the degradation occurs through the formation of two intermediates: formaldehyde and formic acid, for which formaldehyde is bound in two different ways (coordinatively and as bidentate). Finally CO2 and H2O are found as end products, resulting in the complete mineralisation of the pollutant.
Keywords: Photocatalysis; Ethylene; In situ FTIR study; Reaction mechanism; Molecular orbital theory
Reaction mechanism of the glycerol hydrogenolysis to 1,3-propanediol over Ir–ReO x/SiO2 catalyst by Yasushi Amada; Yasunori Shinmi; Shuichi Koso; Takeshi Kubota; Yoshinao Nakagawa; Keiichi Tomishige (pp. 117-127).
Display Omitted► Glycerol hydrogenolysis over Ir–ReO x/SiO2 showed high selectivity to 1,3-propanediol. ► The active site may be the interface between Ir metal and ReO x cluster. ► Ir–ReO x/SiO2 selectively dissociated the C–O bond neighboring to –CH2OH group. ► 1,3-Propanediol is obtained via more stable 6-membered-ring transition state.The mechanism of the hydrogenolysis of glycerol to 1,3-propanediol over Ir–ReO x/SiO2 catalyst was discussed. We investigated the catalytic performance, structure, reaction kinetics and reactivity trends of various substrates over the catalysts with different amount of Re. The conversion in the glycerol hydrogenolysis increased with increasing the amount of Re up to Re/Ir=2, and the high selectivity to 1,3-propanediol (ca. 60%) was almost independent of the Re amount. The average size of Ir metal particle gradually decreased with increasing the amount of Re from XRD and TEM. Characterization results such as CO adsorption, TPR, XANES, EXAFS suggested that Ir metal surface was partially covered with ReO x cluster regardless of the Re amount. The reaction order on H2 pressure over Ir–ReO x/SiO2 (Re/Ir=1) was one, suggesting that one active hydrogen species was produced from one hydrogen molecule. Low reaction order on glycerol concentration represented the strong interaction between glycerol and catalyst surface. This catalyst is also applicable to the selective hydrogenolysis of the C–O bond neighboring a –CH2OH group. These reaction trends and characterization results supported the direct reaction mechanism for the formation of 1,3-propanediol from glycerol via 2,3-dihydroxypropoxide species.
Keywords: Biomass; Iridium; Rhenium; Hydrogenolysis; 1,3-Propanediol
Reduction of highly concentrated nitrate using nanoscale zero-valent iron: Effects of aggregation and catalyst on reactivity by Anna Ryu; Seung-Woo Jeong; Am Jang; Heechul Choi (pp. 128-135).
Display Omitted► NZVIs and Ni-NZVIs were able to effectively reduce highly concentrated nitrate. ► Aggregate size and catalyst (0.2wt% Ni coating) notably affect nitrate reduction. ► Aggregation is more important than catalyst as aggregate size becomes smaller. ► Reduction of 10–10,000ppm nitrate within 1min was obtained by F-NZVI and F-Ni-NZVI.Nanoscale zero-valent iron (NZVI) has been studied as an effective nitrate reduction material. Here, the effect of NZVI aggregation on the reduction reaction order and rate was investigated by comparing the nitrate reduction performances of freshly synthesized NZVI (F-NZVI), dried NZVI (D-NZVI), and dried-sonicated NZVI (DS-NZVI). Also, the effects of a catalyst were evaluated by coating 0.2wt% Ni on previous series of NZVIs: F-Ni-NZVI, D-Ni-NZVI, and DS-Ni-NZVI. Different types of NZVIs could effectively reduce highly concentrated nitrate without requiring pH control. F-NZVI and F-Ni-NZVI showed extremely fast reactions, reducing 10–10,000ppm within 1min, and thus their reaction kinetics could not be evaluated under these experimental conditions. In the case of 10,000ppm of nitrate, NZVI was almost completely consumed after reducing about 5000ppm within 1min. In contrast, nitrate reduction using D-NZVI and D-Ni-NZVI were pseudo-first-order reactions and DS-NZVI and DS-Ni-NZVI were 1.37 and 1.71 order reactions, respectively. D-Ni-NZVI and DS-Ni-NZVI obtained a higher reduction rate than D-NZVI and DS-NZVI due to the existence of the Ni catalyst. These experimental results suggest that the aggregate size and catalyst prominently affect the nitrate reduction rate and that the aggregation effect is more important than the catalyst effect as the aggregate size becomes smaller. Furthermore, the importance of the NZVI structure, the branch of chain-like structures and its edges exposed to the aqueous phase in nanoscale, is proposed in this study in order to explain the ultra fast reaction of F-NZVI and F-Ni-NZVI, which have yet to be reported. The final product of the reaction was ammonium, with nitrite being produced as a byproduct; NZVI changed into different shapes of magnetite (Fe3O4) after the reaction, depending on the reaction conditions.
Keywords: Nanoscale zero-valent iron (NZVI); Nickel; Nitrate reduction; Aggregation; Edge
Catalytic hydrothermal gasification of activated sludge by Elie Afif; Pooya Azadi; Ramin Farnood (pp. 136-143).
Near-critical water gasification of municipal activated sludge at 380°C.Display Omitted► Raney nickel exhibited good activity to gasify municipal activated sludge in near-critical water. ► At 380°C and with 1.8g catalyst/g dry sludge, carbon and hydrogen gasification ratios were 69% and 113%; respectively, after 15min reaction time. ► Raney nickel lost half of its activity after 8min exposure to NCW at 380°C.In this paper, Raney nickel is used as catalyst to gasify activated sludge in near-critical water (NCW) at a temperature range of 320–410°C and a corresponding pressure range of 11.3–28.1MPa in a batch reactor. At 380°C and with 15min reaction time, carbon gasification ratios (CGR) increased with increasing catalyst loading and reached 69% at 1.8g catalyst/g dry sludge. Methane yield also linearly increased with catalyst loading while hydrogen production exhibited a maximum at about 1.5g catalyst/g dry sludge. The gaseous product in this case consisted of 46% hydrogen, 25% methane and 29% carbon dioxide with trace amounts of carbon monoxide. The amount of generated gas as well as its composition did not change significantly after 30min; however, increasing the temperature had a positive effect on the total yield up to 380°C. The addition of sulfur to activated sludge resulted in a significant reduction of the carbon gasification ratio. CGR dropped by about 25% as the sulfur content of the feed increased from 0.8% to 3.0%. The deactivation of the catalyst due to hydrothermal sintering was also examined. Raney nickel significantly lost its activity upon pre-exposure to near-critical water at 380°C for 8min. This loss in activity had a major impact on methane production where methane yield dropped by six folds to a level similar to the catalyst-free gasification reaction and hydrogen yield was decreased by 50%. The decrease in catalytic activity of Raney nickel was likely due to an increase in average nickel crystallite size caused by hydrothermal sintering.
Keywords: Supercritical water; Hydrothermal; Catalytic gasification; Activated sludge; Hydrogen; Raney nickel
Effects of synthesis conditions on the characteristics and reactivity of nano scale zero valent iron by Yu-Hoon Hwang; Do-Gun Kim; Hang-Sik Shin (pp. 144-150).
Display Omitted► The chemical synthesis condition for NZVI had not yet been clearly standardized. ► We verify the effect of reaction conditions on NZVI characteristics and reactivity. ► NZVI morphology was varied under different reaction time and nuclei concentration. ► The reactivity was increased under high nuclei concentration and fast synthesis. ► The nuclei formation step was the key step in determining NZVI characteristics.Application of nano zero valent iron (NZVI) is an innovative technology for water treatment and soil/groundwater remediation. Among various NZVI synthesis methods, chemical reduction is widely used due to its simplicity and chemical homogeneity. However, the synthesis procedure had not yet been clearly standardized. In this study, the effects of reaction conditions such as reaction time and NZVI concentration on NZVI characteristics and reactivity were investigated. Nanocluster and whisker structures were obtained under fast reduction conditions. The particle size was dramatically decreased from 87.4nm to 9.5nm under short reaction time and high reductant concentration. Simultaneously, the BET surface area was increased from 8.4m2/g to 45.4m2/g. The reactivity of NZVI was evaluated by a nitrate reduction test. The experimental data were interpreted by pseudo first order kinetics with first order deactivation. The reactivity was increased in the direction of high reductant concentration and fast synthesis, although deactivation increased in the same direction. Among the 4 reaction steps for NZVI synthesis, the nuclei formation step was determined to be the key step in determining NZVI characteristics. Therefore, it is important to control the reaction time and concentration in order to maximize the efficiency of NZVI.
Keywords: Nano zero valent iron; Synthesis; Nucleation time; Reductant delivery rate; Precursor concentration
Promoting effect of synthesis method on the property of nickel oxide doped CeO2-ZrO2 and the catalytic behaviour of Pd-only three-way catalyst by Guangfeng Li; Qiuyan Wang; Bo Zhao; Renxian Zhou (pp. 151-162).
.Display Omitted► Pd/CZN-s exhibits the best catalytic performance and the widest operation window. ► CZN-s confirms the formation of homogeneous ternary solid solution. ► CZN-s maintains higher thermal and structural stability after aging. ► Pd/CZN-s shows higher concentration of Ce3+ or the formation of oxygen vacancies. ► The more concentration of Ce3+ over CZN-s leads to the enhancement of OSCC.CeO2-ZrO2 doped by nickel oxide (CZN) with different method and Pd-only three-way catalysts (Pd/CZN) were prepared and characterized. The catalyst prepared by co-precipitation and supercritical drying process (Pd/CZN-s) exhibits the best catalytic activity and the widest operation working window before and after aging. Compared with other samples, CZN-s shows the formation of more homogeneous ternary solid solution with the smallest lattice parameter and crystallite size. Moreover, CZN-s maintains the high thermal and structural stability with higher surface area and larger pore volume after aging. Pd/CZN-s exhibits higher relative concentration of Ce3+ associated with the formation of more oxygen vacancies before and after aging, confirmed by X-ray photoelectron spectroscopy and Raman results. The more concentration of Ce3+ or oxygen vacancies leads to the enhancement of oxygen storage complete capacity of CZN-s. Moreover, the higher the oxygen storage capacity, the wider the working ranges of air/fuel variations.
Keywords: CeO; 2; -ZrO; 2; Oxygen storage capacity; Supercritical drying; Pd-only three-way catalysts
Production of nanostructured magnetic composites based on Fe0 nuclei coated with carbon nanofibers and nanotubes from red mud waste and ethanol by Aline A.S. Oliveira; Juliana C. Tristão; José D. Ardisson; Anderson Dias; Rochel M. Lago (pp. 163-170).
.Display Omitted► Conversion of the waste red mud in a magnetic composite by CVD with ethanol. ► Formation of large amounts of carbon (30–50wt%) especially as nanotubes/nanofibers. ► The product can be separated into two fractions, one with average size of 10–100nm. ► The carbon in the composites can be activated with CO2 to double its surface area. ► The composite can be used as adsorbent and support to produce recyclable catalysts.In this work, a catalytic CVD process using ethanol as carbon source was used to convert an iron rich waste, i.e. red mud (RM), in a magnetic composite. TPCVD (temperature programmed CVD), XRD, Mössbauer, EDS, magnetic measurements, TG/DTA, CHN, BET, Raman, SEM and TEM showed that ethanol gradually reduces the iron phases in the RM to Fe3O4 at 500°C and to Fe1− xO at 600°C. At higher temperatures Fe0 and Fe carbide are the main phases produced with the formation of large amounts of carbon (30–50wt%) especially as nanotubes and nanofibers. These magnetic materials can be separated into two fractions by simple dispersion in water, i.e. a settled material composed of large magnetic particles and the suspended material composed of nanoparticles with average size of 10–100nm. The carbon in the composites can be activated with CO2 increasing the surface area from 79 to 185m2g−1. The magnetic composites were used as adsorbent of model dyes methylene blue and indigo carmine showing excellent results. The composites were also used as support to produce a recyclable Pd catalyst. Tests for the 1,5-cyclooctadiene hydrogenation showed that the catalyst can be easily magnetically separated from the reaction medium and reused for five consecutive times with no deactivation or change in selectivity.
Keywords: Red mud; CVD; Magnetic nanoparticles; Ethanol
Cellulose hydrothermal conversion promoted by heterogeneous Brønsted and Lewis acids: Remarkable efficiency of solid Lewis acids to produce lactic acid by Flora Chambon; Franck Rataboul; Catherine Pinel; Amandine Cabiac; Emmanuelle Guillon; Nadine Essayem (pp. 171-181).
.Display Omitted► Solid Lewis acids catalysts exhibited a promoting effect on the cellulose depolymerisation. ► High yields in lactic acid are obtained with the solid Lewis acids catalysts. ► Solid Brønsted catalysts are unstable for cellulose conversion in hydrothermal conditions.Crystalline cellulose treated in hydrothermal conditions (190°C, 24h) is partially solubilised, 30%, into water soluble oligosaccharides/polymers with the formation of small amounts of glucose and 5-HMF. In the presence of solid Brønsted catalysts such as Cs2HPW12O40 and HY zeolite, the extent of the cellulose depolymerisation was not changed when no leaching occurred. However, a quite different products distribution was obtained, in favour of further transformations of glucose and HMF in levulinic and formic acids. On the opposite, solid Lewis acids such as tungstated zirconia (ZrW) and tungstated alumina (AlW) exhibited a remarkable promoting effect on the cellulose depolymerisation which was raised up to 45% while an unexpected decrease of the proportion of water soluble oligosaccharides/polymers was observed. Yields of 27mol% and 18.5mol% in lactic acid were achieved on AlW and ZrW, respectively. Moreover, these tungsten based Lewis acids exhibited a good stability and recyclability. The efficiency of the solid Lewis acids ZrW and AlW to produce lactic acid directly from crystalline cellulose was explained by a positive synergy between water autoprotolysis responsible of the cellulose depolymerisation into soluble intermediates which are further converted on the solid Lewis catalyst surface.
Keywords: Cellulose hydrolysis; Solid Lewis acid catalysts; Tungstated zirconia; Tungstated alumina; Lactic acid
Combustion of propane over novel zinc aluminate-supported ruthenium catalysts by Janina Okal; Mirosław Zawadzki (pp. 182-190).
Display Omitted► Zinc aluminate with high surface area is a promising support for Ru catalysts. ► Novel Ru/ZnAl2O4 catalysts exhibit good activity for propane combustion. ► High activity is attributed to high ruthenium dispersion.Nanocrystalline ZnAl2O4 spinel, with high specific surface area, was synthesized by the improved co-precipitation method and used to prepare novel Ru/ZnAl2O4 catalysts. The catalysts were prepared by impregnation method using Ru(NO)(NO3)3 and their performance in propane combustion was investigated. The structure of the catalysts was characterized by FTIR, BET, XRD, TEM, H2 chemisorption and O2 uptake in order to correlate their performance with physicochemical properties. Dispersion (H/Ru) of the Ru/ZnAl2O4 catalysts was high and decreased from 71 to 56% with the rise of ruthenium content from 0.5 to 4.5wt.%. Dispersion data were consistent with TEM and XRD studies. The O2 uptake results showed that ruthenium in the 0.5–1% Ru/ZnAl2O4 catalysts was oxidized already at 150°C (O/Ru=2), while in the 4.5% catalyst at 400°C. The Ru/ZnAl2O4 catalysts exhibited good activity in propane combustion under oxygen-rich conditions and 100% conversion was reached at about 230°C. The catalyst activities correlate well with a high dispersion and low Ru particle sizes. It was found that specific reaction rate (TOF) does not depend on the Ru loading or the mean Ru particle size. Moreover, only insignificant aggregation of the highly dispersed ruthenium species occurs under the reaction conditions and samples especially at low metal loadings, form a very stable catalyst for propane combustion. The effect of the regeneration treatment in H2 on the activity of the 4.5% Ru/ZnAl2O4 catalyst was also studied. The catalytic performance of Ru slightly declined in the regenerated samples. The large structural changes in the high-loaded Ru/ZnAl2O4 catalyst observed after regeneration treatment, are probably the best explanation for the lower activity of this system.
Keywords: Ruthenium; Zinc aluminate; Propane combustion; TEM; XRD; O; 2; uptake
A comparative study of the activity of TiO2 Wackherr and Degussa P25 in the photocatalytic degradation of picloram by Biljana Abramović; Daniela Šojić; Vesna Despotović; Davide Vione; Marco Pazzi; János Csanádi (pp. 191-198).
Display Omitted► Kinetics and efficiency of photocatalytic degradation of the pesticide picloram. ► Two TiO2 specimens employed and most important operational parameters studied. ► Faster degradation obtained with the TiO2 specimen of the lower surface area. ► Results suggest the importance of other factors (optical properties and back reactions). ► Photocatalytic transformation pathways of picloram including mineralization.A comparative study was carried out of the efficiency of titanium dioxide specimens Wackherr and Degussa P25 toward the photocatalytic degradation of picloram, a widely used herbicide. The study encompassed transformation kinetics and efficiency, identification of intermediates and reaction pathways. In the investigated range of initial concentrations (0.25–1.0mM), the photocatalytic degradation of picloram in the first stage of the reaction followed approximately a pseudo-first order kinetics. The TiO2 Wackherr induced significantly faster picloram degradation than TiO2 Degussa P25 when high photocatalyst loadings and high substrate concentrations were used. By examining the effect of ethanol as a hydroxyl radical scavenger, it was shown that the photocatalytic degradation of picloram takes place mainly via the hydroxyl radicals, while the valence-band holes play a less important role. Total organic carbon analysis showed that complete mineralization of picloram occurred after about 16h of irradiation. Several degradation intermediates were identified by using LC–MS, GC–MS, and1H NMR, which allowed the proposal of a tentative pathway for the photocatalytic transformation of picloram. Finally, the photocatalytic degradation rates of three selected herbicides (picloram, triclopyr and mecoprop) were compared, and the results show that the efficiency of photocatalytic degradation is greatly influenced by the molecular structure.
Keywords: Picloram; Herbicide; Photocatalysis; Titanium dioxide; Photocatalytic degradation pathways
Aluminum doped SBA-15 silica as acid catalyst for the methanolysis of sunflower oil by I. Jiménez-Morales; J. Santamaría-González; P. Maireles-Torres; A. Jiménez-López (pp. 199-205).
Display Omitted► Mesoporous acid solids were obtained by post-synthesis alumination of a SBA-15 silica. ► The catalysts are active in the methanolysis of sunflower oil at 200°C. ► No leaching of aluminum is detected and catalysts can be reutilized. ► These acid catalysts catalyze the FFAs esterification of and oil transesterification.Post-synthesis alumination of a mesoporous SBA-15 silica, with different Si/Al molar ratios, has been successfully carried out and the resulting acid solids were employed as catalysts in the methanolysis of sunflower oil. The acid properties of these catalysts depend upon the aluminum content and the activation temperature (350 or 550°C). Although all the catalysts thermally treated at 550°C were very active, the highest catalytic performance was found with the catalyst containing a Si/Al molar ratio of 20. With only 10wt% of this catalyst in relation to the oil, a 96wt% of biodiesel formation was attained at 200°C and after only 4h of reaction. The catalysts are stable and no leaching of aluminum ions to the liquid medium was found. Moreover, these catalysts are able to simultaneously catalyze the esterification of free fatty acids (FFAs) and the transesterification of triglycerides, even in the presence of 9% of FFAs. The activity of this catalyst is well maintained after three cycles of catalysis without any treatment and in the presence of 5wt% of water. The use of a co-solvent hardly affects the biodiesel formation.
Keywords: Transesterification; Methanolysis; SBA-15; Acid catalysts; Mesoporous solids
Solvothermal synthesis and photocatalytic properties of chromium-doped SrTiO3 nanoparticles by Uyi Sulaeman; Shu Yin; Tsugio Sato (pp. 206-210).
Display Omitted► Synthesis Cr-doped SrTiO3 (SrTi1− xCr xO3) nanoparticles under solvothermal reaction. ► A new band gap in the visible light region could be generated. ► Showing the excellent photocatalytic activity in red light irradiation (λ=627nm). ► Small amount ( x=0.005) of chromium resulted in high photocatalytic activity.Chromium (Cr)-doped SrTiO3 nanoparticles were synthesized by a microwave-assisted solvothermal reaction using SrCl2·6H2O and Ti(OC3H7)4 as starting materials in KOH methanol–oleic acid solution. The products were characterized by XRD, TEM, BET surface area, and XPS. The photocatalytic activity was determined by DeNO x ability using LED lamps with wavelengths of 627nm (red), 530nm (green), 445nm (blue) and 390nm (UV). The nanoparticles of perovskite type Cr-doped SrTiO3 with a particle size of 15–20nm were successfully synthesized. The photocatalytic activity of SrTiO3 for DeNO x ability under visible light (627nm) irradiation was able to be improved by doping with a small amount of Cr. The high photocatalytic activity of Cr-doped SrTiO3 in the visible region was caused by new absorption in the visible region.
Keywords: Solvothermal synthesis; Chromium doping; SrTiO; 3; Photocatalysis
Room-temperature synthesis of single-crystalline Se nanorods with remarkable photocatalytic properties by Yao-De Chiou; Yung-Jung Hsu (pp. 211-219).
Display Omitted► Single-crystalline Se NRs were prepared with a facile chemical reduction approach. ► The dimensions of the resulting NRs can be readily controlled. ► A memory photocatalytic effect in dark environment was demonstrated for Se NRs. ► Se NRs exhibited superb photocatalytic efficiency under UV illumination. ► Recycling test reveals the reusability and stability for Se NRs in photocatalysis.We demonstrated for the first time that single-crystalline Se nanorods (NRs), prepared with a facile chemical reduction approach at room temperature, may display noticeable catalytic activities toward methylene blue degradation in dark environment after subjected to a short period of irradiation. Such capability of photocatalysis in the dark for Se NRs was attributed to the memory effect related to pre-irradiation treatment. The result of spin-trapping electron paramagnetic resonance measurement suggests that a sustained supply ofOH radicals could be attained for Se NRs upon the cease of irradiation, which is accountable for the memory photocatalytic effect as revealed in the dark. As compared to the commercial P-25 TiO2 powder and Se nanoparticles, the as-synthesized Se NRs exhibited superior photocatalytic performance under UV illumination, demonstrating their potential as active photocatalysts in relevant redox reactions. Furthermore, the recycling test reveals that Se NRs could be promisingly utilized in the long-term course of photocatalysis. The present Se NRs may find potential use for unique photocatalytic applications, in which typical photocatalysis prevails under light illumination, while memory photocatalytic effect takes over when irradiation is interrupted.
Keywords: Selenium; Nanorods; Photocatalysis; Memory effect; Carboxylmethyl cellulose
Photocatalytic degradation of low concentration formaldehyde and simultaneous elimination of ozone by-product using palladium modified TiO2 films under UV254+185nm irradiation by Pingfeng Fu; Pengyi Zhang; Jia Li (pp. 220-228).
Display Omitted► Ultra-fine Pd nanoparticles are uniformly dispersed on TiO2 films. ► Formaldehyde can be rapidly degraded to a low level under UV254+185nm irradiation. ► Modification of TiO2 with palladium increases the removal rate of both formaldehyde and O3, with over 3 times improvement of O3 decomposition. ► The PdO x inhibit the recombination of e−/h+ pairs. ► Ozone can be decomposed on UV irradiated TiO2 and PdO x surfaces.Simultaneous elimination of formaldehyde and O3 by-product was investigated in the UV254+185nm photocatalysis with a continuous flow mode using palladium modified TiO2 films (Pd-TiO2). Formaldehyde (HCHO) was introduced at a low concentration (ca. 450ppbv), typical of polluted indoor environments. Pd nanoparticles, deposited via an electrostatic self-assembly method, had uniform distribution on TiO2 films with an average size of 3–4nm. Under UV254+185nm irradiation, the steady state concentration of HCHO was reduced to 10–50ppbv for a long irradiation period (>30h), and catalyst deactivation was not observed. Modification of TiO2 with palladium could simultaneously increase the conversion of HCHO and O3, especially at the high RH level, showing the excellent moisture-resistant behaviors. At the Pd loading of 0.3–0.4μgcm−2, the O3 conversion ratio increased over 3 times compared to pure TiO2. XPS analysis exhibited that PdO on the TiO2 was oxidized to mixture palladium oxides PdO x( x>1) under UV254+185nm irradiation. Due to high electron affinity of formed PdO2, the photogenerated electrons could be trapped by PdO x, thus improving the separation of e−/h+ pairs. As the reduction of PdO2 and oxidation of PdO coexisted, the PdO x could be dynamically stabilized, thus increasing the photoactivity of Pd-TiO2. Under UV254+185nm irradiation, the ozone might be decomposed on the Pd-TiO2 via two different routes, i.e., photocatalytic reduction of O3 on exposed TiO2 and decomposition of O3 on PdO x particles involved with UV irradiation and trapped electrons.
Keywords: Photocatalysis; Formaldehyde; Palladium modified TiO; 2; Ozone decomposition; Vacuum ultraviolet (VUV); Indoor air
Characterization of photocatalyst Bi3.84W0.16O6.24 and its photodegradation on bisphenol A under simulated solar light irradiation by Chunying Wang; Lingyan Zhu; Chao Song; Guoqiang Shan; Peng Chen (pp. 229-236).
Display Omitted► Round disk-like Bi3.84W0.16O6.24 was prepared by hydrothermal method. ► Crystallinity and morphology of Bi3.84W0.16O6.24 depended on reaction temperatures and times. ► Bi3.84W0.16O6.24 exhibited high photodegradation and mineralization activity to BPA. ► NoOH radical was detected by ESR in the degradation system with Bi3.84W0.16O6.24. ► Direct hole and O2− oxidation dominated the photodegradation by Bi3.84W0.16O6.24.Bismuth tungsten oxide Bi3.84W0.16O6.24 was prepared by hydrothermal process under pH 12. Both the hydrothermal reaction temperature and time affected the crystallinity and morphology of the prepared catalysts, which in turn affected their degradation efficiency. Although all the prepared catalysts showed adsorption in the visible region around 450nm, the catalyst synthesized at 140°C for 20h displayed the highest photocatalytic degradation capacity to bisphenol A (BPA) under simulated solar light irradiation due to the combination of its good crystallinity and perfect disk morphology. In the photodegradation system of BPA and Bi3.84W0.16O6.24, noOH was detected by electron spin resonance analysis, suggesting that direct hole is predominant in the degradation of BPA by Bi3.84W0.16O6.24. It displayed high photocatalytic degradation and mineralization capacities to BPA as compared with P25 TiO2 under simulated solar light irradiation. The analytical results of both LC–MS and GC–MS demonstrated that no hydroxylated intermediates were formed. A simple and direct photodegradation pathway of BPA by Bi3.84W0.16O6.24 was proposed by the analysis of intermediates.
Keywords: Bi; 3.84; W; 0.16; O; 6.24; Bisphenol A (BPA); Simulated solar light irradiation; TOC; Hole oxidation
Constructing graphene/InNbO4 composite with excellent adsorptivity and charge separation performance for enhanced visible-light-driven photocatalytic ability by Xiufang Zhang; Xie Quan; Shuo Chen; Hongtao Yu (pp. 237-242).
Improvement of visible photocatalysis was achieved via construction of graphene/InNbO4 composite. The pseudo-first-order kinetic constant of photocatalytic degradation of MB under visible light irradiation was 1.87 times as great as that with InNbO4.Display Omitted► The Gr/InNbO4 composite facilitated the separation of carriers. ► The Gr/InNbO4 improved the adsorption ability and then surface reactions. ► Enhanced photocatalysis was achieved via construction of Gr/InNbO4 composite. ► Introduction of Gr to InNbO4 made the •OH be another kind of photocatalytic oxidant. ► Electrons on Gr transporting from InNbO4 joined the oxidation of MB adsorbed on Gr.Graphene (Gr)/InNbO4 composite with visible light response was fabricated by a facile one-step hydrothermal method. The prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and diffuse reflectance UV–vis spectra (DRS), respectively. The results indicated that InNbO4 particles with monoclinic type mainly distributed on the Gr sheet uniformly. The samples had good visible light response. Photocatalytic degradation of Methylene Blue (MB) was conducted under the visible light irradiation (>400nm) in order to evaluate the photoactivity of this photocatalyst. The kinetic constant of MB removal with Gr/InNbO4 (0.0346min−1) was 1.87 times that with InNbO4 (0.0185min−1). The enhanced photocatalytic performance of Gr/InNbO4 was attributed to the improved adsorption performance and the separation efficiency of the carriers. With Gr/InNbO4 as the photocatalyst theOH radicals be another type of oxidant in the photocatalytic process in addition to holes and electrons on Gr transporting from InNbO4 participated the oxidation of MB adsorbed on Gr. Overall, the result of this work could provide a new way of the construction of a visible-light-driven photocatalyst with high performance.
Keywords: Photocatalysis; Visible light; InNbO; 4; Graphene; Adsorption
The promoted effect of UV irradiation on the oxidation of CO in the presence and absence of hydrogen over the TiO2-supported Pt/Co-B bicomponent catalyst by Huarong Zheng; Haiyan Yang; Ruiru Si; Wenxin Dai; Xun Chen; Xuxu Wang; Ping Liu; Xianzhi Fu (pp. 243-247).
Display Omitted► UV irradiation was firstly introduced into the process of oxidizing CO over the bicomponent Pt/Co/TiO2 catalyst. ► The photogenerated electrons from TiO2 can transfer to Pt species and then promote the oxidation of CO. ► Developing a new approach to promote the selective oxidation of CO in H2 stream for a prospective of fuel cell systems. ► The photoexcitation behavior of TiO2 may be acted as an electron donator instead of the traditional electron additives.Ultraviolet (UV) light is introduced into the process of oxidizing CO over the TiO2 supported Pt/Co-B bicomponent catalyst (Pt/Co-B/TiO2). It is found that UV irradiation can promote the oxidation of CO and the preferential oxidation of CO in the presence of H2 over Pt/Co-B/TiO2. This promoted effect of UV irradiation can also occur on other TiO2 supported Pt catalysts but not on the non-TiO2 supported Pt/Co-B catalysts. It is proposed that the photogenerated electrons induced by the photoexcitation of TiO2 can transfer to the Pt surface, resulting in the increase of surface electron density of Pt species. This further promotes the adsorption of CO and its activation at the surface Pt species, and then the subsequent oxidation of CO over Pt/Co-B/TiO2. This indicates that the photoexciatation behavior of TiO2 can be acted as an electron donator to promote the activity of the Pt/Co bicomponent catalyst for oxidizing CO.
Keywords: Oxidation of carbon monoxide; Platinum cobalt bicomponent catalyst; Photoexciatation of titanium dioxide; Electron donator
Comments on a paper by Cai et al. (Appl. Catal. B. 101 (2010) 160) dealing with XPS spectra of ceria catalysts by Ernesto Paparazzo (pp. 248-251).
XPS; CeO; 2; Ce; 2; O; 3; Ce3d spectra; Iron-doped ceria catalysts
Response to comments on “Enhanced catalytic degradation of AO7 in the CeO2–H2O2 system with Fe3+ doping” by Feng Chen; Xingxing Shen (pp. 252-254).
CeO; 2; Fe; 3+; doped CeO; 2; Ce; 3+; XPS; Ce 3d spectra