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Catalysts, Volume 3, Issue 1 (March 2013), Pages 1-362

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Research

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Open AccessArticle Preparation and Photocatalytic Properties of Sr2−xBaxTa3O10−yNz Nanosheets
Catalysts 2013, 3(1), 1-10; doi:10.3390/catal3010001
Received: 11 November 2012 / Revised: 17 December 2012 / Accepted: 9 January 2013 / Published: 16 January 2013
Cited by 10 | PDF Full-text (462 KB) | HTML Full-text | XML Full-text
Abstract
Sr2−xBaxTa3O10yNz (x = 0.0, 0.5, 1.0) nanosheets were prepared by exfoliating layered perovskite compounds (CsSr2−xBaxTa3O10yNz). The Sr
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Sr2−xBaxTa3O10yNz (x = 0.0, 0.5, 1.0) nanosheets were prepared by exfoliating layered perovskite compounds (CsSr2−xBaxTa3O10yNz). The Sr1.5Ba0.5Ta3O9.7N0.2 nanosheet showed the highest photocatalytic activity for H2 production from the water/methanol system among the Sr2−xBaxTa3O9.7N0.2 nanosheets prepared. In addition, Rh-loaded Sr1.5Ba0.5Ta3O9.6N0.3 nanosheet showed the photocatalytic activity for oxygen and hydrogen production from water. The ratio of hydrogen to oxygen evolved was around two. These results indicate that the Rh-loaded Sr1.5Ba0.5Ta3O9.6N0.3 nanosheet is a potential catalyst for photocatalytic water splitting. Full article
(This article belongs to the Special Issue Photocatalysts)
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Open AccessArticle Partial Oxidation of n-Butane over a Sol-Gel Prepared Vanadium Phosphorous Oxide
Catalysts 2013, 3(1), 11-26; doi:10.3390/catal3010011
Received: 2 October 2012 / Revised: 5 December 2012 / Accepted: 8 January 2013 / Published: 16 January 2013
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Abstract
Vanadium phosphorous oxide (VPO) is traditionally manufactured from solid vanadium oxides by synthesizing VOHPO4∙0.5H2O (the precursor) followed by in situ activation to produce (VO)2P2O7 (the active phase). This paper discusses an alternative synthesis method
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Vanadium phosphorous oxide (VPO) is traditionally manufactured from solid vanadium oxides by synthesizing VOHPO4∙0.5H2O (the precursor) followed by in situ activation to produce (VO)2P2O7 (the active phase). This paper discusses an alternative synthesis method based on sol-gel techniques. Vanadium (V) triisopropoxide oxide was reacted with ortho-phosphoric acid in an aprotic solvent. The products were dried at high pressure in an autoclave with a controlled excess of solvent. This procedure produced a gel of VOPO4 with interlayer entrapped molecules. The surface area of the obtained materials was between 50 and 120 m2/g. Alcohol produced by the alkoxide hydrolysis reduced the vanadium during the drying step, thus VOPO4 was converted to the precursor. This procedure yielded non-agglomerated platelets, which were dehydrated and evaluated in a butane-air mixture. Catalysts were significantly more selective than the traditionally prepared materials with similar intrinsic activity. It is suggested that the small crystallite size obtained increased their selectivity towards maleic anhydride. Full article
(This article belongs to the Special Issue Aerogel Catalyst)
Open AccessCommunication Enzyme-Catalyzed Transetherification of Alkoxysilanes
Catalysts 2013, 3(1), 27-35; doi:10.3390/catal3010027
Received: 27 November 2012 / Revised: 20 December 2012 / Accepted: 8 January 2013 / Published: 18 January 2013
Cited by 2 | PDF Full-text (261 KB) | HTML Full-text | XML Full-text
Abstract
We report the first evidence of an enzyme-catalyzed transetherification of model alkoxysilanes. During an extensive enzymatic screening in the search for new biocatalysts for silicon-oxygen bond formation, we found that certain enzymes promoted the transetherification of alkoxysilanes when tert-butanol or 1-octanol were
[...] Read more.
We report the first evidence of an enzyme-catalyzed transetherification of model alkoxysilanes. During an extensive enzymatic screening in the search for new biocatalysts for silicon-oxygen bond formation, we found that certain enzymes promoted the transetherification of alkoxysilanes when tert-butanol or 1-octanol were used as the reaction solvents. Full article
(This article belongs to the Special Issue Biomimetic Catalysts)
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Open AccessArticle Microvolume TOC Analysis as Useful Tool in the Evaluation of Lab Scale Photocatalytic Processes
Catalysts 2013, 3(1), 74-87; doi:10.3390/catal3010074
Received: 21 November 2012 / Revised: 24 December 2012 / Accepted: 16 January 2013 / Published: 22 January 2013
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Abstract
Analysis methods that require small volumes of aqueous samples can be of large benefit for applications when expensive chemicals are involved or available volumes are substantially small and concentrations are low. A new method is presented to allow microvolume liquid injections on TOC
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Analysis methods that require small volumes of aqueous samples can be of large benefit for applications when expensive chemicals are involved or available volumes are substantially small and concentrations are low. A new method is presented to allow microvolume liquid injections on TOC equipment using a special designed Shimadzu gas injection kit® in combination with a high precision syringe and Chaney adapter. Next to details on the methodology of microvolume TOC injections, the technique is shown to be beneficial to evaluate the efficiency of photocatalytic dye degradation on titania materials in terms of CO2 conversion simultaneously with classic UV-Vis analysis measurements within a lab scale photocatalytic test setup (volume <100 mL). The possibility to allow multiple microvolume samplings in short time intervals during several hours without a substantial decrease in volume/catalyst ratio is of particular value for the evaluation of photocatalysts. By combining both techniques at short time intervals, additional knowledge of the degradation process/mechanism, kinetics and the efficiency can be obtained in a direct way. Moreover, the developed μV-TOC analysis is specifically useful in those applications in which low sample volumes in combination with low concentrations are involved. For example, μV-TOC can similarly be put into service in a wide range of small volume setups, e.g., analytes from high-throughput screening, pharmaceutical applications and other advanced oxidation processes that formally could not be analyzed due to limited sample volumes and often low concentrations. Full article
(This article belongs to the Special Issue Photocatalysts)
Open AccessArticle Coating SiO2 Support with TiO2 or ZrO2 and Effects on Structure and CO Oxidation Performance of Pt Catalysts
Catalysts 2013, 3(1), 88-103; doi:10.3390/catal3010088
Received: 10 November 2012 / Revised: 13 November 2012 / Accepted: 29 January 2013 / Published: 6 February 2013
Cited by 15 | PDF Full-text (720 KB) | HTML Full-text | XML Full-text
Abstract
In this work, we studied how TiO2 and ZrO2 coatings enhance the CO oxidation performance of SiO2-supported Pt catalysts under conditions relevant to automotive emissions control. SiO2 was coated with metal oxides TiO2 or ZrO2 by
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In this work, we studied how TiO2 and ZrO2 coatings enhance the CO oxidation performance of SiO2-supported Pt catalysts under conditions relevant to automotive emissions control. SiO2 was coated with metal oxides TiO2 or ZrO2 by sol-gel method and the subsequent Pt loading was done by incipient wetness method. The prepared catalysts Pt/TiO2-SiO2 and Pt/ZrO2-SiO2 were compared with Pt/SiO2 and Pt/Al2O3 in fresh, sulfated, and hydrothermally aged states. The structure of the catalysts was characterized with BET, XRD, TEM, EDS, EXAFS, XANES, TPD and TPR to help interpret the CO oxidation performance. Higher dispersion, stability, and oxidation state of Pt were achieved on TiO2-SiO2 and ZrO2-SiO2 supports due to stronger metal-support interaction leading to superior CO oxidation performance compared to Pt/SiO2 and Pt/Al2O3. TiO2 and ZrO2 coatings introduced surface acidity but negligible basicity, which is a likely reason for the weak and low adsorption of SO2. The results suggest that the sol-gel coating of SiO2 with metal oxides could be an attractive strategy for designing automotive oxidation catalysts with enhanced performance such as low-temperature activity, sulfur tolerance, and hydrothermal stability. Full article
(This article belongs to the Special Issue Catalytic Combustion)
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Open AccessArticle Preparation of Thiophene-Fused and Tetrahydroquinoline-Linked Cyclopentadienyl Titanium Complexes for Ethylene/α-Olefin Copolymerization
Catalysts 2013, 3(1), 104-124; doi:10.3390/catal3010104
Received: 17 December 2012 / Revised: 25 January 2013 / Accepted: 29 January 2013 / Published: 6 February 2013
Cited by 3 | PDF Full-text (483 KB) | HTML Full-text | XML Full-text
Abstract
A synthetic scheme was developed for the large-scale preparation of a dimethylthiophene-fused and tetrahydroquinaldine-linked dimethylcyclopentadienyl titanium complex (2), which is a high-performance homogeneous Ziegler catalyst. 2,3,4,5-Tetramethyl-4,5-dihydrocyclopenta[b]thiophen-6-one was prepared without chromatography purification on the 40-g scale in a laboratory setting,
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A synthetic scheme was developed for the large-scale preparation of a dimethylthiophene-fused and tetrahydroquinaldine-linked dimethylcyclopentadienyl titanium complex (2), which is a high-performance homogeneous Ziegler catalyst. 2,3,4,5-Tetramethyl-4,5-dihydrocyclopenta[b]thiophen-6-one was prepared without chromatography purification on the 40-g scale in a laboratory setting, from which the ligand precursor for 2 was obtained in 65% yield on a 50-g scale in a one-pot without the need for chromatography purification. Metallation was achieved in a high yield (78%) through reaction of the dilithiated compound with TiCl4. Many derivatives were prepared by employing the same synthetic scheme as applied for 2. Among them, the titanium complex prepared from 2-methyl-4,5-dimethyl-6-(2-n-butyl-2,3,4,5-tetrahydroquinolin-8-yl)-4H-cyclopenta[b]thiophene exhibited an exceptionally high activity. Under commercially relevant high-temperature polymerization conditions (160 °C), this compound showed a higher activity than 2 (126 × 106 g/molTi∙h versus 72 × 106 g/molTi∙h), albeit with the formation of a polymer of slightly lower molecular weight (Mw, 159,000 versus 218,000) and with a slightly lower 1-octene content (9.3 mol% versus 12 mol%). Full article
(This article belongs to the Special Issue Molecular Catalysis for Precise Olefin Polymerization)
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Open AccessArticle Oligomerization of Ethylene to Produce Linear α-Olefins Using Heterogeneous Catalyst Prepared by Immobilization of α-Diiminenickel(II) Complex into Fluorotetrasilicic Mica Interlayer
Catalysts 2013, 3(1), 125-136; doi:10.3390/catal3010125
Received: 13 December 2012 / Revised: 29 January 2013 / Accepted: 29 January 2013 / Published: 6 February 2013
Cited by 4 | PDF Full-text (327 KB) | HTML Full-text | XML Full-text
Abstract
Heterogeneous catalysts for production of linear α-olefins from ethylene were prepared by the direct reaction of the α-diimine ligand [L: R-N=C(R')-C(R')=N-R; R' = Me and R = 2,6-Me2Ph (L5), 2,5-Me2Ph (L1), 2-MePh (
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Heterogeneous catalysts for production of linear α-olefins from ethylene were prepared by the direct reaction of the α-diimine ligand [L: R-N=C(R')-C(R')=N-R; R' = Me and R = 2,6-Me2Ph (L5), 2,5-Me2Ph (L1), 2-MePh (L2), or Ph (L3); R' = 1,8-naphth-diyl and R = Ph (L4)] and Ni2+ ion-exchanged fluorotetrasilicic mica. Only high molecular weight polyethylene was obtained in the reaction using the L5/Ni2+-Mica procatalyst activated by AlEt3 (TEA) as an activator, whereas the TEA-activated L1- and L2/Ni2+-Mica procatalysts afforded a mixture of a large amount of low-molecular weight polyethylene and a small amount of oligomers having 4-22 carbons. The procatalyst consisting of Ni2+-Mica and the L3 ligand that possesses non-substituted phenyl groups on the iminonitrogen atoms effectively promoted the oligomerization of ethylene after its activation with TEA, resulting in the fact that the ethylene oligomers were produced with a moderate catalytic activity (101 g-ethylene g-cat−1 h−1 at 0.7 MPa-ethylene) in the presence of TEA. When the backbone was varied from the butane moiety (L3) to acenaphthene (L4), the solid product dramatically increased. The weight percentage of the oligomers in the total products increased with the increasing reaction temperature; however, an insignificant increase in the oligomers was observed when the ethylene pressure was decreased. Full article
(This article belongs to the Special Issue Molecular Catalysis for Precise Olefin Polymerization)
Open AccessArticle Precise Active Site Analysis for TiCl3/MgCl2 Ziegler-Natta Model Catalyst Based on Fractionation and Statistical Methods
Catalysts 2013, 3(1), 137-147; doi:10.3390/catal3010137
Received: 17 December 2012 / Revised: 30 January 2013 / Accepted: 1 February 2013 / Published: 7 February 2013
Cited by 4 | PDF Full-text (573 KB) | HTML Full-text | XML Full-text
Abstract
In heterogeneous Ziegler-Natta catalysts for olefin polymerization, isolation of a single type of active sites is a kind of ambition, which would solve long-standing questions on the relationship between active site and polymer structures. In this paper, polypropylene produced by TiCl3/MgCl
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In heterogeneous Ziegler-Natta catalysts for olefin polymerization, isolation of a single type of active sites is a kind of ambition, which would solve long-standing questions on the relationship between active site and polymer structures. In this paper, polypropylene produced by TiCl3/MgCl2 model catalysts with minimum Ti heterogeneity was analyzed by combined solvent fractionation and the two-site statistical model. We found that the active sites of the model catalysts were classified into only three types, whose proportions were dependent on the Ti dispersion state. The addition of external donors not only newly formed highly isospecific sites, but also altered the stereochemical nature of the other active sites. Full article
(This article belongs to the Special Issue Molecular Catalysis for Precise Olefin Polymerization)
Open AccessArticle Ethylene Polymerization Using (Imino)vanadium(V) Dichloride Complexes Containing (Anilido)methyl-pyridine, -quinoline Ligands–Halogenated Al Alkyls Catalyst Systems
Catalysts 2013, 3(1), 148-156; doi:10.3390/catal3010148
Received: 25 December 2012 / Revised: 29 January 2013 / Accepted: 30 January 2013 / Published: 7 February 2013
Cited by 3 | PDF Full-text (251 KB) | HTML Full-text | XML Full-text
Abstract
The effect of ligand and Al cocatalysts in ethylene polymerization, using V(N-1-adamantyl)Cl2(L) [L = 2-(2,6-Me2C6H3)NCH2(C9H6N), 8-(2,6-Me2C6H3)NCH2(C9H6
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The effect of ligand and Al cocatalysts in ethylene polymerization, using V(N-1-adamantyl)Cl2(L) [L = 2-(2,6-Me2C6H3)NCH2(C9H6N), 8-(2,6-Me2C6H3)NCH2(C9H6N)] and V(N-2-MeC6H3)Cl2[2-(2,6-R'2C6H3)NCH2(C5H4N)] (R' = Me, iPr), has been explored. The reaction products in the presence of Et2AlCl or Me2AlCl cocatalyst were polyethylene whereas the reaction product of the 2-methylphenylimido analogues in the presence of MAO cocatalyst was 1-butene with high selectivity, suggesting that the catalyst/cocatalyst nuclearity effect plays a role in this catalysis. Full article
(This article belongs to the Special Issue Molecular Catalysis for Precise Olefin Polymerization)
Open AccessArticle A Comparative Study on the Homo-, Co- and Ter-Polymerization Using Ethylene, 1-Decene and p-Methylstyrene
Catalysts 2013, 3(1), 176-188; doi:10.3390/catal3010176
Received: 21 December 2012 / Revised: 1 February 2013 / Accepted: 7 February 2013 / Published: 22 February 2013
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Abstract
We synthesized polyethylene (PE), poly(ethylene-co-1-decene), poly(ethylene-co-p-methylstyrene) and poly(ethylene-ter-1-decene-ter-p-methystyrene) using a rac-Et(Ind)2ZrCl2metallocene catalyst and a methylaluminoxane cocatalyst system. The materials were characterized using nuclear magnetic resonance spectroscopy
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We synthesized polyethylene (PE), poly(ethylene-co-1-decene), poly(ethylene-co-p-methylstyrene) and poly(ethylene-ter-1-decene-ter-p-methystyrene) using a rac-Et(Ind)2ZrCl2 metallocene catalyst and a methylaluminoxane cocatalyst system. The materials were characterized using nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy. We compared and studied the kinetics, thermal properties and mechanical ones of these polymers. Tg was related to the amorphous phase of the polymers, whereas the tensile strength and storage modulus (E’) were related to the crystalline phase. We also found that PE has the highest crystallinity through differential scanning calorimetry and wide-angle X-ray scattering analysis. The polymerization rates of poly(ethylene-co-1-decene) and poly(ethylene-ter-1-decene-ter-p-methystyrene) were always higher than that of polyethylene. Full article
(This article belongs to the Special Issue Molecular Catalysis for Precise Olefin Polymerization)
Open AccessArticle Photocatalytic Oxidation Processes for Toluene Oxidation over TiO2 Catalysts
Catalysts 2013, 3(1), 219-231; doi:10.3390/catal3010219
Received: 23 November 2012 / Revised: 5 January 2013 / Accepted: 5 February 2013 / Published: 4 March 2013
Cited by 7 | PDF Full-text (396 KB) | HTML Full-text | XML Full-text
Abstract
Gas-solid heterogeneous photooxidation of toluene over TiO2 catalyst was studied to investigate the factors controlling the catalytic activities. The toluene photooxidation behavior on TiO2 was strongly affected by the formation and oxidation behavior of intermediate compounds on TiO2, and
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Gas-solid heterogeneous photooxidation of toluene over TiO2 catalyst was studied to investigate the factors controlling the catalytic activities. The toluene photooxidation behavior on TiO2 was strongly affected by the formation and oxidation behavior of intermediate compounds on TiO2, and their accumulation decreased the reaction rate for toluene photooxidation. The formation and oxidation behavior of the byproduct compounds depended on the initial concentration of toluene and water vapor. In situ Fourier transform infrared (FTIR) studies revealed that water vapor promoted the cleavage of the aromatic ring and facilitated CO2 formation. At the reaction temperature of 300 K, the deposition of Pt on TiO2 suppressed CO formation, whereas catalytic activity was decreased due to the increase in the amount of intermediate compounds. On the other hand, Pt/TiO2 showed higher activity than TiO2 at 353 K, in spite of the increase of the intermediate compounds. Full article
(This article belongs to the Special Issue Photocatalysts)
Open AccessArticle Biomimetic Catalysts for Oxidation of Veratryl Alcohol, a Lignin Model Compound
Catalysts 2013, 3(1), 232-246; doi:10.3390/catal3010232
Received: 21 December 2012 / Revised: 8 February 2013 / Accepted: 17 February 2013 / Published: 4 March 2013
Cited by 3 | PDF Full-text (316 KB) | HTML Full-text | XML Full-text
Abstract
Kraft pulp has to be bleached to eliminate the chromophoric structures, which cause a darkening of the pulp. In Nature, an equivalent role is assumed by ligninolytic enzymes such as lignin peroxidases, manganese peroxidases and laccases. The development of low molecular weight manganese
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Kraft pulp has to be bleached to eliminate the chromophoric structures, which cause a darkening of the pulp. In Nature, an equivalent role is assumed by ligninolytic enzymes such as lignin peroxidases, manganese peroxidases and laccases. The development of low molecular weight manganese peroxidase mimics may achieve environmentally-safe bleaching catalysts for the industry. Herein we report the synthesis and characterization of six manganese(III) complexes 16, incorporating dianionic hexadentate Schiff base ligands (H2L1-H2L4) and different anions. Complex 4, Mn2L22(H2O)2(DCA)2 was crystallographically characterized. Complexes 14 behave as more efficient mimics of peroxidase in contrast to 56. We have studied the use of these complexes as catalysts for the degradation of the lignin model compound veratryl alcohol. The biomimetic catalysts were used in conjunction with chlorine-free inexpensive co-oxidants as dioxygen or hydrogen peroxide. Yields up to 30% of veratryl alcohol conversion to veratraldehyde have been achieved at room temperature in presence of air flow using 0.5% of catalyst. Full article
(This article belongs to the Special Issue Biomimetic Catalysts)
Open AccessArticle Inactivation of E. Coli in Water Using Photocatalytic, Nanostructured Films Synthesized by Aerosol Routes
Catalysts 2013, 3(1), 247-260; doi:10.3390/catal3010247
Received: 10 December 2012 / Revised: 13 January 2013 / Accepted: 30 January 2013 / Published: 4 March 2013
Cited by 3 | PDF Full-text (2469 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
TiO2 nanostructured films were synthesized by an aerosol chemical vapor deposition (ACVD) method with different controlled morphologies: columnar, granular, and branched structures for the photocatalytic inactivation of Escherichia coli (E. coli) in water. Effects of film morphology and external applied
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TiO2 nanostructured films were synthesized by an aerosol chemical vapor deposition (ACVD) method with different controlled morphologies: columnar, granular, and branched structures for the photocatalytic inactivation of Escherichia coli (E. coli) in water. Effects of film morphology and external applied voltage on inactivation rate were investigated. As-prepared films were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), and UV-VIS. Photocatalytic and photoelectrochemical inactivation of E. coli using as-prepared TiO2 films were performed under irradiation of UVA light (note: UVA has a low efficiency to inactivate E. coli). Inactivation rate constants for each case were obtained from their respective inactivation curve through a 2 h incubation period. Photocatalytic inactivation rate constants of E. coli are 0.02/min (using columnar films), and 0.08/min (using branched films). The inactivation rate constant for the columnar film was enhanced by 330% by applied voltage on the film while that for the branched film was increased only by 30%. Photocatalytic microbial inactivation rate of the columnar and the branched films were also compared taking into account their different surface areas. Since the majority of the UV radiation that reaches the Earth’s surface is UVA, this study provides an opportunity to use sunlight to efficiently decontaminate drinking water. Full article
(This article belongs to the Special Issue Photocatalysts)
Open AccessArticle Phosphine-Thiophenolate Half-Titanocene Chlorides: Synthesis, Structure, and Their Application in Ethylene (Co-)Polymerization
Catalysts 2013, 3(1), 261-275; doi:10.3390/catal3010261
Received: 28 December 2012 / Revised: 8 February 2013 / Accepted: 17 February 2013 / Published: 6 March 2013
Cited by 3 | PDF Full-text (369 KB) | HTML Full-text | XML Full-text
Abstract
A series of novel half-titanocene complexes CpTiCl2[S-2-R-6-(PPh2)C6H3] (Cp = C5H5, 2a, R = H; 2b, R = Ph; 2c, R = SiMe3) have been synthesized by
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A series of novel half-titanocene complexes CpTiCl2[S-2-R-6-(PPh2)C6H3] (Cp = C5H5, 2a, R = H; 2b, R = Ph; 2c, R = SiMe3) have been synthesized by treating CpTiCl3 with the sodium of the ligands, 2-R-6-(PPh2)C6H3SNa, which were prepared by the corresponding ligands and NaH. These complexes have been characterized by 1H, 13C and 31P NMR as well as elemental analyses. Structures for 2a–b were further confirmed by X-ray crystallography. Complexes 2a–b adopt five-coordinate, distorted square-pyramid geometry around the titanium center, in which the equatorial positions are occupied by sulfur and phosphorus atoms of the chelating phosphine-thiophenolate and two chlorine atoms, and the cyclopentadienyl ring is coordinated on the axial position. The complexes 2a–c were investigated as the catalysts for ethylene polymerization and copolymerization of ethylene with norbornene in the presence of MMAO or Ph3CB(C6F5)4/iBu3Al as the cocatalyst. All complexes exhibited low to moderate activities towards homopolymerization of ethylene. However, they displayed moderate to high activities towards copolymerization of ethylene with norbornene. Full article
(This article belongs to the Special Issue Molecular Catalysis for Precise Olefin Polymerization)
Open AccessArticle Defect-Driven Restructuring of TiO2 Surface and Modified Reactivity Toward Deposited Gold Atoms
Catalysts 2013, 3(1), 276-287; doi:10.3390/catal3010276
Received: 11 January 2013 / Revised: 17 February 2013 / Accepted: 19 February 2013 / Published: 8 March 2013
Cited by 2 | PDF Full-text (1868 KB) | HTML Full-text | XML Full-text
Abstract
A partially reduced TiO2 surface exhibits increasingly complex nature when forming various defects, whose stoichiometry, structure and properties are markedly different from those of bulk TiO2. Using scanning tunneling microscopy and density functional theory, we investigate different types of surface defects formed by
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A partially reduced TiO2 surface exhibits increasingly complex nature when forming various defects, whose stoichiometry, structure and properties are markedly different from those of bulk TiO2. Using scanning tunneling microscopy and density functional theory, we investigate different types of surface defects formed by Ti interstitials on TiO2 (110) and their reactivity toward deposited gold atoms. Sub-stoichiometric strands greatly enhance bonding of Au by transferring the excess charges from the reduced Ti3+ onto the strands. Thus the sub-stoichiometric strands behave as strong electron donor sites toward reactants. On the contrary, fully stoichiometric nanoclusters provide increased Au bonding through its 1-coordinated oxygen, which acts as a strong electron acceptor site. Specific interactions between Au and defects as well as the implication of electron donor/acceptor complexes for catalytic reactions are discussed. Full article
(This article belongs to the Special Issue New Trends in Gold Catalysts)
Open AccessArticle Electron Transfer at Gold Nanostar Assemblies: A Study of Shape Stability and Surface Density Influence
Catalysts 2013, 3(1), 288-309; doi:10.3390/catal3010288
Received: 17 January 2013 / Revised: 25 February 2013 / Accepted: 26 February 2013 / Published: 12 March 2013
Cited by 10 | PDF Full-text (5075 KB) | HTML Full-text | XML Full-text
Abstract
Gold nanostars of ~70 nm tip to tip distances were synthesized by a seed mediated method and covalently self-assembled on 1,5-pentanedithiol modified electrodes. Electron transfer kinetics at the AuNS/dithiol modified electrodes were studied as a function of AuNS surface density which was varied
[...] Read more.
Gold nanostars of ~70 nm tip to tip distances were synthesized by a seed mediated method and covalently self-assembled on 1,5-pentanedithiol modified electrodes. Electron transfer kinetics at the AuNS/dithiol modified electrodes were studied as a function of AuNS surface density which was varied by increasing their self-assembly time from 8 h, 16 h, 24 h to 32 h. Excellent electrocatalytic properties of AuNSs were observed toward electrochemistry of [Fe(CN)6]4−/3− redox couple. The apparent heterogeneous electron transfer constant, ket, has progressively increased with the surface density of AuNSs bonded to the electrodes from 0.65 × 10−5 cm s−1 (8 h), 1.47 × 10−5 cm s−1 (16 h), 3.95 × 10−5 cm s−1 (24 h) to an excellent 85.0 × 10−5 cm s−1 (32 h). Electrochemical charging of nanostars was confirmed, for the first time, by 79 times increase of double layer capacitance, Cdl, from 0.34 µF (8 h) to 27 µF (32 h). The electrochemical charging of AuNSs had also a strong influence on the electron tunneling process through the 1,5PDT molecules being more efficient at dense layers of AuNSs. The tunneling parameter, β, has decreased from 1.13 Å−1 (16 h) to 0.50 Å−1 (32 h). The AuNSs were chemically stable toward [Fe(CN)6]4−/3− showing no change in shape after electrochemical measurements. Full article
(This article belongs to the Special Issue New Trends in Gold Catalysts)
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Open AccessArticle Broad Spectrum Microbicidal Activity of Photocatalysis by TiO2
Catalysts 2013, 3(1), 310-323; doi:10.3390/catal3010310
Received: 3 December 2012 / Revised: 25 January 2013 / Accepted: 6 March 2013 / Published: 21 March 2013
Cited by 16 | PDF Full-text (276 KB) | HTML Full-text | XML Full-text
Abstract
Photocatalytically active titanium dioxide (TiO2) is widely used as a self-cleaning and self-disinfecting material in many applications to keep environments biologically clean. Several studies on the inactivation of bacteria and viruses by photocatalytic reactions have also been reported; however, only few
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Photocatalytically active titanium dioxide (TiO2) is widely used as a self-cleaning and self-disinfecting material in many applications to keep environments biologically clean. Several studies on the inactivation of bacteria and viruses by photocatalytic reactions have also been reported; however, only few studies evaluated the spectrum of the microbicidal activity with photocatalysis for various species. There is a need to confirm the expected effectiveness of disinfection by photocatalysis against multidrug-resistant bacteria and viruses. In this study, microbicidal activity of photocatalysis was evaluated by comparing the inactivation of various species of bacteria and viruses when their suspensions were dropped on the surface of TiO2-coated glass. Gram-positive bacteria, e.g., methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis, and penicillin-resistant Streptococcus pneumoniae, were easily inactivated by photocatalysis, whereas some gram-negative bacteria, e.g., Escherichia coli and multidrug-resistant Pseudomonas aeruginosa, were gradually inactivated by photocatalysis. Influenza virus, an enveloped virus, was significantly inactivated by photocatalysis compared with feline calicivirus, a non-enveloped virus. The effectiveness of microbicidal activity by photocatalysis may depend on the surface structure. However, they are effectively inactivated by photocatalysis on the surface of TiO2-coated glass. Our data emphasize that effective cleaning and disinfection by photocatalysis in nosocomial settings prevents pathogen transmission. Full article
(This article belongs to the Special Issue Photocatalysts)
Open AccessArticle Hydroformylation of 1-Hexene over Rh/Nano-Oxide Catalysts
Catalysts 2013, 3(1), 324-337; doi:10.3390/catal3010324
Received: 26 January 2013 / Revised: 25 February 2013 / Accepted: 6 March 2013 / Published: 21 March 2013
Cited by 4 | PDF Full-text (1874 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The effect of nanostructured supports on the activity of Rh catalysts was studied by comparing the catalytic performance of nano- and bulk-oxide supported Rh/ZnO, Rh/SiO2 and Rh/TiO2 systems in 1-hexene hydroformylation. The highest activity with 100% total conversion and 96% yield
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The effect of nanostructured supports on the activity of Rh catalysts was studied by comparing the catalytic performance of nano- and bulk-oxide supported Rh/ZnO, Rh/SiO2 and Rh/TiO2 systems in 1-hexene hydroformylation. The highest activity with 100% total conversion and 96% yield of aldehydes was obtained with the Rh/nano-ZnO catalyst. The Rh/nano-ZnO catalyst was found to be more stable and active than the corresponding rhodium catalyst supported on bulk ZnO. The favorable morphology of Rh/nano-ZnO particles led to an increased metal content and an increased number of weak acid sites compared to the bulk ZnO supported catalysts. Both these factors favored the improved catalytic performance. Improvements of catalytic properties were obtained also with the nano-SiO2 and nano-TiO2 supports in comparison with the bulk supports. All of the catalysts were characterized by scanning electron microscope (SEM), inductively coupled plasma mass spectrometry (ICP-MS), BET, powder X-ray diffraction (PXRD) and NH3- temperature-programmed desorption (TPD). Full article

Review

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Open AccessReview Brookite, the Least Known TiO2 Photocatalyst
Catalysts 2013, 3(1), 36-73; doi:10.3390/catal3010036
Received: 12 November 2012 / Revised: 9 January 2013 / Accepted: 10 January 2013 / Published: 18 January 2013
Cited by 80 | PDF Full-text (1949 KB) | HTML Full-text | XML Full-text
Abstract
Brookite is the least studied TiO2 photocatalyst due to the difficulties usually encountered in order to obtain it as a pure phase. In this review, a comprehensive survey of the different methods available for preparing brookite powders and films is reported. Attention
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Brookite is the least studied TiO2 photocatalyst due to the difficulties usually encountered in order to obtain it as a pure phase. In this review, a comprehensive survey of the different methods available for preparing brookite powders and films is reported. Attention has been paid both to the most traditional methods, such as hydrothermal processes at high temperatures and pressures, and to environmentally benign syntheses using water soluble compounds and water as the solvent. Papers reporting the photocatalytic activity of pure and brookite-based samples have been reviewed. Full article
(This article belongs to the Special Issue Photocatalysts)
Open AccessReview Half-Titanocenes Containing Anionic Ancillary Donor Ligands: Effective Catalyst Precursors for Ethylene/Styrene Copolymerization
Catalysts 2013, 3(1), 157-175; doi:10.3390/catal3010157
Received: 25 December 2012 / Revised: 21 January 2013 / Accepted: 25 January 2013 / Published: 18 February 2013
Cited by 4 | PDF Full-text (476 KB) | HTML Full-text | XML Full-text
Abstract
This review summarizes recent results for ethylene/styrene copolymerization using half-titanocenes containing anionic donor ligands, Cp’TiX2(Y) (X = halogen, alkyl; Y = aryloxo, ketimide etc.)–cocatalyst systems. The product composition, the styrene incorporation and microstructures in the resultant copolymers are highly influenced
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This review summarizes recent results for ethylene/styrene copolymerization using half-titanocenes containing anionic donor ligands, Cp’TiX2(Y) (X = halogen, alkyl; Y = aryloxo, ketimide etc.)–cocatalyst systems. The product composition, the styrene incorporation and microstructures in the resultant copolymers are highly influenced by the anionic donor employed. A methodology for an exclusive synthesis of the copolymers even under high temperature and high styrene concentrations has been introduced on the basis of a proposed catalytically-active species in this catalysis. Full article
(This article belongs to the Special Issue Molecular Catalysis for Precise Olefin Polymerization)
Open AccessReview Heterogeneous Photocatalysis: Recent Advances and Applications
Catalysts 2013, 3(1), 189-218; doi:10.3390/catal3010189
Received: 28 November 2012 / Revised: 18 December 2012 / Accepted: 25 January 2013 / Published: 1 March 2013
Cited by 116 | PDF Full-text (1729 KB) | HTML Full-text | XML Full-text
Abstract
Semiconductor heterogeneous photocatalysis, the subject of this review, is a versatile, low-cost and environmentally benign treatment technology for a host of pollutants. These may be of biological, organic and inorganic in origin within water and air. The efficient and successful application of photocatalysis
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Semiconductor heterogeneous photocatalysis, the subject of this review, is a versatile, low-cost and environmentally benign treatment technology for a host of pollutants. These may be of biological, organic and inorganic in origin within water and air. The efficient and successful application of photocatalysis demands that the pollutant, the catalyst and source of illumination are in close proximity or contact with each other. The ability of advanced oxidation technology to remove low levels of persistent organic pollutants as well as microorganisms in water has been widely demonstrated and, progressively, the technology is now being commercialized in many areas of the world including developing nations. This review considers recent developments in the research and application of heterogeneous semiconductor photocatalysis for the treatment of low-level concentrations of pollutants in water and air using titanium dioxide as a “model” semiconductor. The review considers charge transport characteristics on the semiconductor surface, photocatalyst reactor design and organic degradation mechanistic pathways. The effects of photoreactor operating parameters on the photocatalytic process are discussed in addition to mineralization and disinfection kinetics. Full article
(This article belongs to the Special Issue Photocatalysts)
Open AccessReview The Influence of Surface Alumina and Silica on the Photocatalytic Degradation of Organic Pollutants
Catalysts 2013, 3(1), 338-362; doi:10.3390/catal3010338
Received: 23 November 2012 / Revised: 21 January 2013 / Accepted: 7 February 2013 / Published: 21 March 2013
Cited by 5 | PDF Full-text (865 KB) | HTML Full-text | XML Full-text
Abstract
Practical photocatalysis for degradation of organic pollutants must take into account the influence of other chemicals. Significant Al deposition on titania can occur at naturally occurring concentrations of dissolved Al. This paper reviews the author’s work on the influence of deliberately deposited hydrous
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Practical photocatalysis for degradation of organic pollutants must take into account the influence of other chemicals. Significant Al deposition on titania can occur at naturally occurring concentrations of dissolved Al. This paper reviews the author’s work on the influence of deliberately deposited hydrous oxides of aluminium on the behavior of a ~130 m2 g−1 rutile TiO2, and then compares the behavior of deposited alumina with that of deposited silica. On rutile some adsorbed nitrogen is infrared-active. Alumina and silica deposited on the rutile reduce, and ultimately eliminate, this infrared-active species. They also reduce photocatalytic oxidation of both propan-2-ol and dichloroacetate ion and the photocatalytic reduction of diphenyl picryl hydrazine. The surface oxides suppress charge transfer and may also reduce reactant adsorption. Quantitative measurement of TiO2 photogreying shows that the adsorbed inorganics also reduce photogreying, attributed to the capture of photogenerated conduction band electrons by Ti4+ to form Ti3+. The influence of adsorbed phosphate on photocatalysis is briefly considered, since phosphate reduces photocatalytic disinfection. In the context of classical colloid studies, it is concluded that inorganic species in water can significantly reduce photoactivity from the levels that measured in pure water. Full article
(This article belongs to the Special Issue Photocatalysts)

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