Anne Giroir-Fendler

Light changes the atmospheric reactivity of soot

Soot particles produced by incomplete combustion processes are one of the major components of urban air pollution. Chemistry at their surfaces lead to the heterogeneous conversion of several key trace gases; for example NO2 interacts with soot and is converted into HONO, which rapidly photodissociates to form OH in the troposphere. In the dark, soot surfaces are rapidly deactivated under atmospheric conditions, leading to the current understanding that soot chemistry affects tropospheric chemical composition only in a minor way. We demonstrate here that the conversion of NO2 to HONO on soot particles is drastically enhanced in the presence of artificial solar radiation, and leads to persistent reactivity over long periods. Soot photochemistry may therefore be a key player in urban air pollution.

Characterization of a zeolite membrane for catalytic membrane reactor application

Abstract This paper describes the morphological and transport properties of a composite zeolite (silicalite)-alumina membrane. Some advantages obtained in combining the membrane with a conventional fixed-bed catalyst are also reported.

Separation of alcohols and alcohols/O2 mixtures using zeolite MFI membranes

Abstract Two different types of supported silicalite membranes were employed for the separation of alcohols and alcohols/O 2 mixtures: in one of them the zeolite material was deposited on the top of the γ -alumina supports, while in the other the zeolitic material was mainly present in the porous structure of the α -alumina supports. While both kinds of membranes were able to separate the above mixtures, the second type of membranes having the zeolite material inside the support performed more efficiently. The maximum selectivity reported in this work is 7415 for the ethanol/O 2 separation in an ethanol/methanol/O 2 mixture. For a better understanding of the separation mechanism, the performance of both zeolite membranes was compared to that of a mesoporous silica membrane. Also, the adsorption of methanol and propanol on silicalite crystals was measured using a microbalance.

Xylene Vapor Mixture Separation in Nanocomposite MFI-Alumina Tubular Membranes: Influence of Operating Variables

In this study, we present the results of a preliminary investigation on the influence of operating variables (temperature, sweep gas flow rate, and total feed vapor pressure) on xylene vapor mixture separation using tubular nanocomposite MFI-alumina zeolite membrane prepared by the pore-plugging synthesis technique. Within the detection limit of our analytical system, neither m- nor o-xylene was detected in the permeate stream, the membranes displaying therefore “infinite” p-xylene selectivity. The mixtures p-xylene flux displayed a maximum value of ca. 3.5 µmol·m−2·s−1, corresponding to a mixture permeance of 11 nmol·m−2·s−1·Pa−1, at 473 K and for a feed composition 0.63 kPa p-xylene/0.27 kPa m-xylene/0.32 kPa o-xylene, being almost unchanged for sweep gas flow rates (N2) higher than 20 mL(STP)/min and increasing with the total xylene vapor pressure at 1 : 1 : 1–3 p/m/o-xylene composition. The experimental p-xylene fluxes can be well predicted by a Maxwell-Stefan model, as expected for a mass transfer process driven by competitive adsorption / surface diffusion. Unlike film-like MFI membranes, the membranes presented here preserved their selectivity to p-xylene for total xylene pressures as high as 150 kPa. This behavior is attributed to the intimate contact between the alumina confining pores and MFI nanoparticles, reducing long-term stresses and thus preventing distortion of the MFI framework during p-xylene adsorption. These results open up potential applications of nanocomposite MFI-alumina for selective p-xylene separations at high loadings, for instance in pervaporation, where the use of film-like MFI membranes is discouraged.

Remarkable Enhancement of O2 Activation on Yttrium-Stabilized Zirconia Surface in a Dual Catalyst Bed

Yttrium-stabilized zirconia (YSZ) has been extensively studied as an electrolyte material for solid oxide fuel cells (SOFC) but its performance in heterogeneous catalysis is also the object of a growing number of publications. In both applications, oxygen activation on the YSZ surface remains the step that hinders utilization at moderate temperature. It was demonstrated by oxygen isotope exchange that a dual catalyst bed system consisting of two successive LaMnO3 and YSZ beds without intimate contact drastically enhances oxygen activation on the YSZ surface at 698 K. It can be concluded that LaMnO3 activates the triplet ground-state of molecular oxygen into a low-lying singlet state, thereby facilitating the activation of the O2 molecule on the YSZ oxygen vacancy sites. This phenomenon is shown to improve the catalytic activity of the LaMnO3-Pd/YSZ system for the partial oxidation of methane.

The Role of Support Acidity in the Selective Catalytic Reduction of NO by C3H6 Under Lean-Burn Conditions

Mechanical mixtures consisting of a catalyst (Pt/SiO2 or Pt/SiO2–Al2O3) and supports of varying acidity (hydrotalcite, SiO2, SiO2–Al2O3, and ZSM-5 zeolite) were tested for the selective reduction of NO by C3H6. A certain degree of support acidity appears to favour N2 selectivity, but if there are too many acid sites, carbon deposition becomes extensive and leads to catalyst deactivation.

Low-temperature catalytic oxidation of vinyl chloride over Ru modified Co3O4 catalysts

Ruthenium modified cobalt oxides were prepared by (1) impregnating ruthenium chloride hydrate on cobalt oxides, Ru-supported catalysts (Ru/Co3O4), and (2) Ru-doped catalysts (Ru–Co3O4) where the ruthenium ions were added to the precursor solution, by a one-step sol–gel method with cobalt nitrate. The physicochemical properties of the catalysts were characterized by ICP, BET, XRD, HR-TEM, TPR, and XPS analysis. The effects of ruthenium were studied for the total oxidation of vinyl chloride. This Ru modifier was observed to enhance oxygenate formation. The different preparation methods made contributions to the different amounts of Ru4+ on the surfaces of the catalysts while Ru4+ would be in synergy with Co2+ concentration, and this also changed the chemical coordination of oxygen on the surface. Dispersion of Ru oxides on the cobalt oxides surface could not only improve the catalytic activity and stability on steam, but also decrease the amount of chlorinated by-products and increase HCl selectivity.

State of Pt/SiO2 Catalysts After Reaction with a Lean NO–C3H6–O2 Mixture

During the selective reduction of NOx under lean-burn conditions with Pt/SiO2 solids, a particle size dependency has previously been observed. Furthermore, under the reactant mixture up to 773 K, the Pt particles sinter at the same time as the solids are activated. In fact, the size dependency is linked to the strength of the Pt–O bond and to the ease of NO dissociation.

Biovalorization of saccharides derived from industrial wastes such as whey: a review

Whey is a liquid waste issued from the transformation of milk into cheese. Whey is a major environmental problem for the dairy industry due to its high organic load, linked to its high content of lactose. It can be valorized by biological processes based on lactose fermentation into different products such as (1) lactic acid (as food additive), (2) 2,3-butanediol (as feedstock to get products such as methyl-ethyl-ketone or 2-butene for the pharmaceutical and chemical industries), (3) biogas (to obtain energy). The production of 2,3-butanediol from saccharides, such as glucose, has been actively studied over previous decades using several types of microorganisms such as Enterobacter aerogenes, Paenibacillus polymyxa, Klebsiella sp., Serratia marcescens and Escherichia coli. Some of these have even been genetically modified to improve the 2,3-butanediol production. The potential whey fermentation process into 2,3-butanediol depends on several operating conditions such as microorganisms, composition of the culture medium, temperature, pH and aeration. This review first presents a summary of the situation of milk and cheese production in Canada and around the world. It also describes the different kinds of whey and their treatment techniques. Finally, this paper describes the production of 2,3-butanediol from saccharides by various microorganisms under different operating conditions.

Study of Lanthanum Manganate and Yttrium-Stabilized Zirconia-Supported Palladium Dual-Bed Catalyst System for the Total Oxidation of Methane: A Study by 18O2/16O2 Isotopic Exchange

A significant enhancement of the yttrium‐stabilized zirconia‐supported palladium (0.2 wt % Pd/YSZ) catalytic activity for the total oxidation of methane was achieved in a dual‐bed system by the association of LaMnO3+Pd/YSZ materials. The combination with the best performance was 40 wt % LaMnO3+60 wt % Pd/YSZ. Pd/YSZ and LaMnO3 perovskite were characterized by using the 18O2 exchange technique. A Mars–van Krevelen mechanism was demonstrated over Pd/YSZ at 425 °C. Additionally, it was evidenced that LaMnO3 activated the O2 molecule on the YSZ oxygen vacancy sites to result in a significant increase of the oxidation rate characterized by a correlating decrease of the light‐off temperature of 65 °C.