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

Research activities in the development of reliablecomputational models for aftertreatment systems areconstantly increasing in the automotive field. Theseinvestigations are essential in order to get a complete understandingof the main catalytic processes which clearly have agreat impact on tailpipe emissions.In this work, a 1D chemical reaction model to simulatethe 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 ofa Synthetic Gas Bench (SGB) has been collected to investigatethe methane abatement pathways, linked to the lambda variationand oxide formation on palladium surface. Specificsteady-state tests have shown a dynamics of the methaneconversion even at fixed ? and temperature conditions, essentiallydue to the Pd/PdO ratio. Furthermore, combining theresults of such test with dedicated Rich-Lean ? transitions ithas been demonstrated that the presence of NO reduces therate of the methane oxidation reaction.Given the high reliability of the experimental data andthe possibility of managing the chemical composition of thegas entering the catalyst, important aspects related to the NH3formation were analyzed. In the proposed kinetic scheme,NH3 decomposition phenomena are also present at hightemperature due to the presence of Rh in the catalyst.Reactions involving Cerium for oxygen storage andrelease characterization are included in the proposed modelin addition to the surface reaction mechanism, reasonablydetermining the TWC conversion efficiency of the main species