The effect of chloride on the point of zero charge of. gamma. -Al sub 2 O sub 3

A convenient and simplistic index to determine the capacity for adsorption of negative or positive species onto oxides is the point of zero charge (pzc). It corresponds to that pH value at which there exists no net charge on the oxide surface. The pzc is the average of the pKs of the two intrinsic a...

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Bibliographic Details
Published in:Journal of catalysis 1990-03, Vol.122:1
Main Authors: Mieth, J.A., Schwarz, J.A., Huang, Y.J., Fung, S.C.
Format: Article
Language:English
Subjects:
02 PETROLEUM
020400 - Petroleum- Processing
400201 - Chemical & Physicochemical Properties
ADSORPTION
ALKALI METALS
ALKALINE EARTH METALS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CATALYST SUPPORTS
CATALYTIC EFFECTS
CATALYTIC REFORMING
CHALCOGENIDES
CHEMICAL PREPARATION
CHEMICAL REACTIONS
CHLORIDES
CHLORINE COMPOUNDS
ELEMENTS
FLUORINE
HALIDES
HALOGEN COMPOUNDS
HALOGENS
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
LITHIUM
MAGNESIUM
METALS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
PH VALUE
POTENTIALS
REFORMER PROCESSES
SODIUM
SORPTION
SURFACE POTENTIAL
SURFACE PROPERTIES
SYNTHESIS
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Summary:A convenient and simplistic index to determine the capacity for adsorption of negative or positive species onto oxides is the point of zero charge (pzc). It corresponds to that pH value at which there exists no net charge on the oxide surface. The pzc is the average of the pKs of the two intrinsic acidity constants and, therefore, its value depends on the sample used. As a measure of the adsorption capacity, the pzc value provides a measure of the range of pH values that can be used to prepare metal-supported catalyst precursors by adsorption. Recently, it was shown that by either changing the temperature of the supporting electrolyte or adding dopants, the pzc of {gamma}-alumina could be shifted so as to expand the range of pH values that can be used to prepare metal-supported catalytic precursors. The dopants considered to date have been electropositive elements: lithium, sodium, magnesium, and electronegative fluorine. Less work has been done to learn the effects of chlorine as a dopant, but such information is valuable since the chloride concentration on typical reforming catalysts is an important consideration in the performance of these catalysts. The objective of this report is to present their findings on the effect of varying low levels of chloride additions on the pzc of a commercial alumina typically used as a support for preparing reforming catalysts. The highest level of Cl{sup {minus}} studied corresponds to that value found on a 0.3% by weight Pt/Al{sub 2}O{sub 3} catalyst.
ISSN:0021-9517
1090-2694
DOI:10.1016/0021-9517(90)90272-L