Plasma assisted heterogeneous catalytic oxidation of carbon monoxide and unburned hydrocarbons: Laboratory-scale investigations

The use of upstream plasma treatment and ozone injection for the amelioration of the performance of diesel oxidation catalysis was investigated. Experiments presented here were performed in preparation for full scale tests on diesel engines. A significant augmentation of the oxidation rate of carbon monoxide was observed when plasma was applied upstream of a diesel oxidation catalyst and was attributed to a heterogeneous reaction of ozone with carbon monoxide. This observation led to ozone injection being investigated as an alternative to the direct application of dielectric barrier discharge type plasma to the gas upstream of the diesel oxidation catalyst. Results are presented about the two modes of the combination of the non-thermal plasma with the catalyst when they were applied during the catalyst light off, and are compared in terms of pollutant removal and energy cost for carbon monoxide and hydrocarbons. Mechanisms for these effects are proposed and the performances of the two approaches are discussed.

Graphical abstract.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Heterogeneous oxidation of carbon monoxide by ozone on a diesel oxidation catalyst was observed. ► Non-thermal plasma upstream of catalyst acts mostly to reduce emission of hydrocarbons and not CO. ► Ozone injection upstream of catalyst results in reduction of both CO and hydrocarbon emissions. ► The reduction in CO emission exhibited a rebound effect with ozone injection. ► Energy cost for a 25% reduction in HCs was 77 J/L for ozone injection and 120 J/L for direct plasma.