Planar laser-induced fluorescence with laser synchronized flow control is employed as a non-invasive in situ technique to investigate a NOx storage catalyst, especially to grant a deeper insight into the...

Water, which is an intrinsic part of the exhaust gas of combustion engines, strongly inhibits the methane oxidation reaction over palladium oxide-based catalysts under lean conditions and leads to severe catalyst deactivation. In this combined experimental and modeling work, we approach this challenge with kinetic measurements in flow reactors and a microkinetic model, respectively. We propose a mechanism that takes the instantaneous impact of water on the noble metal particles into account. The dual site microkinetic model is based on the mean-field approximation and consists of 39 reversible surface reactions among 23 surface species, 15 related to Pd-sites, and eight associated with the oxide. A variable number of available catalytically active sites is used to describe light-off activity tests as well as spatially resolved concentration profiles. The total oxidation of methane is studied at atmospheric pressure, with space velocities of 160,000 h−1 in the temperature range of 500–800 K for mixtures of methane in the presence of excess oxygen and up to 15% water, which are typical conditions occurring in the exhaust of lean-operated natural gas engines. The new approach presented is also of interest for modeling catalytic reactors showing a dynamic behavior of the catalytically active particles in general.

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A key concept for hydrogen-fueled internal combustion engines is reducing NO x emissions with direct H 2 -SCR. Besides platinum as an active noble metal component, palladium-based catalysts are attractive for NO reduction with high selectivity. However, reliability of the catalytic activity in the presence of water with persistently low side product formation remains challenging. Therefore, a monolithic 1%Pd/5%V 2 O 5 /20%TiO 2 -Al 2 O 3 model catalyst is studied extensively under different conditions, showing that NO x conversion remains high even in the presence of 5% water, maintaining over 65% selectivity toward N 2 . Additionally, the catalyst remained active in a long-term experiment over 12 h in the absence and presence of water with an NO conversion over 45%. Finally, steady-state measurements and a kinetic analysis reveal overall concentration dependencies alongside trends of the reduction reaction competing with the hydrogen combustion reaction.

The presence of water vapor during the oxidation of the strong greenhouse gas methane over PdO‐based catalysts is known to result in severe inhibition and catalyst deactivation. In this context, our current study elucidates the role of the support material for different water concentrations in the reaction gas mixture. Compared to a reference PdO/Al2O3 catalyst, the catalytic activity can be significantly enhanced when using SnO2 and ZrO2 as support materials and remains stable during 24 h of operation at 823 K in the presence of 12 % H2O, whereas under identical conditions CH4 conversion drops by 68 % over PdO/Al2O3. The interplay between Pd species and catalyst support was systematically characterized by thermogravimetric analysis, temperature‐programmed reduction experiments and TEM measurements. Finally, a kinetic scheme was derived based on the experimental data.