Applied Catalysis in the Automotive Industry: Development of a Commercial Diesel Oxidation Catalyst Simulation Model Balanced for the Requirements of an Original Engine Manufacturer. Part 1, NOx Chemistry

Abstract

Driven by a need for simulations in exhaust aftertreatment system R&D, a simulation model of a commercial diesel oxidation catalyst has been developed. Considering near future legislation demands in which cold starts will be of high importance, focus has been to develop a model which can be used to simulate as many engine operating points as possible and not just those at normal driving conditions. In order to emulate as many operating points as possible, the model has been calibrated and validated against synthetic gas bench tests in which inlet composition, temperature, and space velocity were varied. The model, which is of Langmuir-Hinshelwood type, incorporates three catalytic sites: one representing the precious metal, one NO/NO2 storage site, and one site with a high affinity to oxidation by NO2 with a concomitant NO production. The oxidation of the latter site by NO2 and simultaneous production of NO was found in the experimental data and contradicts the equilibrium thermodynamics of the NO + ½O2 ⇌ NO2 reaction, commonly used to describe the activity of diesel oxidation catalysts. The attitude in most of industry towards simulation models is that they represent a means to an ultimate objective, which is to understand the complete exhaust aftertreatment system. In this paper we present and discuss the performance of our diesel oxidation catalyst simulation model, developed solely using synthetic gas bench data, with this objective in mind.