Reaction mechanism study of the Di-Air system and selectivity and reactivity of NO reduction in excess O2

Paper #:
  • 2017-01-0910

Published:
  • 2017-03-28
Abstract:
Next Generation Automotive DeNOx Catalysts: Ceria what else? The NOx abatement of the more fuel economic lean-burn engines remains a demanding challenge. The Di-Air system opts to meet future stringent emission standards, especially under realistic driving conditions [1]. It is claimed that this system is able to maintain high NOx conversion to N2 at high temperatures and exhaust flow rates by applying direct high frequency high intensity fuel injections just upstream of a NSR catalyst in the exhaust with only a very small fuel penalty. How this system can achieve this performance remains largely unresolved. A detailed investigation is required in order to elucidate the role that the different potential catalyst components play. Among other our TAP study shows NO reduction to N2 over H2 and hydrocarbons reduced (La-Zr doped) ceria [2]. Ceria is found to be capable of fuel oxidation (above 500 oC) and NO reduction. NO dissociates on oxygen anion defects, thereby refilling these vacancies with oxygen anions and forming N2. The carbonaceous deposits, in the case the catalyst was reduced by hydrocarbons, are oxidized by oxygen species originating from the lattice. This recreates oxygen anion defects, which enables substantial additional NO reduction. Ceria is capable of NO reduction even in the presence of excess O2 and CO2. The role of Pt, Rh, and Pd on ceria is lowering the hydrocarbons activation temperature, i.e. lower the temperature for carbon deposition and reduction of ceria support, while K and Ba are not beneficial for both NO reduction and hydrocarbon oxidation. Al2O3 has no catalytic effect, but only interacts by adsorbing and desorbing all components in the exhaust gas. These findings may open a new perspective in designing an Automotive DeNOx catalyst meeting the future stringent emission regulations (Euro 7) in a dynamic and realistic driving mode. [1] M. Inoue, Y. Bisaiji, K. Yoshida, N. Takagi, and T. Fukuma., Top. Catal. 56 (2013) 3. [2] Y. Wang, J. Posthuma de Boer, F. Kapteijn, and M. Makkee, ChemCatChem. 8 (2016) 102,
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