Applied Catalysis B, Environmental (v.80, #1-2)
Editorial Board (i).
Inside Front Cover (CO2).
Contents Continued (I).
Influence of the acidity of nanostructured CoMo/P/Ti-HMS catalysts on the HDS of 4,6-DMDBT reaction pathways by B. Pawelec; J.L.G. Fierro; A. Montesinos; T.A. Zepeda (1-14).
The influence of catalyst acidity on the reaction mechanism of the 4,6-dimethyldibenzothiophene (4,6-DMDBT) hydrodesulfurization (HDS) over CoMo hydrotreating catalysts was studied using a batch autoclave and fixed-bed reactor (T = 598 K and P = 5.5 MPa). P-free Ti-HMS and P-containing P/Ti-HMS mesoporous siliceous materials were synthesized and used as supports. The effect of the catalyst preparation method (successive vs. simultaneous impregnation) and phosphorous addition on catalyst acidity was studied by TPD-NH3 and DRIFT-NH3 techniques. For all synthesized catalysts, the reaction proceeds via dealkylation (DA) and isomerization (ISO) pathways, with the later being the main reaction route. Incorporation of Co and Mo phases by simultaneous impregnation was found to be the best method for catalyst preparation, whereas P-addition promote the isomerization route of 4,6-DMDBT transformation to a greater extent than the dealkylation route. On the contrary, the reaction on a CoMoP/γ-Al2O3 reference catalyst proceeds via HYD and DDS reaction pathways, the later being the main reaction route. The catalyst acidity–activity correlation indicates that both activity and selectivity depend largely on the presence of Brønsted acid sites as well as on the total amount of Brønsted and Lewis acid sites. By correlating HRTEM-activity data, the enhancement of activity and isomerization observed with the catalyst prepared by simultaneous impregnation and modified with P was related to the cumulative effects of the lower size of MoS2 slabs and their higher surface density.
Keywords: HDS; DBT; 4,6-DMDBT; CoMo catalysts; Mesoporous silica; Phosphorous; Brønsted acidity;
Catalytic stability of Ni3Al powder for methane steam reforming by Yan Ma; Ya Xu; Masahiko Demura; Toshiyuki Hirano (15-23).
We previously found catalytic activity for methane steam reforming in atomized Ni3Al powder which was pretreated by acid and subsequent alkali leaching. In this study the catalytic stability of the pretreated Ni3Al powder was investigated by isothermal test in the temperature range of 873–1173 K for 10 h. The activity was relatively stable over time at low temperatures below 973 K, especially at 873 K, where it retained the initial activity even after 10 h. However, it rapidly decreased with time at temperatures above 1073 K. Fine Ni particles, which were produced on the outer surface of Ni3Al powder during the pretreatment and served as a catalyst, survived on the surface after tests at all the temperatures. They remained almost unchanged below 973 K, leading to the good stability, while sintering and oxidation occurred at high temperatures, leading to the rapid deactivation.
Keywords: Hydrogen production; Ni3Al; Stability; Methane steam reforming;
A temperature programmed desorption investigation on the interaction of Ba0.5Sr0.5Co0.8Fe0.2O3−δ perovskite oxides with CO2 in the absence and presence of H2O and O2 by Aiyu Yan; Bin Liu; Yonglai Dong; Zhijian Tian; Dezheng Wang; Mojie Cheng (24-31).
The adsorption of CO2 on Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) perovskite oxides in the absence and presence of O2 and H2O at various temperatures was investigated by temperature programmed desorption (TPD). XRD was used to characterize the phase of the samples before and after adsorption. No CO2 desorption peak was observed when CO2 was adsorbed on BSCF at room temperature. A CO2 desorption peak from the decomposition of surface Sr0.6Ba0.4CO3 appeared after CO2 was adsorbed at 400–700 °C. The reactivity of CO2 with BSCF increased with increasing temperature, and the resulted carbonate became more stable. When CO2 and O2 were co-adsorbed, the CO2 desorption peak shifted to lower temperature and the peak area decreased compared with when only CO2 was adsorbed, which was due to the competitive adsorption of CO2 and O2. The adsorption of CO2 on BSCF was promoted in the presence of H2O. A CO2 desorption peak ranging from ca. 250 to 500 °C, assigned to the decomposition of the bicarbonate, was observed when H2O was added. The amount of CO2 adsorbed on Ba1−x Sr x Co0.8Fe0.2O3−δ increased when the barium doping level increased from 0.3 to 1.
Keywords: Ba0.5Sr0.5Co0.8Fe0.2O3−δ ; Perovskite oxides; Temperature programmed desorption; Carbon dioxide;
Synthesis, characterization and catalytic activity of easily recyclable zinc oxide nanobundles by M. Muruganandham; J.J. Wu (32-41).
A new self-assembly of ZnO nanobundle has been successfully synthesized in this research by thermal decomposition of zinc oxalate at atmospheric pressure without using any catalyst or solvent at moderate temperature. The XRD analysis showed that the synthesized nanobundles are hexagonal wurtzite-type pure polycrystalline zinc oxide and high resolution transmission electron microscope (HR-TEM) analysis showed that the synthesized nanoparticles size was 0–30 nm, and increases up to 10–70 nm during the bundle formation. To test the catalytic activity of ZnO nanobundles in catalytic ozonation process, 2-ethoxy ethyl acetate (2-EEA) was used as the model organic pollutant. The results show that the presence of ZnO nanobundles in ozonation process could further enhance 39.7% of 2-EEA decomposition and 9.5% of TOC removal. Increase the catalyst loading from 0.2 to 2 g/l would increases the removal rate appreciably. Further increase in the catalyst loading could not enhance the removal rate significantly. Since the direct reaction rate constant (k D) was found to be 0.675 M−1 S−1, implying that ozone is not a potential oxidizing agent for 2-EEA direct oxidation, catalytic ozonation is thus necessitated to accelerate the decomposition of 2-EEA by hydroxyl radicals produced in the catalytic ozonation process. AAS analysis showed that zinc ion was not leached from the catalysts in all experiments. The catalytic reusability was investigated up to four successive cycles and found that the catalytic efficiency was not decreased appreciably. The catalytic recyclability of nanobundles are investigated and compared with other nanoparticles such as ZnO and TiO2-P25, and found that nanobundles are easily recyclable when compared to the above said nanoparticles. It is concluded that the nanobundles are effective and easily recyclable in catalytic ozonation process.
Keywords: Nanobundles; ZnO; Catalytic ozonation; Ozone; 2-EEA;
Solar photo-Fenton degradation of Reactive Blue 4 in a CPC reactor by A. Durán; J.M. Monteagudo; E. Amores (42-50).
Solar photo-Fenton and solar photo-Fenton–ferrioxalate processes using a compound parabolic collector (CPC) were applied to the degradation of Reactive Blue 4 (RB4) solutions, proving to be an efficient method. Multivariate experimental design (including the following variables: pH and initial concentrations of Fe(II), oxalic acid, H2O2 and RB4) was used. The efficiency of photocatalytic degradation was determined from the analysis of the following parameters: color removal, total organic carbon (TOC) and chemical oxygen demand (COD). The decoloration rate pseudoconstant was calculated as a function of the accumulated solar energy received by the water solution.Experimental data were fitted using neural networks (NNs) which reproduce experimental data within 86% of confidence and allows the simulation of the process for any value of parameters in the experimental range studied. Analysis of dissolved H2O2 during reaction also helps to explain the scavenger effect and the dye mineralization grade.The solar photo-Fenton–ferrioxalate process increases degradation rate of RB4 since ferrioxalate complexes absorb strongly and a higher portion of the solar spectrum can be used. Although the addition of oxalic acid increases operating costs, it improves the process and it also helps to reduce pH in solution, decreasing charges derived from this operation. Under the optimum conditions, ([H2O2] = 120 ppm (in two additions), [Fe(II)] = 7 ppm, [(COOH)2] = 10 ppm, pH 2.5), color and COD were completely removed whereas TOC was reduced up to 66%.
Keywords: Dye; Ferrioxalate; Neural networks; Mineralization; Textile wastewater;
Mechanism of stearic acid oxidation over nanocrystalline L a 1 − x A ′ x B O 3 (A′ = Sr, Ce; B = Co, Mn): The role of oxygen mobility by S. Royer; B. Levasseur; H. Alamdari; J. Barbier; D. Duprez; S. Kaliaguine (51-61).
Catalytic wet air oxidation reaction (CWAO) of stearic acid is carried out in a batch reactor over a series of transition metal-based perovskite samples synthesized by reactive grinding. It is observed that the LaCoO3 sample presents the highest initial activity for this reaction. For comparison, pure and substituted LaMnO3 samples show largely smaller activity in spite of similar specific surface areas. The results show that the accessibility of the low temperature active oxygen (or the reducibility of the transition metal) on the surface of the catalyst conditioned the initial activity of the catalyst. Then, a mechanism involving the reaction of stearic acid molecules with adsorbed oxygen surface site (Co3+O2 −) is proposed on the basis of the experimental results. Stearic acid oxidation proceeds via a recurrent decarboxylation process that results in the reduction of cobalt surface sites and formation of surface carbonate species (CO3 −). In opposition to what was observed for gas phase oxidation reactions, lanthanum (and Ce or Sr) is found to be massively carbonated during the reaction, leading to the destruction of the perovskite structure and loss of the catalytic activity.
Keywords: Perovskite; Catalytic wet air oxidation; Stearic acid; Catalytic activity; Stability;
Impact of the support oxide and Ba loading on the sulfur resistance and regeneration of Pt/Ba/support catalysts by E.C. Corbos; X. Courtois; N. Bion; P. Marecot; D. Duprez (62-71).
The influence of both the support oxide (Al2O3, SiO2, Al2O3–5.5 wt% SiO2 and Ce0.7Zr0.3O2) and the barium loading of Pt/Ba/Support model catalysts on sulfur resistance was investigated by hydrogen temperature programmed reduction (TPR), X-ray diffraction (XRD) and NO x storage capacity measurements. The sulfation of catalysts under lean conditions in the presence of water and carbon dioxide led to the formation of both surface and bulk sulfates, except for silica supported catalyst on which mainly bulk barium sulfates were formed. Sulfate stability was influenced by the support oxide and the Ba loading. For alumina containing catalysts, both the amount of deposited sulfur and the sulfate stability under hydrogen increase with the Ba loading. Conversely the same sulfates stability was observed for Ce–Zr supported samples, whatever the Ba loading. The thermal treatment of the sulfated catalysts under oxidizing conditions at 800 °C favored the formation of less reducible bulk barium sulfates on all the catalysts. Ceria–zirconia led to a decrease of bulk BaSO4 stability under hydrogen, their reduction temperature being about 100 °C lower than on alumina containing materials. The elimination of sulfates under rich conditions (H2, CO2, H2O, N2) was more effective on the ceria–zirconia supported sample compared to alumina containing catalysts, even after ageing at 800 °C.Sulfation of the catalysts induced a loss of NO x storage capacity depending on catalyst composition. All the catalysts recovered their initial NO x storage capacity after regeneration at 550 °C, even with an improvement in the case of the ceria–zirconia supported material. The ageing at 800 °C of sulfated catalysts before regeneration did not lower the performance of the Pt/10Ba/CeZr catalyst, contrary to the alumina containing samples.
Keywords: NO x storage; Barium sulfate; Ceria–zirconia; Alumina; Silica; Sulfur elimination; Regeneration;
Effects of CO2 on synthesis of isobutene and isobutane from CO2/CO/H2 reactant mixtures over zirconia-based catalysts by Yingwei Li; Dehua He; Shaohui Ge; Rongjun Zhang; Qiming Zhu (72-80).
The effects of CO2 on the selective formation of i-C4 hydrocarbons (isobutene and isobutane) from CO2/CO/H2 reactant mixtures were studied. Three ZrO2-based catalysts including unmodified ZrO2, 8.6%Y2O3-ZrO2, and 15.3%Al2O3-0.5%K2O-ZrO2, were used in this study. The catalysts were characterized by N2 adsorption, X-ray diffraction (XRD), Raman, spectra, temperature-programmed desorption (TPD) of ammonia and carbon dioxide, and temperature-programmed reduction (TPR). The influences of CO2 on the catalytic performances of the catalysts were investigated by varying the content of CO2 in the feed up to 20%. It was found that the addition of CO2 in the synthesis gas (CO/H2) significantly reduced the net formation of CO2, but did not affect the formation of hydrocarbons. For the distribution of hydrocarbons, the selectivity to i-C4 in total hydrocarbons decreased with increasing the content of CO2 in the feed, while the selectivities to C1–C3 hydrocarbons increased. However, the i-C4 selectivities in all products were enhanced significantly because of the inhibition of CO2 formation with CO2 adding in the feed. The predominant products in CO2 hydrogenation on the ZrO2-based catalysts were CO and H2O at 648–723 K, indicating that the ZrO2-based catalysts were not active in the reactions towards hydrocarbons from CO2/H2. A 5–6% yield of i-C4 hydrocarbons with ∼62% selectivity in the products was achieved on 15.3%Al2O3-0.5%K2O-ZrO2 catalyst at 8–9% CO conversion with 20% CO2 adding in the feed at 698 K. The yield of CO2 was only 0.5% (∼5% CO2 selectivity in the products). Our results would suggest one potential way of using the recycle of CO2 formed to selectively synthesize i-C4 hydrocarbons from coal or natural gas-derived syngas (CO + H2) with high carbon efficiency (with free or very low CO2 emission).
Keywords: CO2 recycle; CO2 inhibition; CO hydrogenation; Isobutene; ZrO2-based catalysts;
Preparation of a visible sensitive carbon doped TiO2 photo-catalyst by grinding TiO2 with ethanol and heating treatment by In-Cheol Kang; Qiwu Zhang; Shu Yin; Tsugio Sato; Fumio Saito (81-87).
We have synthesized a carbon doped titanium oxide powder (C-TiO2) which is a photo-catalytic material acting under irradiation of light of wave length in visible region, by mechanochemical (MC) and heating operations. The MC operation is conducted by grinding TiO2 with ethanol (C2H5OH) in air, and the heating is carried out at different temperatures in air. The prepared samples were characterized by a series of analytical methods including X-ray diffraction, thermogravimetry-mass spectroscopy, Fourier transform infrared spectroscopy, specific surface area measurement, X-ray photoelectron spectroscopy (XPS), NO x gas decomposition and ultraviolet visible spectroscopy (UV–vis). XPS analysis particularly demonstrates the existence of C–Ti and C–O bindings, to which the improvement in photo-catalyst is attributed.
Keywords: Grinding; Carbon doping; Carbonate species; Solid–liquid reaction; TiO2 photo-catalyst;
Modification of the photocatalytic activity of Pd/TiO2 and Zn/TiO2 systems through different oxidative and reductive calcination treatments by M.A. Aramendía; V. Borau; J.C. Colmenares; A. Marinas; J.M. Marinas; J.A. Navío; F.J. Urbano (88-97).
Two different solids consisting of Pd or Zn-containing titania systems (metal/titanium nominal ratio of 1%) were submitted to diverse oxidative and reductive calcination treatments and tested for gas-phase selective photooxidation of 2-propanol. As regards the Pd system, reduction at low temperature (≤500 °C) resulted in a gradual increase in catalytic activity which was ascribed to the gradual reduction of bulk palladium to Pd0. Thermal treatment of the system at high temperature (850 °C) in static air, air flow or hydrogen flow led to a decrease in activity as the result of the sharp decrease in surface area. Nevertheless, those systems containing Pd0 only were more active than the one consisting of Pd + PdO. Finally, Pd-system overcame Pd migration to the surface on reduction at 850 °C which resulted in a significant increase in selectivity to acetone up to 97% for a time on stream of 5 h. As regards the Zn-containing system, none of the applied treatments resulted in improvement in photocatalytic activity. It seems that the most favourable situation for photocatalysis is that on which Zn atoms are substituting titanium ones in the lattice, whereas segregation of Zn to form small ZnO clusters is especially detrimental to activity.
Keywords: Photocatalysis; Selective photooxidation; Titania-based catalysts; Paladium-doped catalyst; Zinc-doped catalyst; 2-Propanol; Strong metal-support interaction (SMSI) effect;
Effects of CeO2 addition on Ni/Al2O3 catalysts for the reaction of ammonia decomposition to hydrogen by Weiqing Zheng; Jian Zhang; Qingjie Ge; Hengyong Xu; Wenzhao Li (98-105).
Effects of CeO2 addition on the catalytic performance of Ni/Al2O3 catalysts for ammonia decomposition to hydrogen were investigated by activity studies and some physico-chemical methods like N2-adsorption/-desorption, H2-chemisorption, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR) and NH3 temperature-programmed surface reduction (NH3-TPSR). The results showed that the addition of CeO2 greatly improved the catalytic activity and stability of Ni/Al2O3 catalysts for ammonia decomposition to CO x -free hydrogen. 98.3% NH3 conversion and 32.9 mmol/(min gcat) H2 formation rate were achieved over CeO2 promoted Ni/Al2O3 catalyst at 823 K and 30 000 ml/(h gcat) NH3 space velocity. The characterization results indicate that the addition of CeO2 enlarged the catalyst pores, moderated the interaction between Ni and alumnia, suppressed Ni0 crystallites from sintering, and improved the recombinative desorption of N adatoms from the Ni0 surface.
Keywords: Ni-based catalyst; CeO2 promotion; Hydrogen production; Ammonia decomposition;
Catalytic activity of polyaniline/MnO2 composites towards the oxidative decolorization of organic dyes by Ali H. Gemeay; Rehab G. El-Sharkawy; Ikhlas A. Mansour; Ahmed B. Zaki (106-115).
The kinetics of the oxidative reaction of the textile dyes: direct red 81 (DR-81), indigo carmine (IC), and acid blue 92 (AB-92) with H2O2 in the presence of polyaniline (PANI)/MnO2 composites has been investigated. Experiments were carried out in batch reactor under pseudo-first order conditions with respect to the [dye]. Effects of the preparation conditions of the composites on the reaction rate have been investigated. Among these conditions are [aniline], [acid], type of acid, mass of β-MnO2, polymerization time, and annealing temperatures. At fixed [dye], [H2O2], and mass of composite, the rate constants increased upon increasing (i) the doping ratio of PANI, (ii) the percentage of PANI content, (iii) the degree of crystallinity of PANI, and (iv) the molecular weight of PANI. The presence of MnO2 counterpart kept the medium at pH range (3–4) via adsorption of H+. The oxidation rate was enhanced with the increase in the initial concentration of H2O2, attained a maximum at 0.01 M and thereafter decreased. In contrast, the rate was inhibited with the increase in the initial dye concentration, and the pH. The activation parameters were determined. From the isokinetic relationship it was concluded that the catalytic reactions are entropy controlled. A reaction mechanism involving electron transfer from H2O2 to the PANI counterpart has been proposed. These results demonstrate that the PANI/MnO2–H2O2 catalytic system may be envisaged as a method for the treatment of colored wastewaters.
Keywords: Polyaniline composites; Catalyst; Decolorization; H2O2; Textile dyes; Kinetics;
Performance of nano-Co3O4/peroxymonosulfate system: Kinetics and mechanism study using Acid Orange 7 as a model compound by Xiaoyang Chen; Jingwen Chen; Xianliang Qiao; Degao Wang; Xiyun Cai (116-121).
Nano-Co3O4 was prepared by precipitation method and was successfully applied as heterogeneous catalyst to activate peroxymonosulfate (PMS) and degrade a model compound Acid Orange 7 (AO7). The catalyst exhibits spherical morphologies with minor particle agglomeration, small particle average size (20 nm) and high specific surface area (18 m2/g). The degradation kinetics of AO7 induced by nano-Co3O4/PMS system was investigated at both acidic and neutral pH conditions. The heterogeneous character of PMS activation with nano-Co3O4 is more pronounced at neutral pH as indicated by fast degradation rate of AO7 and low dissolved Co ion. The catalyst presented a long-term stability through using the catalyst for multiple runs in the degradation of AO7. The main degradation intermediates of AO7 identified by GC/MS and LC/MS were 4-hydroxybenzenesulfonic acid, 1,2-naphthalenedione, coumarin, phthalic anhydride, phthalimide and 2-formyl-benzoic acid. Proposed degradation pathways were elucidated in light of the analyzed degradation products and frontier electron density theory.
Keywords: Wastewater treatment; Peroxymonosulfate; Dissolved cobalt ion; Heterogeneous catalysis; Intermediates;
Electrocatalytic hydrodehalogenation of pentachlorophenol at palladized multiwalled carbon nanotubes electrode by Chunyue Cui; Xie Quan; Hongtao Yu; Yanhe Han (122-128).
The palladized multiwalled carbon nanotubes (MWCNTs) electrode was prepared for electrocatalytic hydrodehalogenation (HDH) of pentachlorophenol (PCP). The MWCNTs grew directly on graphite by chemical vapor deposition (CVD), and Pd was loaded on MWCNTs with electrochemical deposition. The MWCNTs and Pd catalyst were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption (BET surface area) and X-ray diffraction (XRD). The diameter and surface area of MWCNTs were 40–60 nm and 54 m2/g, respectively. The particle size of Pd was about 13 nm. Electrocatalytic HDH of PCP by Pd/MWCNTs/graphite electrode was performed in H2SO4 anolyte separated by Nafion membrane H-cell. The complete degradation of 0.15 mM PCP was achieved at 180 min with the dechlorination efficiency being 96%, and the yield of cyclohexanone was 60% (7.4% current efficiency). Compared with the Pd/graphite electrode, the Pd/MWCNTs/graphite electrode exhibited higher dechlorination efficiency and hydrogenation activity of the carbon–carbon double bond for PCP. The effects of anolyte and potential on HDH, electrode stability were also investigated.
Keywords: Carbon nanotubes; Electrocatalytic hydrodehalogenation; Pentachlophenol; Palladium;
Role of Re in Pt–Re/TiO2 catalyst for water gas shift reaction: A mechanistic and kinetic study by K.G. Azzam; I.V. Babich; K. Seshan; L. Lefferts (129-140).
Transient kinetic studies and in situ FTIR spectroscopy were used to follow the reaction sequences that occur during water gas shift (WGS) reaction over Pt–Re/TiO2 catalyst. Results pointed to contributions of an associative formate route with redox regeneration and two classical redox routes involving TiO2 and ReO x , respectively. Under WGS reaction condition rhenium is present at least partly as ReO x providing an additional redox route for WGS reaction in which ReO x is reduced by CO generating CO2 and re-oxidized by H2O forming H2. The overall reaction rate, based on steady state kinetics, was given by r H 2 = 0.075 e 31 kJ mo l − 1 / R T × p H 2 O × p H 2 − 0.5 ( 1 − β ) , where β is the approach to equilibrium. Results obtained in the study indicated that the reaction between CO adsorbed on Pt and OH groups on titania is the rate-determining step.
Keywords: Water gas shift (WGS); Platinum; Rhenium; Titania; Kinetics; Reaction mechanism; Reaction orders;
Lanthania promoted MgO: Simultaneous highly efficient catalytic degradation and dehydrochlorination of polypropylene/polyvinyl chloride by Qian Zhou; Wenwen Lan; Anke Du; Yuzhong Wang; Jiawei Yang; Yanhui Wu; Keke Yang; Xiuli Wang (141-146).
A lanthania modified MgO catalyst, La-MgO, has been developed and characterized by adsorption methods, X-ray diffraction method (XRD), scanning electron microscopy (SEM), temperature-programmed desorption of ammonia (NH3-TPD) and CO2 (CO2-TPD). The La-MgO has been proved to be a highly efficient and stable dehydrochlorination chemsorbent; moreover, it shows prominent catalytic degradation ability for a typical PVC-containing polyolefins (polypropylene/polyvinyl chloride), i.e., higher degradation rate and superior liquid quality, which will be very useful in the recycling of chlorine-containing waste plastics.
Keywords: Lanthania promoted MgO; Dechlorination; Catalytic degradation; Polyvinyl chloride; Polypropylene; Recycling;
Bimodal mesoporous TiO2–P25 composite thick films with high photocatalytic activity and improved structural integrity by Yongjun Chen; Dionysios D. Dionysiou (147-155).
Bimodal mesoporous TiO2–P25 composite thick films with improved structural integrity (less crack formation) were successfully synthesized by employing an environmental friendly and highly viscous nonionic surfactant Tween 20 as a tri-functional template, which can simultaneously improve film texture, bimodal mesopore structure and structural integrity in the films. It was found that increasing Tween 20 loading from 10% to 50% (v/v) could simultaneously increase both volumes of small mesopore and secondary large mesopore. Degussa P25 nanoparticle can function as a kind of pore wall contributing to the formation of secondary large mesopore. Optimizing the loading of Tween 20 could result in optimum film thickness, even with only one dip-coating cycle. The final film at optimum Tween 20 loading (50%, v/v) exhibited large porosity (50.6%) and bimodal mesoporous size distribution with small mesopore size of ∼5 nm and large mesopore size of ∼34 nm. Compared with mono-modal mesoporous TiO2 film (no Degussa P25) at optimum preparation conditions (Tween 20, 50% (v/v), six dip-coating layers), the TiO2–P25 composite films prepared with the same Tween 20 loading (one dip-coating layer) or with 25% (v/v) Tween 20 loading (two dip-coating layers) demonstrated higher photocatalytic activities in the degradation of creatinine, an important human metabolite present in human urine. These results prove that bimodal mesoporous TiO2–P25 composite films have promising properties for photocatalytic water treatment.
Keywords: Surfactant; Tween 20; Self-assembling; Sol–gel; TiO2; P25; Photocatalysis; Films;
Transmission electron microscopic observation on reduction process of copper–iron spinel catalyst for steam reforming of dimethyl ether by K. Eguchi; N. Shimoda; K. Faungnawakij; T. Matsui; R. Kikuchi; S. Kawashima (156-167).
The reduction process of copper–iron spinel oxide, which is active for steam reforming of dimethyl ether after mixing with alumina, has been investigated by a transmission electron microscope (TEM), scanning TEM (STEM), and energy dispersive X-ray (EDX) analyzer. The catalyst preparation was started from formation of well-sintered CuFe2O4 by calcination in air at 900 °C. After reduction of CuFe2O4 with hydrogen at 250 °C, metallic copper grains were developed on reduced spinel surface by the phase separation from the oxide. Strong chemical interaction between deposited Cu and reduced spinel oxide was expected from their intimate interfacial contact and lattice matching. The reduced sample contained metallic Cu, reduced spinel, and spinel oxide with super-lattice structure. Partial elimination of Cu and lattice oxygen resulted in formation of pores in and between the oxide grains. The size of the deposited Cu particle and Cu grain was largely distributed. After heating at higher temperature of 350 °C, the large spinel oxide particles are decomposed into small particles via formation of cracks. The resultant catalyst powder was very porous and consisted of very small particles of Cu, iron oxide, and spinel oxide. STEM–EDX analyses clarified the phase separation process of metallic Cu and iron oxide from host CuFe2O4 upon reduction.
Keywords: TEM; EDX; CuFe2O4 spinel; Reduction; Dimethyl ether; Steam reforming;
Influence of TiO2 concentration on the synergistic effect between photocatalysis and high-frequency ultrasound for organic pollutant mineralization in water by Ricardo A. Torres; Jessica I. Nieto; Evelyne Combet; Christian Pétrier; Cesar Pulgarin (168-175).
This work deals with the coupling of sonolysis (300 kHz, 80 W) and solar photocatalysis using titanium dioxide, two advanced oxidation processes for the degradation of a model organic pollutant, bisphenol A (BPA). Initially, the performances of the two separate processes in both the elimination and mineralization of BPA were compared. Even if identical BPA byproducts were formed, the two processes were complementary, while ultrasound was better able to eliminate the target pollutant, photocatalysis proved to be more efficient for reaching mineralization. Using the combined system, an interesting synergistic effect, which depends on the titanium dioxide loading, was observed for BPA mineralization. The best synergistic effect was found at low catalyst loading. After 4 h of combined treatment using 0.05 g L−1 of titanium dioxide, 62% of dissolved organic carbon (DOC) was eliminated. In contrast, 6 or 12% of DOC was removed by ultrasound alone or photocatalysis alone, respectively. Using 1 g L−1 of catalyst, 68 or 50% of DOC was removed by ultrasound/photocatalysis or photocatalysis, respectively. The poor synergistic effect at this catalyst loading can be explained by an inhibiting effect of the titanium dioxide on the cavitational activity.
Keywords: Sonochemical degradation; Photocatalysis; Sonophotocatalysis; Endocrine disrupting chemical; Bisphenol A elimination; Water treatment; Advanced oxidation;
Supported and mixed oxide catalysts based on iron and titanium for the oxidative decomposition of chlorobenzene by Abbas Khaleel; Aysha Al-Nayli (176-184).
Iron oxide supported on titanium dioxide (Fe2O3/TiO2) and iron–titanium mixed oxide (Fe–Ti-oxide) catalysts were prepared via wetness impregnation and sol–gel methods, respectively. The catalytic activity of the two materials for the oxidation of chlorobenzene was studied and compared with the activity of pure titanium and iron oxides as well as MgO-supported iron oxide. Fe2O3/TiO2 and Fe–Ti-oxide have shown higher catalytic activities for the oxidation of chlorobenzene than the corresponding pure iron and titanium oxides at a reaction temperature of 325 °C, and this enhanced activity was more pronounce at higher temperatures. The Fe–Ti-oxide, in particular, exhibited a unique activity for the complete oxidation at relatively low temperature, 325 °C, without the formation of other chlorinated organics. Chlorine, measured by iodometric titration was the only Cl-containing product. The absence of HCl as a product and the negative effect of water suggest that the surface active sites are more likely to be Lewis acid–base sites on which chlorobenzene molecules dissociatively adsorb forming metal–Cl bonds and surface phenolate intermediates. Desorption of Cl2 from the surface and possible interaction of the aromatic ring with metal sites result in the activation of the ring forming partially oxidized intermediates involving lattice oxygen ions. Finally, reactions with molecular oxygen result in the complete oxidation to CO2 and regenerate the surface.
Keywords: Chlorobenzene; Catalytic oxidation; Iron–titanium oxides;