The Kinetics of Formaldehyde Oxidation and Emissions Reduction in Methanol Fueled Vehicles

Abstract

Oxidation of formaldehyde over supported platinum catalyst produced CO₂ as a major product and CO as a minor product under a wide range of Inlet concentrations and reaction temperatures. The temporal variation of CO yield proceeded through a maximum suggesting that it was produced as an intermediate in the pathway leading to CO₂. CO selectivity (S _co = y _co/x _HCHO) was maximized by operating at oxygen concentration below the stoichiometric point and at high reaction temperatures. A mechanism for formaldehyde oxidation is proposed which involves adsorption of formaldehyde followed by catalytic decomposition to CO and H₂ and oxidation of the surface species; the rate limiting step apparently shifts from the decomposition at high oxygen concentration to the oxidation of surface species at low concentration. The rate expression was obtained from the postulated mechanism and found to be consistent with the experimental results. The maximum for the yield of CO provided a second method by which to confirm the postulated rate expression.