Influence of the preparation method on the acidic properties of WOx-ZrO2 catalysts.

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Tuning of the acid-base properties of primary Me2O3 (Me = Al, Ga, In) and binary (ZrO2-Me2O3) (Me = B, Al, Ga, In) oxides by adding WO3: A calorimetric study

EAU:ENERGIE+RKO:SBE:AAUIn this work two series of samples were prepared by impregnation of Me (Me = Al, Ga, In) hydroxides and Zr-Me (Me = B, Al, Ga, In) mixed hydroxides with an ammonium metatungstate hydrate solution followed by calcination at 400 degrees C. The obtained WO3/Me2O3 and WO3/(ZrO2-Me2O3) samples have been characterized in terms of their structural, textural, and surface properties, including the acid features, by a variety of techniques (BET, XRD, TG) and microcalorimetry. The acid-base properties were estimated by the adsorption of NH3 and SO2 as probe molecules, respectively. The prepared mixed oxide samples showed very different properties in terms of surface area and X-ray diffractograms. All obtained samples showed a specific acidic-basic character influenced by the relative amounts of each oxide, the most acidic samples being WO3/ZrO2 and WO3/Al2O3 and WO3/(Al2O3-ZrO2). (C) 2013 Elsevier B.V. All rights reserved

Acid and redox properties of tungstated zirconia catalysts

EAU:ENERGIE+RKO:SBE:AAUVarious tungstated zirconia catalysts with a WO3 loading of about 16 wt% were characterized both in their acid and oxidation properties. The samples have been characterized in their micro-structural and surface properties by BET, X-ray diffraction, Raman spectroscopy, temperature programmed reduction, elemental chemical analysis. The surface acidity was determined by the techniques of NH3 adsorption microcalorimetry and pyridine infrared spectroscopy (FT-IR). Improved acidity has been detected upon addition of WO3 to zirconia by both techniques. The global acid strength and the total number of acid sites increased greatly with the formation of WOx clusters on the zirconia support. This acidity increase can be attributed to the creation of Bronsted acid sites generated by the well dispersed WOx domains, as observed by FT-IR pyridine desorption

Study of acidic commercial WOx/ZrO2 catalysts by adsorption microcalorimetry and thermal analysis techniques

ENERGIE+AAU:RKO:SBENon

Relation between surface acidity and reactivity in fructose conversion into 5-HMF using tungstated zirconia catalysts

Catalytic dehydration of fructose and its conversion to 5-hydroxymethylfurfural was studied using tungstated zirconia oxides, with various tungsten oxide loadings (1-20 wt.%). The samples were prepared by incipient wetness impregnation and thoroughly characterized using a combination of different techniques: structural, thermal and calorimetric analyses. Zirconia was predominantly present in the investigated samples in the tetragonal phase when the WO3 loading was above 10 wt.%. The samples exhibited amphoteric characteristics, as they adsorbed both ammonia and sulfur dioxide on their surface. The number of surface acid sites increased with increasing WO3 content. Fructose dehydration tests evidenced the formation of 5-hydroxymethylfurfural and by-products (formic and levulinic acids). The results show that the ratio of basic to acidic sites of the solid catalysts is the key parameter for the selectivity in 5-HMF, while the global fructose conversion was mainly related to the presence of acid sites of a given strength with 150 > Q(diff) > 100 kJ.mol(NH3)(-1)

Activity in the cellobiose hydrolysis of the surface acid sites of tungstated zirconia catalysts

International @ ENERGIE+SBE:AAUInternational audienceCellobiose (a disaccharide derived from the condensation of two glucose molecules linked by a ß(1?4) bond) can be obtained by enzymatic or acid inorganic hydrolysis of cellulose and cellulose rich materials. The difficulties connected to cellobiose hydrolysis are due to strong-inter- and intra-molecular hydrogen bonds which are formed from the eight free alcohol (COH) groups and three ether linkages of the cellobiose molecule. Only catalysts with strong protonic acidity (Brönsted sites) are suitable for this reaction. Moreover, when the heterogeneous catalytic reaction occurs in water, the catalyst has to maintain its acidity even in this protic and polar solvent which is known to quench the acidity of many good solid acids. A series of WOx/ZrO2 samples with various tungsten oxide loadings (120) wt.% was prepared by co-precipitation and their surface properties characterized in particular by NH3 adsorption microcalorimetry to determine the number and strength of acid sites. Concerning the acid site nature, a progressive increase of the amount of Brřnsted sites with the WO3 loading was observed. The catalytic reaction of cellobiose disaccharide hydrolysis showed a better catalytic performance on the highest WO3 loaded catalysts, associated to the presence of Zr-stabilized WOx clusters and a strong protonic acidity

Investigation of the WO3/ZrO2 surface acidic properties for the aqueous hydrolysis of cellobiose

A series of WO x/ZrO 2 with various tungsten oxide loadings (1-20) wt.% was prepared by co-precipitation. The catalysts were characterized by XRD, BET, XPS, Raman spectroscopy, TPR, ammonia adsorption microcalorimetry and pyridine FT-IR spectroscopy. XRD and Raman results showed that the ZrO 2 support is predominantly present in the monoclinic phase when the WO 3 loading was less than 5 wt.% and predominantly in the tetragonal phase above 10 wt.%. No formation of bulk WO 3 was detected for the catalysts calcined at 700 \ub0C, which is also the case for the highest loaded samples. TPR results revealed that isolated WO 3 species are easier to reduce than amorphous WO x. The ammonia adsorption microcalorimetric study evidenced acid sites with adsorption heats in the range 90 < Q diff < 130 kJ.mol -1, in amounts which increase with increasing WO 3 loading until reaching the monolayer. Concerning the acid site nature, a progressive increase of the amount of Br\uf8nsted sites with the WO 3 loading was observed. The catalytic reaction of cellobiose disaccharide hydrolysis showed a better catalytic performance on the highest WO 3 loaded catalysts, associated to the presence of Zr-stabilized WO x clusters and a strong protonic acidity

Influence of the Acidic Properties of ZrO2 Based Mixed Oxides Catalysts in the Selective Reduction of NOx with n-Decane

AIR:EAU:ENERGIE:INGENIERIE+RKO:SBE:AGF:AAUThe selective catalytic reduction of NOx by decane (C10H22-SCR) has been studied over mixed oxides of zirconia with boria, alumina, gallia, india and tungsta. The samples were prepared by coprecipitation and thoroughly characterized using a combination of different techniques to determine their structural and surface properties. Moreover a WO3-containing sample supported on Al2O3-ZrO2 sample was prepared to verify the influence of the tungsta active phase deposited by impregnation. The surface acidity and basicity of the samples (measured by NH3 and SO2 adsorption microcalorimetry) varied in relation to the kind of co-oxide added to zirconia. In particular, the number of surface acid sites expressed in mu g(-1) increased in the following order WO3-ZrO2 > Al2O3-ZrO2 > Ga2O3-ZrO2 > In2O3-ZrO2 > WO3/(Al2O3-ZrO2) > ZrO2 > B2O3-ZrO2. Correlations between the catalytic behaviour and the samples surface acidity were found and the results show that a moderate acidity (i.e. for Ga2O3-ZrO2) is one of the key parameter for high N-2 selectivity and NOx conversion

Epidemiology of Epstein-Barr virus infection and infectious mononucleosis in the United Kingdom

Background: Epstein-Barr Virus (EBV) is a ubiquitous gamma-herpesvirus with which ∼ 95% of the healthy population is infected. EBV infection has been implicated in a range of haematological malignancies and autoimmune diseases. Delayed primary EBV infection increases the risk of subsequent complications. Contemporaneous seroepidemiological data is needed to establish best approaches for successful vaccination strategies in the future. Methods: We conducted a sero-epidemiological survey using serum samples from 2325 individuals between 0 and 25 years old to assess prevalence of detectable anti-EBV antibodies. Second, we conducted a retrospective review of Hospital Episode Statistics to examine changes in Infectious Mononucleosis (IM) incidence over time. We then conducted a large case-control study of 6306 prevalent IM cases and 1,009,971 unmatched controls extracted from an East London GP database to determine exposures associated with IM. Results: 1982/2325 individuals (85.3%) were EBV seropositive. EBV seropositivity increased more rapidly in females than males during adolescence (age 10-15). Between 2002 and 2013, the incidence of IM (derived from hospital admissions data) increased. Exposures associated with an increased risk of IM were lower BMI, White ethnicity, and not smoking. Conclusions: We report that overall EBV seroprevalence in the UK appears to have increased, and that a sharp increase in EBV seropositivity is seen in adolescent females, but not males. The incidence of IM requiring hospitalisation is increasing. Exposures associated with prevalent IM in a diverse population include white ethnicity, lower BMI, and never-smoking, and these exposures interact with each other. Lastly, we provide pilot evidence suggesting that antibody responses to vaccine and commonly encountered pathogens do not appear to be diminished among EBV-seronegative individuals. Our findings could help to inform vaccine study designs in efforts to prevent IM and late complications of EBV infection, such as Multiple Sclerosis

Paul Valéry, Cahiers 1894-1914. Edition intégrale, sous la responsabilité de N. Celeyrette-Pietri et R. Pickering.

Intense travail de Valéry sur la forme brève. Classement de grands thèmes: Attention, Attente, Langage, Mémoire, Rêve, Sommeil, Conscience, Sensation. Reflexion sur le "Moi" liée au projet d'une représentation du fonctionnement humain. Développement des thèmes du "Narcisse" et de "Protée"