Chemistry of the surface and the activity of alumina-silica cracking catalyst

Abstract

Alumina-silica cracking catalyst owes its activity primarily t o a number of acid sites located in the catalyst surface. These sites are formed in the preparation of catalyst by the condensation of the surface hydroxyl groups of the incompletely polymerized silica hydrogel with the hydroxyl groups of the hydrolyzed aluminium ions. The formation of acid is explained by the known tendency of the aluminium atom t o acquire a pair of electrons, enhanced by the displacement of electrons in the A1-0-Si bonds towards the silicon atom carrying four positive charges. The electron pair is donated by water, the hydroxyl group becomes part of the structure, and the hydrogen ion is held by electrostatic attraction. The activity of the catalyst is thus reduced t o the same general basis as the activity of aluminium halides.The acidity (acid strength) of the surface of the catalyst has been shown t o be in the range of strong acids known t o promote hydrocarbon reactions. A linear relationship was found between the activity of the catalyst for polymerization of propylene and the number of acid sites in the surface. A more complex relationship was observed in the cracking of isopropylbenzene.

Structures and transformation mechanisms of the η, γ and θ transition aluminas

“…(f) The abnormally coordinated Al cations are responsible for the strong Lewis acidity (electronacceptor property) observed on the surfaces of r/-and y-alumina (Tamele, 1950;Milliken, Mills & Oblad, 1950) and must result in the catalytic activity of these phases.…”

“…Quasi-trihedral AI ions are therefore found in B-alumina and quasi-octahedral A1 ions in y-alumina because r/, derived from bayerite, has a much higher specific surface area, and presumably higher residual surface energy, than y which is derived from boehmite. These abnormally coordinated AI cations are obviously responsible for the strong Lewis acidity (electron-acceptor property) observed on the surfaces of "q-and y-alumina (Tamele, 1950;Milliken, Mills & Oblad, 1950) and clearly must result in the catalytic activity of these phases. The above conclusion is also supported by the following evidence:…”

Structural Organization in Amorphous Silico-Aluminas

“…The formation of acid sites is explained by the condensation of the surface hydroxyl groups of the incompletely polymerized silica hydrogel with the hydroxyl groups of the hydrolyzed aluminium ions (Tamele, 1950). Milliken et al (1950) and consider that silico-aluminas are made up of silica and alumina particles, interbonded by the condensation of the hydroxyls at their interfaces.…”

Analysis of the Content of Carboxyl Groups on the Surface of Chemically Modified Copper Phthalocyanine

“…Такой анализ может быть проведен различными способами, [11] из которых наиболее приемлемым для данного случая является титрование аминами. Данный метод впервые был опи-сан в работе [12] и состоял в титровании поверхностных кислых групп твердого вещества, суспендированного в бензоле, н-бутиламином в присутствии индикатора п-диметиламиноазобензола. Сорбированный кислот-ными центрами индикатор окрашивал систему в крас-ный цвет, а титрование проводилось до исчезновения окраски.…”