الفهرس 
Chabter 1 : introductionOnly 14 pages are availabe for public view
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Abstract
Studies summarized above were designed and undertaken to accomplish the following objectives:
a) A prober characterization of the influence of preparation variables on
properties and activity of catalysts;
b) Probing of changes induced by the presence of MnOx species to the known dehydrating activity of alumina in alcohol decomposition reaction;
c) Elucidation of relationships existing between surface acid-base properties of catalysts and their performances in alcohol decomposition reactions; and
d) Establishment of correlations between the alcohol adsorbed specIes and catalytic decomposition pathways.
2.1 Catalyst bulk characteristics
Unsupported a-Mn203 is produced by calcination of either of the precursor compounds used at 6000e for 5h. It is converted into Mn304 in different structural modifications, depending on the parent compound, by elevating the calcination temperature up to 1000°C. This thermochemical behaviour is considerably suppressed on alumina surfaces, and monolayer-type non-crystalline MnOx species are formed at 600 and 1000oe. Meanwhile, the presence of MnOx enhances transformation of the otherwise stable, ’Y-alumina structure into the a-modification at 1000oe. On silica surfaces, the formation of a-Mn203 at 6000e is retarded to occur at 1000°C. Thus, it is stabilized against phase modification into Mn304 at 1000°C. Meanwhile, silica remains non-crystalline, and non-crystalline MnOx/Si02 interfacial compounds are formed (e.g., Mn2Si04)·
2.2 Catalyst surface characteristics
Silica supported catalysts expose more accessible surfaces than the alumina supported ones at a given calcination temperature. Surfaces exposed on the alumina supported catalysts assume stronger acidic properties than those of the silica supported ones. While both sets of catalysts expose H-bond donor OH’s, the silica supported catalysts are distict by presence of Bronsted acid sites whereas the alumina supported catalysts are distinct by much stronger Lewis acidity. MnOx dispersed on alumina provides reactive basic sites (OH-, 02-) capable of an oxidative cracking of adsorbed pyridine into carboxylate species. In contrast, MnOx on silica does do likewise.
2.3 Isopropanol adsorbed species
Room-temperature chemisorption of the alcohol results III formation of differently-structured isopropoxides (terminal and bridging) and H-bonded molecules. The latter species are eliminated on outgassing at ~100°C, whereas the isopropoxides are converted into carboxylate species at ~300°C. Surfaces void of strong Lewis acid sites, for example of silica, were incapable of stabilizing appreciable amounts of isoprpoxides. On the other hand surfaces capable of pyridine cracking were equally capable of isopropoxide cracking. On certain catalysts, for example lOMCA(600) and IOMAC(600), .... etc., coordinated acetone-like species were formed, however at intermediate temperatures.
Hydrogen-bonded isopropanol molecules occur evidently on protonic surface OH groups, whereas isopropoxides are coordinated to Lewis acid sites. Coordination of acetone molecules, or acetone-like species, is activated and requires probably stronger Lewis acid sites than those involved in isopropoxide formation.
2.4 Isopropanol decomposition pathways
Isopropanol decomposes over the catalyst by dehydration to give propene and by dehydrogenation to give acetone. In most cases the dehydrogenation preceeds.