(8d) Rational Design of Improved Low-Temperature Diesel Oxidation Catalysts | AIChE

(8d) Rational Design of Improved Low-Temperature Diesel Oxidation Catalysts


Song, Y. - Presenter, University of Houston
Grabow, L., University of Houston
Low temperature combustion (LTC) diesel engines have higher fuel efficiency and produce less NOx and particulate matter (PM) compared to traditional diesel engines. However, this benefit comes at the cost of higher concentrations of CO and unburned hydrocarbons (HC) emissions.1 Meanwhile, the low exhaust temperature results in a reduction of the activity of commonly used diesel oxidation catalysts (DOC). Thus, improved DOC with superior activity at reduced exhaust temperatures are needed.
In this work, we use a combination of density functional theory and descriptor-based microkinetic modeling to computationally screen a large number of bimetallic alloys. This approach enables us to quickly search for promising DOC under different reaction conditions.2 Based on the computational results, we propose that a better low temperature DOC can be synthesized from alloys of coinage metals with Pt or Pd. Compared to the commonly used DOC, which are Pt and Pd alloys, these coinage metal alloys will not only achieve higher activity at the reduced temperature, but also eliminate the mutual inhibition between CO and NO oxidations. Besides, manufacturing cost of the catalytic converter is reduced by replacing costly Pt or Pd with coinage metals. These promising alloys have been synthesized and their activity has been experimentally tested using temperature programmed oxidation.
Under real working conditions the exhaust containing CO, NO and HC is oxidized along the DOC reactor and the different local reaction conditions require different optimal catalyst compositions. Through reactor models we have predicted that a DOC reactor with catalyst composition gradients, where the local alloy formulation is optimized for the local temperature
and exhaust gas compositions, can save up to 70% of the reactor volume. To obtain this initial estimate we only considered CO oxidation and selected the optimal catalyst for each position from our descriptor-based catalyst design study. Our ongoing efforts aim towards our ultimate goal of optimizing the DOC composition in the presence of CO, NO and HC. With this optimized DOC, we expect to make significant advances to meet tailpipe emission regulations at the low exhaust temperatures of LTC engines, which will enable the widespread adoption of LTC and other more efficient low-temperature engine designs.

1. Musculus, M. P. B., Miles, P. C., and Pickett, L. M. Prog. Energy Combust. Sci. 39, 246 (2013).
2. Nørskov, J. K., Bligaard, T., Rossmeisl, J., and Christensen, C. H. Nat. Chem. 1, 37 (2009).