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  • 1
    ISSN: 0924-2031
    Keywords: Diffuse reflectance ; Glass-covered samples ; Hydrogen spillover ; Infrared spectrometry ; Zeolites
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract Влияние водорода на активность и селективность цеолита Pt/H-ZSM-5 в ароматизации этана сказывается так, что он благоприятствует гидрогенолизу и подавляет дегидрирование и крекинг. H2, образующийся в ходе реакции, ингибирует ароматизацию.
    Notes: Abstract Hydrogen influences the activity and selectivity of a Pt/H-ZSM-5 zeolite in ethane aromatization by favoring hydrogenolysis and suppressing dehydrogenation and coking. H2 formed during the reaction inhibits the aromatization activity.
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  • 3
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract Studies of the infra-red spectra of the framework of RECaNaY and RENaY zeolites after vacuum dehydration indicate that Ca2+ ions occupy SI positions and direct RE3+ into the supercavities. The 640 cm−1 band is attributed to Ca2+ ions located in hexagonal prisms. (sym and) asym of TO4 modes are observed to be split.
    Notes: Abstract Изучены спектры колебаний каркаса цеолитов типа У с обменными катионами Ca2+ и РЗЭ3+. Найдено, что Ca2+ предпочтительно занимают места SI и направляют РЗЭ3+ в большую полость. Полоса 640 cm−1 приписана катиону Ca2+, находящемуся в гексагональной призме. Найдено расщепление полос симметричных и антисимметричных колебаний TO4.
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  • 4
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract Исследовали каталитическое поведение бифункциональных Zn- и Mn-ZSM-5 цеолитов, содержащих Pt или Pd. Результаты обсуждают, сравнивая электронные взаимодействия между металлическими центрами и электроно-акцепторами носителя.
    Notes: Abstract The catalytic behavior of bifunctional Pt- or Pd-containing Zn- and Mn-ZSM-5 zeolites in ethane aromatization was investigated. The results are discussed considering the electronic interaction between metallic sites and electron acceptor sites of the support.
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  • 5
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract В проточном реакторе исследовали влияние температуры реакции и объемной скорости на активность и селективность Ru/H-ZSM-5 в ароматизации этана.
    Notes: Abstract The influence of the reaction temperature and of the space velocity on the activity and selectivity in the aromatization of ethane on Ru/H-ZSM-5 was investigated in a flow reactor.
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  • 6
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Hydroxide Groups on Zeolites. III. Properties of Hydroxide Groups on ZnNaY, CuNaY, NiNaY, and CrNaY ZeolitesThe properties of hydroxide groups in dependence on the degree of exchange were studied by IR spectroscopy of ZnNaY, CuNaY, NiNaY, and CrNaY zeolites. Five kinds of hydroxide groups occur on these zeolites: Hydroxid groups limiting the lattice, 3 kinds of structural hydroxide groups, and MeOH+ groups. These are the same kinds of hydroxide groups as exist on alkaline earths-Y-zeolites. Some of the OH groups act as acid Brönsted centers. The number of acid Brönsted centers reaches maximum values at degrees of exchange of 40-50% after a pretreatment at 300-400°C. The zeolitic structure is partially destroyed in ZnNaY, CuNaY, and especially CrNaY, at high degree of exchange.
    Notes: An ZnNaY-, CuNaY-, NiNaY- und CrNaY-Zeolithen wurden die Eigenschaften der Hydroxidgruppen in Abhängigkeit vom Austauschgrad infrarotspektroskopisch untersucht. An diesen Zeolithen treten fünf Arten von Hydroxidgruppen auf, nämlich gitterbegrenzende Hydroxidgruppen, drei Arten von strukturellen Hydroxidgruppen und MeOH+-Gruppen. Dabei handelt es sich um die gleichen Arten von Hydroxidgruppen wie an Erdalkali-Y-Zeolithen. Einige der OH-Gruppen wirken als saure Brönsted-Zentren. Die Zahl der sauren Brönsted-Zentren erreicht Maximalwerte bei Austauschgraden von 40-50% nach einer Vorbehandlung bei 300-400°C. Bei ZuNaY-, CuNaY- und besonders stark bei CrNaY-Zeolithen wird bei hohen Austauschgraden die Zeolithstruktur teilweise zerstört.
    Additional Material: 7 Ill.
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  • 7
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Hydroxide Groups on Zeolites. I. Number and Properties of Hydroxide Groups on CaNaY and MgNaY Zeolites of Different Degree of Ion ExchangeThe number of hydroxide groups was studied on CaNaY and MgNaY zeolites by D2 exchange in dependence on the degree of exchange, and their properties were examined by infrared spectroscopy. At these zeolites there exist five types of hydroxide groups which differ by their concentration, their acidic strength, and their thermal stability. The OH-groups are produced mainly by dissociative chemisorption of water at the bivalent cations. The concentration of OH groups shows a characteristic dependence on the degree of ion exchange. There are OH groups which are strongly acid BRÖNSTED centers, capable of protonisation of pyridine, and others which are only capable of weak interactions with pyridine. The number of the acid BRÖNSTED centers increases with the degree of ion exchange analogous to the total number of the hydroxide groups and is highly dependent on the species of the cations exchanged and on the preheating temperature. Compared with CaNaY zeolites, MgNaY zeolites posess a greater number of hydroxide groups which are thermally more stable.
    Notes: An CaNaY- und MgNaY-Zeolithen wurden in Abhängigkeit vom Austauschgrad durch D2-Austausch die Zahl und infrarotspektroskopisch die Eigenschaften der Hydroxidgruppen untersucht. Es existieren an diesen Zeolithen fünf Arten von Hydroxidgruppen, die sich in ihrer Konzentration, ihrer Säurestärke und ihrer thermischen Stabilität unterscheiden. Die OH-Gruppen entstehen vorwiegend durch dissoziative Chemisorption von Wasser an den zweiwertigen Kationen. Die Konzentration der OH-Gruppen hängt charakteristisch vom Austauschgrad ab. Es gibt OH-Gruppen, die stark saure BRÖNSTED-Zentren sind und Pyridin protoisieren können, und solche, die nur schwache Wechselwirkung mit Pyridin eingehen können. Die Zahl der sauren BRÖNSTED-Zentren steigt analog der Gesamtzahl der Hydroxidgruppen mit dem Austauschgrad an, sie hängt von der Art der eingetauschten Kationen und der Vorerhitzungstemperatur stark ab. MgNaY-Zeolithe besitzen mehr und thermisch stabilere Hydroxidgruppen als CaNaY-Zeolithe.
    Additional Material: 6 Ill.
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  • 8
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Hydroxide Groups on Zeolites. II. Number and Properties of Hydroxide Groups on CeNaY and HNaY Zeolites of Different Exchange DegreeThe number of hydroxide groups on CeNaY and HNaY zeolites was examined by D2 exchange, and their properties in dependence of the cation exchange degrees were studied by IR spectroscopy. On CeNaY zeolites there exist six kinds and on HNaY zeolites at least seven kinds of hydroxide groups.On the CeNaY zeolites, the hydroxide groups are produced by dissociative chemisorption of water on Ce3+ ions. Their total number increases continuously with increasing exchange degree. Some of the hydroxide groups are acid BRÖNSTED centers whose number increases with increasing exchange degree and decreases with the temperature of preheating increasing to about 600°C.On the HNaY zeolites, the hydroxide groups are produced by thermal decomposition of the NH+4 ions, by dealumination and interaction of the Al3+ ions produced in this way in the place of cations with water. Above the threshold value of 35% the total number of the hydroxide groups increases very rapidly with increasing exchange degree. One part of the hydroxide groups decreasing with increasing exchange degree acts as acid BRÖNSTED centers. The number of these centers does not decrease until at preheating temperatures above 450°C.
    Notes: An CeNaY- und HNaY-Zeolithen wurden durch D2-Austausch die Zahl und infrarotspektroskopisch die Eigenschaften der Hydroxidgruppen in Abhängigkeit vom Kationenaustauschgrad untersucht. Es existieren an CeNaY-sechs Arten und an HNaY-Zeolithen mindestens sieben Arten von Hydroxidgruppen.An den CeNaY-Zeolithen entstehen die Hydroxidgruppen durch dissoziative Chemisorption von Wasser an Ce3+-Ionen. Ihre Gesamtzahl wächst kontinuierlich mit steigendem Austauschgrad. Einige der Hydroxidgruppen sind saure BRÖNSTED-Zentren, deren Zahl mit steigendem Austauschgrad wächst und mit steigender Vorerhitzungstemperatur bis etwa 600°C sinkt.An den HNaY-Zeolithen entstehen die Hydroxidgruppen durch thermische Zersetzung der eingetauschten NH+4-Ionen und mit wachsendem Austauschgrad zunehmend durch das Herauslösen von Gitteraluminium und Wechselwirkung der so entstehenden Al3+-Ionen auf Kationenplätzen mit Wasser. Die Gesamtzahl der Hydroxidgruppen wächst oberhalb des Schwellenwertes von 35% sehr stark mit steigendem Austauschgrad an. Ein mit steigendem Austauschgrad abnehmender Anteil der Hydroxidgruppen wirkt als saure BRÖNSTED-Zentren, deren Zahl erst bei Vorerhitzungstemperaturen oberhalb von 450°C abnimmt.
    Additional Material: 13 Ill.
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  • 9
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Hydroxide Groups on Zeolites. IV. Formation of Hydroxide Groups by Reduction of Y-Zeolites Containing Transition Metal IonsThe formation of hydroxide groups as result of the reduction is studied by IR spectroscopy on NiNaY, CuNaY, and ZnNaY zeolites. After transformation of the OH groups into OD groups it was found that D2 reduces the transition metal ions at 350°C and that simultaneously the concentrations of two types of the hydroxides groups which are already present before this treatment are increased markedly, viz. the concentration of an acid species and that of a weakly acid species. In NiNaY and CuNaY zeolites, the reduction at 350°C proceeds much more slowly than in ZnNaY zeolites. The reduction of ZnNaY zeolites is connected with their transformation to ultrastable zeolites.
    Notes: An NiNaY-, CuNaY- und ZnNaY-Zeolithen wurde infrarotspektrospisch die Entstehung von Hydroxidgruppen bei der Reduktion untersucht.Nach Umwandlung der OH-Gruppen in OD-Gruppen wurde gefunden, daß D2 bei 350°C die übergangsmetallionen reduziert und gleichzeitig die Konzentration von zwei der bereits vorhandenen Arten von Hydroxidgruppen wesentlich erhöht wird, nämlich die einer sauren und einer nur schwach sauren Art. Bei NiNaY- und CuNaY-Zeolithen erfolgt die Reduktion bei 350°C sehr viel langsamer als bei ZnNaY-Zeolithen. Die Reduktion von ZnNaY-Zeolithen ist mit deren Umbildung zu ultrastabilen Zeolithen verbunden.
    Additional Material: 5 Ill.
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  • 10
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: In order to elucidate the mode of alkali bonding on Al2O3 surfaces, η-Al2O3 has been modified in nonaqueous, isopropanolic suspension by increasing amounts of sodium isopropylate. Acidimetric, catalytic activity and IR-spectroskopic measurments reveal that alkali, fixed from nonaqueous solution on Al2O3 catalysts, poisons only the acid surface centres; first, strongly acidic BR∅NSTED centres, then Lewis centres and, finally, weakly acidic OH groups. The dehydration of isopropanol seems to be due to two types of active centres: strongly acidic BR∅NSTED centres, and LEWIS centres acting synergistically together with weakly acidic OH groups. For the cracking of cumene, only the OH groups appear to be catalytically active.
    Notes: Um Aussagen über die Art der Alkalibindung auf Al2O3-Oberflächen treffen zu können, wurde η-Al2O3 in isopropanolischer Suspension mit steigenden Mengen Natriumisopropylat modifiziert. Durch Messung der Acidität, der katalytischen Aktivität und durch IR-spektroskopische Untersuchungen konnte festgestellt werden, daß das Alkali, wenn es aus nichtwäßriger Lösung auf Al2O3-Katalysatoren aufgetragen wird, nur die sauren Zentren der Oberfläche vergiftet. Mit zunehmender Alkalikonzentration werden stark saure Brönsted-Zentren, Lewis-Zentren und schwach saure OH-Gruppen in dieser Reihenfolge definiert vergiftet. Aus der Abhängigkeit der katalytischen Aktivität von der Alkalikonzentration wird geschlossen, daß bei der Isopropanoldehydratisierung zwei Arten aktiver Zentren wirksam sind, nämlich stark saure Brönsted-Zentren und gemeinsam mit schwach sauren OH-Gruppen wirkende LEWIS-Zentren. Für die Cumolspaltung scheinen nur die OH-Gruppen katalytisch aktiv zu sein.
    Additional Material: 5 Ill.
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