Carsten Plog

Selective Ammonia Exhaust Gas Sensor for Automotive Applications

In order to meet future NOx emission standards for commercial vehicles, so called urea selective catalytic reduction (SCR) systems will be introduced. In the SCR converter ammonia serves as a reducing agent for selective NOx reduction. An ammonia exhaust gas sensor is required to optimize the injected amount of urea and to assure that no ammonia emissions occur. This paper reports on the development of a selective thick film ammonia sensor that can meet the requirements for applications in automotive exhaust gas. Main topic is the development of the functional gas sensitive film. Zeolites were successfully investigated as selective functional materials for this kind of sensors. It is shown, that the type of the zeolite, its module, the working temperature and the working frequency determine sensitivity and selectivity of the sensor. From the most promising zeolite material—zeolite H-ZSM5 with a module of 140, sensors were manufactured and tested in engine test benches. It could be shown, that this kind of sensors is a useful tool to control an ammonia-SCR system and to detect ammonia slip.

Combustion gas sensitivity of zeolite layers on thin-film capacitors

Abstract Y-zeolites doped with platinum by an ion-exchange process have been used as gas-sensitive layer material on thin-film interdigital capacitors (IDCs). The zeolite-IDC sensor sensitivity has been determined for C 4 H 10 , CO and H 2 in wet air by exciting the sensor with an alternating voltage and determining the impedance response.

Impedance of zeolite-based gas sensors

Abstract Changes in conductivity and capacitance of NaY- and NaPtY-zeolites allow concentrations of butane, ammonia and other gases to be determined by zeolite interdigital sensors. By means of impedance spectroscopy, hydrocarbon conversion can be separated from the effect of water, which appears in a different frequency range. NaY-zeolites show a moderate conductivity which is due to the mobility of sodium and is influenced by the presence of gases adsorbed at the pore surfaces.

Development of a high-temperature basic device for chemical sensors based on an IDC with on-chip heating

A device for chemical sensors has been developed based on a thin-film interdigital capacitor (IDC) with on-chip heating for temperatures up to 450 °C. The concept of direct heating of the sensor reduces the heating power significantly. Furthermore good control of the operating temperature and its uniformity can be obtained under various operating conditions. On the basis of a refined finite-element analysis simulation model, two heater elements have been designed for operating temperatures of 200 and 380 °C. The heating powers are 1.2 and 3.5 W and the maximum temperature deviations across the IDC area are ±2.6 and ±2.8%, respectively.

Ptrh-Doped Zeolites as Three-Way-Catalysts: Sims Analysis as a Tool for the Selection of Suitable Zeolite Types

Abstract Principal questions in the development of exhaust catalysts are related to an increase of the λ-window and a reduction of the noble metal content. In these areas the use of noble-metal-doped zeolites is advantageous. The selection of PtRh-doped Y-zeolite and mordenite as three-way-catalysts by the additional use of the surface analytical method SIMS is presented. Depth profiles showed that there exists a clear correlation for the reactions of the catalytic conversion of the emission of Otto-cycle engine exhausts between catalyst activity and the chemical composition of the surface of the zeolite crystals.

Metal-Doped Zeolites for Selective Catalytic Reduction of Nitrogen Oxides in Combustion Gases

Abstract In the present work it is demonstrated that the activity of zeolites concerning the SCR-process can be increased significantly by metal doping. The SCR catalysts prepared by metal ion exchange of mordenite and Y-zeolite were tested in a laboratory plant to determine the efficiency of the conversion of nitric oxides with ammonia. Copper-doped Y-zeolite can be used as a SCR catalyst in a wide temperature range. Therefore, the operation is possible as well in a low-dust region, such as behind a desulphurization plant. A complicated temperature control for optimum conversion is not necessary. Also the excellent ammonia storage capacities of the zeolite catalysts can be demonstrated. Therefore, changes in the ammonia feed or the NO content in the exhaust gas can be compensated.

Effect of Impregnation and Activation Conditions of Al2O3/CuO Supported Monolith Catalysts in the Reduction of NO

Reduction of NO in the presence of CO and Ar was examined on two series of monolithic sheets carrying an active CuO/Al 2 O 3 layer. In the impregnation procedure the ratio of Al 2 O 3 to CuO was varied in a wide range. The texture of the layer and the dispersion of CuO therein was controlled by mercury porosimetry, scanning electron microscopy and secondary ion mass spectrometry (SIMS). It could be established that the surface concentration of CuO determined by SIMS measurements is the most decisive quantity of the catalyst correlating linearly with the conversion of NO.