Formaldehyde Oxidation Over Platinum: On the Kinetics Relevant to Exhaust Conditions of Lean-Burn Natural Gas Engines

Kinetics of formaldehyde oxidation over Pt-based catalytic converters at oxygen-rich conditions related to the exhaust of lean-burn natural gas engines is investigated experimentally and numerically. The numerical model proposed in this work is based on a thermodynamically consistent detailed surface reaction mechanism consisting of 30 elementary-like-steps among six gas-phase and ten surface species. The surface mechanism is evaluated by comparison of the results of the numerical simulation with the experimental measurements. The experimental data are derived from isothermal end-of-pipe tests over a powdered Pt–TiO₂–SiO₂ catalyst as well as spatially resolved concentration measurements conducted with a catalytic monolith sample over a wide range of temperature. The measurements were performed in a gas mixture of 80 ppm HCHO, 10 vol% O₂, 12 vol% H₂O and 6 vol% CO₂ balanced with N₂, containing a formaldehyde concentration typical in the exhaust of lean-burn gas engines. The simulations are based on a one-dimensional approach for the description of a packed-bed reactor and a two-dimensional model for the calculation of flow field and chemical reactions inside a single channel of a monolith.