Ce0.78Sn0.2Pt0.02O2-delta: A new non-deactivating catalyst for hydrogen production via water-gas shift reaction

We demonstrate the activity of Ce0.78Sn0.2Pt0.02O2-delta, a new catalyst, towards water-gas shift (WGS) reaction. Over 99.5% CO conversion to H-2 is observed at 300 +/- 25 degrees C. Based on different characterization techniques we found that the present catalyst is resistant to deactivation due to carbonate formation and sintering of Pt on the surface when subjected to longer duration of reaction conditions. The catalyst does not require any pre-treatment or activation between start-up/shut-down reaction operations. Formation of side products such as methane, methanol, formaldehyde, coke etc. was not observed under the WGS reaction conditions indicating the high selectivity of the catalyst for H-2. Temperature programmed reduction of the catalyst in hydrogen (H-2-TPR) shows reversible reduction of Ce4+ to Ce3+, Sn4+ to Sn2+ and Pt4+ to Pt-0 oxidation state with oxygen storage capacity (OSC) of 3500 mu mol g(-1) at 80 degrees C. Such high value of OSC indicates the presence of highly activated lattice oxygen. CO oxidation in presence of stoichiometric O-2 shows 100% conversion to CO2 at room temperature. The catalyst also exhibits 100% selectivity for CO2 at room temperature towards preferential oxidation (PROX) of residual CO in presence of excess hydrogen in the feed. (C) 2010 Elsevier B.V. All rights reserved.

Elucidation of the conformational free energy landscape in H.pylori LuxS and its implications to catalysis

Background: One of the major challenges in understanding enzyme catalysis is to identify the different conformations and their populations at detailed molecular level in response to ligand binding/environment. A detail description of the ligand induced conformational changes provides meaningful insights into the mechanism of action of enzymes and thus its function. Results: In this study, we have explored the ligand induced conformational changes in H. pylori LuxS and the associated mechanistic features. LuxS, a dimeric protein, produces the precursor (4,5-dihydroxy-2,3-pentanedione) for autoinducer-2 production which is a signalling molecule for bacterial quorum sensing. We have performed molecular dynamics simulations on H. pylori LuxS in its various ligand bound forms and analyzed the simulation trajectories using various techniques including the structure network analysis, free energy evaluation and water dynamics at the active site. The results bring out the mechanistic details such as co operativity and asymmetry between the two subunits, subtle changes in the conformation as a response to the binding of active and inactive forms of ligands and the population distribution of different conformations in equilibrium. These investigations have enabled us to probe the free energy landscape and identify the corresponding conformations in terms of network parameters. In addition, we have also elucidated the variations in the dynamics of water co-ordination to the Zn2+ ion in LuxS and its relation to the rigidity at the active sites. Conclusions: In this article, we provide details of a novel method for the identification of conformational changes in the different ligand bound states of the protein, evaluation of ligand-induced free energy changes and the biological relevance of our results in the context of LuxS structure-function. The methodology outlined here is highly generalized to illuminate the linkage between structure and function in any protein of known structure.

Hemin-mediated oxidation of dithiothreitol reduces oxygen to H2O

Hemin catalyses the oxidation of dithiothreitol. One mole of oxygen is consumed for every 2 moles of dithiothreitol oxidized and the product is shown by spectral studies to be the intramolecular disulphide. The reaction shows a specificity for dithiol and for free heme moieties. Hemin molecules exhibit cooperativity in oxygen reduction. Oxygen radicals do not seem to be involved. H2O2 is not required for this oxidation of dithiothreitol and does not appear to be an intermediate in the reduction of O2 to H2O. However, an independent minor reaction involving a 2-electron transfer with the formation of H2O2 also occurs. These studies on the hemin-catalyzed oxidation of dithiothreitol provide a chemical model for a direct 4-electron reduction of O2 to H2O.

Pd Supported on Titanium Nitride for Efficient Ethanol Oxidation

The excellent metal support interaction between palladium (Pd) and titanium nitride (TiN) is exploited in designing an efficient anode material. Pd-TN, that could be useful for direct ethanol fuel cell in alkaline media. The physicochemical and electrochemical characterization of the Pd-TiN/electrolyte interface reveals an efficient oxidation of ethanol coupled with excellent stability of the catalyst under electrochemical conditions. Characterization of the interface using in situ Fourier transform infrared spectroscopy (in situ FITR) shows the production CO2 at low overvoltages revealing an efficient cleaving of the C-C bond. The performance comparison of Pd supported on TiN (Pd-TiN) with that supported on carbon (Pd-C) clearly demonstrates the advantages of TiN support over carbon. A positive chemical shift of Pd (3d) binding energy confirms the existence of metal support interaction between pd and TiN, which in turn helps weaken the Pd-CO synergetic bonding interaction. The remarkable ability of TiN to accumulate -OH species on its surface coupled with the strong adhesion of Pd makes TiN an active support material for electrocatalysts.

Synthetic studies in aromatic hemiterpenes of natural origin, Part 5: Synthesis of 6-acetyl-2,2-dimethyl-8-methoxychromene via benzylic oxidation route

The synthesis of 6-acetyl-2,2-dimethyl-8-methoxychromene (lc), a naturally occurring isomer of encecalin (la)h~s been described startilag from 2,2,6- trimethyl-8-methoxyclaromene (2e) which was obtained from creosol (4) in two steps involving condensation of the phenol with malic acid to the coumarin (3), followed by Grignard reaction with CHaMgI. The transformation of (2e) to the natural product (lc) was effeeted by oxidative dehydrogenation by DDQ of the 6-meth~r function to the formyl group (2f), Grignard reaction to the carbinol (2g) and finally its oxidation to the acetyl moiety (lc), the sequence of the essential steps schematically summarised as : Ar-CHs --* Ar-CHO --* Ar-CH (OH) CHs --* Ar---COCHs.

Sonochemical synthesis of Ce1-xFexO2-delta (0 <= x <= 0.45) and Ce0.65Fe0.33Pd0.02O2-delta nanocrystallites: oxygen storage material, CO oxidation and water gas shift catalyst

Nanocrystalline Ce1-xFexO2-delta (0 <= x <= 0.45) and Ce0.65Fe0.33Pd0.02O2-delta of similar to 4 nm sizes were synthesized by a sonochemical method using diethyletriamine (DETA) as a complexing agent. Compounds were characterized by powder X-ray diffraction (XRD), X-ray photo-electron spectroscopy (XPS) and transmission electron microscopy (TEM). Ce1-xFexO2-delta (0 <= x <= 0.45) and Ce0.65Fe0.33Pd0.02O2-delta crystallize in fluorite structure where Fe is in +3, Ce is in +4 and Pd is in +2 oxidation state. Due to substitution of smaller Fe3+ ion in CeO2, lattice oxygen is activated and 33% Fe substituted CeO2 i.e. Ce0.67Fe0.33O1.835 reversibly releases 0.31O] up to 600 degrees C which is higher or comparable to the oxygen storage capacity of CeO2-ZrO2 based solid solutions (Catal. Today 2002, 74, 225-234). Due to interaction of redox potentials of Pd2+/0(0.89 V) and Fe3+/2+ (0.77 V) with Ce4+/3+ (1.61 V), Pd ion accelerates the electron transfer from Fe2+ to Ce4+ in Ce0.65Fe0.33Pd0.02O1.815, making it a high oxygen storage material as well as a highly active catalyst for CO oxidation and water gas shift reaction. The activation energy for CO oxidation with Ce0.65Fe0.33Pd0.02O1.815 is found to be as low as 38 kJ mol(-1). Ce0.67Fe0.33O1.835 and Ce0.65Fe0.33Pd0.02O1.815 have also shown high activity for the water gas shift reaction. CO conversion to CO2 is 100% H-2 specific with these catalysts and conversion rate was found to be as high 27.2 mu moles g(-1) s(-1) and the activation energy was found to be 46.4 kJ mol(-1) for Ce0.65Fe0.33Pd0.02O1.815.

Nucleation and growth of Al2O3/metal composites by oxidation of aluminum alloys

The nucleation and growth mechanisms during high temperature oxidation of liquid Al-3% Mg and Al-3% Mg-3% Si alloys were studied with the aim of enhancing our understanding of a new composite fabrication process. The typical oxidation sequence consists of an initial event of rapid but brief oxidation, followed by an incubation period of limited oxide growth after which bulk Al2O3/Al composite forms. A duplex oxide layer, MgO (upper) and MgAl2O4 (lower), forms on the alloy surface during initial oxidation and incubation. The spinel layer remains next to the liquid alloy during bulk oxide growth and is the eventual repository for most of the magnesium in the original alloy. Metal microchannels developed during incubation continuously supply alloy through the composite to the reaction interface. During the growth process, a layered structure exists at the upper extremity of the composite, consisting of MgO at the top surface, MgAl2O4 (probably discontinuous), Al alloy, and finally the bulk Al2O3 composite containing microchannels of the alloy. The bulk oxide growth mechanism appears to involve continuous formation and dissolution of the Mg-rich oxides at the surface, diffusion of oxygen through the underlying liquid metal, and epitaxial growth of Al2O3 on the existing composite body. The roles of Mg and Si in the composite growth process are discussed.

Oxidation Of 1-(2-Hydroxybenzyl)-2-Naphthols

Condensation of salicyl alcohol with 2-naphthols (9a-d) furnishes 1-(2-hydroxybenzyl)-2-napthols (6a-d). Methylation of 6a gives the dimethyl ether 11, which has also been prepared by Grignard reaction of 2-methoxyphenylmagnesium bromide with 2-methoxy-1-naphthaldehyde followed by reduction with AlCl3-LiAlH4. Compounds 6a-d undergo facile oxidation with either K3Fe(CN)6 or KOBr to give spironaphthalenones 12a-d. Surprisingly, no reaction occurs with either DDQ or o-chloranil.

Oxidation of Quinolinols - Synthesis of Spirodienones Containing Nitrogen

Reaction of 6-quinolinol with formaldehyde and sodium sulphite gives the bisquinolinol (1b). Similar reaction of 6-quinolinol with sodium 2-hydroxy1-naphthylmethanesulphonate gives 1c. Oxidation of 1b with K3Fe(CN)6 or KOBr gives the spiroquinolinone 2b, while oxidation of 1c with K3Fe(CN)6 results in the formation of spirodienones 2c and 2d, and the dispiroketones 7b and 7c. Oxidation of 1c with DDQ, however, results in only the spirodienones 2c and 2d. The spirodienone 2d and the bromospiroquinolinone 2e are formed in the reaction of 1c with KOBr.

Oxidation Of Spiroalcohols With 2,3-Dichloro-5,6-Dicyano-1,4-Benzoquinone (Ddq) .4. Structure Of A Novel Dioxepin Derivative

DDQ oxidation of the spiroalcohol 7a gives exclusively a compound to which the 13a-methyl-13aH-7a, 15-methano-15H-dinaphtho[2,1-b:2',1'-e][1,4]-dioxepin structure 8a has been assigned on the basis of two-dimensional homonuclear (H-1-H-1) and heteronuclear (H-1-C-13; FUCOUP) correlation spectroscopy experiments. Similar oxidation of spiroalcohols 7b-h gives the dioxepin derivatives 8b-h.