General information
| Title: | Microkinetic modeling of the oxidative dehydrogenation
of propane for the analysis of structure-activity relationships |
| Research areas: | Technical
chemistry, reaction kinetics of heterogeneous systems, kinetic modeling |
| Leader:
|
Prof. Dr. Reinhard Schomäcker Institut für Chemie |
Abstract:
The oxidative dehydrogenation of propane (OPD) catalyzed by
transition metal oxides was chosen as model reaction for partial oxidation reactions
of small hydrocarbons due to its complex reaction network of parallel and consecutive
reactions, in which the rate of each single reaction depends very sensitively
on the chemical composition, oxidation state and structure of the catalyst.
In order to discuss structure-activity relationships, simple activity-selectivity
measurements are useless as long as there is no clarity on the molecular reaction
mechanism with each catalyst. This project aims in the investigation of the
reaction network of ODP over a selected group of vanadia catalysts and the experimental
determination of kinetic and thermodynamic parameters. Our criterion for the
choice of the catalysts is a very different activity-selectivity relation observed
in previous experiments. Industrial vanadia or VPO catalysts may be included
in experimental program as references. Since the partial oxidation of hydrocarbons
is an extremely exothermic reaction, experiments in tubular reactors are in
general disadvantageous for a detailed kinetic analysis. In order to avoid strong
temperature profiles in the reactor, reactants have to be diluted or low conversions
have to be adjusted. Better experimental conditions are ensured by a gradient-free
differential reactor, in which the reaction rate can be measured directly under
isothermic conditions. On the basis of results from the partial project B3,
an experimental set-up was developed including a differential reactor, which
allows measurements in a wide range of experimental conditions (partial pressures,
temperature, amount of catalyst). The temperature inside the reactor is controlled
by a combination of wall cooling and pre-heating/cooling of the reactant mixture.
Model development and determination of kinetic and thermodynamic parameters
give independant data for a discussion of the results of structure analysis
and theoretical calculation.
In a second part of the project, niobia and niobic acid catalysts
will be prepared on porous support and also tested for its activity in ODP.
The experimental program begins with the variation of the support in order to
test the influence of the support material on the catalytic activity.