Abstract
Low temperature combustion (LTC) diesel engines are being developed to meet increased fuel economydemands. However, some LTC engines emit higher levels of CO and hydrocarbons and therefore dieseloxidation catalyst (DOC) efficiency will be critical. Here, CO and propylene oxidation were studied, asrepresentative LTC exhaust components, over model bimetallic Pt-Pd/-Al2O3catalysts. During CO oxi-dation tests, monometallic Pt suffered the most extensive inhibition which was correlated to a greaterextent of dicarbonyl species formation. Pd and Pd-rich bimetallics were inhibited by carbonate formationat higher temperatures. The 1:1 and 3:1 Pt:Pd bimetallic catalysts did not form the dicarbonyl speciesto the same extent as the monometallic Pt sample, and therefore did not suffer from the same level ofinhibition. Similarly they also did not form carbonates to as large an extent as the Pd-rich samples andwere therefore not as inhibited from this intermediate surface species at higher temperature. The Pd-richsamples were relatively poor propylene oxidation catalysts; and partial oxidation product accumulationdeactivated these catalysts. Byproducts observed include acetone, ethylene, acetaldehyde, acetic acid,formaldehyde and CO. For CO and propylene co-oxidation, the onset of propylene oxidation was notobserved until complete CO oxidation was achieved, and the bimetallics showed higher activity. Thiswas again related to less extensive poisoning, less dicarbonyl species formation and less overall partialoxidation product accumulation.
