Impact of the Support on the Catalytic Performance, Inhibition Effects and SO₂ Poisoning Resistance of Pt-Based Formaldehyde Oxidation Catalysts

Formaldehyde emissions in addition to the methane-slip have recently been addressed for natural gas fueled combustion engines and thus require an aftertreatment catalyst system. In this work, two Pt-based catalysts supported on Al₂O₃ and TiO₂–SiO₂ were investigated by considering their activity, inhibition and stability towards SO₂-poisoning. The catalysts were analyzed by X-ray diffraction, electron microscopy, BET surface area, ex situ and operando X-ray absorption spectroscopy, which revealed differences in the oxidation state of Pt depending on the support material and that slightly reduced Pt sites seem to be the active species for this reaction. Systematic activity tests showed that NO_x presence leads to a significant inhibition, possibly due to oxidation of the active species, whereas CO addition promotes formaldehyde oxidation above the onset temperature of CO oxidation. These results were supported by spatially resolved concentration profiles along the channel of a catalyst coated monolith. Addition of small amounts of SO₂ to the gas mixture resulted in a complete loss of the low-temperature activity, slightly more pronounced for the TiO₂–SiO₂ supported catalyst.