Impact of the Gas Mixture and Aging Conditions on Formaldehyde Conversion over a Series of Commercial Pt-Based Catalysts

The emission of formaldehyde and its removal has recently been brought into the focus of exhaust gas catalysis beside reduction off pollutants like hydrocarbons, carbon monoxide and nitrogen oxides. In this study, five commercial Pt-based catalysts were tested on their ability to oxidize formaldehyde under a variety of gas mixtures representing typical conditions of lean burn gas engines. In general, most of the formaldehyde could be removed almost as efficiently as carbon monoxide and much easier than saturated hydrocarbons. The catalysts were aged in different simulated exhaust gas mixtures including varying SO₂ concentrations at 500 °C for 100 h to investigate a possible loss of activity due to thermal aging and poisoning. In a sulfur-free simulated exhaust gas very high conversion with no detectable loss of activity due to the aging was observed. Also small amounts of SO₂ (1.75 ppm) had only minor effects on formaldehyde conversion. However, exposure to gas mixtures with a higher SO₂ concentration (7 ppm) over 100 h at 500 °C resulted in a significant loss of activity. This activity loss is accelerated for catalysts aged under dynamic conditions, i.e. multiple cold-starts per day of combined heating and power plants. In addition, all catalysts were field-aged for 200 days on a combined heat and power plant fueled by biogas with an estimated SO₂ concentration of 3.5 ppm. The deactivation was found to be similar to the laboratory-aged catalysts with high sulfur concentrations.