Platinum-alumina Catalysts Research Articles

Effect of the conditions of n-decane dehydrogenation on deactivation of the alumina-platinum catalyst

1. Deactivation of the alumina-platinum catalyst in the n-decane dehydrogenation increases with an increase in temperature (430–500°C), and decreases with an increase in either the presence of hydrogen (1·105−2.3·105 Pa) or the molar dilution of the hydrocarbon with hydrogen (4–16). 2. Under all conditions, the degree of deactivation of the catalyst, the accumulation of carbon on the catalyst surface, and combined yield of olefins and diolefins vary in parallel. 3. The degree of deactivation of the catalyst in n-decane dehydrogenation depends on both the amount of coke formed on the catalyst surface, decreasing as the latter increases. 4. Any alteration of parameters (temperature, space velocity, partial pressure of hydrogen, hydrogen dilution) which increases the yield of monoolefins and diolefins in the n-decane dehydrogenation reduces the stability of operation of the catalyst. By varying two of these parameters simultaneously it is possible to increase the yield of unsaturated hydrocarbons and to decrease the degree of deactivation of the catalyst.

The combustion of methane on platinum-alumina fibre catalysts—III. The kinetics of the water gas shift reaction

The combustion of methane on platinum-alumina fibre catalysts—III. The kinetics of the water gas shift reaction

X-ray diffraction studies of reforming platinum-alumina catalysts in a high-temperature chamber

X-ray diffraction studies of platinum-alumina catalysts in a high-temperature chamber indicate that in a stream of hydrogen starting from 550–600 K, platinum is practically completely reduced. In several cases at higher temperatures a platinum hydride is also formed.

Mechanism of the aromatization of n-hexane on alumina-platinum catalysts with additions of cadmium and rhenium

1. The influence of additions of Re and Cd to an alumina-platinum catalyst on the mechanism of the aromatization reaction has been studied with the aid of the kinetic isotope method. 2. The formation of benzene from hexane on alumina-platinum catalysts with addition of Re and Cd takes place with the participation both of hexene and of methylcyclopentane. Cyclohexane is not formed under the reaction conditions. 3. Additions of Re and Cd do not appreciably change the routes of the aromatization of n-hexane. The addition of Cd somewhat inhibits the reactions taking place on the acidic centers of the catalyst-in particular, the dehydroisomerization of five-membered rings to aromatic systems. Consequently, the introduction of Re and Cd somewhat changes the relative roles of each of the routes mentioned in the overall benzene-forming process. 4. On alumina-platinum catalysts, hexenes participate not only in aromatization but also in the C5-dehydrocyclization reaction, the contributions of the hexenes to the two reactions being comparable.

Influence of the thermal treatment of platinum alumina catalysts with exhaust gases on their activity in cyclopropane hydrogenation

The activity of platinum/alumina catalysts in cyclopropane hydrogenation has been investigated. Catalysts heated in exhaust gases are considerably less active in cyclopropane hydrogenation as compared to samples calcined in air. A relatively stable modification of the metallic surface is formed, probably as a result of coke or poison deposition.

Performance of periodic pulse technique. 1. Dehydrogenation of cyclohexane on a platinum-alumina catalyst.

Performance of periodic pulse technique. 1. Dehydrogenation of cyclohexane on a platinum-alumina catalyst.

Catalytic and infrared demonstrations of the effect of hydrogen spillover on a gel of silica

A silica aerogel was prepared by hydrolysis of tetramethylsilane in methanol and evacuated; it was used with the resulting O-CH/sub 3/ surface groups or after calcination to convert these groups into OH groups. It was activated by hydrogen spillover during hydrogen treatment at 430/sup 0/C in contact with platinum-alumina catalyst as previously described for alumina activation The hydrogen taken up by the silica (900 sq m/g) was approx. 1.4 cc/g at 200/sup 0/C. The silica was then active for the hydrogenation of ethylene to ethane in excess hydrogen at 200/sup 0/C, and the catalyst was not deactivated by evacuation at 200/sup 0/C, exposure to air at 25/sup 0/-400/sup 0/C, or the introduction of ammonia. If the silica with spilled-over hydrogen was evacuated, it catalyzed the reaction of benzene in excess hydrogen to ethane via an acetylene intermediate; if the spilled-over hydrogen was not evacuated, a small amount of cyclohexane and cyclohexene, corresponding to the amount of hydrogen spillover, were also formed. In the absence of hydrogen, only acetylene was formed from benzene. The reactions of 1,3-cyclohexadiene corresponded to those of benzene, but 1,4-cyclohexadiene yielded only acetylene in the presence or absence of hydrogen. The surface species generated by hydrogen spillovermore » were studied by IR spectroscopy.« less

Poisoning by carbon monoxide in the hydrogen exchange reaction between deuterium gas and water preadsorbed on a platinum-alumina catalyst

Poisoning by carbon monoxide in the exchange reaction between deuterium and the water preadsorbed on a platinum-alumina catalyst was studied, by measuring not only the rate of reaction but also its kinetic behavior and the adsorption of reactants on the catalyst surface. The shape of the poisoning curve is closely associated with the kinetic behavior and exhibited an abrupt change on freezing the adsorbed water below 273 K. When the rate is proportional to deuterium pressure and independent of the amount of water adsorbed, the exchange rate dropped sharply by carbon monoxide adsorbed of a few percent coverage without any marked changes in the amount and the rate of hydrogen adsorption on the platinum surface. However, at temperatures lower than 273 K and at higher deuterium pressures, the rate depends not on the deuterium pressure but on the amount of water adsorbed. The migration of hydrogen in or through the adsorbed water is seemingly sufficiently suppressed by freezing to control the overall reaction rate. In this case, a small amount of adsorption of carbon monoxide did not show any toxicity, but then a steep poisoning started accompanying a change in the kinetic behavior. It was accordingly demonstrated that the mechanism of the reaction may be better understood by studying poisoning and measuring adsorption, overall rate, and kinetic behavior.

Aromatization of n-octane on an alumina-platinum oxide catalyst activated by oxides of alkaline-earth elements

Aromatization of n-octane on an alumina-platinum oxide catalyst activated by oxides of alkaline-earth elements

Interaction of oxygen and hydrogen with platinum in pulse gas chromatography

The interaction of oxygen and hydrogen with the surfaces of platinum black, platinum-silica and platinum-alumina catalysts within the temperature range 196–970°K was examined by pulse gas chromatography. Chemisorption of oxygen and hydrogen was carried out on a “clean” platinum surface and titrations of the oxidized surface with hydrogen were performed together with those of the reverse reaction, i.e., titration of the reduced surface with oxygen.We were able to define the extent of slow, reversible hydrogen sorption within a wide temperature range, desorption of oxygen from the platinum surface and the formation of an oxide multilayer at higher temperatures. The results indicate that the stoichiometries of the surface interactions between platinum and oxygen and between platinum and irreversibly chemisorbed hydrogen are the same and approximate to unity: O/Pt2 ≈ H/Pt5 ≈ 1. The temperature range 300–570°K is suitable for determining platinum dispersions by means of oxygen and hydrogen chemisorption.

Transformations of cyclohexanol on a platinum-alumina catalyst: Effect of poisons

Vapor-phase dehydrogenation/dehydration of cyclohexanol has been investigated over a bifunctional platinum-alumina catalyst. The products of the reactions are cyclohexane, cyclohexene, benzene, cyclohexanone and phenol. Studies using the poisons CO, H2S and NH3 have been made in order to elucidate the nature of the sites responsible for the formation of the various products.

Diluent gas effect in SO 2 oxidation over a platinum-alumina catalyst

Diluent gas effect in SO 2 oxidation over a platinum-alumina catalyst

ChemInform Abstract: REACTIONS OF BENZENE, CYCLOHEXANE AND N‐HEPTANE DURING THERMODESORPTION FROM PLATINUM ALUMINA CATALYSTS

Chemischer InformationsdienstVolume 8, Issue 22 Preparative Organic Chemistry ChemInform Abstract: REACTIONS OF BENZENE, CYCLOHEXANE AND N-HEPTANE DURING THERMODESORPTION FROM PLATINUM ALUMINA CATALYSTS W. WALKOV, W. WALKOVSearch for more papers by this authorM. W. GENKIN, M. W. GENKINSearch for more papers by this authorA. W. SKLYAROV, A. W. SKLYAROVSearch for more papers by this authorJ. VOELTER, J. VOELTERSearch for more papers by this author W. WALKOV, W. WALKOVSearch for more papers by this authorM. W. GENKIN, M. W. GENKINSearch for more papers by this authorA. W. SKLYAROV, A. W. SKLYAROVSearch for more papers by this authorJ. VOELTER, J. VOELTERSearch for more papers by this author First published: May 31, 1977 https://doi.org/10.1002/chin.197722086AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume8, Issue22May 31, 1977 RelatedInformation

Alkylation of isobutane by ethylene on Al 2O 3 modified with BF 3: Yu. I. Kozorezov and V. I. Lisin, Neftekhimiya 17, No. 3, 396–400, 1977

1.1. Five isoheptanes and three alkylcyclopentanes were studied in the presence of “acid” and “alkali” alumina-platinum catalyst samples at atmospheric pressure in hydrogen at temperatures of 370 to 520° under microcatalytic pulse conditions.2.2. Aromatization of isoheptanes takes place as a result of C5 and C6 dehydrocyclization.3.3. It was found that the structure of the initial isoheptane influenced the relative rôle of C5 and C5 dehydrocyclization during aromatization.

ChemInform Abstract: ACTIVATION OF PLATINUM‐ALUMINA CATALYSTS FOR THE HYDROGENATION OF AROMATIC HYDROCARBONS

AbstractPlatin‐Aluminiumoxidkatalysatoren, die während der Imprägnierstufe chloriert wurden (0,4 ‐ 0,87% Chlorgehalt), erwiesen sich beim Hydrieren von Benzinfraktionen als deutlich aktiver als entsprechende nicht chlorierte Katalysatoren.

Mechanisms of methylcyclopentane ring opening over platinum-alumina catalysts

Ring opening of methylcyclopentane has been investigated over mono-functional platinum/ silica and acidic alumina catalysts as well as a dual-functional platinum/alumina reforming catalyst. Both platinum and the acidic alumina catalyze ring opening. The acid-catalyzed ring-opening reaction occurs by direct opening of the methylcyclopentane ring and is inhibited by methylcyclopentenes. The acid-catalyzed reaction leading to an acyclic olefin is proposed to proceed via a protonated ring structure and an acyclic carbonium ion.

Characteristics of mechanism for formation of cyclopentanes on alumina-platinum catalysts

1. The catalytic transformations of 3-methylpentane and 3-methy1-2-pentene were studied on the bifunctional catalyst Pt/Al2O3 (0.6% of Pt) in the range 275–400°. 2. In a H2 stream the Pt/Al2O3 catalyst leads to the cyclization of 3-methy1-2-pentene and 3-methyl-pentane to methylcyclopentane. It was discovered that H2 plays an important role in these transformations. 3. The theory was expressed that on Pt/Al2O3 the reaction for the C5-dehydrocyclization of alkanes proceeds, even if only partially, via the direct closure of the five-membered ring by the scheme; alkane → cyclane.

Aromatization of isoheptanes in the presence of an alumina-platinum catalyst

1. 1. Five isoheptanes and three alkylcyclopentanes were studied in the presence of “acid” and “alkali” alumina-platinum catalyst samples at atmospheric pressure in hydrogen at temperatures of 370 to 520° under microcatalytic pulse conditions. 2. 2. Aromatization of isoheptanes takes place as a result of C 5 and C 6 dehydrocyclization. 3. 3. It was found that the structure of the initial isoheptane influenced the relative rôle of C 5 and C 5 dehydrocyclization during aromatization.

Study of the activity of alumina-platinum catalysts with varying metal contents in model reactions of benzene hydrogenation

Study of the activity of alumina-platinum catalysts with varying metal contents in model reactions of benzene hydrogenation

Hydrogenation of aromatic hydrocarbons in 140?240�c cut on platinum-rhenium catalyst

1. A study has been made of the conditions for hydrogenation of a 140–240 °C straight-run fraction on platinum-rhenium catalyst. The optimal process regime has been found, giving almost 90% conversion of the aromatic hydrocarbons. 2. With alumina-platinum catalyst, a pressure of 40 kg/cm2 and a temperature of 300°C are required to achieve this conversion.