Catalytic Combustion of Propane/Air Mixtures on Platinum

Abstract

A honeycomb catalyst of platinum (4.2 kg/m³ loading) over cordierite, with y-alumina washcoat, 2.4 × 2.4 cm² in crosssection, 7·6 cm long and with characteristic channel diameter of 1·4 mm was used in a steady flow reactor. Measurements were made with CaHs/air mixtures at 650 to 800 K inlet temperatures, 110 KPa pressure, 10 to 40 m/s inlet velocity, 0·19 to 0·32 equivalence ratios, and about 1·5 mole percent water content. The measured quantities were substrate temperature at ten axial locations, exhaust gas temperature, exhaust concentrations of CO, CO₂, O₂, and total hydrocarbons, and pressure drop across the monolith. A number of temperature and concentration measurements were also made inside the monolith at half its length. The measured quantities were compared with those computed with a two-dimensional steady-state model for axial and radial convection and diffusion of mass, momentum, energy and homogeneous (three overall reactions) and heterogeneous (infinitely fast) reactions. Thus the model consisted of the complete two-dimensional steady laminar flow equations and required the use of the measured substrate temperatures. The equations were solved numerically by a method based on the TEACH code. Trends of computed and measured quantities are close but magnitudes are often different It is concluded, that, under the tested conditions, most of the fuel is converted to CO₂ and H₂O at the surface. Gas-phase reactions tend to become rapidly more important as temperature and equivalence ratio are increased and flow velocity decreased. Surface fuel conversion is much faster than fuel diffusion, resulting in a diffusion-controlled oxidation.