With emission legislation becoming ever more stringent,
automotive companies are forced to invest heavily into solutions to
meet the targets set. To date the most effective way of treating
emissions is through the use of catalytic converters. Current
testing methods of catalytic converters whether being tested on a
vehicle or in a lab reactor can be expensive and offer little
information about what is occurring within the catalyst. It is for
this reason and the increased price of precious metal that kinetic
modeling has become a popular alternative to experimental
testing.
Many kinetic models and kinetic parameters have appeared in
literature in recent years, a comparison of these kinetic
parameters for the global reaction of CO oxidation is presented.
The parameters from literature are used for an experimental
simulation using the Queen's University kinetic model and then
compared with experimental data obtained from a synthetic gas
reactor and kinetic parameters determined at the Queen's
University, Belfast. The model uses a global kinetic technique
integrating the Langmuir Hinshelwood approach for kinetics, with
the rate constant obtained from the Arrhenius equation and
inhibitions determined using the Voltz method. A quasi-steady state
two-dimensional approach has been used for flow, with the catalyst
split into meshes in both the axial and radial directions.
The parameters are then used for various simulations, varying
gas concentrations of CO and O₂ for light-off experiments. Varying
the gas concentrations highlights the lack of versatility of the
parameters, as the parameters for global kinetic models generally
only work for simulations for the experimental conditions in which
they were determined. Finally a drive cycle simulation is compared
with data from emissions testing of a vehicle. This identifies how
the kinetic parameters determined from reactor simulations apply to
drive cycle simulations, a short coming identified in
literature.
The comparisons in this study will highlight the problems that
are present in global kinetic modeling for automotive application
and indicate the direction for further developments in catalyst
modeling.