Molecular sieves early investigations

Characteristics of attrition and adsorption were investigated to remove CO2 in fluidized hed using activated carhon, activated alumina, molecular sieve 5 A and molecular sieve 13X. For every dry sorbent, attrition mainly still occurs in the early stage of fluidization and attrition indexs(AI) of molecular sieve 5A and molecular sieve 13X were higher than those of activated carbon and activated alumina. Percentage loss of adsorption capacity of molecular sieve 5A and molecular 13X were 14.5% and 13.5%, but that of activated carbon and activated alumina were 8.3% and 8.1%, respectively. Overall attrition rate constant (Ka) of activated alumina and activated carbon were lower than other sorbents. 

The reaction mechanism for the conversion of methanol to hydrocarbons over molecular sieve catalysts has been extensively investigated over the past 25 years. It is widely accepted that methanol conversion initially proceeds through equilibration with DME. Early work with ZSM-5 showed that light olefins are then the initial hydrocarbon products, followed by heavier olefins, paraffins and aromatics (Figure 12.5) (2). 

These complexes are the first examples of multifunctional catalysts and demonstrate impressively the opportunities that can reside with the as yet hardly investigated bimetallic catalysis. The concept described here is not limited to lanthanides but has been further extended to main group metals such as gallium [31] or aluminum [32]. In addition, this work should be an incentive for the investigation of other metal-binaphthyl complexes to find out whether polynuclear species play a role in catalytic processes there as well. For example, the preparation of ti-tanium-BINOL complexes takes place in the presence of alkali metals [molecular sieve ( )]. A leading contribution in this direction has been made by Kaufmann et al, as early as 1990 [33], It was proven that the reaction of (5)-la with monobromoborane dimethyl sulfide leads exclusively to a binuclear, propeller-like borate compound. This compound was found to catalyze the Diels-Alder reaction of cyclopentadiene and methacrolein with excellent exo-stereoselectivity and enantioselectivity in accordance with the empirical rule for carbonyl compounds which has been presented earlier. 

Patents and literature reviews reveal that a wide range of catalysts has been investigated for the production of pyridine bases [5,9-11,14-18]. Up to 1980, FCC-based catalysts, often in combination with metal promoters, featured heavily as supports. The list of early solid-acid supports includes AI2O3, clays (e. g. mont-morillonite), amorphous Si02-Al203, molecular sieves (i. e. LTA), zeolites MOR and FAU (i. e. H -Y) [19], and metal phosphates [20]. 

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