Thermal Ageing Induced Effects on Pd/LaFeO3 for NOx Reduction by Hydrocarbons: Influence of the Preparation Method

The influence of the support synthesis for the preparation of supported Pd/LaFeO₃ perovskite based catalysts and the nature of the palladium precursor on the catalytic performances in the selective reduction of NO to N₂ by hydrocarbons have been investigated. According to the preparation method, subsequent surface and bulk characterisation revealed significant changes in the degree of dispersion and the chemical environment of oxidic palladium species depending on the extent of interaction with the support. Pd nitrate precursor leads to the stabilisation of the Pd surface concentration. The metal support interactions thus obtained strongly enhance the catalytic performances, particularly the resistance to thermal ageing whereas sol–gel synthesis produces the higher support activity.     

Solid State and Gas Phase NMR Studies of Immobilized Catalysts and Catalytic Active Nanoparticles

In the current study two new classes of stabile, catalytic active nanomaterials are investigated. The first class of nanoparticles consists of an inner metal core. To stabilize their structure the metal core is surrounded by organic ligands or embedded in a polymer. The second class consists of catalysts immobilized on mesoporous silica supports of SBA-3 type silica. Employing a combination of ¹H, ²H, ¹³C and ²⁹Si-solid state NMR spectroscopy the structure of the catalysts is analyzed. As a simple model for the catalytic properties of the particles, the activation of ²H₂ gas on the surface of the particles is studied. Employing ¹H and ²H gas phase NMR the kinetics of simple catalytic model reactions is studied. Employing ²H-NMR solid state NMR spectroscopy, the interaction of the metal surface with the substrate is characterized and kinetic data, which characterize the mobility of the deuterium on the surface, are extracted. For the interpretation of these data, parallel NMR studies of model η²-bound transition metal complexes are employed, which allow, owing to their simpler geometry and higher sensitivity, a quantitative modeling of the spin dynamics in the NMR experiment.     

High-throughput approach to the catalytic combustion of diesel soot

A methodology for the evaluation of diesel soot oxidation catalysts by high-throughput (HT) screening was developed. The optimal experimental conditions (soot amount, catalyst/soot ratio, type of contact, composition and flow rate of gas reactants) ensuring a reliable and reproducible detection of light-off temperatures in a 16 parallel channels reactor were set up. The temperature profile measured in the catalyst/soot bed under TPO conditions when the exothermic combustion of soot takes place was shown to provide an accurate measurement of the ignition. Its reproducibility and relevance were checked. The results obtained with a reference noble metal free catalyst (La_0.8Cr_0.8Li_0.2O₃ perovskite) agree very well with literature data. Qualitative mechanistic features could be derived from these experiments, stressing the likely limiting step of oxygen transfer from catalyst surface to soot particulates to ignite the soot combustion. Ceria material was shown to be more appropriate than perovskite one. From an HT screening of a large diverse library (over 100 mixed oxides catalysts) under optimized conditions, about 10 new formulations were found to perform better than selected noble metal free reference materials.     

Quantification of clay dispersion in nanocomposites of styrenic polymers

Polymer‐clay nanocomposites are materials with many interesting structures, properties, and potential applications. Microstructural evaluation of a nanocomposite is not an easy task, as clay may form hierarchical structures which may look different when observed at various magnifications under a microscope, and also as the concepts of “intercalation” and “exfoliation” are not self‐sufficient to describe its morphology. In this work polymer‐clay nanocomposites of polystyrene and two styrene‐containing block copolymers (styrene‐butadiene‐styrene and styrene‐ethylene/butylene‐styrene) were prepared using three different techniques. Clay dispersion was evaluated by a recently developed microscopy image analysis procedure, combining the analysis of optical and transmission electron micrographs, and the characterization was complemented by X‐ray diffraction and rheological measurements. The results showed better clay dispersion for both block copolymers nanocomposites, mainly due to their molecular architectures. Moreover, the techniques which showed the best results involved mixing the materials in a solvent medium. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Dry vs soaked wood: Modulating the volatile extractible fraction of oak wood by heat treatments

The aim of this study was to analyze the impact of the water content of wood on the concentrations of volatile compounds which can be extracted after heat treatments. Head Space-Solid Phase Micro Extraction Gas Chromatography coupled to Mass Spectrometry (HS-SPME GC–MS) has been used to compare the concentrations of six aroma compounds (vanillin, furfural, eugenol, guaïacol and cis- and trans-whisky lactones) in hydroalcoholic extracts of heated oak wood samples either previously soaked in hot water or not. Except for eugenol, concentrations of extracted aromas appeared to be lower in soaked woods than in dry woods for temperatures up to 200 °C. If a delaying effect of water could explain such overall lower extracted concentrations from soaked woods, a PCA analysis revealed that for the longer duration (25 min of heat treatment), the adsorbed water could promote a higher impact of furfural, eugenol and both whisky lactones on the composition of hydroalcoholic extracts, suggesting that alternative mechanisms of thermal modifications of the wood macromolecular network could exist at high temperatures in presence of adsorbed water.     

Identification of a triacylglycerol lipase gene family in Candida deformans: molecular cloning and functional expression

The yeast Candida deformans CBS 2071 produces an extracellular lipase which was shown to catalyse the production of various esters by the esterification of free fatty acids, even in the presence of a large molar excess of water. To clone the gene encoding this extracellular lipase, Saccharomyces cerevisiae was transformed with C. deformans genomic libraries and screened for lipolytic activity on a medium containing rapeseed oil emulsion and rhodamine B. Three members of a lipase gene family (CdLIP1, CdLIP2 and CdLIP3) were cloned and characterized. Each deduced lipase sequence has a Gly-His-Ser-Leu-Gly-(Gly/Ala)-Ala conserved motif, eight cysteine residues and encodes an N-terminal signal sequence. MALDI-TOF mass spectrometry analysis of a proteolytic digest of the lipase produced was used to obtain experimental evidence that the CdLIP1 gene encoded the extracellular lipase. Recombinant expression studies confirmed that the cloned genes encoded functional lipases. The three lipases are very similar to lipases from the related species Yarrowia lipolytica. Significant homologies were also found with several yeast and fungal lipases. As C. deformans CBS 2071 was previously considered to be synonymous with Y. lipolytica, the strains were compared for the extent of nucleotide divergence in the variable regions (D1/D2) at the 5'-end of the large-subunit (26S) ribosomal DNA (rDNA) gene. This rDNA region has diverged sufficiently to suggest that C. deformans is a separate species. The nucleotide sequences of the CdLIP1, CdLIP2 and CdLIP3 genes will appear in the EMBL nucleotide sequence database under Accession Nos AJ428393, AJ428394 and AJ428395, respectively.     

One‐Pot Synthesis of Functional Helicoidal Hybrid Organic–Inorganic Nanofibers with Periodically Organized Mesoporosity

The one‐pot synthesis and properties of multifunctional hybrid mesoporous organosilica fibers with helical shapes are described. These hybrid mesoporous fibers are prepared without chiral elements and functionalized with a large variety of organic R functions (R = alkylthiols, phenylsulfonates, alkylphosphonates, dansyl, aminopropyl, fluoroalkyl, etc.). The resulting nanomaterials are thoroughly characterized by a variety of techniques. The use of a synergetic combination of achiral molecules as co‐directing structuring agents, a surfactant, and an organofunctional silica precursor R‐Si(OR)₃ allows, via carefully tuning of the main synthesis parameters and processing conditions, to control the shape, which is the anisotropic factor, of the hybrid nanofibers. The functionalization of the hybrid materials with fluorescent molecules (dansyl) and gold nanoparticles opens possibilities for sensor and catalytic applications, respectively. Moreover, these hybrid nanofibers can be easily transferred in organic solvents or in a “green” solvent such as water to make stable colloidal dispersions. This tunable functionality of nanofibers also allows their transferability into a variety of polymeric hosts (PVDF, PVBu, and PVP) allowing the formation of functional homogeneous nanocomposite hybrid membranes.     

Replacing the ({beta}{alpha})-unit 8 of E.coli TIM with its chicken homologue leads to a stable and active hybrid enzyme

In order to investigate how structural modifications interferewith protein stability, we modified a (ß)-unit inE.coli triosephosphate isomerase (TIM), a typical (ß)-barrelprotein, assuming that the pseudosymmetrical ß-barrelcan be divided into eight successive loop/ß-strand/loop/-helixmotifs. We replaced the eighth (ß)-unit of E.coliTIM with the corresponding chicken (ß)-unit. The substitution,involving the replacement of 10 of the 23 residues of this (ß)-unit, was evaluated first by modelling, then experimentally.Modelling by bomology suggests how the amino add replacementsmight be accommodated in the hybrid E.coli/chicken TIM (ETCM8CHI).Both natural and hybrid recombinant TIMs, overproduced in E.coli,were purified to homogeneity and characterized as to their stabilityand kinetics. Our kinetic studies show that the modificationperformed here leads to an active enzyme. The stability studiesindicate that the stability of ETIM8CHI is comparable to thatof the wild type TIM.