Renewables and energy efficiency measures represent an important way to improve the security of energy supply and to bring to Europe the other important advantages of environmental benefits together with technological development. The EU has put in place a new regulatory framework, with a view to accelerating the growth of EU markets for renewable electricity. In this context, an important instrument is the Directive on electricity produced from renewable energy sources. The future development of photovoltaics is supported through the EU Framework Programme, for both research and demonstration activities and through the Intelligent Energy - Europe Programme for non-technological actions. Research focuses on the next generation of PV technologies while the aim of the demonstration activities is to accelerate the market penetration of more cost-effective PV technologies. To stimulate public-private partnerships between the research community, industry and policy makers with the aim of mobilising greater research and innovation effort the Commission has supported the launching of a Technology Platform on Photovoltaics. To accelerate the development, demonstration and market introduction of a new generation of PV systems, the European Commission is combining an intense legislative initiative with a strong research and demonstration effort.
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The synthesis method of a stable, large-pore tantalum-pillared montmorillonite family (Ta-PILC) and its physicochemical characterization are reported. The clay used is a sodium montmorillonite. The tantalum pillaring solution is prepared by careful control of the hydrolysis of a tantalum alkoxide precursor, Ta(OC2H5)5, in an ethanolic acidic solution. From XRD analysis it has been concluded that the Ta-PILC possesses a high thermal stability, the pillared structure is preserved even after calcination at 600°C, and the basal spacing, 26 Å at 500°C, is one of the greatest values described in the literature. On the basis of the bibliographic data concerning tantalum alkoxide hydrolysis and condensation, and taking into account the experimental results obtained for this series of Ta-PILCs, a structure of type [Ta8O10(OR)20],R=H, C2H5, has been proposed as the precursor molecule of the tantalum pillars.
The acidic and catalytic properties of a series of Ta-PILCs synthesized with a different initial tantalum content were characterized by adsorption of gaseous probe molecules (TPD of ammonia and FTIR spectra of absorbed pyridine) and by the test reaction of 1-butanol dehydration. A large increase of acidity was noted in Ta-PILCs compared to Na-montmorillonite or tantalum oxide. Cross-linking pillars and silica layers of the clay induce stronger Lewis and new Brønsted sites. The lack of basic sites formation is evidenced by the dehydration of 1-butanol to butene selectivity (100%). The incorporation of the tantalum oxide between the montmorillonite sheets produce, within Ta-PILC, acid centers of the same nature as observed for the silicon–tantalum mixed oxides.
AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
The acidic and catalytic properties of a series of silicon-tantalum mixed oxides containing between 0 and 30 at% tantalum were characterized by temperature-programmed desorption of ammonia, by FTIR spectra of adsorbed pyridine, and by the test reaction of 1-butanol dehydration at 250-300 degrees C. Probe molecule adsorption and catalytic testing show an acid site generation in silicon-tantalum mixed oxides compared to pure tantalum oxide. Both Bronsted and Lewis acid sites are present on the mixed oxide surface. Bronsted and Lewis acid sites seem to be weaker in SiO2-Ta2O5 mixed oxide than in analogous SiO2-Al2O3, since a greater reaction temperature is required to achieve the same conversion in the above test reaction. However, a great advantage of this new solid acid is the production of butenes with 100% selectivity. (C) 1995 Academic Press, Inc.
AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
The preparation and characterization of silica-alumina pillared clays have been studied. The formation and aging of hydroxy-alumina oligocations followed by reaction with Si(OEt)(4) have been studied in order to obtain hydroxy-SiAl oligocations. Two solutions of Al-13 (Keggin cation) containing an OH/Al mole ratio equal to 2 have been used in the preparation of the hydroxy-silica-alumina solutions: solution A aged at room temperature for 48 h, and solution B aged at 393 K: for 4 h. Different Si/Al ratios (0, 0.5, 1, and 2) and Al/clay ratios (7, 11, and 22 mM Al (g of clay)(-1)) have been used to obtain clays with different accessibility and acidic properties. The Al/clay ratio played an important role in the properties of the samples obtained. Micropore size distributions obtained with the Horvath-Kawazoe approach confirmed the existence of two sizes of micropores for samples (solution A or B) with a Si/Al less than or equal to 1. On the other hand, measurable differences in the micropore distributions were observed when the Al/clay ratio was varied. The acidity of hydroxy-alumina and hydroxy-silica-alumina pillared clays observed is mainly Lewis type, but the nature of the acid sites detected by pyridine adsorption seems to be independent of Si/Al ratio.
Mixed oxides, especially silica containing multicomponent oxides, have recently found many applications in the production of glasses, ceramics and catalysts. This paper reports for the first time the synthesis of SiO2-Ta2O5 mixed oxide by the sol-gel method. The advantage of the sol-gel method is that a relatively large concentration of tantalum can be incorporated in the mixed oxide structure. Physicochemical characterization shows that tantalum atoms are incorporated into the silica matrix producing Si-O-Ta bonds.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Careful control of (i) the hydrolysis of Ta(C2H5)(5) in ethanolic solution and (ii) of the pillaring process allows the synthesis of a stable tantalum pillared montmorillonite (Ta PILC). This solid presents a basal spacing of 26 Angstrom after calcination at 500 degrees C. The surface area and the microporosity were evaluated by N-2 adsorption isotherms and through the alpha(s)-plot method.
The preparation of tantalum pillared montmorillonite, resulting in a basal spacing of 26 Angstrom at 500 degrees C, is described; dehydration of butan-1-ol results in a 100% selectivity to butene with no detectable formation of butylaldehyde or dibutyl ether.
