The Experts below are selected from a list of 54 Experts worldwide ranked by ideXlab platform
Erhard Kemnitz - One of the best experts on this subject based on the ideXlab platform.
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a facile preparation of hydroxylated Magnesium Fluorides as an active catalyst for biodiesel production the effect of different aging times
Materials Letters, 2018Co-Authors: S Indrayanah, Erhard Kemnitz, I N Marsih, Irmina Kris MurwaniAbstract:Abstract The MgF2−x(OH)x with various aging times (1, 3, 6 and 12 h) have been obtained from sol-gel technique. The structure, chemical bonding and porosity of material were studied by X-ray diffraction, Fourier-transform infrared spectrofotometer and N2 adsorption-desorption isotherms. The crystallinity and the number of OH groups of solids increase linearly with increasing of aging time. Moreover, the pore diameter and volume decrease from 4.79 to 2.82 nm and from 0.165 to 0.107 cm3/g, while the surface area increases from 137.84 to 150.55 m2/g with the increase in aging times, respectively. The catalytic activity of materials to yield biodiesel from Crude Palm Oil shows that the biodiesel yield decreases from 64.43 to 14.89, 12.17 and 10.49% with increasing aging times, respectively. The best performance of the catalyst depends on the greater values of pore size and volume as well as the lower crystallinity and the smaller number of OH groups.
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quantification of acidic sites of nanoscopic hydroxylated Magnesium Fluorides by ftir and 15n mas nmr spectroscopy
RSC Advances, 2015Co-Authors: I Agirrezabaltelleria, Felix Hemmann, Christian Jaeger, Erhard KemnitzAbstract:Lewis and Bronsted sites were quantified in a series of weak acidic hydroxylated Magnesium Fluorides by Fourier transform infrared spectroscopy (FTIR) and solid state nuclear magnetic resonance spectroscopy (NMR) with pyridine as probe molecule. Molar extinction coefficients, which are necessary for quantitative FTIR measurements, were calculated by an easy approach. It utilizes the fact that both signals, used for the quantification by FTIR, are caused by the same deformation vibration mode of pyridine. Comparison of quantitative FTIR experiments and quantification by NMR shows that concentrations of acidic sites determined by FTIR spectroscopy have to be interpreted with caution. Furthermore, it is shown that the transfer of molar extinction coefficients from one catalyst to another may lead to wrong results. Molar extinction coefficients and concentrations of acidic sites determined by FTIR spectroscopy are affected by grinding and probably the particle size of the sample. High temperature during FTIR experiments has further impact on the quantification results.
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hydroxylated Magnesium Fluorides as environmentally friendly catalysts for glycerol acetylation
Applied Catalysis B-environmental, 2011Co-Authors: Simona B Troncea, Stefan Wuttke, Erhard Kemnitz, Simona M Coman, Vasile I ParvulescuAbstract:Abstract The increase of biodiesel production during the next years will result in an overproduction, and therefore, an accumulation of glycerol on the market. The use of glycerol-based additives to improve the properties of biodiesel or gasoline is one of the possibilities currently being explored to utilize this renewable feedstock. In this context, partly hydroxylated Magnesium Fluorides have demonstrated catalytic activity in the esterification of glycerol with acetic acid to yield diacetylglycerine (DAG) and triacetylglycerine (TAG). The catalytic activity depends on the density of acid sites at the external catalytic surface while the selectivity to different acylated products is influenced by the nature of the acid sites (Lewis and/or Bronsted). Using non-conventional activation methods of the reactant molecules, as microwave or ultrasound irradiation, optimal glycerol conversions (>90%) and selectivities to the desired compounds (over 85%) were obtained. The activities and selectivities achieved using partly hydroxylated Fluorides as catalysts are comparable or even superior to those displayed by conventional oxide based acid catalysts under thermal activation.
A P Stupak - One of the best experts on this subject based on the ideXlab platform.
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luminescence of irradiated lithium sodium and Magnesium Fluorides nanocrystals formation of self assembled structures and point defects with new properties
Journal of Luminescence, 2020Co-Authors: A P Voitovich, V S Kalinov, A N Novikov, O E Kostik, S B Lastovskii, V V Mashko, A V Pushkarou, A P StupakAbstract:Abstract The luminescence and absorption properties of LiF, NaF and MgF2 nanocrystals containing radiation-induced point defects with new properties are investigated. The influence of temperature, at which nanocrystals are maintained after their manufacture, on the efficiency and kinetics of such defects formation is examined. For LiF samples, the activation energy of fotmation processes is determined. X-ray diffraction reflections are compared for LiF nanocrystals, unannealed and annealed after fabrication, unannealed and irradiated with γ-rays or electrons, as well as those manufactured by fragmentation of an irradiated crystal plate. Conclusions are drawn about the processes of self-assembled nanostructures formation, the presence of which is a prerequisite for the creation of radiation-induced point defects with new properties.
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luminescent properties of radiation induced defects in sodium and Magnesium Fluorides nanocrystals
Journal of Luminescence, 2018Co-Authors: A P Voitovich, V S Kalinov, Pavel Loiko, E F Martynovich, Xavier Mateos, A N Novikov, P P Pershukevich, L P Runets, Josep Maria Serres, A P StupakAbstract:Abstract The possibility of formation of radiation defects with new luminescent properties is investigated in sodium and Magnesium Fluorides nanosized crystals. Nanocrystals obtained by mechanical fragmentation of the single crystals have been irradiated by γ-rays at 77 K or electron beams at room temperature. Their TEM images have been received. Luminescence, luminescence excitation and absorption spectra of nanocrystals have been measured immediately after γ-irradiation without samples defrosting and after termination of the defects aggregation processes at room temperature. The formation of radiation color centers with previously unknown optical characteristics has been discovered in nanocrystals. Numbers of anion vacancies and electrons entering into these centers composition were established in sodium fluoride. The structure transformation of the centers, containing two anion vacancies and an electron, was revealed after sodium fluoride samples defrosting. For sodium fluoride the data on the Huang-Rhys parameters and lifetimes of the photoluminescence for here studied and previously known centers of the same composition are determined and compared. The results obtained show that near-clusters color centers can be formed in crystals with different structures and atomic compositions.
A P Voitovich - One of the best experts on this subject based on the ideXlab platform.
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luminescence of irradiated lithium sodium and Magnesium Fluorides nanocrystals formation of self assembled structures and point defects with new properties
Journal of Luminescence, 2020Co-Authors: A P Voitovich, V S Kalinov, A N Novikov, O E Kostik, S B Lastovskii, V V Mashko, A V Pushkarou, A P StupakAbstract:Abstract The luminescence and absorption properties of LiF, NaF and MgF2 nanocrystals containing radiation-induced point defects with new properties are investigated. The influence of temperature, at which nanocrystals are maintained after their manufacture, on the efficiency and kinetics of such defects formation is examined. For LiF samples, the activation energy of fotmation processes is determined. X-ray diffraction reflections are compared for LiF nanocrystals, unannealed and annealed after fabrication, unannealed and irradiated with γ-rays or electrons, as well as those manufactured by fragmentation of an irradiated crystal plate. Conclusions are drawn about the processes of self-assembled nanostructures formation, the presence of which is a prerequisite for the creation of radiation-induced point defects with new properties.
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luminescent properties of radiation induced defects in sodium and Magnesium Fluorides nanocrystals
Journal of Luminescence, 2018Co-Authors: A P Voitovich, V S Kalinov, Pavel Loiko, E F Martynovich, Xavier Mateos, A N Novikov, P P Pershukevich, L P Runets, Josep Maria Serres, A P StupakAbstract:Abstract The possibility of formation of radiation defects with new luminescent properties is investigated in sodium and Magnesium Fluorides nanosized crystals. Nanocrystals obtained by mechanical fragmentation of the single crystals have been irradiated by γ-rays at 77 K or electron beams at room temperature. Their TEM images have been received. Luminescence, luminescence excitation and absorption spectra of nanocrystals have been measured immediately after γ-irradiation without samples defrosting and after termination of the defects aggregation processes at room temperature. The formation of radiation color centers with previously unknown optical characteristics has been discovered in nanocrystals. Numbers of anion vacancies and electrons entering into these centers composition were established in sodium fluoride. The structure transformation of the centers, containing two anion vacancies and an electron, was revealed after sodium fluoride samples defrosting. For sodium fluoride the data on the Huang-Rhys parameters and lifetimes of the photoluminescence for here studied and previously known centers of the same composition are determined and compared. The results obtained show that near-clusters color centers can be formed in crystals with different structures and atomic compositions.
Irmina Kris Murwani - One of the best experts on this subject based on the ideXlab platform.
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a facile preparation of hydroxylated Magnesium Fluorides as an active catalyst for biodiesel production the effect of different aging times
Materials Letters, 2018Co-Authors: S Indrayanah, Erhard Kemnitz, I N Marsih, Irmina Kris MurwaniAbstract:Abstract The MgF2−x(OH)x with various aging times (1, 3, 6 and 12 h) have been obtained from sol-gel technique. The structure, chemical bonding and porosity of material were studied by X-ray diffraction, Fourier-transform infrared spectrofotometer and N2 adsorption-desorption isotherms. The crystallinity and the number of OH groups of solids increase linearly with increasing of aging time. Moreover, the pore diameter and volume decrease from 4.79 to 2.82 nm and from 0.165 to 0.107 cm3/g, while the surface area increases from 137.84 to 150.55 m2/g with the increase in aging times, respectively. The catalytic activity of materials to yield biodiesel from Crude Palm Oil shows that the biodiesel yield decreases from 64.43 to 14.89, 12.17 and 10.49% with increasing aging times, respectively. The best performance of the catalyst depends on the greater values of pore size and volume as well as the lower crystallinity and the smaller number of OH groups.
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Glycerol Acetylation Using Magnesium Fluoride Catalyst to Produced DAG and TAG
2017Co-Authors: Qurrota A’yuni, Syafsir Akhlus, Harsasi Setyawati, Irmina Kris MurwaniAbstract:Glycerol acetylation with acetic acid using Magnesium fluoride catalyst have been investigated. Magnesium fluoride catalyst was prepared by sol-gel method with ethanol as gelating agent. The glycerol acetylation produced monoacetylglyceride (MAG), diacetylglyceride (DAG) and triacetylglyceride (TAG). The catalytic reaction carried out by thermal methods reflux under ambient conditions. The influence of reaction conditions such as the reaction time on the product distribution was investigated. The optimum of glycerol conversion was achieved at 5 hours of reaction time by 78.34% with selectivity of 30, 62 and 8% for MAG, DAG and TAG respectively. The reaction route over Magnesium Fluorides was observed by product as reactants, gradually. The results showed that the acetylation reaction of glycerol occurs via a parallel route to the first, followed by the consecutive route to produce DAG and TAG.
Felix Hemmann - One of the best experts on this subject based on the ideXlab platform.
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quantification of acidic sites of nanoscopic hydroxylated Magnesium Fluorides by ftir and 15n mas nmr spectroscopy
RSC Advances, 2015Co-Authors: I Agirrezabaltelleria, Felix Hemmann, Christian Jaeger, Erhard KemnitzAbstract:Lewis and Bronsted sites were quantified in a series of weak acidic hydroxylated Magnesium Fluorides by Fourier transform infrared spectroscopy (FTIR) and solid state nuclear magnetic resonance spectroscopy (NMR) with pyridine as probe molecule. Molar extinction coefficients, which are necessary for quantitative FTIR measurements, were calculated by an easy approach. It utilizes the fact that both signals, used for the quantification by FTIR, are caused by the same deformation vibration mode of pyridine. Comparison of quantitative FTIR experiments and quantification by NMR shows that concentrations of acidic sites determined by FTIR spectroscopy have to be interpreted with caution. Furthermore, it is shown that the transfer of molar extinction coefficients from one catalyst to another may lead to wrong results. Molar extinction coefficients and concentrations of acidic sites determined by FTIR spectroscopy are affected by grinding and probably the particle size of the sample. High temperature during FTIR experiments has further impact on the quantification results.
