Jürgen Dr. Gieshoff

Modeling of SCR DeNOx Catalyst - Looking at the Impact of Substrate Attributes

The present work intends to examine the selective NOx reduction efficiency of a current commercial Titanium-Vanadium washcoated catalyst and to develop a transient numerical model capable of describing the SCR process while using a wide range of inlet conditions such as space velocity, oxygen concentrations, water concentration and NO 2 /NO ratio. The concentrations of different components (NO, NO 2 , N 2 O, NH 3 , H 2 O and HNO 3 ) were analyzed continuously by a FT-IR spectrometer. A temperature range from 150°C up to 650°C was examined and tests were carried out using a model exhaust gas comparable to the real diesel exhaust gas composition. There is a very good correlation between experimental and calculated results with the given chemical kinetics.

Overview: Status of the Microwave-Based Automotive Catalyst State Diagnosis

The oxygen loading degree in TWCs, the amount of stored ammonia in SCR catalysts, the NOx loading degree in LNTs, or the soot loading of DPFs play a key role in automotive exhaust gas aftertreatment. Today’s methods determine the catalyst state indirectly. They utilize gas sensors installed up- or downstream of the catalysts and the catalyst state is inferred from the sensor signals. This overview reports on the status of an alternative approach based on the interaction of electromagnetic microwaves with the catalyst material. Since the catalyst state is strongly correlated with the electrical properties of the catalyst material itself, this concept shows a great potential.

Microwave Cavity Perturbation as a Tool for Laboratory In Situ Measurement of the Oxidation State of Three Way Catalysts

Three-way catalyst-based automotive exhaust gas aftertreatment is of high importance to meet today’s emission standards. To determine in situ the oxygen loading state of three-way catalysts, a microwave cavity perturbation method is used. In this study, it is investigated whether this measurement setup that had originally been described for full-sized catalysts can be transferred to a lab test bench using cores of 1″ diameter. The initial tests were successful and a high correlation between the oxygen loading degree dependent resonance frequency and the conversion was found. As an application example of the new in situ characterization technique, the steady state degree of oxidation of a three way catalyst was measured as a function of the exhaust stoichiometry. The experimental results are compared with the prediction of a recently published improved kinetic model that takes into account the oxidation of reduced ceria by H2O and CO2. It is shown that the experimental observations agree very well with this improved model. This result provides evidence that under typical operating conditions, the degree of oxidation of the three way catalyst is controlled by equilibrium effects.