Methane Conversion and Ammonia Formation Model over a Pd-Rh Three-Way Catalyst for CNG Heavy-Duty Engines

Research activities in the development of reliable
computational models for aftertreatment systems are
constantly increasing in the automotive field. These
investigations are essential in order to get a complete understanding
of the main catalytic processes which clearly have a
great impact on tailpipe emissions.
In this work, a 1D chemical reaction model to simulate
the catalytic activity of a Pd/Rh Three-Way Catalyst (TWC)
for a Natural Gas heavy-duty engine is presented.
An extensive database of tests carried out with the use of
a Synthetic Gas Bench (SGB) has been collected to investigate
the methane abatement pathways, linked to the lambda variation
and oxide formation on palladium surface. Specific
steady-state tests have shown a dynamics of the methane
conversion even at fixed ? and temperature conditions, essentially
due to the Pd/PdO ratio. Furthermore, combining the
results of such test with dedicated Rich-Lean ? transitions it
has been demonstrated that the presence of NO reduces the
rate of the methane oxidation reaction.
Given the high reliability of the experimental data and
the possibility of managing the chemical composition of the
gas entering the catalyst, important aspects related to the NH3
formation were analyzed. In the proposed kinetic scheme,
NH3 decomposition phenomena are also present at high
temperature due to the presence of Rh in the catalyst.
Reactions involving Cerium for oxygen storage and
release characterization are included in the proposed model
in addition to the surface reaction mechanism, reasonably
determining the TWC conversion efficiency of the main species