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Catalytic oxidation of organic pollutants is an attractive and sustainable method of water purification. This paper focuses on discussion of catalytic activity, selectivity, and stability in cataly...

The catalytic properties of physical mixtures of Ni particles (100–200 nm) with nanoparticles of anatase TiO2 (TiO2-A), ZrO2, Al2O3, rutile TiO2 (TiO2-R), and CeO2 were investigated for the hydrode...

Cu-modified Au/TiO2 (anatase, 200 m2/g) has been prepared by the incipient-wetness technique with introduction of the modifier either before or after Au loading. Such catalysts gave higher catalytic activities for the water–gas shift (WGS) reaction when compared to the unmodified catalysts mainly because of the existence of a synergetic interaction between Cu and Au, as the activities of both Cu/TiO2 and Au/TiO2 are lower than that of the bimetallic system. The WGS activities of both the as-prepared Au/TiO2 and a Au–Cuc/TiO2 catalyst were found to be high and stable. The presence of nitrates on Cuc–Au/TiO2 was found to be detrimental to the activity of Au on TiO2, as a result of the poisoning of Au and enhanced Au agglomeration by NO2 formed during reaction. The activities of Au/TiO2 catalysts modified with Cu-containing acetate counterions were found to decrease during the first 30 min on stream, reaching a constant value of (45 ± 2)%. However, when the poisoning by the acetate anion was eliminated throu...

A discrete nanocage of core-shell design, in which carboxylic acid groups were tethered to the core and silanol to the shell interior, was found to react with Co2(CO)8 to form and stabilize a Co(I)-CO species. The singular CO stretching band of this new Co species at 1958 cm(-1) and its magnetic susceptibility were consistent with Co(I) compounds. When exposed to O2, it transformed from an EPR inactive to an EPR active species indicative of oxidation of Co(I) to Co(II) with the formation of H2O2. It could be oxidized also by organoazide or water. Its residence in the nanocage interior was confirmed by size selectivity in the oxidation process and the fact that the entrapped Co species could not be accessed by an electrode.

A combination of two synchrotron X-ray techniques, X-ray absorption spectroscopy (XAS), and pair distribution function analysis (PDF) with complementary Fourier transform infrared (FTIR) spectroscopy measurement, was used to characterize the composition distributions of PdAu and PtCu bimetallic particles after treatment in H2 or CO and in the presence of these gases. This is the first reported application of PDF to the study of supported bimetallic nanoparticles. We found that XAS was informative in determining the component distribution of an initial sample, but PDF was better suited to following changes in the distribution upon changing the gas environment. Thus, the surface of a PtCu bimetallic particle of about 2.5 nm after treatment in H2 was found to be enriched in Cu, while the core was bimetallic. There was no evidence of a component-segregated core−shell structure. Treatment in CO caused enrichment of Pt to the surface layer, with a concomitant migration of Cu to the core. The average particle si...

Ethylene glycol (EG) reforming was investigated as a method to generate H2 and CO reductants for low-temperature lean NOx reduction. Stable production of H2 was obtained at 230 °C over a Pt/Al2O3 catalyst using a feed consisting of 2−5% O2 and >2.2% EG. The presence of H2O in the feed enhanced H2 production, as did Na modification of the catalyst. Water gas shift was determined not to contribute significantly to H2 production during EG reforming.

The adsorption of CO and its reaction with oxygen were investigated using a combination of in situ Fourier transform infrared spectroscopy, step response measurements in a microreactor, (18)O isotopic labeling, and X-ray absorption near edge structure spectroscopy. An as-prepared sample in which Au is present as a surface oxyhydroxy complex does not adsorb CO. On an activated sample in which only metallic Au is detected, 0.18 +/- 0.03 mol CO/(mol Au) are adsorbed on Au at -60 degrees C, which shows an IR band at 2090 cm(-1). When oxygen is present in the gas phase, this species reacts with a turnover rate of 1.4 +/- 0.2 mol CO(mol Au min)(-1), which is close to the steady-state turnover rate. In contrast, there is a very small quantity of adsorbed oxygen on Au. A small IR peak at 1242 cm(-1) appears when an activated sample is exposed to CO. It reacts rapidly with oxygen and is shifted to 1236 cm(-1) if (18)O is used. It is assigned to the possible intermediate hydroxycarbonyl.

Anodic aluminum oxide (AAO) membranes were characterized by UV Raman and FT-IR spectroscopies before and after coating the entire surface (including the interior pore walls) of the AAO membranes by atomic layer deposition (ALD). UV Raman reveals the presence of aluminum oxalate in bulk AAO, both before and after ALD coating with Al2O3, because of acid anion incorporation during the anodization process used to produce AAO membranes. The aluminum oxalate in AAO exhibits remarkable thermal stability, not totally decomposing in air until exposed to a temperature900 degrees C. ALD was used to cover the surface of AAO with either Al2O3 or TiO2. Uncoated AAO have FT-IR spectra with two separate types of OH stretches that can be assigned to isolated OH groups and hydrogen-bonded surface OH groups, respectively. In contrast, AAO surfaces coated by ALD with Al2O3 display a single, broad band of hydrogen-bonded OH groups. AAO substrates coated with TiO2 show a more complicated behavior. UV Raman results show that very thin TiO2 coatings (1 nm) are not stable upon annealing to 500 degrees C. In contrast, thicker coatings can totally cover the contaminated alumina surface and are stable at temperatures in excess of 500 degrees C.

Gold catalysts supported on γ-Al2O3 (Au/γ-Al2O3) were prepared by deposition-precipitation of aqueous HAuCl4 and, alternatively, by deposition of Au(CH3)2(acac) from pentane solution. The samples were characterized by in situ XANES and temperature-programmed reduction and by their performance as CO oxidation catalysts at room temperature. The Au was found to be present as Au(III) in both as-prepared catalysts, and the Au(III) was stable upon exposure to reducing gases at room temperature. Reduction of Au(III) occurred at elevated temperatures, and the rate and extent of reduction were found to depend strongly on the reducing conditions. Water vapor facilitated reduction, but only after the sample had been reduced to some extent by CO or H2. Exposure of an as-prepared catalyst to a catalytically reacting mixture of CO + O2 at 100 °C was effective in activating it, though to a lesser extent. The data indicate that zerovalent Au is necessary for catalytic activity, but there is no correlation between the act...

A designer polymethylhydrosiloxane molecule, modified with nitrile and silanol groups, offers independent control of metal loading and particle size distribution when used to assist the preparation of metal nanoparticles.

Carbon-encapsulated Si nanoparticles were formed by carbonizing a resorcinol−formaldehyde gel polymerized in the presence of phenol-functionalized Si particles. These encapsulated Si showed higher reversible charge capacity and Coulombic efficiency for use as lithium ion battery anode than samples prepared with Si nanoparticles without phenol functionalization.

The organofunctional silicon hydride halides R(CH3)SiHCl were prepared in high yields from CH3SiHCl2, employing CH3SiH2Cl as an intermediate. CH3SiHCl2 was converted to CH3SiH2Cl by chloride−hydride redistribution in 41% yield (based on Si−H). The chloride substituent in CH3SiH2Cl reacted selectively with the Grignard reagent RMgX to form the corresponding dihydride R(CH3)SiH2, where R = H2C═CH−, H2C═C(CH3)−, H2C═CHCH2−, (CH3)2CH−, H2C═CHCH2CH2−, c-C5H9−, PhCH2−, and p-Cl(C6H4)−. Cl(CH2)3(CH3)SiH2 was also prepared by reduction of the corresponding dichloride. Monohalogenation of R(CH3)SiH2 with CuCl2/CuI in THF then gave CH3RSiHCl in 60−88% overall yield (starting from CH3SiH2Cl).

An example of unusual addition of a main-group-metal alkoxide across an alkene C═C bond was demonstrated with a dimethylvinylsilyl-substituted Sn-POSS complex (POSS = incompletely condensed polyhedral oligomeric silsesquioxane). The structure of the pentacoordinated Sn chelate product was confirmed by 1H, 13C, and 119Sn NMR and ESI-MS.

A fourth-generation dendrimer with immolative carbamate linkages was used as a structural template to synthesize a discrete, molecular-sized (∼10 nm) nanocage with a ∼4.5 nm cavity. Shell cross-linkage was achieved using the self-terminating, catalytic hydrosilylation to generate a carbosilane shell that exhibits size-selectivity.

NO x reduction with hydrocarbons is studied at temperatures around 150 °C to develop an easy retrofit NO x removal process to be located downstream of the particulate control device for flue gas cleanup. Acetone is the most active hydrocarbon reductant for NO reduction in the presence of O2 and H2O. At 150 °C, 35% NO reduction was obtained over 5% Cu-2% Ag/PCB. The activity, however, is greatly decreased by the presence of SO 2 . NO oxidation to NO 2 is studied for further improving the NO reduction activity because NO 2 is known to be more reactive than NO. Active carbon fibers and PCB active carbon are both active for NO oxidation at low temperature, but the activity decreased with temperature. Ten percent Co 3 O 4 /Al 2 O 3 and 5% Au/Co 3 O 4 are not active for NO oxidation in the absence of SO 2 and at 150 °C, but are very active in the presence of SO 2 and H2O. Five percent Au/Co 3 O 4 is especially stable for NO oxidation to N0 2 at temperatures from 120 to 150 °C for more than 15 h.

The M(r) = 94,000 heavy chain of bovine factor Va contains 10 cysteine residues which are distributed in the 2 A domains which make up this portion of the factor V molecule. The A1 domain contains four cysteines while the A2 domain contains six cysteines. The locations of disulfide bridges and free cysteines in bovine factor Va heavy chain were analyzed using iodo[14C]acetamide-labeled factor Va heavy chain digested with trypsin, plasmin, V-8 protease, and cyanogen bromide. Following HPLC separation of the resulting peptides, free cysteines were identified by the incorporation of radioactivity while disulfide-containing peptides were detected using an SBD-F fluorometric assay after reduction. All cysteine-containing peptides were analyzed by amino acid sequence analysis. The four cysteines in the A1 domain are associated with two disulfide bonds, Cys139-Cys165 and Cys220-Cys301. One disulfide bond was explicitly identified in the A2 domain; Cys471-Cys497, and a free cysteine was found in the A2 domain at Cys538. Significant difficulties were encountered in preparing identifiable or soluble peptides which would permit the explicit identification of the three remaining cysteines in the A2 domain. On the basis of homology, it is likely that Cys589 is a free SH while a disulfide bridge exists between Cys579 and Cys660. Thus, three major disulfide bonding patterns, characterized as "alpha", "beta", and "gamma" loops, are found in factor V. Each A domain contains a 26 residue "alpha loop at positions 139-165, 471-497, and 1684-1710. The A1 and A2 domains each contain 81 amino acid residue "beta" loops at 220-301 and 579-660.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding of AuCl(4)(-) to amine groups tethered to the interior of a 2 nm siloxane nanocage was determined in solutions containing various concentrations of acid. The mode of binding was inferred from EXAFS and UV-vis spectra to be by ligand exchange of amine for chloride, which implies that the amines remain unprotonated. Cyclic voltammetry confirmed that the Au complexes bind to the nanocage interior and established a 1:1 relationship between bound Au complex and amine groups. The results suggested a 5-7 pH unit shift in the protonation constant of the interior amines relative to free amines in solution.

A new structure, consisting of a shell cross-linked, 2 nm size siloxane nanocage containing propylamine groups tethered to the interior face of the shell was synthesized, starting with micelles of the surfactant molecule, (triethoxysilyl)propylcetylcarbamate. After hydrolysis of the ethoxysilyl groups and condensation and capping of the silanols to form a cross-linked, one-atom-layer-thick siloxane shell, the carbamate was converted to amine, releasing the cetyl group from the structure and resulting in the desired spherical nanocage. The intermediates in the synthesis process and the final structure were characterized by 1H and 29Si NMR, DLS, TEM, and mass spectroscopy. The amine groups tethered to the interior surface of the shell react readily with ninhydrin but do not interact with the larger ZnTPP, indicating molecular size selectivity by the cross-linked shell. The structure also exhibits confinement effect in the amine-catalyzed decarboxylation of acetoacetic acid, exhibiting higher activity and higher selectivity for acetal than (aminopropyl)triethoxysilane.

Catalytic sites on an iron oxide surface, active in the selective oxidation of butene to butadiene, were studied by adsorption and temperature-programmed desorption of cis-2-butene, butadiene, and carbon dioxide. Three distinct types of sites were identified: isomerization site, selective oxidation site, and combustion site. Results indicate that the three sites are independent of each other. Interaction of hydrocarbons was the weakest with the isomerization site, and strongest with the combustion site. Desorption from the oxidation sites can be identified. By quantitatively determining the desorption products in the adsorption of cis-2-butene and butadiene, concentrations of th selective oxidation and the combustion sites were estimated. 8 figures, 4 tables.

Adsorption, temperature-programed desorption, and pulse reaction studies of cis-2-butene and butadiene on spinel zinc ferrite by previously described methods provided evidence that the selectivity for oxidative dehydrogenation of butenes increases when zinc is added to the iron oxide catalyst because selective oxidation and complete oxidation proceed on separate sites, as they do on pure iron; because the density of sites for selective oxidation is higher and the density of sites for complete combustion is lower than on pure iron oxide; and because the activity of the combustion sites is lower.