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

[Display omitted] •The effect of NO depends on whether the catalyst is in fresh or SO2 poisoned state.•On a fresh catalyst, NO decreases methane conversion due to site blocking.•On an SO2 poisoned catalyst, NO inclusion promotes methane conversion.•The promotional effect due to hydroxyl group removal on PdSO4.•NO inclusion causes more Al2(SO4)3 to form relative to PdSO4 due to SO2 poisoning. 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 Al2(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.