K.-H. Steinberg

Aromatization of ethane on platinum containing ZSM-5 zeolites

Abstract The conversion of ethane into aromatics on Pt/H-ZSM-5 zeolites starts at 670 K. The composition of the reaction products strongly depends on the temperature and gas space velocity (GHSV). Above 900 K the alkylaromatics formed preferentially at lower temperatures were dealkylated and disproportionated giving benzene and C 8+ aromatics as well. The reaction mechanism involves the primary dehydrogenation of ethane to ethene followed by oligomerization and aromatization. The influence of hydrogen on the reaction pathway is explained in terms of the concept of spillover.

Studies of the influence of a magnetic field on the diffusion of spilt-over deuterium on Y zeolites

After deuterium spillover from Pt supported on NaY zeolite onto NaY, the spilt-over particles diffuse into the HNaY part of a two-component Pt/NaY–HNaY sample where an H–D exchange of the OH groups takes place, as shown by diffuse-reflectance near-infrared spectroscopy, and where a reservoir of such activated spilt-over deuterium species is formed, remaining adsorbed after pumping off the D2 gas atmosphere at room temperature. The chief result is that on loading the sample with D2 in the presence of a magnetic field B perpendicular to the main direction of diffusion of the spilt-over particles, H–D exchange is less than without B, which leads to the conclusion that the diffusing spilt-over particles are electrically charged.

Conversion of Ethane into Aromatic Compounds on Zsm-5 Zeolites Modified by Zinc

Abstract H-ZSM-5 zeolites modified by zinc exhibit a high activity for the conversion of ethane into aromatics, even at the relatively low temperature of 773 K. The activity and selectivity of these catalysts are related to the zinc species introduced via various methods but, surprisingly, not to the acidic properties.

Type, stability, and acidity of hydroxyl groups of HNaK-erionites

Abstract The concentration and acid strength of the hydroxyl groups of a series of HNaK erionites have been investigated by means of temperature programmed activation (t.p.a.), temperature programmed desorption (t.p.d.) of ammonia, and transmission absorption i.r. spectroscopy. With an increasing degree of NH 4 + exchange, primarily Na + , at first, and, subsequently, K + cations are replaced. During activation of these materials, NH 3 desorbs in a temperature interval from 540 to 900 K, leading to hydroxyl groups. However, it is impossible to decompose NH 4 + quantitatively without dealumination, if the degree of NH 4 + exchange is higher than 85%. Five types of hydroxyl groups are present, characterized by i.r. bands at approximately 3741, 3691, 3660, 3618-3608, and 3566 cm −1 . The assignment of these bands is discussed. Only the OH groups represented by the bands at 3660, 3618–3608, and 3566 cm −1 adsorb ammonia under the conditions employed. The concentration and strength of the bridging hydroxyls (3618-3608 cm −1 ), associated with framework Al 3+ , increase with increasing degree of ion exchange.

I.r. and n.m.r. 1H longitudinal relaxation studies of the cation distribution in rare-earth and calcium exchanged Y zeolites

Abstract I.r. spectroscopy of OD vibration, lattice vibration and CO adsorption, together with n.m.r. longitudinal relaxation measurements of adsorbed water, were used to study the cation distribution in dehydrated calcium and rare-earth (RE3+) Y zeolites. In this Paper it is shown that in CaNaY zeolites the Ca2+ ions are selectively located in SI positions up to an exchange degree of 60%. The RE3+ ions introduced consecutively into CaNaY are directed to sites in the supercages. This directing effect depends on the order of ion exchange. In dehydrated RENaY the RE3+ ions preferentially occupy SI′ sites. Depending on the exchange and pretreatment conditions, there are different REO species in RENaY and RECaNaY zeolites. The unexpected high activity of 0.28RE0.60CaNaY in the isomerization of light gasoline is explained in terms of the observed cation distribution.

Influence of platinum dispersion on the ethane aromatization on Pt/H-ZSM-5 zeolites

The influence of the platinum dispersion and of the metal particle size distribution on the catalytic activity in the ethane aromatization over Pt/H-ZSM-5 zeolites was investigated at 823 K in a plug flow reactor. Comparatively high platinum dispersion and low average particle size caused by impregnation of the zeolite with ethanolic H2PtCl6 solution lead to a close vicinity of metal and acid sites which is accompanied by an increased electrophilicity of the metal. Such a catalyst posesses a higher deactivation rate than those with more bulky platinum. The rapid deactivation is effected by a higher stability of the chemisorption complex metal-ethylene and by favouring of consecutive reactions of olefinic intermediates towards coke information.

Infrared spectroscopic study on the location of the hydroxyl groups in erionite

Abstract The location of hydroxyl groups in synthetic erionite was studied by i.r. spectroscopy using adsorption of ammonia and n-hexane and ione exchange with caesium. The OD-bands at 2640 and 2670 cm −1 were assigned to hydroxyl groups located in the gmelinite cage and that at 2710 cm −1 to groups located in the small cavities inaccessible for hydrocarbons and large ions.

Aromatization of ethane on Pt and Pd supported Zn- and Mn-ZSM-5 zeolites

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.AbstractИсследовали 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.

On the position of rare earth cations in zeolite Y

The number Ns′ of rare earth (RE) ions located in the supercage can be derived from the longitudinal proton n.m.r. relaxation time T1 of water adsorbed in 0.64 RENaY zeolite. This is because about 70% of these RE ions are paramagnetic and thus dominate the proton T1. The results do not agree completely with X-ray diffraction studies, but Ns′, is in good agreement with recent results of Lee and Rees.

Influence of hydrogen on the aromatization of ethane over Pt/H-ZSM-5 zeolite

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.AbstractВлияние 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.