Water accelerates and directly participates soot oxidation: An isotopic study

Water vapor is inevitable in automobile exhaust and its influence on soot oxidation is of great interests to many researchers. In this paper, we utilized heavy-oxygen water ((H2O)-O-18) to investigate the water participation extent and its relationship with soot oxidation activity. By comparing the quantity of labeled species in products, we noticed water participated in both bare and catalytic soot oxidation. The tighter contact between soot and catalyst, the more involvement of water. But the extent was not affected by the redox property of Mn2O3 catalysts. The promotional effect of water on activity was observed in all investigated conditions, which was probably because water could be dissociated to more active oxygen species and accelerate the regeneration of oxygen vacancies. But hydrogen atoms left by water still need to be eliminated by dioxygen. Hence in general water worked as an accelerator rather than oxidant.

Automated summary

In this study, heavy-oxygen water was used to investigate the influence of water on soot oxidation in automobile exhaust. It was found that water participated in the oxidation process, acting as an accelerator rather than an oxidant. The promotional effect of water on activity was observed in all conditions, likely due to its ability to dissociate into more active oxygen species and facilitate oxygen vacancies regeneration.