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Styrene has been polymerized to syndiotactic polystyrene (sPS) over a layer of heterogeneous Cp*Ti[(OC[H.sub.3]).sub.3]/MAO catalyst immobilized onto the surfaces of silica nanotube reactor (SNTR) arrays of 60-200 nm in diameter. The polymer produced in the SNTR arrays has been found to have the molecular weights much larger than the polymers synthesized by a liquid slurry polymerization over silica-supported catalysts. A dynamic reactor model that consists of diffusion and reaction terms has been derived and solved to quantify the kinetics of styrene polymerization in a single nanotube reactor. The two-site kinetic model applied to the silica nanotube reactor model shows that the experimentally observed high polymer molecular weight can be fitted if the chain transfer rate constants for monomer and fl-hydride elimination are reduced significantly. The simulation results suggest that the presence of dense crystalline sPS nanofibrils filling the nanotubes constrain the molecular movements of polymer chain ends in the proximity of catalyst sites to limit the chain transfer reactions., INTRODUCTION Syndiotactic polystyrene (sPS) is an interesting high-performance engineering polymer derived from styrene. The structure and properties of sPS are totally different from those of general purpose polystyrene (gPS) derived [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2008.12.017 Byline: Chi-Yuan Lu (a), Hui-Hsin Tseng (b), Ming-Yen Wey (c), Kui-Hao Chuang (c), Jia-Hong Kuo (c) Abstract: This study investigated the use of Cu/Al.sub.2O.sub.3, Co/Al.sub.2O.sub.3, Fe/Al.sub.2O.sub.3, and Ni/Al.sub.2O.sub.3 catalysts for the growth of carbon nanotubes (CNTs). These CNTs were used as support for Co catalyst preparation and Co/CNT catalysts were applied to a catalytic reaction to remove BTEX, PAHs, SO.sub.2, NO, and CO simultaneously in a pilot-scale incineration system. The analyzed results of EDS and XRD showed low metal content and good dispersion characteristics of the Al.sub.2O.sub.3-supported catalysts by excess-solution impregnation. FESEM analyzed results showed that the CNTs that were synthesized from Co, Fe, and Ni catalysts had a diameter of 20nm, whereas those synthesized from Cu/Al.sub.2O.sub.3 had a diameter of 50nm. Pilot-scale test results demonstrated that the Co/CNT catalyst effectively removed air pollutants in the catalytic reaction and that there was no obvious deactivation by Pb, water vapor, and coke deposited in the process. The thermal stabilization at 250[degrees]C and hydrophobicity properties of CNTs enhanced the application of CNT catalysts in flue gas. Author Affiliation: (a) Department of Public Health, Chung Shan Medical University, Taichung 402, Taiwan, ROC (b) Department of Occupational Safety & Health and Graduate Program, Chung Shan Medical University, Taichung 402, Taiwan, ROC (c) Department of Environmental Engineering, National Chung Hsing University, 250, Kuo Kuang Road, Taichung 402, Taiwan, ROC Article History: Received 28 November 2007; Revised 26 November 2008; Accepted 21 December 2008

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2006.12.017 Byline: Meena Marafi, Antony Stanislaus, Ezra Kam Keywords: Hazardous waste; Hydroprocessing; Spent catalyst recycling; Rejuvenation; Economic assessment; Waste utilisation Abstract: Spent hydroprocessing catalysts from refineries have been classified as hazardous solid waste by the United States Environmental Protection Agency (USEPA), refiners must find a viable but economical solution to solve this serious environmental issue. Catalyst rejuvenation is an attractive option for minimizing the environmental problems associated with spent catalysts. In this study, a preliminary design for such a process and the corresponding economic analysis are performed to assess the proposed catalyst rejuvenation process for metal-fouled spent catalysts generated in residue hydroprocessing units. The scenarios used in the economic assessment are based on three options of process synthesis and two operator modes. It is found that the option of rejuvenating medium and lightly fouled spent catalyst produced by the refinery will be the best solution for refiners, both environmentally and economically. Author Affiliation: Petroleum Refining Department, Petroleum Research and Studies Center, Kuwait Institute for Scientific Research, P.O. Box 24885, Safat 13109, Kuwait Article History: Received 23 April 2006; Revised 10 December 2006; Accepted 12 December 2006

The adsorption of CO on a ternary Cu catalyst was studied at room temperature in a static Tian-calvet microcalorimeter. For carbon monoxide adsorption on a hydrogen-reduced Cu/ZnO/Al(sub 2)O(sub 3) catalyst, the adsorption rate constant (K(sub a)) is found to be in the range from 10(super -6) to 10(super -4) Pa(super -1) S(super -1), and the desorption rate constant (k(sub d) from 10(super -4) to 10(super -2) S(super -1), both increasing with fractional coverage theta.

An investigation on the effect of catalyst support and reactant on the yield and structure of carbon growth is conducted in the chemical vapor deposition (CVD) process. It is stated that the tubular structures were grown by continuous carbon supply directly to the tube, but the fiber structures were grown in a layer-by-layer manner.

A low-temperature grafting approach using two Cu(super I) molecular precursors ([CuOSi(O(super t)Bu)3](sub 4) and [CuO(super t)Bu](sub 4) and a high-temperature exchange reaction using CuCl were utilized with a mesoporous silica support (SBA-15). This was done to investigate the effects of catalyst preparation on the nature of copper-support interactions and site speciation.

A novel and highly efficient solvent-free protocol for Friedel-Crafts acylation compounds using nontoxic and inexpensive ZnO powder is proposed. This environmentally benign and safe protocol includes a simple reaction setup not needing specialized equipment, very mild reaction conditions, high product yields, very short reaction times and the elimination of solvents.

Nickel (II) complex of salicylaldehyde (Ni (sal)(sub 2)) is an excellent catalyst for Michael additions giving less side products than Ni (acac)(sub 2) is discussed. Mechanistic studies based on UV-VIS, IR, and electrospray ionization mass spectrometry indicate that copper enolates of the beta-dicarbonyl formed in situ are the active nucleophilic species.

The synthesis and catalytic activity of two types of PEG-supported nitroxyl catalysts is described. The high activity of fresh and recycled catalysts was attributed to the rapid intramolecular regeneration of the catalyst through synproportionation.

DNA sequences capable of cleaving an internal ribonucleoside linkage are generated, when in vitro selection are performed in the presence of Mg(super 2+). This study of a specific catalytically active DNAzyme is an example of studies that would be necessary generally to permit in vitro selection to help one understand the distribution of function in sequence space.

Abstract: The oxidation of phenetidine with sodium vanadate is proposed for determining phenothiazine derivatives by the kinetic method. The reaction rate was studied depending on the solution acidity and reagent concentrations, and the optimum determination conditions were selected. The analytical range was 3--100 ng/mL for six phenothiazine alkyl derivatives (aminazine, diprazine, promazine, meterazine, tisercine, and triphtazine). The detection limits (3 to 10 ng/mL) depend on the substituent in the phenothiazine molecule. The relative standard deviations were from 3 to 20%. Article History: Registration Date: 07/10/2004

A detailed comparative study of CO adsorption on two categories of oxide-supported palladium catalysts is discussed. The assignment of the CO vibrational frequencies to different types of sites on these systems has allowed a detailed structural characterization.

A series of zinc beta-diiminate (BDI) complexes and their solid-state structures, solution dynamics, and copolymerization behavior with CO2 and cyclohexene oxide (CHO) is reported. Stoichiometric reactions of the copolymerization initiation steps demonstrate that zinc alkoxide and bis(trimethylsily)amido complexes insert CO2, whereas zinc acetates react with CHO.

The role of potassium cation content and catalyst activation temperature on zeolite stability and overall catalyst performance is studied. It is shown that improved catalytic activity and selectivity toward reduced trimethylamine yield is the result of optimizing potassium cation content and activation temperature.

A general model for selectivity and stereoselectivity in olefin cross metathesis is presented. The study shows that by employing a metathesis catalyst with the appropriate activity, selective cross metathesis reactions can be achieved with a wide variety of electro-rich, electro-deficient, and sterically bulky olefins.

Oxidation reactions were studied using a synthetic heme-thiolate (SR complex) in order to ascertain the contributions of multiple intermediates derived from heme-thiolate to the oxygen atom transfer reaction to substrate. The substrate and oxidant interact with each other during the oxygen atom transfer reaction.

Research shows that the acidic protons can be localized in anhydrous solid acid catalysts by REDOR NMR and density functional theory methods, suggesting that these techniques can be applied to localize protons in heteropolyacid systems. Data indicate that the protons locate at a distance from the Keggin anion central phosphorous.

Research demonstrates that both molybdenum and bismuth are required for allylic oxidation of propene with bismuth being present as oxo clusters and in close proximity that of molbdenum oxo units as determined by elemental analysis, infrared- and nuclear magnetic resonance spectroscopy and X-ray diffraction. The bismuth alkoxides aggregate in contact with silica.

Results indicate that in diastereomeric substrate-catalyst systems, the ketone-hydride insertion is rapid and exergonic. The rate of hydrolysis is higher than the rate of reversion to catalyst and ketone. Further, the catalytic hydrogenations operate via the diastereomeric catalyst that is present in highest concentration to form major enantiomer product.

A highly unusual way of insertion in propylene polymerizations is examined using the phenoxy-imine-based titanium catalyst system. Results show that chain propagation occurs with regular secondary regiochemistry with insertion of propylene into the initiating titanium hydride occurring with 1,2-regiochemistry, while insertions into secondary titanium alkyls occurring by 2,1-regioselectivity.

Results demonstrate that Cp*(sub)2TiMe(sub)2 is an excellent catalyst for intramolecular addition of n-alkyl- and benzylamines to internal alkynes. Data show that at 2.0-6.0 percent mol of the catalyst, hydroamination reaction between n-propyl-, n-hexyl-, benzyl-, p-methoxybenzyl and diphenylacetylene, 3-hexyne or 4-octyne is completed within 24 hours at 114 C.

Research describes a methodology for the dimerization of substituted 2-bromopyridines in the context of formation of stable complexes of transition-metal catalysts in the reactions involving heterocyclic substrates. The electrochemical approach described is based on the combination of the nickel complex catalysis and the sacrificial anode.

Cyclopropanation of terminal olefins including aryl, alkyl with O-containing substituents, and the industrially important 2,5-dimethyl-2, 3-hexadiene substrate, using readily available ethyl diazoacetate as a carbene source catalyzed by a family of catalysts having general formula Tp(super x)Cu generated in situ. According to the kinetic studies, homoscorpionate[Tp(super x)] ligands act in a dihapto form during the carbene-transfer reaction, with the noncoordinated pyrazolyl ring playing a substantial role in the induction of the diastereoselectivity.

[beta]-Lactamases are the resistance enzymes for [beta]-lactam antibiotics, of which four classes are known. [beta]-lactamases hydrolyze the [beta]-lactam moieties of these antibiotics, rendering them inactive. It is shown herein that the class D OXA-10 [beta]-lactamase depends critically on an unusual carbamylated lysine as the basic residue for both the enzyme acylation and deacylation steps of catalysis. The formation of carbamylated lysine is reversible. Evidence is presented that this enzyme is dimeric and carbamylated in living bacteria. High-resolution x-ray structures for the native enzyme were determined at pH values of 6.0, 6.5, 7.5, and 8.5. Two dimers are present per asymmetric unit. One monomer in each dimer was carbamylated at pH 6.0, whereas all four monomers were fully carbamylated at pH 8.5. At the intermediate pH values, one monomer of each dimer was carbamylated, and the other showed a mixture of carbamylated and non-carbamylated lysines. It would appear that, as the pH increased for the sample, additional lysines were 'titrated' by carbamylation. A handful of carbamylated lysines are known from protein crystallographic data, all of which have been attributed roles in structural stabilization (mostly as metal ligands) of the proteins. This paper reports a previously unrecognized role for a noncoordinated carbamylate lysine as a basic residue involved in mechanistic reactions of an enzyme, which indicates another means for expansion of the catalytic capabilities of the amino acids in nature beyond the 20 common amino acids in development of biological catalysts.

We report the development and initial experimental validation of a computational design procedure aimed at generating enzyme-like protein catalysts called 'protozymes.' Our design approach utilizes a 'compute and build' strategy that is based on the physical/chemical principles governing protein stability and catalytic mechanism. By using the catalytically inert 108-residue Escherichia coli thioredoxin as a scaffold, the histidine-mediated nucleophilic hydrolysis of p-nitrophenyl acetate as a model reaction, and the ORBIT protein design software to compute sequences, an active site scan identified two promising catalytic positions and surrounding active-site mutations required for substrate binding. Experimentally, both candidate protozymes demonstrated catalytic activity significantly above background. One of the proteins, PZD2, displayed 'burst' phase kinetics at high substrate concentrations, consistent with the formation of a stable enzyme intermediate. The kinetic parameters of PZD2 are comparable to early catalytic Abs. But, unlike catalytic Ab design, our design procedure is independent of fold, suggesting a possible mechanism for examining the relationships between protein fold and the evolvability of protein function.