20 resultados para ALKALI PROMOTION


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Templated, macroporous Mg-Al hydrotalcites synthesised via alkali-free co-precipitation exhibit superior performance in the transesterification of C4 -C18 triglycerides for biodiesel production, with rate-enhancement increasing with alkyl chain length. Promotion reflects improved diffusion of bulky triglycerides and accessibility of active sites within the hierarchical macropore-micropore architecture. © 2012 The Royal Society of Chemistry.

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A series of alkali-doped metal oxide catalysts were prepared and evaluated for activity in the transesterification of rapeseed oil to biodiesel. Of those evaluated, LiNO3/CaO, NaNO3/CaO, KNO3/CaO and LiNO3/MgO exhibited >90% conversion in a standard 3 h test. There was a clear correlation between base strength and activity. These catalysts appeared to be promising candidates to replace conventional homogeneous catalysts for biodiesel production as the reaction times are low enough to be practical in continuous processes and the preparations are neither prohibitively difficult nor costly. However, metal leaching from the catalyst was detected, and this resulted in some homogeneous activity. This would have to be resolved before these catalysts would be viable for large-scale biodiesel production facilities.

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A series of Rh2/AlO3 catalysts have been prepared using untreated or pre-sulphated alumina supports. The effect of support sulphation on catalyst activity towards propene and propane combustion has been explored as a function of Rh loading. Light-off temperatures for the total oxidation of both hydrocarbons decrease with increasing Rh content, associated with a transition from small oxidic clusters to large metallic Rh particles. Sulphate promotes both propene and propane combustion equally, with the magnitude of promotion exhibiting only a weak loading dependence. Enhanced catalytic performance is accompanied by Rh reduction and sintering. © 2006 Elsevier B.V. All rights reserved.

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The ability of Cu and Sn to promote the performance of a 20% Ni/Al2O3 catalyst in the deoxygenation of lipids to fuel-like hydrocarbons was investigated using model triglyceride and fatty acid feeds, as well as algal lipids. In the semi-batch deoxygenation of tristearin at 260 °C a pronounced promotional effect was observed, a 20% Ni-5% Cu/Al2O3 catalyst affording both higher conversion (97%) and selectivity to C10-C17 alkanes (99%) in comparison with unpromoted 20% Ni/Al2O3 (27% conversion and 87% selectivity to C10-C17). In the same reaction at 350 °C, a 20% Ni-1% Sn/Al2O3 catalyst afforded the best results, giving yields of C10-C17 and C17 of 97% and 55%, respectively, which contrasts with the corresponding values of 87 and 21% obtained over 20% Ni/Al2O3. Equally encouraging results were obtained in the semi-batch deoxygenation of stearic acid at 300 °C, in which the 20% Ni-5% Cu/Al2O3 catalyst afforded the highest yields of C10-C17 and C17. Experiments were also conducted at 260 °C in a fixed bed reactor using triolein − a model unsaturated triglyceride − as the feed. While both 20% Ni/Al2O3 and 20% Ni-5% Cu/Al2O3 achieved quantitative yields of diesel-like hydrocarbons at all reaction times sampled, the Cu-promoted catalyst exhibited higher selectivity to longer chain hydrocarbons, a phenomenon which was also observed in experiments involving algal lipids as the feed. Characterization of fresh and spent catalysts indicates that Cu enhances the reducibility of Ni and suppresses both cracking reactions and coke-induced deactivation.

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Background. Sports and arts based services for children have positive impacts on their mental and physical health. The charity sector provides such services, often set up in response to local communities expressing a need. The present study maps resilience promoting services provided by children's charities in England. Specifically, the prominence of sports and arts activities, and types of mental health provisions including telephone help-lines, are investigated. Findings. The study was a cross-sectional web-based survey of chief executives, senior mangers, directors and chairs of charities providing services for children under the age of 16. The aims, objectives and activities of participating children's charities and those providing mental health services were described overall. In total 167 chief executives, senior managers, directors and chairs of charities in England agreed to complete the survey. From our sample of charities, arts activities were the most frequently provided services (58/167, 35%), followed by counselling (55/167, 33%) and sports activities (36/167, 22%). Only 13% (22/167) of charities expected their work to contribute to the health legacy of the 2012 London Olympics. Telephone help lines were provided by 16% of the charities that promote mental health. Conclusions. Counselling and arts activities were relatively common. Sports activities were limited despite the evidence base that sport and physical activity are effective interventions for well-being and health gain. Few of the charities we surveyed expected a health legacy from the 2012 London Olympics. © 2010 Bhui et al; licensee BioMed Central Ltd.