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379 results on '"Čejka J."'

71. Structural analysis of IPC zeolites and related materials using positron annihilation spectroscopy and high-resolution argon adsorption

Author

Jagiello, J., primary, Sterling, M., additional, Eliášová, P., additional, Opanasenko, M., additional, Zukal, A., additional, Morris, R. E., additional, Navaro, M., additional, Mayoral, A., additional, Crivelli, P., additional, Warringham, R., additional, Mitchell, S., additional, Pérez-Ramírez, J., additional, and Čejka, J., additional

Published
2016
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76. Vibrational Spectroscopy and Related In situ Studies of Catalytic Reactions within Molecular Sieves

Author

Stavitski, I., Weckhuysen, B.M., Čejka, J., Corma, A., Zones, S., Inorganic Chemistry and Catalysis, and Sub Inorganic Chemistry and Catalysis

Subjects
Operando spectroscopy, Process (engineering), Chemistry, Infrared spectroscopy, Nanotechnology, Biochemical engineering, Science, technology and society, Molecular sieve, Catalysis
Abstract

Scientists in the field of catalysis are in a perpetual pursuit of optimization of existing processes in terms of activity/selectivity as well as development of new ones. In many cases, trial-and-error modus operandi prevails upon the rational approach, even with a level of sophistication and knowledge modern science and technology delivers. In order to improve on this situation, catalyst scientists require better insight into the key stages of the reaction process and, in particular, the catalyst’s modus operandi. Armed with a rigorous understanding of this, it could then be possible to prepare the archetypal designer catalyst with the desired superior performance for the reaction in question. However, such information can only be obtained reliably by monitoring a catalyst ‘‘in action.’’ In order to do this, it is essential to adapt catalytic reactors and/or spectroscopic/scattering techniques to study the processes in real time – an approach that gives rise to the field of in situ or operando spectroscopy [1, 2].

Published
2013

77. Textural Characterization of Mesoporous Zeolites

Author

Zhang, L., van Laak, A.N.C., de Jongh, P.E., de Jong, K.P., Čejka, J., Corma, A., Zones, S., Inorganic Chemistry and Catalysis, and Sub Inorganic Chemistry and Catalysis

Abstract

Zeolites and related zeolite-analog materials have found major industrial applications as catalysts and adsorbents, especially in refinery and petrochemical processes where zeolite catalysts exhibit unique shape selectivity endowed by their crystalline yet highly porous structures with well-defined channels of molecular dimensions [1–5]. However, as one side effect of their microporous structure, zeolite catalysts often suffer from restricted diffusion of guest species [6, 7]. Mass transport to and from the active sites inside the micropores (known as configurational diffusion) is much slower than that of molecular and Knudsen diffusion, which has led to lower catalyst utilization, and sometimes fast deactivation due to coke formation. Different approaches have been proposed to alleviate the diffusion limitation and enhance the accessibility of the internal sites [8–21]. One strategy is to synthesize novel zeolitic structures with a larger pore size. Various large-pore zeolites and zeolite analogs have been obtained, for example, VPI-5 [22], UTD-1 [23], SSZ-53 and SSZ-59 [24], ITQ-15 [25], ITQ-21 [26], ITQ-33 [27], and ITQ-37 [28]. However, despite the fact that a considerable amount of knowledge has been gained on the formation mechanisms of zeolites and numerous types of theoretical structures have been proposed for predicative synthesis, synthesis by design of novel zeolite structure is still a challenging topic, and most new structures are discovered by trial-and-error processes.

Published
2013

80. Textural Characterization of Mesoporous Zeolites

Author

Zhang, L., van Laak, A.N.C., de Jongh, P.E., de Jong, K.P., Čejka, J., Corma, A., Zones, S., Inorganic Chemistry and Catalysis, and Sub Inorganic Chemistry and Catalysis

Subjects
Materials science, Knudsen diffusion, Chemical engineering, Restricted Diffusion, Diffusion, Mineralogy, Microporous material, Mesoporous material, Zeolite, Catalysis, Characterization (materials science)
Abstract

Zeolites and related zeolite-analog materials have found major industrial applications as catalysts and adsorbents, especially in refinery and petrochemical processes where zeolite catalysts exhibit unique shape selectivity endowed by their crystalline yet highly porous structures with well-defined channels of molecular dimensions [1–5]. However, as one side effect of their microporous structure, zeolite catalysts often suffer from restricted diffusion of guest species [6, 7]. Mass transport to and from the active sites inside the micropores (known as configurational diffusion) is much slower than that of molecular and Knudsen diffusion, which has led to lower catalyst utilization, and sometimes fast deactivation due to coke formation. Different approaches have been proposed to alleviate the diffusion limitation and enhance the accessibility of the internal sites [8–21]. One strategy is to synthesize novel zeolitic structures with a larger pore size. Various large-pore zeolites and zeolite analogs have been obtained, for example, VPI-5 [22], UTD-1 [23], SSZ-53 and SSZ-59 [24], ITQ-15 [25], ITQ-21 [26], ITQ-33 [27], and ITQ-37 [28]. However, despite the fact that a considerable amount of knowledge has been gained on the formation mechanisms of zeolites and numerous types of theoretical structures have been proposed for predicative synthesis, synthesis by design of novel zeolite structure is still a challenging topic, and most new structures are discovered by trial-and-error processes.

Published
2010
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91. Textural Characterization of Mesoporous Zeolites

Author

Inorganic Chemistry and Catalysis, Sub Inorganic Chemistry and Catalysis, Zhang, L., van Laak, A.N.C., de Jongh, P.E., de Jong, K.P., Čejka, J., Corma, A., Zones, S., Inorganic Chemistry and Catalysis, Sub Inorganic Chemistry and Catalysis, Zhang, L., van Laak, A.N.C., de Jongh, P.E., de Jong, K.P., Čejka, J., Corma, A., and Zones, S.

Published
2013

94. Švenekite, Ca[AsO2(OH)2]2, a new mineral from Jáchymov, Czech Republic

Author

Ondruš, P., primary, Skála, R., additional, Plášil, J., additional, Sejkora, J., additional, Veselovský, F., additional, Čejka, J., additional, Kallistová, A., additional, Hloušek, J., additional, Fejfarová, K., additional, Škoda, R., additional, Dušek, M., additional, Gabašová, A., additional, Machovič, V., additional, and Lapčák, L., additional

Published
2013
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96. Omezení Wittigovy-Hornerovy cyklizace fluorbutenolidové skupiny na 3-hydroxychinoline-2,4(2H,3H)-diony. Nové modifikace Perkowovy reakce s odstupující fluorovanou acyloxylovou skupinou.

Author

Pomeisl, K., Kvíčala, J., Paleta, O., Klásek, Antonín, Kafka, Stanislav, Kubelka, V., Havlíček, J., Čejka, J., Pomeisl, K., Kvíčala, J., Paleta, O., Klásek, Antonín, Kafka, Stanislav, Kubelka, V., Havlíček, J., and Čejka, J.

Abstract

3-(Fluoracyloxy)chinolin-2,4(1H,3H)-diony reagují s triethyl-fosfitem buď za vzniku produktu Perkowovy reakce nebo za vzniku odpovídajícího 4-ethoxychinolin-2(1H)-onu. V obou reakcích je odstupující skupinou fluorkarboxylátový anion. U odpovídajícího 3-(fluorjodacetoxy)derivátu toto pozorování vylučuje využití intramolekulární Wittigovy-Hornerovy syntézys k modifikaci chinolin-2,4(1H, 3H)-dionů cyklizací fluorované but-2-enolidové skupiny., 3-(Fluoroacyloxy)quinoline-2,4(1H,3H)-diones react with triethyl phosphite to afford either the product of the Perkow reaction or the corresponding 4-ethoxyquinolin-2(1H)-one. In both reactions, the fluorocarboxylate anion acts as the leaving group. For the corresponding 3-(fluoroiodoacetoxy) derivative this observation precludes the application of the intramolecular Wittig-Horner synthesis to modify quinoline-2,4(1H, 3H)-diones by the annulation of a fluorinated but-2-enolide moiety.

Published
2007

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