Julius Scherzer

Infrared spectra of ultrastable zeolites derived from type Y zeolites

Abstract An infrared spectroscopic study has been carried out on ultrastable zeolites derived from type Y zeolites and on their precursors. Both the hydroxyl stretching (3400 to 3800 cm −1 ) and the silica-alumina vibrational (300 to 1300 cm −1 ) regions of the spectra have been investigated. The effect of moisture content in the zeolite environment during calcination on the infrared spectrum of the zeolite has been established. An increase in moisture content at fixed calcination temperature results in additional absorption bands in the hydroxyl stretching region and in shifts to higher frequencies of absorption bands in the framework vibrational region, due primarily to dealumination of the zeolite framework. An increase in calcination temperature at fixed moisture content has a similar effect. Other effects observed are the suppression of dehydroxylation with increasing moisture content at temperatures up to 760 °C, and an increase in the degree of ordering of the zeolite structure under 100% steam at high temperatures. The last phenomenon is interpreted as being due to a structural rearrangement, involving silica migration into the vacancies created by the dealumination process. Pyridine adsorption experiments were done to determine the type of acid sites on ultrastable zeolites.

Cation positions in cerium X zeolites

Abstract The cation positions and the resulting changes, which were caused by the replacement of sodium ions by cerium ions, in the zeolite framework of cerium exchanged 13X-type molecular sieves, 0.3 Na2O · 13.0 Ce2O3 · 44.0 Al2O3 · 104.0 SiO2 · n H2O1, have been determined by structural studies using X-ray powder data. In the exchanged sieve ( a 0 = 25.10 ± 0.02 A ), in which nearly all of the remaining 2% of sodium oxide has been removed by (NH4SO4 exchange, cerium ions were found to partially occupy site S4 in the large cavity and site S2 in the sodalite cage. When this material was calcined at 540 ° C in a nitrogen atmosphere ( a 0 = 24.94 ± 0.02 A ), the cerium cations were found to migrate to sites S1, S2, and S5 with the majority of the cations being in S2. Site S1 is in the hexagonal prism and is the least accessible site. Upon dehydration of the material at 540 ° C in air ( a 0 = 24.86 ± 0.02 A ), however, the cations moved to sites S1 and S2 only, with the majority of them being in S2 sites. The three cations (on the average) per sodalite cage which occupied S2 sites displayed a strong repulsion for each other. This repulsion resulted in a significant distortion of the sodalite cage. The greater cationic repulsion observed when calcination was done in air versus a much lesser repulsion when calcination was done in a nitrogen atmosphere is due to the oxidation of at least 50% of the Ce3+ cations to the 4+ oxidation state. For the hydrated sample the occupancy factor of S4 sites is 0.66. The population parameter of S2 is 0.69 and 0.74 for the nitrogen calcined zeolite and for the air calcined zeolite with the corresponding closest CeO distances for this site being 2.56 and 2.66 A, respectively.

Ion exchanged ultrastable Y zeolites: I. Formation and structural characterization of lanthanum-hydrogen exchanged zeolites

Abstract The preparation, composition and structural characteristics of a variety of lanthanum-hydrogen exchanged ultrastable Y zeolites (La,H-USY) is described and discussed. A general discussion of reactions taking place between acidic metal salt solutions and USY zeolites is also presented. La,H-USY zeolites were prepared by two methods: (a) acid treatment of ultrastable Y zeolites at controlled pH followed by lanthanum exchange; (b) treatment of ultrastable Y zeolites with acidic solutions of lanthanum salts at controlled pH. The resulting materials have high thermal and hydrothermal stability. They possess both Bronsted and Lewis type acidity. The infrared spectra of La,H-USY zeolites in the OH stretching region and in the framework vibrational region are described. The spectra are similar to those of ultrastable Y zeolites. The effect of steaming on the zeolitic structure, as reflected in the infrared spectra, is discussed.

Zeolite-supported metal catalysts for Fischer-Tropsch reactions: I. A new preparation method

Abstract A new preparation method of zeolite-supported metal catalysts is described. The method is based on the reaction between a metal-exchanged zeolite and an anionic, metal-containing coordination compound, specifically a water-soluble, metal cyanide complex. The reaction product is an insoluble compound distributed throughout the zeolite. Subsequent reduction in hydrogen results in finely dispersed metal in the zeolite. The method described can be used in the preparation of single or polymetallic catalysts. A single metal catalyst is obtained when the metal in the exchanged zeolite is the same as the one in the coordination compound. If the metals are different, a bimetallic catalyst will result. The method can be used for the preparation of a variety of zeolite-supported metal catalysts. In this paper the preparation of catalysts to be used in Fischer-Tropsch reactions is described. The materials prepared have been characterized by infrared and TGA DTA methods.

Ion-exchanged ultrastable Y zeolites: II. Alkaline earth-exchanged zeolites

The preparation and structural characteristics of alkaline earth-exchanged ultrastable Y zeolites (MII, H-USY) are described and discussed. MII, H-USY zeolites were prepared at different exchange pH. These materials have good crystallinity and stability. Their thermal stability decreases with increasing ionic radius of the alkaline earth metal. The Bronsted acidity shows a similar trend. However, the affinity for zeolitic sites increases with ionic radius. The infrared spectra of MII, H-USY zeolites in the OH stretching region and in the framework vibrational region are described. Pyridine adsorption experiments indicate the presence of both Bronsted and Lewis acidity. Steaming results in decrease of Bronsted acidity, shrinking in unit cell size, further dealumination of the zeolitic framework, and cationic migration.