Effects of NO and NO2 on fresh and SO2 poisoned methane oxidation catalyst - Harmful or beneficial?

Even though hazardous for the environment and human health, NOx can protect a methane oxidation catalyst (MOC) from hydrothermal and sulphur deactivation. However, the details remain unclear. We applied experimental and DFT methods to study the effects of NO and NO2 pollutants on the MOC. Results in this paper indicate that inclusion of NO to exhaust instantly demotes methane conversion on a non-poisoned catalyst, but respectively promotes it on a SO2 poisoned state. On a non-poisoned catalyst, NO and NO2 block active sites on PdO due to strong adsorption, which instantly demotes conversion. Because of this, relatively more Al-2(SO4)(3) relative to PdSO4 during SO2 poisoning, retarding catalyst deactivation in the process. On a poisoned catalyst, NO2 efficiently removes hydrogen from hydroxyl groups on the catalyst surface via HNO2 formation. HNO2 formation may explain the promotion of methane conversion. Results can be applied in development of new environmentally friendly solutions to meet pollution regulations for lean-operating heavy-duty vehicles industry.

Automated summary

Despite being harmful to the environment and human health, NOx can protect a methane oxidation catalyst from deactivation. The presence of NO and NO2 can block active sites on a non-poisoned catalyst, reducing methane conversion, but promote it on a poisoned catalyst. This research provides insights for developing new environmentally friendly solutions for the heavy-duty vehicle industry.