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Applied Catalysis B, Environmental (v.86, #1-2)
Synthesis and photocatalytic properties of dense and porous TiO2-anatase thin films prepared by sol–gel by N. Arconada; A. Durán; S. Suárez; R. Portela; J.M. Coronado; B. Sánchez; Y. Castro (pp. 1-7).
Porous TiO2-anatase films were prepared by sol–gel route showing higher photocatalytic activity in degradation of trichloroethylene (TCE) in air compared to dense titania films. Titania sols were synthesized with and without a pore generating agent, polyethylene glycol (PEG), to evaluate the effect of porosity in the photocatalytic activity of the coatings. The films were deposited by dipping and sintered at different temperature and time. The characterisation was performed by profilometry, Fourier transform infrared spectroscopy (FTIR), grazing X-ray diffraction (GXRD) and field emision scan electron microscopy (FE-SEM), observing that anatase phase is obtained at temperatures as low as 350°C. The maximum specific surface area ( Ss=43m2/g) was obtained for coatings prepared from TiO2 sol with PEG and sintered at 400°C. Porous TiO2-anatase films present TCE conversion around 20% higher than that of dense films. Porous volume, surface area and thickness of the coating play a key role in the photocatalytic activity. On the other side, variation in particle size seems not to be a critical parameter in the studied range.
Keywords: Sol–gel TiO; 2; coatings; Template (PEG); Photocatalysis; Trichloroethylene
Visible-induced photocatalytic reactivity of polymer–sensitized titania nanotube films by Hai-chao Liang; Xiang-zhong Li (pp. 8-17).
In this study, polythiophene–TiO2 nanotube films (PTh/TNT) were successfully prepared by a two-step electrochemical process of anodization and electropolymerization, in which a highly ordered TiO2 nanotube (TNT) film was anodized at a low-voltage with post calcination first and then the prepared TNT film was deposited with a polythiophene layer by electropolymerization in the BFEE electrolyte. The morphology and structures of PTh/TNT composites were examined by FESEM, EDX, XRD and XPS methods. XPS spectra of PTh/TNT composites indicate the strong interaction between S sites of polymer backbone and TiO2 nanotubes, in which electron transfer from polythiophene to titania takes place. UV–vis DRS analysis shows that these composites have a strong photoresponse in the visible region at 500nm. The prepared PTh/TNT films revealed significant activity for 2,3-dichlorophenols (2,3-DCP) degradation under visible light irradiation and also sunlight irradiation, in which the PTh3/TNT film achieved the best performance. On the other hand, this study also confirmed that the side-chains of polythiophene could influence its photocatalytic activity significantly in an order from high to low as poly3-methylthiophene≈polythiophene>polythiophenecarboxylic acid>poly3-hexylthiophene. The results may provide useful information to further develop some effective polymer-semiconductor catalysts for pollutant degradation under sunlight irradiation for water and wastewater treatment.
Keywords: Polymer; Photosensitizer; Titania nanotubes; Visible photocatalysis
Catalytic properties of Pd supported on ZnO/ZnAl2O4/Al2O3 mixtures in dimethyl ether autothermal reforming by Marita Nilsson; Kjell Jansson; Peter Jozsa; Lars J. Pettersson (pp. 18-26).
The catalytic properties of Pd supported on mixtures of zinc oxide, zinc aluminate, and alumina, prepared from γ-alumina and zinc nitrate, were studied for autothermal reforming (ATR) of dimethyl ether (DME). The performance of the catalysts was tested in a small-scale reactor, using cordierite monoliths as substrate. The catalysts exhibited high activity and generated hydrogen-rich product gases with CO concentrations below 5vol.% in the temperature range between 350 and 450°C (at O2:DME=0.7, H2O:DME=2.5, and GHSV=15000h−1). The highest DME conversion was obtained for a catalyst in which the support comprised mainly ZnAl2O4. Physical mixing of the catalysts with γ-Al2O3 resulted in increased DME conversion but a lowering of the CO2 selectivity.The catalysts were characterized by CO chemisorption, liquid nitrogen adsorption, temperature-programmed desorption of ammonia, temperature-programmed reduction, transmission electron microscopy, and X-ray diffraction. It was found that decreasing surface area and decreasing number of acid sites, caused by thermal treatment during generation of the supports, did not affect the activity negatively. The high CO2 selectivity of the catalysts was correlated with PdZn alloy formation.
Keywords: Hydrogen; Dimethyl ether; Autothermal reforming; Pd catalyst; PdZn alloy
Heterogeneous and homogeneous photocatalytic degradation of the insecticide imidacloprid in aqueous solutions by V. Kitsiou; N. Filippidis; D. Mantzavinos; I. Poulios (pp. 27-35).
The heterogeneous and homogeneous photocatalytic degradation of imidacloprid, a systemic chloronicotinoid insecticide, has been investigated in aqueous solutions using artificial UV-A or visible illumination. Three processes under various experimental conditions were evaluated namely, TiO2/UV-A, photo-Fenton/UV-A and photo-Fenton/vis with respect to their activity for substrate degradation and mineralization. The initial apparent photonic efficiency decreased in the order photo-Fenton/UV-A>TiO2/UV-A>photo-Fenton/vis. For the TiO2/UV-A process, the efficiency increased considerably when TiO2 is combined with Fe3+ and H2O2 presumably due to the synergistic effect of homogeneous and heterogeneous photocatalytic reaction. On the other hand, the homogeneous photocatalytic reactions were enhanced in the presence of the oxalate ions. Imidacloprid degradation was accompanied by the formation of several reaction by-products as confirmed by GC/MS analysis, while ammonium, nitrate and chloride ions have been detected in the liquid phase as mineralization products. By-products were less ecotoxic to marine bacteria than the insecticide itself.
Keywords: Photocatalysis; Imidacloprid; TiO; 2; Photo-Fenton; Intermediates; Toxicity
Promoting effect of MgO addition to Pt/Ni/CeO2/Al2O3 in the steam gasification of biomass by Kazuya Nakamura; Tomohisa Miyazawa; Takuya Sakurai; Toshihiro Miyao; Shuichi Naito; Noorjahan Begum; Kimio Kunimori; Keiichi Tomishige (pp. 36-44).
Pt/Ni/CeO2/Al2O3 catalyst showed the high performance in the steam gasification of cedar wood at the initial stage, however, the catalyst was deactivated within 2h. According to the catalyst characterization by means of XRD and Ni K-edge EXAFS, it is found that aggregation of Ni metal particles causes the deactivation. In contrast, the Pt/Ni/CeO2/MgO/Al2O3 showed the high catalytic activity and stability. The addition of MgO to Pt/Ni/CeO2/Al2O3 decreased the reduction degree of Ni, but increased the dispersion of the Ni metal particles. As a result, the activity of Pt/Ni/CeO2/MgO/Al2O3 was comparable to that of Pt/Ni/CeO2/Al2O3. The Pt/Ni/CeO2/MgO/Al2O3 had high resistance to the aggregation, which can be related to high stability. Another important point is that the aggregated Ni particles on the Pt/Ni/CeO2/MgO/Al2O3 became re-dispersed by the catalyst regeneration (oxidation and reduction). The re-dispersion can proceed via the formation of the NiO–MgO solid solution by oxidation and the reduction of the NiO–MgO from the results of XRD and Ni K-edge EXAFS.
Keywords: Steam gasification; Biomass; Steam reforming; Tar; Regeneration; Re-dispersion; Ni; MgO; Solid solution; Synthesis gas
Effect of iron impurities on the catalytic activity of BEA, MOR and MFI zeolites in the SCR of NO by ethanol by Stanislaw Dzwigaj; Janusz Janas; Wojciech Rojek; Lorenzo Stievano; Friedrich E. Wagner; Frédéric Averseng; Michel Che (pp. 45-52).
The combined use of chemical analysis, XRD, EPR and Mössbauer techniques provides detailed information on the nature of iron impurities in commercial BEA, MOR and MFI zeolites. EPR and Mössbauer spectroscopies evidence that iron impurities are present mainly as tetrahedral Fe(III) species and to a minor extent as octahedral Fe(III) species, with relative amounts depending on the type of zeolite. Iron impurities present in commercial BEA, MOR and MFI zeolites are active in the selective catalytic reduction (SCR) of NO by ethanol, with NO conversion higher than 37, 43 and 50% for BEA, MOR and MFI, respectively, and with selectivity toward N2 higher than 90% for all zeolites in the temperature range 575–775K. The much higher activity of commercial BEA, MOR and MFI than that of FeSiBEA and CoSiBEA, both prepared by a two-step postsynthesis method, suggests that Fe(III) impurities in commercial zeolites are present in tetrahedral and/or octahedral environments, possibly close to lattice Al, which make them active in the SCR of NO by ethanol. The Brønsted and Lewis acidic sites in studied zeolites are determined by FTIR measurements of pyridine adsorption.
Keywords: BEA; MOR; MFI; Iron impurities; SCR of NO; XRD; EPR; Mössbauer
Simultaneous photocatalytic reduction of silver and oxidation of cyanide from dicyanoargentate solutions by María-José López-Muñoz; José Aguado; Rafael van Grieken; Javier Marugán (pp. 53-62).
The feasibility of heterogeneous photocatalysis for the treatment of dicyanoargentate complexes in solution using titanium dioxide was investigated. The best results were obtained in the presence of oxygen, as the simultaneous deposition of metallic silver on the catalyst and oxidation of released cyanide ions to cyanate species was achieved. It is proposed that O2 plays a dual role in the reaction: it supports the reduction of the metal acting as intermediate in the transfer of electrons and acts as reagent in the oxidation of released cyanide to cyanate species. The influence on the kinetics of the addition of methanol was studied. In anoxic conditions the rate of silver reduction was increased, what is attributed to the effectiveness of methanol as hole scavenger and its ability to form reducing radicals, whereas the oxidation of released CN− was inhibited. On the contrary, in aerobic medium the presence of the alcohol had a detrimental effect on the metal reduction but no cyanide accumulation was produced. The photocatalytic treatment of an industrial spent silver plating bath was carried out. In anoxic conditions, the recovery of silver upon deposition on the catalyst as Ag0 was achieved. As the large amount of organic matter in the solution inhibited the oxidation of cyanide ions, a two-step procedure is proposed for the overall treatment of those wastewaters.
Keywords: Photocatalytic reduction; Photocatalytic oxidation; Silver recovery; Cyanide; Dicyanoargentate; Plating baths
Titanium-doped nanocomposite of Al2O3 and ZrO2–TiO2 as a support with high sulfur durability for NO x storage-reduction catalyst by Haruo Imagawa; Toshiyuki Tanaka; Naoki Takahashi; Shin’ichi Matsunaga; Akihiko Suda; Hirofumi Shinjoh (pp. 63-68).
A nanocomposite of Al2O3 and a ZrO2–TiO2 solid solution (AZT) doped with Ti (Ti–AZT) was synthesized as a support for a NO x storage-reduction (NSR) catalyst in order to achieve sulfur durability. Ti–AZT maintained the original structure of AZT after the Ti doping step and exhibited lower basicity. Energy dispersive X-ray spectroscopy revealed that the Ti concentration on the Al2O3 particles was more than 10at.% on average for a sample containing 3.3at.% of doped titanium. Doped titanium was homogeneously distributed on the surface without the formation of discrete TiO2 particles. SO2-temperature programmed desorption at less than 823K indicated that the catalyst containing Ti–AZT had larger sulfur desorption than that containing AZT. After sulfur aging tests, the Ti–AZT catalyst provided a large amount of NO x storage. The improved sulfur durability in the NSR catalyst resulted from the presence of TiO2 as a Al2O3–TiO2 solid solution in Ti–AZT.
Keywords: Titanium-doped; Nanocomposite; Solid solution; Sulfur durability; NO; x; storage-reduction catalyst
Catalytic wet peroxide oxidation of phenol over Fe/AC catalysts: Influence of iron precursor and activated carbon surface by A. Rey; M. Faraldos; J.A. Casas; J.A. Zazo; A. Bahamonde; J.J. Rodríguez (pp. 69-77).
Different activated carbon-supported Fe catalysts have been prepared and tested in CWPO of phenol. Three well characterized activated carbons and two iron precursors (iron nitrate and iron pentacarbonyl) have been used. The behavior of these catalysts in CWPO has been related with their porous structure, surface composition, in terms of oxygen groups and Fe distribution onto the catalyst particles. The catalysts with a more uniform distribution of Fe showed a higher oxidation activity than the ones with an internal (egg-yolk type) or external (egg-shell type) distribution. These last provoke a faster decomposition of H2O2 mainly to O2, non-reactive at the mild reaction temperature used (50°C). No significant differences were observed from the iron precursors. Complete conversion of phenol and almost 80% mineralization were obtained in less than 2h with the best catalyst. The residual by-products consisted in short-chain organic acids without significance in terms of toxicity. Fe leaching was observed in all the cases which can be mainly attributed to the presence of oxalic acid as oxidation by-product, refractory to the CWPO process investigated. The intensity of Fe leaching was related with the concentration of oxalic acid.
Keywords: Oxidation; Hydrogen peroxide; Catalyst; Activated carbon; Iron; Phenol
Thermal and catalytic pyrolysis of polyethylene over HZSM5 and HUSY zeolites in a batch reactor under dynamic conditions by A. Marcilla; M.I. Beltrán; R. Navarro (pp. 78-86).
The thermal and catalytic pyrolysis of LDPE and HDPE over HZSM5 and HUSY have been studied under dynamic conditions in a batch reactor. The products evolved have been analyzed, and results have been compared with those found in the bibliography. Particular attention was paid to any coincidences and differences encountered. The yields of gases, liquids and waxes for all the systems employed are presented, along with the composition of each fraction. The general carbon number distribution is shown, as well as the carbon number distribution for the main compounds present in the gaseous and the liquid fractions. Finally, the 10 major compounds obtained for each system are described.
Keywords: Batch reactor; Thermal pyrolysis; Catalytic pyrolysis; LDPE; HDPE; HZSM5; HUSY
Characteristics of Pt/WO3/CeO2/ZrO2 catalysts for catalytic reduction of NO by CO by Hai-ou Zhu; Jeong-Rang Kim; Son-Ki Ihm (pp. 87-92).
Various supported Pt catalysts (Pt/WO3/CeO2/ZrO2; Pt/ZrO2, Pt/CeO2, Pt/CeZrO, Pt/WO3/ZrO2, and Pt/WO3/CeZrO) were prepared and characterized, and their characteristics of catalytic reductions of NO by CO with or without oxygen were investigated. TPR and CO-TPD showed that Pt/CeO2 and Pt/CeZrO could be easily reduced by CO while the reduction by CO was inhibited with the introduction of WO3 in the case of Pt/WO3/CeZrO. According to NO-TPD, NO reduction could not proceed over the catalysts (Pt/WO3/CeZrO, Pt/ZrO2, Pt/WO3/ZrO2) to remain in an oxidized state even after reduction by CO, but NO reduction was possible over Pt/CeO2 and Pt/CeZrO catalysts when reduced by CO. For NO+CO reaction without oxygen, those easily reducible catalysts (Pt/CeO2 and Pt/CeZrO) exhibited better catalytic performances. With excess oxygen, however, Pt/WO3/CeZrO and Pt/WO3/ZrO2 catalysts exhibited higher NO conversions to N2 and N2O especially at a low temperature. The acidity from ZrO2 and WO3 in Pt/WO3/CeO2/ZrO2 catalysts should play an important role on their NO conversion only in the presence of excess oxygen.
Keywords: Pt; CeO; 2; ZrO; 2; CeO; 2; –ZrO; 2; Precipitation; WO; 3; NO; +; CO reaction; Excess oxygen; Acidity; Pt dispersion
Use of oxalate sacrificial compounds to improve the photocatalytic performance of titanium dioxide by Salah Bassaid; Didier Robert; Messaoud Chaib (pp. 93-97).
Our study demonstrated that the performance of TiO2 photocatalysts in eliminating organic compounds in water can be improved by combining them with calcium oxalate. The adsorption maximum capacity of Orange II on various pure photocatalysts is dependent on the specific area. Concerning the mixed TiO2/calcium oxalate catalysts, we observed that adsorption is still higher than that of pure correspondent photocatalysts. The influence of the sacrificial agent differs according to the photocatalyst used. Thus performance of the P25-TiO2 photocatalyst is positively slightly affected by the presence of calcium oxalate, whereas with TiO2-PC500 a decline in photocatalytic activity can be noted. The use of calcium oxalate significantly improves the performance of titanium dioxide prepared by sol–gel. We observed similar results with the kinetics of mineralization. It seems that the effect of oxygen is the same whether pure TiO2 samples or 70%TiO2/30%calcium oxalate mixtures are used, regarding the rate of conversion of Orange II after 30min of irradiation.
Keywords: Photocatalysis; TiO; 2; Calcium oxalate; Sacrificial compound
Photocatalytic reductive–oxidative degradation of Acid Orange 7 by polyoxometalates by A. Troupis; T.M. Triantis; E. Gkika; A. Hiskia; E. Papaconstantinou (pp. 98-107).
A series of polyoxometalates (POM) PW12O403−, SiW12O404−, P2W18O626− and P2Mo18O626− have been used as photocatalysts for the destruction of the azo dye Acid Orange 7 (AO). There are two ways to consider: reductive and oxidative decomposition. The reductive decomposition involves absorption of light by polyoxometalates, oxidation of an organic substrate, for instance propan-2-ol as sacrificial reducing reagent and reoxidation-recycling of the reduced polyoxometalates by the azo dye via a thermal (dark) reaction. AO is reduced to aromatic amine derivatives in a multi-electron process, as suggested by the analysis of the detected products and the obtained stoichiometry of the electron transfer process, following a first-order dependence for AO. This process takes place within a few minutes. On the other hand, photooxidative decomposition involves again absorption of light by POM followed by direct or OH-mediated oxidation of the dye. This process is an order of magnitude slower than reductive elimination, but leads to mineralization of AO. Several intermediates have been detected prior to evolution of CO2.The nature of the POM catalyst is decisive in the efficiency of reductive AO decoloration, following the order PW12O403−>SiW12O404−>P2W18O626−>P2Mo18O626−, that is their photooxidizing ability, in one-pot photolysis experiments. On the other hand the efficiency of thermal (dark) reaction between reduced POM and AO follows the reductive ability of POM, i.e., SiW12O405−>PW12O404−>P2W18O627−>P2Mo18O628−. The presence of electron scavengers suppresses the reductive degradation rate according to the trend Ag+>O2>Cu2+>Ni2+, while increase of pH retards decoloration.Contrary to TiO2, sensitized photodecomposition, i.e., absorption of light by AO and electron injection to POM has not been observed.
Keywords: Photocatalysis; Polyoxometalates; Azo dye; Acid Orange 7; Titanium dioxide