Hilario Vidal

Lanthanide salts as alternative corrosion inhibitors

Abstract Lanthanum and samarium nitrates and chlorides have been investigated as corrosion inhibitors of AISI 434 SS in sodium chloride solutions, at room temperature. Electrochemical techniques allowed to evaluate the degree of protection and the cathodic nature of the inhibitors. Scanning electron microscopy and energy dispersive spectrometry were used to analyze the composition of the protective films formed after full-immersion tests.

Non-cordierite clay-based structured materials for environmental applications.

The applications of clay-based structured materials, excluding cordierites, for environmental protection are examined. In particular, their use in the abatement of some of the main hazardous species in polluted emissions such as nitrogen oxides, carbon monoxide, volatile organic compounds and heavy metals is discussed. A distinction is made between adsorption and catalytic processes. In addition, a general overview of the methods and general principles followed to prepare structured materials from clays is also given. Special attention is paid to those employed to obtain honeycomb monoliths and foams.

XPS analysis and microstructural characterization of a Ce/Tb mixed oxide supported on a lanthana‐modified transition alumina

In the framework of a research project aimed at developing alternative materials for application in three-way catalysis, this work reports on the preparation and characterization of a ceria-terbia mixed oxide supported on a lanthana-modified transition alumina. This complex multicomponent oxide system has been characterized by combining x-ray diffraction (XRD), high-resolution electron microscopy (HREM), temperature-programmed desorption mass spectrometry (TPD-MS), Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). Following a dry impregnation procedure, the lanthana-containing phase was deposited first, the ceria-terbia oxide being dispersed on the modified alumina in a subsequent step. The structural and chemical characterization studies carried out on the La 2 O 3 /Al 2 O 3 binary system provide no evidence of a crystalline lanthana-containing phase. Neither lanthanum oxide nor the phases resulting from its aging in air could be identified. Likewise, no lanthana-alumina mixed oxide phases could be deduced from analysis of the HREM micrographs, selected-area electron diffraction (SAED) or XRD patterns. As deduced from the H 2 O and CO 2 TPD studies, the chemisorptive properties of the La 2 O 3 /Al 2 O 3 are significantly different from those of the alumina and the bulk lanthana. We conclude, accordingly, that the supported lanthana consists of a highly dispersed oxide in strong interaction with the alumina support. By contrast, after deposition and further calcination of the cerium-terbium nitrate precursors, the presence of fluorite microcrystals of average size 5 nm could be identified both by XRD and HREM. The XPS studies carried out on the alumina support, La 2 O 3 /Al 2 O 3 and CeTbO x /La 2 O 3 /Al 2 O 3 , as well as a series of reference systems consisting of aged-in-air lanthana, CeLaO x and CeTbO x mixed oxides, have revealed the presence in the ternary system (CeTbO x /La 2 O 3 /Al 2 O 3 ) of at least two different types of chemical environments for the lanthanum ions. With the help of the La 3d 5/2 spectra recorded for the different reference systems, we conclude that these two environments correspond to highly dispersed lanthana strongly interacting with OH- and/or CO 3 2- groups, and to La 3+ species incorporated in the Ce/Tb mixed oxide phase.

TAP study of toluene total oxidation over a Co3O4/La-CeO2 catalyst with an application as a washcoat of cordierite honeycomb monoliths

The total oxidation of toluene was studied over a Co3O4/La-CeO2 catalyst in a Temporal Analysis of Products (TAP) set-up in the temperature range 713 K to 873 K in the presence and absence of dioxygen. It has been demonstrated that the reaction proceeds via a Mars-van Krevelen mechanism. The reaction rate increased 8.4 times if both toluene and dioxygen were present in the feed. The partial reaction order with respect to O2 diminished from 0.9 to 0.6 with an increase in temperature from 763 to 873 K. Adsorbed oxygen species with a lifetime of ∼8 s have been found on a catalyst fully oxidized by dioxygen. Catalysis of isotopically labeled (18)O2/(12)C6H5(13)CH3 results in the formation of products containing (18)O, which indicates that both lattice and adsorbed oxygen are involved in the total oxidation of toluene. The role of adsorbed oxygen is activation of the C-H bond in toluene. The reaction network of the catalytic total oxidation of toluene consists of the following sequence: adsorption of toluene on the catalyst surface; activation of toluene by dehydrogenation with adsorbed oxygen; oxidation of activated toluene mainly by the lattice oxygen and re-oxidation of the reduced catalyst by dioxygen.

Influence of the preparation procedure on the chemical and microstructural properties of lanthana promoted Rh/SiO2 catalysts: A FTIR spectroscopic study of chemisorbed CO

Abstract In this work, the influence of the preparation procedure on the chemical and microstructural properties of a series of Rh/La 2 O 3 /SiO 2 catalysts has been investigated. The catalysts were characterized by using HREM, H 2 and CO volumetric adsorption and FTIR spectroscopy of chemisorbed CO. From our study, significant effects were observed for the following preparative variables: (a) the lanthana loading; (b) the way of introducing the metal and promoter, either consecutive (lanthana first and then the rhodium salt) or by co-impregnation; and (c) the calcination temperature (873 K or 1173 K) applied for preparing the La 2 O 3 /SiO 2 intermediate phase onto which the noble metal was deposited.

Effectiveness of acid-treated agricultural stones used in biopurification systems to avoid pesticide contamination of water resources caused by direct losses: part I. Equilibrium experiments and kinetics.

Several recent publications report the use of low-cost and locally available adsorbents in biopurification systems to eliminate pesticides from water. Nonetheless, the literature is insufficient to cover this problem, and more investigations are needed in this field to evaluate the possible application of economical adsorbents to prevent pesticide water resources contamination caused by direct losses. This study focuses on the fate of endosulfan metabolites, in small-scale biopurification systems, using as adsorbents treated and untreated organic agricultural stones (date, olive and avocado). The effects of sorbent particle size, adsorbent dose, contact time, concentration of pesticide solution and temperature on the adsorption processes were systematically studied in batch experiments. Pesticide determination was carried out using stir bar sorptive extraction and gas chromatography coupled with mass spectroscopy. Maximum removal efficiency (94.8%) was reached for endosulfan sulfate (0.1 mg L(-1)) using the acid-treated date stones (ATOS) fraction <125 microm (solid/liquid ratio: 1 g L(-1)). According to the general behavior of the adsorption mechanism, date stones show the higher removal efficiency followed by olive and avocado stones, respectively. The analyses of the results reveal that the thermo chemical treatment improves notably the pesticides adsorption efficiency of the studied sorbents and that the adsorption decreases when the pesticide solubility rises. Experimental adsorption data were analyzed according to various kinetic models. Lagergren and Morris-Weber equations were applied to fit the kinetic results. The second order model was the most suitable and intra-particle diffusion was found to be the rate controlling the adsorption process.

Fundamental properties of a new cerium-based mixed oxide alternative as TWC component

This work reports on the redox behaviour of a CeTbOx mixed oxide. As revealed by TPR and TPD experiments, the oxide, with 80% Ce-20% Tb atomic composition, exhibits interesting properties for TWC applications. It is shown that its redox behaviour is much less sensitive than that of ceria to successive high temperature reduction/reoxidation cycles, thus indicating that the inherent sintering effect does not imply a drastic loss of chemical activity. Upon comparison of the TPR diagrams for CeTbOx and CeO2, it is shown that their redox properties are rather complementary, the Tb containing mixed oxide allowing the aim of lowering the operative temperature window. This may improve the TWC response under cold start operation conditions. Our Ce/Tb mixed oxide also shows interesting redox properties in a flow of both inert gas and O2(5%)/He.

Easy extrusion of honeycomb-shaped monoliths using Moroccan natural clays and investigation of their dynamic adsorptive behavior towards VOCs

In the present work, honeycomb-shaped monoliths were easily extruded using local natural clays without the need of chemical binders. This finding allows significant cost reduction, in terms of not only additives and solvents but also the energy consumption required for their elimination by thermal treatment. The extruded monoliths were subject to mechanical strength testing in addition to the study of their thermal behavior, structural and textural properties. Moreover, one of their potential uses as VOCs adsorbents was evaluated in comparison with conventional packed bed by investigating their dynamic adsorptive and desorption behavior towards a model VOC of o-xylene type.

Synthesis, characterization and performance of sol-gel prepared TiO2-SiO2catalysts and supports

Summary Tetraethoxysilane and tetrabutylorthotitanate were used as precursors to obtain a series ofTiO 2 -SiO 2 gels. The use of ultrasound, and the type of drying treatment followed to obtain catalytic materials, play a significant role in the dispersion of Ti atoms. The structural properties of these gels, studied by XRD, XANES and FTIR spectroscopy can be related to their acidity. Thus, the trends of activities for tert-butanol decomposition to isobutene are in tight connection both with the TiO 2 content and with the observed levels of Ti dispersions. Rh and Pt supported catalysts, prepared from several TiO 2 -SiO 2 gels, present higher activities and selectivities for n-butane hydrogenolysis than other preparations used as references.

Acyloxylation of 1,4-Dioxanes and 1,4-Dithianes Catalyzed by a Copper−Iron Mixed Oxide

The use of a copper-iron mixed oxide as a heterogeneous catalyst for the efficient synthesis of α-acyloxy-1,4-dioxanes and 1,4-dithianes employing t-butyl peroxyesters is reported. The preparation and characterization of the catalyst are described. The effect of the heteroatoms and a plausible mechanism are discussed. The method is operationally simple and involves low-cost starting materials affording products in good to excellent yields.