Zeolite L

Zeolite A [1318-02-1] Zeolite (aluminosilicate) Zeolite catalysts Zeolite L Zeolites... 

Aromatic brominations have been mainly carried out using X, Y and L zeolites. Improved para/ortho ratios have been observed upon brominating halobenzenes, benzyl halides, and biphenyl. The side product HBr leads to decreased activity and selectivity. This problem has been addressed by adding scavengers, by working in the gas phase, and by applying oxidative bromination. 

The effect of crystallite size and shape of K-L zeolite on the dispersion of Pt was examined by a variety of techniques by Resasco and coworkers [143], They obtained multiple overlapping CO bands on these samples and were able to assign them to Pt clusters located inside the zeoHte pores (<2050cm ), near the pore mouth (2050-2075 cm" ) and outside the pores (>2075 cm" ). They were able to correlate high -octane aromatization activity with the K-L zeolite samples with short channels where most of the Pt is inside the pores. 

McCulloch, B. and Oroskar, A.R. (1990) Process for extracting 2,5-dichlorotoluene from isomer mixtures with sodium-L zeolite adsorbents. U.S. Patent 4,922,040. 

A reasonable distribution of cations on the six kinds of site D can be described as follows. A cation selectively occupies the site with the strongest cation affinity among the available sites. When there are several kinds of cations, there occurs competition among them to occupy the favorable site. In the case of (K,H)-L zeolite, K" " ions should eliminate protons in the competition. The residual K ions in (H,K)-L must preferentially occupy sites B and B . Since the cation affinity of site C is considered to be similar to that of site D, site C is assumed to be occupied... 

Patents cover a new reforming catalyst based on L-zeolite which gives a significantly higher yield of BTX, especially benzene, from light paraffinic feeds (11). Other new zeolites (12) may also offer advantages over the traditional reforming catalyst supports. 

Hay, R. L., Zeolites and Zeolitic Reaction in Sedimentary Rocks, Geol. Soc. Amer., Spec. Paper, (1966) 85. 

Physicochemical properties of L zeolites and of clinoptilolite were studied by adsorption, chromatographic, spectral, and ther-mogravimetric methods. The sodium form of L zeolite is characterized by better adsorption with respect to water and benzene vapor and by higher retention volumes of C C hydrocarbons and CO than potassium and cesium forms. The activation energy of dehydration determined by the thermogravimetric method decreases on going from the sodium to cesium form of L zeolite. When calcium is replaced by potassium ions in clinoptilolite, the latter shows a decreased adsorption with respect to water vapor. The infrared spectra of the L zeolite at different levels of hydration show the existence of several types of water with different bond characters and arrangements in the lattice. 

TTigh silica zeolites attract great attention since they are characterized by relatively high thermal stability and considerable acid resistance. Physicochemical properties of high silica zeolites, despite a number of investigations, have not been sufficiently studied. The same is true for L- and clinoptilolite zeolite. The data on synthesis, structure, adsorption properties, decationization, dealuminization, adsorption heats, and other properties of the above-mentioned zeolites have been given (1-15). Results of studies of physicochemical properties of L zeolites and of natural and modified clinoptilolite are given here. 

We have studied the potassium form of zeolite L (batch 385-386), the same zeolite enriched with sodium and cesium ions (NaL and CsL), and a sample of potassium L-zeolite (sample A). Both zeolites were experimental batches. The chemical composition of dehydrated zeolites is given in Table I. 

Natural zeolite was enriched with potassium ions and dealuminized. Enrichment of exchangeable ions of L zeolites and of clinoptilolite was done by multiple treatment with 0.52V solutions of the corresponding nitrates. Decationization and dealuminization were done by treating the natural zeolite with solutions of hydrochloric acid 0.25-12.02V. The Si02/Al203 ratio increased from 8.0 to 69.5, and the CaO content decreased from 6.30 to 1.00 wt % (Table II). 

We studied adsorption properties of L-zeolites with respect to water and benzene vapors. The experimental data are given as isotherms for... 

Potassium, sodium, and cesium forms of the L zeolite were studied by the thermogravimetric method. There is an endothermal effect on the initial potassium zeolite KL-DTA curve within 50°-300°C caused by the loss of adsorbed water. Most of the water (15.1%) is lost in this narrow... 

Zeolite catalysts in many forms are used for important commercial processes. The studies were extended to L zeolites, mordenite, erionite, and dealuminated faujasites and mordenites. More attention is paid now to zeolites with univalent and multivalent cations and to multicomponent catalysts. Among these some important examples are the tellurium-containing catalyst for hydrocarbon dehydrocyclization (42), the difunctional Ni- and Pd-zeolite catalysts for benzene hydrodimerization to phenylcyclohexane (42), the catalyst for the hydrogenation of phenol cyclohexanol (44), the 4% Ni/NaY which forms butanol, 2-ethylhexanol, 2-ethylhexanal, and 2-ethylhexanol from a mixture of n-butyraldehyde and hydrogen. 

In this paper, the results of the isomerization of hexane, heptane and octane over a Mo2C-oxygen-modified-catalyst, a Mo03-carbon-modified catalyst and a Pt//l-zeolite catalyst, at atmospheric pressure, are presented. Also, the results for a conventional Pt/Al203 catalyst are presented for the isomerization of hexane. Then, the effect of pressure on the isomerization of heptane and octane over the molybdenum catalysts and the Pt//l-zeolite catalyst is shown. Finally, the ability of the molybdenum catalysts to catalyse the isomerization reaction at high conversion with high selectivity even with hydrocarbons larger than hexane is demonstrated this is not possible over the Pt catalysts. The differences between the catalysts are discussed in terms of the reaction mechanisms. 

The effect of pressure on the isomerization of n-heptane and n-octane was determined over the Pt//l-zeolite, Mo2C-oxygen-modified and M0O3-carbon-modified catalysts. The weight hour space velocity (WHSV) was changed with the pressure to keep the conversion at a similar level, enabling the effect on the isomerization selectivity and the product distributions to be seen. Other conditions were kept constant. 

To improve process economics, further work is needed to improve catalyst lifetimes. A more stable system employed a noble metal-loaded potassium L-zeolite catalyst for the condensation of ethanol with methanol to produce a 1-propanol and 2-methyl-l-propanol (US patent no. 5,300,695) (18). However, yields were small compared with the large amounts of CO and C02 produced from the methanol. More recently, Exxon patented a noble metal-loaded alkali metal-doped mixed metal (Zr, Mn, Zn) oxide (US patent nos. 6,034,141 and 5,811,602) (19,20). The catalyst was used in a syngas atmosphere. As with other catalysts, the higher temperatures resulted in decomposition of methanol. Changes in catalyst composition were noted at higher temperatures, but the stability of the catalyst was not discussed. Recently, compositions including Ni, Rh, Ru, and Cu were investigated (21,22). 

The situation was not so simple since similar results, conversion and selectivity, were obtained when comparing Ti-Y with the TiC>2-P25 catalyst from Degussa. Again, Ti-free materials were also found to be active. ZSM-5, Mordenite and L zeolites were shown to have nearly comparable glucose conversions (around 30%) and gluconic acid selectivity (around 20%), whereas Y and MCM-41 zeolites were found to be less active, but more selective, particularly in the case of Y (27%). Although the activity of the Ti-free Y catalyst is lower than that of the Ti-Y catalyst, a similar selectivity in gluconic acid is obtained for both catalytic materials, but the selectivity in other acids is less over the Ti-Y catalyst. 

The characteristic properties of zeolites, namely thermal stability, shape selectivity and variable acidity and/or basicity, render them an attractive host for halogenation as well as other organic reactions122,123. Unfortunately, irreversible damage is caused to zeolites upon exposure to wet hydrogen halides which results in loss of catalytic activity. Nonetheless, there are numerous reports on the application of X, Y and L zeolites, sometimes exchanged with various metals, in halogenation reactions in addition to isomerizations and separation of alkyl and aryl halides. 

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