High-Temperature ceramic coatings with geopolymeric binders

High-temperature (HT) resistant coatings represent an updating subject of high industrial interest on account of their relevant applications (turbines, engines, aeronautic, ecc.). While many HT resistant products are known, not simple appears to satisfy the requirement of their high and stable adhesion on the support. The aim of this work was to develop novel HT resistant ceramic coatings based on silicon carbide and/or zirconium oxide, using geopolymeric resins as binders. Geopolymers show many advantages respect to organic polymers, first of all their high heat resistance and refractoriness. Moreover, they are fully inorganic, do not require organic solvents and are not off-gassing. During the geopolymerization step, the polymineral resin (alumino-silicate binders) is formed, acting as glue sticking together the unreacted Al-Si source materials and fillers (ceramic powders), forming the ceramic-geopolymer composite coatings. In order to optimize the geopolimeric binders, different raw materials have been tested (caolins, meta-kaolins and alumina/silica fine powders), while the alkali aqueous solution was KOH/K2SiO3, fixing the ratios SiO2/Al2O3 = 4 and SiO2/K2O = 2. Setting conditions, microstructural evolution as a function of the temperature and thermal evolution either in air or inert atmosphere were deeply investigated in order to set-up the best preparation conditions. HT resistant coatings were prepared by mixing the ceramic fillers (90 wt%) with geopolimeric binders, then applying the obtained mixture on ceramic substrates by brushing. After a first setting, coatings were stabilized by a thermal treatment in inert atmosphere at 1350?C and then the oxidation behaviour and adhesion level on the substrates were studied. A key role of new glass-ceramic phases formed during the thermal treatments has been evidenced

Geopolymerization of meta-kaolins with different morphologies

The reactivity of two commercial meta-kaolins with similar composition and specific surface areas but different morphologies was tested during geopolymerization with potassium silicate alkaline solution. Manual and short term mechanical stirrings were used to not complete geopolymerization and to emphasize the powders surface reactivity. Moreover, radiation, infra red, micro waves heating were used during curing. The degree of geopolymerization was checked by SEM and N2 adsorption (BET), FTIR and 27Al MAS NMR spectroscopies. The meta-kaolin powder with rounded agglomerates was the less reactive, but it was the more sensitive to the various geopolymerization conditions. The fine dispersed lamellar powder was more reactive and it was mainly affected by mixing. The addition to the potassium silicate alkaline solution of a small alkaline cation such as lithium favoured the dissolution stage during geopolymerization, but decreased the melting temperatur

Screening heteroatom distributions in zeotype materials using an effective Hamiltonian approach: the case of aluminogermanate PKU-9

We introduce a method to allow the screening of large configurational spaces of heteroatom distributions in zeotype materials. Based on interatomic potential calculations of configurations containing up to three heteroatoms, we parameterize an atomistic effective Hamiltonian to describe the energy of multiple substitutions, with consideration of both short- and long-range interactions. Then, the effective Hamiltonian is used to explore the full configurational space at other compositions, allowing the identification of the most stable structures for further analysis. We illustrate our approach with the aluminogermanate PKU-9, where we show that increasing the aluminium concentration changes the likely siting of Al, in agreement with experiment

Inorganic molecular sieves: Preparation, modification and industrial application in catalytic processes

[EN] The increasing environmental concern and promotion of “green processes” are forcing the substitution of traditional acid and base homogeneous catalysts by solid ones. Among these heterogeneous catalysts, zeolites and zeotypes can be considered as real “green” catalysts, due to their benign nature from an environmental point of view. The importance of these inorganic molecular sieves within the field of heterogeneous catalysis relies not only on their microporous structure and the related shape selectivity, but also on the flexibility of their chemical composition. Modification of the zeolite framework composition results in materials with acidic, basic or redox properties, whereas multifunctional catalysts can be obtained by introducing metals by ion exchange or impregnation procedures, that can catalyze hydrogenation–dehydrogenation reactions, and the number of commercial applications of zeolite based catalysts is continuously expanding. In this review we discuss determinant issues for the development of zeolite based catalysts, going from zeolite catalyst preparation up to their industrial application. Concerning the synthesis of microporous materials we present some of the new trends moving into larger pore structures or into organic free synthesis media procedures, thanks to the incorporation of novel organic templates or alternative framework elements, and to the use of high-throughput synthesis methods. Post-synthesis zeolite modification and final catalyst conformation for industrial use are briefly discussed. In a last section we give a thorough overview on the application of zeolites in industrial processes. Some of them are well established mature technologies, such as fluid catalytic cracking, hydrocracking or aromatics alkylation. Although the number of zeolite structures commercially used as heterogeneous catalysts in these fields is limited, the development of new catalysts is a continuous challenge due to the need for processing heavier feeds or for increasing the quality of the products. The application of zeolite based catalysts in the production of chemicals and fine chemicals is an emerging field, and will greatly depend on the discovery of new or known structures by alternative, lower cost, synthesis routes, and the fine tuning of their textural properties. Finally, biomass conversion and selective catalytic reduction for conversion of NOx are two active research fields, highlighting the interest in these potential industrial applications.The authors acknowledge financial support from Ministerio de Ciencia e Innovacion (project Consolider-Ingenio 2010 MULTICAT).Martínez Sánchez, MC.; Corma Canós, A. (2011). Inorganic molecular sieves: Preparation, modification and industrial application in catalytic processes. Coordination Chemistry Reviews. 255(13-14):1558-1580. doi:10.1016/j.ccr.2011.03.014S1558158025513-1

Reduction catalytique sélective de NO par NH3 sur Fe-ZSM-5

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Influence of fine structural characteristics of VPO catalysts on the formation of maleic and phthalic anhydrides in the oxidation of n-pentane

We report on the influence of the stages of preparation of a vanadium phosphate on the selectivity to phthalic anhydride (PA) and maleic anhydride (MA) in n-pentane oxidation. The attention was mainly focused on the extent of structural defects observed in precursors and catalysts. Vanadium phosphate catalysts were obtained from precursors prepared by a two-step synthesis. In the first step VOPO4-mixed isobutanol-water intercalates, with the amount of isobutanol per VOPO4 molecule varying from 1.6 to 0.05, were prepared by precipitation from a solution containing vanadyl isobutoxide and H3PO4 and a carefully adjusted water content. In the second step the precursors were formed by reflux using two different procedures: (i) in an inert medium (n-octane) or (ii) in a reductive medium (isobutanol). Catalysts were obtained by treating the precursors under the reaction conditions for about 40 h. By such procedures VPO precursors and catalysts with bulk P/V atomic ratio equal to 1.05 and displaying widely different structural defects were obtained. Precursors and catalysts were characterised by elementary chemical analysis, carbon analysis, oxidation state of vanadium, BET, XRD, FTIR, and XPS. Long range and short range orders were considered. Results show that the parallel routes of the n-pentane oxidation into MA and PA require different structural features of the catalyst. The formation of phthalic anhydride demands an ordered structure while maleic anhydride could be formed on a highly defective VPO catalyst. It is suggested that this high structural order for PA formation is necessary to create the complex active structure to provide the concerted process of PA formation. (C) 1999 Academic Press