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Applied Catalysis B, Environmental (v.76, #1-2)
Thioacetamide and thiourea impact on visible light activity of TiO2 by Adriana Zaleska; Paulina Górska; Janusz W. Sobczak; Jan Hupka (pp. 1-8).
Visible-light activated titanium dioxide photocatalysts were prepared by hydrolysis of titanium (IV) isopropoxide with thioacetamide or thiourea, followed by calcinations at 450°C. The experiments demonstrated that phenol and 4-chlorophenol in aqueous solutions were successfully degraded under visible light ( λ>400nm) using doped TiO2. The major effort was aimed at evaluation of the effect of thioacetamide and thiourea amount (from 0.5 to 5wt%) used during synthesis on the photodegradation efficiency. It was found that thioacetamide and thiourea dosage of 5% in doped TiO2 resulted in the most pronounced photocatalytic activity––phenol was photooxided in 93 and 97% within 60min, respectively. Gradual loss of photoactivity was observed due to ageing of modified TiO2––even 70% after six months of storage.The catalyst powder was characterized by X-ray diffraction (XRD), X-ray photoelectron emission spectroscopy (XPS) and UV–vis absorption measurements. For TiO2 modified with thiourea, light absorption in the visible region gradually increased with the increasing dopant content.
Keywords: Titanium dioxide; Thioacetamide; Thiourea; Visible light
Activity and deactivation of sulphated TiO2- and ZrO2-based V, Cu, and Fe oxide catalysts for NO abatement in alkali containing flue gases by A.L. Kustov; S.B. Rasmussen; R. Fehrmann; P. Simonsen (pp. 9-14).
Vanadia, copper and iron oxide catalysts supported on conventional TiO2, ZrO2, and sulphated-TiO2 and ZrO2 have been prepared. These catalysts were characterized by elemental analysis, N2-BET, XRD, and NH3-TPD methods. The influence of potassium oxide additives on the acidity and activity in NO selective catalytic reduction (SCR) with ammonia was studied. The absolute activity of the samples does not vary significantly depending on the nature of the active metal and the acidic properties of the support used, seem to be influenced mainly by the concentration of active metal. Loading of the catalysts with potassium leads to a considerable decrease of their catalytic activity. In the case of the traditional carriers (TiO2, ZrO2), the poisoning of the catalyst with small amounts of potassium oxide (K/metal ratio <0.5) leads to almost complete deactivation of the catalysts. The use of transition metals which reveal mainly Lewis acidity (Fe, Cu), slightly increase the resistance towards alkali poisoning in comparison with V-based catalyst. For the sulphated systems, strongly acidic surface sulphate groups represent attractive sites for hosting potassium oxide at temperatures below 400°C. The resistance of corresponding catalysts towards poisoning correlates well with the strength of acid sites of the support used. The highest resistance was observed for the catalyst based on sulphated-ZrO2. At temperatures above 375–400°C, potassium additives become more mobile and are no longer bonded by the sulphated groups of the carrier and potassium migration leads to its preferential localization at the active sites responsible for the SCR activity, which is followed by considerable decrease of the activity.
Keywords: NO SCR with ammonia; Potassium poisoning; Deactivation; Sulphated-ZrO; 2; Sulphated-TiO; 2; Vanadium oxide; Copper oxide; Iron oxide; NH; 3; -TPD
Enhanced photoelectrocatalytic performance of polyoxometalate-titania nanocomposite photoanode by Yibing Xie; Limin Zhou; Haitao Huang (pp. 15-23).
Polyoxophosphotungstate-incorporated titania/titanium nanocomposite (POPTA-TiO2/Ti) has been developed as a photo-anode for photo-electro-catalytic application. Highly-ordered anatase TiO2 nanotube array with a vertical orientation is synthesized by a controlled anodization plus a post-calcination. Hybrid incorporation is followed by embedding POPTA into TiO2 tubule channels. The morphological characteristics, crystal behavior and chemical structure of POPTA-TiO2 are examined by field emission scanning electron microscopy, X-ray diffraction (XRD), thermogravimetry analysis and Fourier transformed infra-red spectroscopy. Electrochemical properties and photocurrent responses have been investigated by linear sweep voltammetry. Photo-catalytic and photo-electro-catalytic applications for recalcitrant organic pollutant degradation have been investigated to examine photo-electrochemical efficiency and effectiveness of POPTA-TiO2/Ti nanocomposite photo-anode. Electro-generation hydrogen pyroxide (H2O2)-assisted TiO2 photo-electro-catalysis has been also conducted by using dual functional electrodes of a nanotubular POPTA-TiO2/Ti photo-anode and a vitreous carbon cathode for enhanced photo-electrochemical performance.
Keywords: Nanocomposite photo-anode; Photo-electro-catalytic; Polyoxophosphotungstate; Titania nanotube array
Environmentally friendly efficient synthesis and mechanism of triazenes derived from cyclic amines on clays, HZSM-5 and sulfated zirconia by H.A. Dabbagh; A. Teimouri; A. Najafi Chermahini (pp. 24-33).
Diazotization and diazocoupling reactions of para-aminobenzene-1-sulfonyl azide and para-aminobenzene-1-sulfonyl amide with cyclic amines of various ring sizes (pyrrolidine, piperidine, 4-methylpiperidine, N-methylpiperazine, morpholine and hexamethyleneimine over eco-friendly clay catalysts, HZSM-5 and sulphated zirconia are described. These inexpensive, noncorrosive and reusable catalysts appear to exhibit bifunctional catalytic properties for these reactions. No considerable decreases in the efficiency of the catalysts were observed after four cycles of operation. The new method totally avoids the use of acid, alkali or toxic solvents in diazotization and diazocoupling reactions.
Keywords: Environmental compatibility; Heterocyclic amines; Diazotization; Diazocoupling; Triazenes; Clays; HZSM-5; Sulfated zirconia
Individual and competitive liquid-phase hydrodechlorination of chlorinated pyridines over alkali-modified Pd/ZrO2 by José M. Moreno; Maria A. Aramendía; Alberto Marinas; José M. Marinas; Francisco J. Urbano (pp. 34-41).
Individual and competitive liquid-phase hydrodechlorination of chlorinated pyridines has been studied over alkali-modified zirconia-supported palladium catalysts. All experiments proceed without catalyst deactivation as a result of the interaction of the reaction products (HCl and pyridine) forming pyridinium chloride, thus avoiding the detrimental effect of HCl on palladium particles. Individual experiments indicate a different behaviour for 2-chloropyridine and 3-chloropyridine. Catalyst modification with alkali metals improves the catalytic activity for 3-chloropyridine but not for 2-chloropyridine hydrodechlorination. 2,3-Dichloropyridine hydrodechlorination yields lower reaction rates than 2- or 3-chloropyridine. Moreover, no partially chlorinated compounds were detected. Competitive hydrodechlorination of equimolecular mixtures of 2-and 3-chloropyridine allow us to obtain both the reactivity and adsorption coefficient of 3-chloropyridine with respect to 2-chloropyridine. Again, in competitive hydrodehalogenation, 3-chloropyridine reacts faster than 2-chloropyridine for all catalysts. However, results indicate that the alkali-modified catalysts adsorb preferably 2-chloropyridine instead of 3-chloropyridine. Moreover, competitive hydrodehalogenation carried out for the couples 3-chloropyridine/chlorobenzene, 2-chloropiridine/chlorobenzene and 2,3-dichloropyridine/chlorobenzene revealed that chlorinated pyridines are reduced to the detriment of chlorobenzene due to the preferential adsorption of chlorinated pyridines against chlorobenzene. All data support a reaction mechanism based on an electrophilic attack to the carbon bearing the chlorine atoms.
Keywords: Alkali-modification; Zirconia; Palladium catalyst; Hydrodechlorination; Hydrodehalogenation; Chloropyridine; Competitive reaction; Adsorption coefficient
Evaluation of Pd-based catalysts and the influence of operating conditions for autothermal reforming of dimethyl ether by Marita Nilsson; Peter Jozsa; Lars J. Pettersson (pp. 42-50).
A series of different Pd-based catalysts supported on ceramic monoliths were synthesized and tested in a screening study for autothermal reforming of dimethyl ether (DME). Alumina-supported Pd was shown to be very active for this reaction at temperatures between 350 and 400°C. Adding Zn to Pd/γ-Al2O3 decreased the activity of decomposition reactions leading to better reforming activity, and resulting in high selectivity to carbon dioxide. Pd-Zn/γ-Al2O3 was further evaluated in a parameter study varying oxygen-to-DME ratio, steam-to-DME ratio and temperature. The effect on the reformer performance of changing the operating conditions is discussed. The Pd-Zn/γ-Al2O3 catalyst generated carbon monoxide concentrations below 5%, and hydrogen concentrations close to 50%. The catalyst performance was significantly improved by preconditioning in hydrogen. Results from a first round of catalyst characterization studies suggest that Pd–Zn species are formed on the alumina support following reduction.
Keywords: Hydrogen; Autothermal reforming; Dimethyl ether; Auxiliary power unit
Development of environmentally friendly photocatalyst with nano-size pore structure coated with thin Ti-oxide by Yasuo Iizuka; Takashi Kubo; Atsushi Nakahira; Daisuke Onodera; Naoshi Ozawa; Takeshi Yao (pp. 51-56).
An environmentally friendly Ti-oxide/SiO2 photocatalyst was developed by using hydrolysis reaction of titanium fluoro-complex in aqueous solution which was permeated into the pores of silica support with nano-size pore structure and with high specific surface area. The catalyst prepared was photocatalytically active for the decomposition of formaldehyde in air under illumination with ordinary commercial fluorescent light at ambient temperature and pressure.
Keywords: Titanium fluoro-complex; Ti-oxide/SiO; 2; Photocatalyst; Formaldehyde; Fluorescent light
New photocatalytic reactor with TiO2 coating on sintered glass cylinders by H.D. Mansilla; A. Mora; C. Pincheira; M.A. Mondaca; P.D. Marcato; N. Durán; J. Freer (pp. 57-63).
The antibiotic flumequine was used to evaluate the photocatalytic activity of TiO2 coating on sintered glass cylinders (SGC) tailored on a 0.5-l annular reactor. The cylinders were prepared with finely powdered silicate glass (150–600μm) and then coated with titania Degussa P-25 by thermal treatment. The impregnated SGC were characterized by surface techniques such as EDS, SEM and XRD. The coated cylinders present homogeneous porosity, high mechanical strength, and good light transparency. The photocatalytic activity evaluated against flumequine was found to be comparable to the photocatalytic activity presented by titania in aqueous suspension. After 20min irradiation, around 55% and 80% of 18ppm flumequine was degraded by irradiation with black light (360nm) or germicidal lamp (254nm), respectively. A high reproducibility of the activity was observed when the reaction was continually repeated using the impregnated cylinders. The antibactericidal activity of irradiated solutions was evaluated in Escherichia coli cultures showing significant inhibition.
Keywords: Antibiotic; Flumequine; Immobilized TiO; 2; Photocatalysis; Sintered glass
An investigation of trichloroethylene photocatalytic oxidation on mesoporous titania-silica aerogel catalysts by Shengli Cao; King Lun Yeung; Po-Lock Yue (pp. 64-72).
Freestanding blocks of mesoporous, titania-silica aerogel catalyst were prepared and tested for gas phase photocatalytic oxidation of trichloroethylene (TCE) in a new photoreactor where the reactant gases flow through the aerogel block. The intimate contact between the reactants and catalyst resulted in a higher conversion. TS01 aerogel was prepared by ethanol supercritical drying, and contained nanometer-sized crystalline domains of anatase TiO2 (i.e., TiOTi sites) within an amorphous SiOTi and SiOSi network. The TS02 aerogel prepared by CO2 supercritical drying remained amorphous even after high temperature treatment, and analysis indicated that the TiOSi is the predominant site on this catalyst. The reaction results indicated that only the TS01 aerogel containing anatase TiO2 was active, but the formation of dichloroacetaldehyde on the amorphous SiOSi sites led to a rapid catalyst deactivation. However, a stable catalyst was obtained after these sites were passivated by ozone pretreatment under ultraviolet (UV) irradiation. The TS01 aerogel catalysts exhibited an average conversion of 30% and a quantum yield of 0.27 at a TCE concentration of 56ppm, feed flow rate of 40sccm and UV irradiation of 710μWcm−2.
Keywords: Nano-TiO; 2; Sol–gel; Gas transport; Photoreactor and in situ FTIR
Raschig rings-Fe2O3 composite photocatalyst activate in the degradation of 4-chlorophenol and Orange II under daylight irradiation by J. Bandara; U. Klehm; J. Kiwi (pp. 73-81).
Fe2O3 on Raschig glass rings (Fe2O3/RR) was investigated as photocatalyst under simulated solar radiation during the degradation of 4-chlorophenol (4-CP) and the azo dye Orange II (Or II). Thin films of Fe2O3 particles were coated on glass rings using polyethylene-graft-maleic anhydride (PEGMA) as a negative interfacial agent. The Fe2O3/RR photocatalyst presented absorption in the visible range up to 535nm. The catalytic activity of Fe2O3/RR coated with preformed Fe2O3 (11.4m2/g) was found to be superior to that of Fe2O3/RR1 catalyst obtained by the precipitation of Fe-ions on the glass rings surface. The photoactivated degradation of 4-CP and Or II was possible at pH values of 5.5 using both catalysts. The Fe2O3/RR photocatalyst shows a stable catalytic performance during long-term operation under simulated sunlight radiation. The Fe2O3/RR and Fe2O3/RR1 photocatalysts were characterized by diffusion reflectance spectroscopy (DRS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), atomic absorption spectroscopy (AAS) and gas adsorption measurements (BET). The Fe 2p binding energy (BE) in the Fe2O3/RR samples was 711.6eV before the catalysis and 711.7eV after the catalysis, indicating the stability of the Fe-oxidation state on the glass rings. The pore diameter did not decrease when going from Fe2O3 powder to the Fe2O3 attached on the Raschig glass rings but the Fe2O3 BET area decreased considerably involving restructuring of the Fe2O3 particles. The experimental data allows to formulate a mechanism of reaction for the degradation of 4-CP on the Fe2O3/RR catalyst.
Keywords: Fe; 2; O; 3; /glass rings preparation; Catalyst synthesis; 4-Chlorophenol degradation; Orange II degradation; DRS; XPS; EM; BET
Nanocrystalline anatase TiO2 photocatalysts prepared via a facile low temperature nonhydrolytic sol–gel reaction of TiCl4 and benzyl alcohol by Jian Zhu; Jun Yang; Zhen-Fen Bian; Jie Ren; Yong-Mei Liu; Yong Cao; He-Xing Li; He-Yong He; Kang-Nian Fan (pp. 82-91).
Nanocrystalline anatase TiO2 photocatalysts prepared by a facile nonhydrolytic sol–gel (NSG) reaction of TiCl4 and benzyl alcohol at low temperature, followed by subsequent calcination at elevated temperatures were investigated in relation to their performance in the photocatalytic degradation of phenol. A variety of techniques including N2 adsorption, X-ray powder diffraction (XRD), diffuse reflectance FTIR spectroscopy (DRIFTS), thermogravimetric measurements (TG/DTA), transmission electron micrographs (TEM), and X-ray photoelectron spectroscopy (XPS) were employed to characterize the resulting materials. It is shown that the fresh nanocrystalline TiO2 sample obtained by the low temperature NSG process exhibits considerable activity comparable to that of commercial photocatalyst Degussa P-25, although evidence shows it to be surface-capped with appreciable amount of organic moieties. Moreover, it is demonstrated that the catalytic efficiency of the as-prepared nanocrystalline TiO2 sample can be further markedly enhanced by subsequent thermal treatment at elevated temperatures ranging from 300 to 600°C. Both the calcination temperature and calcination time appear to be crucial factors in influencing a number of critical properties of the calcined TiO2 samples such as the surface area, particle size, crystallinity, amount of surface hydroxyl groups, as well as carbonaceous residues. The TiO2 photocatalyst obtained by calcination at 400°C for 3h exhibits the highest activity toward photocatalytic degradation of phenol.
Keywords: Photocatalytic; TiO; 2; Nonhydrolytic; Sol–gel; TiCl; 4; Benzyl alcohol
Catalytic wet air oxidation of 2-chlorophenol over Ru loaded Ce xZr1− xO2 solid solutions by Ning Li; Claude Descorme; Michèle Besson (pp. 92-100).
A series of Ce xZr1− xO2 mixed-oxide-supported Ru catalysts were unprecedentedly evaluated in the catalytic wet air oxidation (CWAO) of 2-chlorophenol (2-CP) solutions (2gL−1). They were shown to exhibit higher performances than the corresponding CeO2 or ZrO2-supported catalysts. The ceria–zirconia solid solution structure appeared to be crucial for the higher activity of the 3wt.% Ru/Ce xZr1− xO2 catalysts. After introduction of praseodymium or neodymium in the Ce xZr1− xO2 lattice, the activity of the 3wt.% Ru/Ce xZr1− xO2 catalysts was further improved. Pr was shown to have a greater effect than Nd, especially at low Pr concentration. Further investigations indicated that Ce xZr1− xO2 solid solutions loaded Ru catalysts could maintain outstanding catalytic performances even at low temperature (393K) and low pressure (3MPa).
Keywords: Catalytic wet air oxidation; Chlorophenol; Ru; Ce; x; Zr; 1−; x; O; 2; Pr; Nd
Spectroscopic evidence for the mode of action of alkali promoters in Pt-catalyzed de-NOx chemistry by S. Koukiou; M. Konsolakis; R.M. Lambert; I.V. Yentekakis (pp. 101-106).
The interaction of NO with sodium-dosed Pt(Na)/γ-Al2O3 catalysts was studied by means of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). With increasing sodium loading, pronounced and progressive red shifts of the NO stretching frequency associated with molecular NO adsorbed on the Pt component were observed. This decrease in ν(NO) correlates with enhancement of NO dissociation at higher temperatures on Na-promoted Pt catalysts under conditions where clean Pt is almost ineffective. These spectroscopic observations provide a clear and consistent explanation for the recently reported very strong promotion by alkalis of the performance of supported Pt catalysts in de-NOx chemistry [I.V. Yentekakis, M. Konsolakis, R.M. Lambert, N. Macleod, L. Nalbandian, Appl. Catal. B 22 (1999) 123; I.V. Yentekakis, V. Tellou, G. Botzolaki, I.A. Rapakousios, Appl. Catal. B 56 (2005) 229].
Keywords: Infrared spectroscopy; Platinum; Sodium; Al; 2; O; 3; NO adsorption
NO reduction by CO in the presence of water over gold supported catalysts on CeO2-Al2O3 mixed support, prepared by mechanochemical activation by L. Ilieva; G. Pantaleo; J.W. Sobczak; I. Ivanov; A.M. Venezia; D. Andreeva (pp. 107-114).
The reduction of NO by CO was studied on gold catalysts supported on ceria-alumina, prepared by mechanochemical activation. The samples were characterized by means of XRD, TPR, XPS and Raman spectroscopy. The influence of water in the feed on the catalytic activity was evaluated as well. It was established that the addition of hydrogen and water improves NO reduction activity by CO. The role of water was connected to the hydrogen production by WGS. The role of oxygen vacancies created in ceria structure in the presence of alumina was also discussed. The 100% selectivity to N2 at about 200°C was kept in all cases of catalytic measurements, making the studied gold catalysts promising for practical application.
Keywords: Gold; Ceria-alumina; Mechanochemical activation; NO reduction by CO; Effect of water
Methane combustion over Pd supported on MCM-41 by Juan A.C. Ruiz; Marco A. Fraga; Heloise O. Pastore (pp. 115-122).
This work aimed at studying the feasibility of using mesoporous molecular sieves (MCM-41) as supports for palladium-based catalysts for methane combustion. The effects brought about by the chemical composition as well as by the presence of cerium and lanthanum were investigated. The MCM-41 structures were found to be thermally stable under air: the MCM-41 is stable until 1273K while the [Al]-MCM-41 resists up to 1173K. Silicate-based catalysts are more active than the aluminosilicate-supported Pd samples; while no changes were observed on the structure of the materials during the catalytic test, it was found that the addition of La and Ce decreased their activity. The catalytic activity was correlated with the hydrophobic character of the supports, and with the smaller temperature of PdO reduction presented by the catalysts.
Keywords: MCM-41; Methane combustion; PdO reducibility; Natural gas
Surface characterization studies of TiO2 supported manganese oxide catalysts for low temperature SCR of NO with NH3 by Padmanabha Reddy Ettireddy; Neeraja Ettireddy; Sergey Mamedov; Punit Boolchand; Panagiotis G. Smirniotis (pp. 123-134).
A series of TiO2 supported manganese oxide catalysts were prepared by wet-impregnation method for the low temperature selective catalytic reduction (SCR) of NO with ammonia as a reductant. A combination of various physico-chemical techniques such as N2 physisorption, O2 chemisorption, TPR, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman were used to characterize the chemical environment of these catalysts. O2 chemisorption and XRD results suggest that Mn exist in a well-dispersed state at below 16.7wt.% of Mn on TiO2 anatase (Hombikat), 7.5wt.% on TiO2 rutile (Kemira) and P-25 (80% anatase+20% rutile), and in microcrystalline phase above these loading levels on respective support materials. These results also reveal that Mn interacts very well with pure anatase phase compared to rutile. XPS results of Mn/TiO2 anatase (Hombikat) catalysts illustrated the presence of MnO2 as a major phase (peak at 642.0eV) along with Mn2O3 as the minor phase at lower loadings. The presence of Mn2O3 disappears at higher loadings. The characterization results indicated that the manganese oxide exists as an isolated species at very low loadings, highly dispersed state probably as two dimensional monolayer species at intermediate loadings, polymeric or microcrystalline form of manganese oxide at higher (above monolayer capacity) loadings was envisaged. The catalytic performance of various amounts of Mn loaded on different TiO2 supported catalysts for low temperature SCR reaction at catalyst bed temperature 175°C under power plant conditions using GHSV=50,000h−1 was studied. The catalyst with 16.7wt.% Mn/TiO2 anatase (Hombikat) was found to be highly active and selective catalyst for this reaction. The Raman studies acted as complimentary tool to XPS in order to characterize the manganese oxides (MnO, Mn2O3, Mn3O4, MnO2). Raman data show that there is a strong interaction between the Mn oxides and the support, which is responsible for the impressive catalytic performance in comparison with other systems we investigated.
Keywords: TiO; 2; anatase; TiO; 2; rutile; MnO; 2; XPS; Raman; Low temperature SCR; NO; NH; 3
Catalytic wet air oxidation of phenol with modified activated carbons and Fe/activated carbon catalysts by A. Quintanilla; J.A. Casas; J.J. Rodríguez (pp. 135-145).
A commercial activated carbon was modified by different oxidative treatments to introduce different oxygen surface groups. A gentle oxidation in gas phase with a poor oxygen stream and a more severe oxidation in liquid phase with a HNO3 solution were used. The resulting activated carbons and the corresponding Fe-impregnated (2.5% Fe) ones were tested for the wet air oxidation of phenol. A trickle-bed reactor at 400K and 8atm of total pressure in a wide range of space time (20–320gCATh/gPhenol) was used. The performance of the carbon supports and Fe catalysts was assessed by following phenol and TOC conversions, as well as the toxicity of the effluents. The fresh and used catalysts were characterized by nitrogen adsorption, TPD analyses and pHslurry. Gas-phase oxidation increased mainly the carbonyl/quinone groups and also carboxylic anhydride groups, whereas HNO3 oxidation significantly increased all the oxygen surface groups, but more significantly phenol, carbonyl/quinone and lactone groups. Regarding the preparation of the catalysts, Fe itself plays a promoting role in the formation or destruction of oxygen surface groups during calcinations, the latter being only observed when the activated carbon was oxidized with HNO3.Phenol and TOC conversions increased with the initial acidity of the catalyst. The introduction of Fe enhanced the activity and toxicity abatement at high enough space times, compared to an activated carbon with the same amounts of oxygen surface groups. This can be attributed to the increase in the acidity that the Fe itself provokes and the promoter role of Fe in the oxidation reaction of phenol. After the catalytic wet air oxidation process, surface area and micropore volume decreased whereas the amount of oxygen surface groups increased, as well as the total acidity, except for the activated carbon treated with HNO3. Also Fe dispersion significantly diminishes. However, the final surface distribution did not affect the catalyst activity. The presence of Fe reduced the detrimental effect of wet oxidation on the porous structure of the activated carbons.
Keywords: Catalytic wet air oxidation; Phenol; Activated carbon; Fe/AC catalyst; Oxygen surface groups
New hydrogen-producing photocatalysts—A combinatorial search by Michael Seyler; Klaus Stoewe; Wilhelm F. Maier (pp. 146-157).
A high-throughput (HT) method for the discovery of new heterogeneous catalysts for photocatalytic hydrogen production from aqueous methanol solutions is presented. The HT workflow includes the preparation of libraries containing multi-component metal oxides following a modified sol–gel route, the irradiation of catalyst suspensions with a custom illumination setup and fast sequential product gas analysis by gas chromatography to evaluate catalyst performance. The influence of reaction parameters, as e.g. catalyst grain size, light intensity on the results is discussed. Results of the screening of diverse mixed metal oxide libraries are shown. An evolutionary search strategy involving doping of active oxides and screening of variations in material compositions was applied to discover new photocatalysts. As a new lead structure, an aluminium–lead–bismuth-oxide has been discovered. Further activity increases have been achieved through doping.
Keywords: Photocatalysis; Heterogeneous catalysis; High-throughput; Combinatorial chemistry; Hydrogen
Palladium nanoparticles for catalytic reduction of Cr(VI) using formic acid by Marcells A. Omole; Isaac O. K’Owino; Omowunmi A. Sadik (pp. 158-167).
Cr(VI), a leading contaminant in most hazardous waste sites, is acutely toxic, a proven mutagen and a carcinogen whereas Cr(III) is believed to be an essential element. We describe a one-pot synthesis and characterization of palladium nanoparticles (PdNPs) using transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and13C nuclear magnetic resonance (NMR). The resulting PdNPs were used as catalyst to demonstrate a new concept for the reduction of Cr(VI) to Cr(III) using formic acid as a reducing agent. Percentage decrease in the concentration of Cr(VI) as a function of time was monitored using UV/vis spectroscopy at a fixed wavelength of 350nm. Results showed that the reduction follows first-order reaction kinetics with respect to initial concentrations of Cr(VI) and HCOOH. The leveling off in reaction rate with respect to PdNPs loading confirms the importance of surface reaction as the rate-controlling step. The rate of Cr(VI) reduction was found to be dependent on temperature, pH, amount of PdNPs and formic acid concentrations, with the optimum at 45°C under acidic conditions. For every 0.1M increment in formic acid concentration, there was a corresponding 18.4% enhancement in the reduction rate. Consequently, it took 5min for the PdNPs to catalyze the reduction of a 7.14mM concentration of Cr(VI) at 99.8% efficiency. Subsequent practical application in environmental samples indicates a complete elimination of Cr(VI) from the tested soil and aqueous media.
Keywords: Pd; Nanoparticles; Reduction; Catalyst; Formic acid
Anatase TiO2 nanoparticles immobilized on ZnO tetrapods as a highly efficient and easily recyclable photocatalyst by Qinghong Zhang; Wugang Fan; Lian Gao (pp. 168-173).
Anatase TiO2 nanoparticles in the size of ca. 6nm were immobilized on the single-crystalline tetrapod-like ZnO (denoted as T-ZnO in the text) with dimensions up to 20–50μm by vapor hydrolysis method (VHM). Compared to the wet chemical deposition method, more uniform TiO2 layers with a tunable thickness were achieved by VHM. T-ZnO showed a relatively low efficiency in the photooxidation reaction of phenol. After coating of anatase nanoparticles, the photocatalytic activity of the nanocomposite (TiO2/T-ZnO) was significantly enhanced in photooxidation of phenol. Moreover, in contrast to the discrete nanoparticles, TiO2/T-ZnO could be very easily recovered from the treated solution by a most common filter paper. The easily recyclable feature and the high efficiency made TiO2/T-ZnO act as low-cost and feasible photocatalysts for the large-scale applications.
Keywords: Titanium dioxide; Photocatalytic degradation; Phenol; Zinc oxide; Anatase
Synthesis and catalytic property of a Co2+-exchanged Beta/Y composite for the selective catalytic reduction of NO by CH4 in the presence of excess oxygen by Jinqiao Zhang; Weibin Fan; Yuying Liu; Ruifeng Li (pp. 174-184).
A new composite of zeolite Beta and zeolite Y (denoted as Beta/Y) has been synthesized by overgrowing and/or epitaxially growing a layer of zeolite Beta on the pseudo-crystals of zeolite Y. The prepared sample was different from the mechanical mixture of these two phases, as shown by NH3-TPD and FE-SEM measurements. One type of remarkably strong acid site was observed for the H-type and the (Co, H)-type composite samples, whereas it is absent in the corresponding analogues of zeolite Beta, Y and their mechanical mixtures. This provides one type of new cationic site for Co2+ in the composites. With comparable contents of zeolite Beta and zeolite Y phases, (Co, H)-Beta/Y catalysts showed much higher catalytic activity than the physical mixture of (Co, H)-Y and (Co, H)-Beta and also the pure phases of these two materials for the reduction of NO by methane (CH4-SCR) in the presence of excess oxygen. This resulted from the formation of a large number of more stable NO y (with y=2, 3) species enhanced by the presence of such type of strong acid site, and hence one type of new Co2+ ion as well, and more highly dispersed Co xO y species, as revealed by NH3-TPD, NO-TPD, NO2-TPD, (NO+O2)-TPD and DR UV–vis spectroscopy. It was shown that the Co2+ cations in the ion-exchanged sites, strong Brösted acid sites and probably Co oxide-like species collaboratively contribute to the CH4-SCR of NO at high reaction temperature. In contrast, when the reaction was carried out below 700K, it seems that Co2+ cations play a major role.
Keywords: Beta/Y composite; Co-zeolite; Acid; deNO; x; CH; 4; -SCR
ZnSO4–TiO2 doped catalyst with higher activity in photocatalytic processes by Yu Zhiyong; M. Bensimon; V. Sarria; I. Stolitchnov; W. Jardim; D. Laub; E. Mielczarski; J. Mielczarski; L. Kiwi-Minsker; J. Kiwi (pp. 185-195).
This study presents the synthesis and activity of ZnSO4–TiO2 coated Raschig rings (RR). The activity of the Zn-doped catalyst (from now on Zn–TiO2/RR) was found to be higher than of the pure Degussa P25 TiO2 during the photodegradation of organic compounds. The most suitable doping level of TiO2 for Zn was 4mol% noted as Zn (4% mol)–TiO2/RR during the degradation of azo-dye Orange II and of the transparent 2-propanol solutions. The degradation kinetics of the probe molecules was systematically investigated as a function of the catalyst make-up and some of the solution parameters. XPS measurements show Zn 2p3/2 peak positions for Zn–TiO2 sample in the range 1021.58–1022.00eV. This energy range was observed to be lower than 1022.54eV recorded for the reference ZnSO4 sample. This shift indicates that the Zn-atoms act as electron acceptors in the Zn-doped TiO2 and may be responsible for the higher catalytic activity observed for the Zn (4% mol)–TiO2/RR compared to the TiO2/RR photocatalyst during Orange II degradation. Insight is given onto the complex oxidation/reduction processes takes place at the interface of Zn–TiO2. The changes occurring in the Zn, TiO2 and S catalyst components are discussed as a function of the time of reaction. The Zn–TiO2 catalyst was characterized by elemental analysis (EA), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), confocal microscopy, X-ray photoelectron microscopy (XPS) and X-ray diffraction (XRD).
Keywords: Photocatalysis; Orange II discoloration; XPS; Zn-Doping
Synthesis and characterization of phosphor and nitrogen co-doped titania by L. Lin; R.Y. Zheng; J.L. Xie; Y.X. Zhu; Y.C. Xie (pp. 196-202).
Phosphor and nitrogen co-doped titania were prepared by a simple modified sol–gel method with hypophosphorous acid and ammonia as the P and N sources, respectively. The resulting materials were characterized by X-ray diffraction (XRD), nitrogen physical adsorption at 77K, Fourier transformed infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and UV–vis spectroscopy. It was found that modification by phosphor could retard the phase transformation of anatase to rutile and increase the surface area significantly, while the doped nitrogen had little influence on the thermal stability and texture of the titania. The chemical nature of N and P was identified by XPS as NTiO and TiOP in the anatase TiO2 lattice. UV–vis spectra showed that modification by phosphor or nitrogen extended the spectral response of titania into the visible region. The photocatalytic activity of titania modified by only nitrogen was limited, much lower than that of phosphor-doped titania. However, when titania was co-doped with both phosphor and nitrogen, the photocatalytic activity was further enhanced efficiently.
Keywords: Titania; Phosphor; Nitrogen; Photocatalysis; 4-Chlorophenol (4CP)