1,721,008 research outputs found
"Journal of Materials Chemistry A Poster Prize" at Asia-Pacific Conference on Electrochemical Energy Storage & Conversion
No full textHigh catalytic performance of surfactant-directed nanocrystalline zeolites for liquid-phase Friedel-Crafts alkylation of benzene due to external surfaces
No full textBeta zeolite is known as an efficient catalyst for Friedel-Crafts alkylation. In liquid phase reactions, however, beta zeolite catalyst is often deactivated rapidly. We discovered that the maximum possible catalytic turnovers in benzene alkylation with benzyl alcohol could be increased by six times by using a beta zeolite with a nanosponge-like morphology, in comparison to bulk beta zeolites. The nanomorphic zeolite was obtained using a hydrothermal synthesis method which uses multiammonium surfactants as a meso-micro hierarchical structure-directing agent. The origins of the high catalytic performance were investigated by measuring the catalytic conversions after selectively poisoning acid sites located on external surfaces and in internal micropores selectively. The result indicated that the high catalytic performance was due to the alkylation reactions occurring on external surfaces. External active sites were able to perform the catalytic function even after active sites inside the zeolite micropores were deactivated. Similar results were obtained with other nanomorphic zeolites such as MFI nanosheets, MTW nanosponge and MRE nanosponge. © 2013 Elsevier Ltd. All rights reserved.134361sciescopu
Characterization of the Surface Acidity of MFI Zeolite Nanosheets by 31P NMR of Adsorbed Phosphine Oxides and Catalytic Cracking of Decalin
No full textMFI zeolite nanosheets tailored to 2.5-nm thickness were
synthesized using a surfactant-type zeolite structure-directing agent,
[C22H45−N+(CH3)2−C6H12−N+(CH3)2−C6H13](Br−)2. The zeolite nanosheets
possessed Brønsted acid sites on their external surfaces as well as in
the internal micropore walls. The acid strength and concentration was
characterized by the 31P NMR signals of the adsorbed trimethylphosphine
oxide and tributylphosphine oxide. The 31P NMR investigation identified
three types of Brønsted acid sites with different strengths on external
surfaces; there were four types inside the micropores. A linear correlation
has been established between the number of the external strongest acid sites
and the catalytic activity in decalin cracking for the MFI zeolite catalysts
investigated in this work.174781sciescopu
Characterization of Surface Acidity of MFI zeolite Nanosheets by 13P NMR of Adsorbed Phosphine Oxides and Decalin Cracking
No full textMFI zeolite nanosponges possessing uniform mesopores generated by bulk crystal seeding in the hierarchical surfactant-directed synthesis
No full textThe synthesis of a mesoporous material with uniform mesopore diameters and crystalline MFI zeolite walls has been achieved, simply by seeding the multiammonium surfactant-directed synthesis with bulk zeolite crystals. The bulk seeds disappeared in the final product. As a result of seeding, the mesoporous zeolites could be generated rapidly even at high Al content. © the Partner Organisations 2014.133361sciescopu
Mesopore wall-catalyzed Friedel-Crafts acylation of bulky aromatic compounds in MFI zeolite nanosponge
No full textWe investigated the effects of mesopore generation in a MFI zeolite when used as a catalyst in liquid-phaseFriedel.Crafts acylation reactions of bulky aromatic compounds. For this investigation, we obtained anMFI zeolite with nanosponge morphology, following a seed-assisted hydrothermal synthesis route usingC22H45.N+(CH3)2.C6H12.N+(CH3)2.C6H13. The zeolite nanosponge exhibited a narrow distribution ofmesopore diameters centered at 4 nm, in which the mesopores were built with a disordered networkof 2.5-nm thick MFI zeolite layers. This zeolite exhibited high catalytic performance in various acylationreactions, compared with bulk MFI zeolites, beta zeolite and mesoporous materials composed of amor-phous aluminosilicates. The high catalytic performance corresponded to the strong Bronsted acid sitesexisting on the mesopore walls. © 2014 Elsevier B.V. All rights reserved111111sciescopu
Mesoporous MFI zeolite nanosponge supporting cobalt nanoparticles as a Fischer-Tropsch catalyst with high yield of branched hydrocarbons in the gasoline range
No full textA zeolite nanosponge was obtained by a seed-assisted hydrothermal synthesis route using C22H45− N+(CH3)2−C6H12−N+(CH3)2−C6H13 as the structure-direct-ing agent. The zeolite was composed of disordered network of 2.5-nm-thick MFI zeolite nanolayers having a narrow distribution of mesopore diameters centered at 4 nm. The highly mesoporous texture (mesopore volume = 0.5 cm3 g−1) was suitable for supporting cobalt nanoparticles with a narrow distribution of particle diameters centered at 4 nm. The Co/MFI zeolite exhibited high stability of the Co nanoparticles against particle growth, and there was accordingly high catalytic conversion of carbon monoxide to hydrocarbons and long catalytic lifetime in the Fischer−Tropsch synthesis.
Furthermore, the Co/MFI catalyst exhibited high selectivity for branched hydrocarbons in the gasoline range (C5−C11), compared to conventional alumina-based catalysts. This high selectivity could be attributed to hydroisomerization in the extremely thin zeolite frameworks that provided short diffusion path lengths for branched hydrocarbons.137371sciescopu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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