| dc.description.abstract | The catalytic decomposition of 2-propanol has
been investigated by a micropulse reactor technique in the
temperature range from 461 to 547 K on nickel oxide and
alumina doped nickel oxide. Nickel oxide is active for
the dehydrogenation of 2-propanol, yielding acetone, but
the introduction of A1[superscript 3+] ions leads to the development
of some dehydration activity; nickel alumlnate is purely
a dehydrating catalyst. X-ray diffraction data indicate
the formation of the nickel aluminate at the higher
dopant concentrations. The variations in catalyst activity
and selectivity as a function of catalyst compositions
have been roughly divided into three regions: region I,
in which there is a significant change in activity and
selectivity with very small concentrations of Al[superscript 3+] ions;
region II, in which the activity and selectivity remains
virtually constant with changes in composition; region III,
in which there is a marked increase in activity and dehydration selectivity with Increasing concentrations of Al[superscript 3+] ions
The behavior in region I is believed to be associated with
electronic changes in nickel oxide brought about by the
substitutional incorporation of Al[superscript 3+] ion, while the behaviour
in region III is ascribed to increasing amounts of
nickel aluminate in the surface zones of the samples.
Self-poisoning in the dehydrogenation reaction
has been observed and an equation accounting for the self-poisoning
kinetics has been proposed. It is suggested
that in the dehydrogenation reaction each alcohol
molecule uses one active site on the catalyst, while
self-poisoning causes elimination of three sites per
deactivating event. Strong chemisorption of acetone on
the surface is considered to be responsible for the self-poisonlng
of the dehydrogenation reaction. The conclusions
are supported by conductivity studies of the catalysts
under reaction conditions.
A characteristic feature of the dehydration
reaction is the deviation from linearity in the Arrhenius
plots at higher reaction temperatures. Isotope effect
measurements show that this is not due to a diffusion controlled
reaction. The deviation is believed to be
associated with the decomposition of hydroxyl groups on
the catalyst surface and investigations of the thermal
dehydroxylation of mixed nickel-aluminium hydroxides
support this proposal. | |
