AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
The Catalytic Effect of Potassium Salts on Diesel Soot Oxidation
REINHARD NIESSNER, Alexander Rinkenburger, Kazuhiro Yasuda, Technical University of Munich, Germany
Abstract Number: 30 Working Group: Combustion
Abstract Health issues as well as global warming potential are the main reasons why diesel soot is removed by car exhaust after treatment. These filter systems minimize emissions, but require periodic regeneration by oxidation (combustion). Uncatalyzed oxidation needs temperatures >600oC in O2 (5 vol% in N2), which results in poor fuel efficiencies. These temperatures can be lowered down to exhaust gas temperatures i.e. by additives, which enhance soot reactivities during soot formation, leading to internally-mixed soot and possible oxidation temperatures <400oC. Besides oxidic additives, alkali metal salts are very effective. Unfortunately, combustion processes are still not fully understood and require further research.
In this work, different soot aerosols internally-mixed with salts were produced. Combustion in a Diesel Particulate Filter was simulated by applying Temperature-programmed oxidation (TPO). Soot samples were combusted under a defined atmosphere (5 vol% O2 in N2) and temperature range (100 - 700oC; 5oC/min), combustion products were detected in a FTIR spectrometer. All salts led to a pronounced decrease of the TPO temperatures of maximum CO + CO2 emissions (Tmax) with K2CO3 being one of the most effective salts leading to a decrease of up to Tmax = 300oC compared to uncatalyzed soot. Structural parameters derived from Raman microspectroscopy, scanning electron microscopy, and scanning mobility particle sizing measurements did not vary significantly compared to undoped soot. BET surface area only showed slight trends to lower surface areas with higher salt content.
On the contrary, parameters derived from High-resolution Transmission electron microscopy (HRTEM) and electron paramagnetic resonance (EPR) measurements could be correlated to the oxidation reactivity. The salt doping is influencing the nanostructure of the graphene layers as well as the electronic structure, giving rise to a temperature-dependent chemical equilibrium depending on the K+/anion binding strength.