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This paper reports the oxidation reactivities of three hydrocarbons over an aged palladium (Pd) catalyst during simulated cold-start conditions. Local reaction rates and species concentration profiles on a catalyst of Pd on Al2O3 with ceria are reported for A/F ratios from 14 to 15 at a temperature of 300°C. The synthetic exhausts contain 1-butene (C4H8) as a surrogate for the most reactive hydrocarbons, and C3H8 and CH4 as surrogates for species with intermediate and very low reactivities, respectively. All gas mixtures contain representative amounts of CO, CO2,O2, H2, and H2O in N2. The results demonstrate that the control system on our catalytic flow reactor maintains the desired temperature to within 3°C at the highest conversions ever encountered with auto exhausts, and that our product analysis scheme monitors local reactivities of all species simultaneously, regardless of the conversion level.

This study compares global rate expressions for CO oxidation over Pt/Al2O3 catalysts from the literature to a recent rate law based on a novel experimental approach. Our new method infers local values of reaction rates from measured concentration profiles along an enlarged isothermal catalytic passage at typical automotive exhaust conditions. Experimental uncertainties are relatively small, so parameters in the rate law can be assigned within close tolerances. Rate laws based on dual-site Langmuir Hinshelwood (LH) mechanisms correlate several of the available databases, including the new one. And activation energies for the CO-O2 reaction in several global rate laws agree with values reported in the surface science literature. However, assigned energies in the CO adsorption equilibrium constant are 25 to 35 kcal/mole lower than they should be.

The efficiency and durability of catalytic converters for automobiles are determined by several heat and mass transport mechanisms acting in concert. This study characterizes these mechanisms with measured temperature and concentration profiles throughout a large-scale catalytic passage at fixed wall temperature. The increased passage size allows the concentration field within the passage to be accurately monitored. A small isokinetic sampling probe and laser positioning system enable the concentrations to be spatially resolved to within 0.04 mm and ten transverse locations are sampled at each axial station. The active walls are coated with a Pt catalyst over a production alumina washcoat containing 28% Ceria on a metal substrate. The walls are 2 cm apart, which is roughly 16 times larger than in a conventional monolith passage, so the Reynolds number is adjusted for scale similarity with commercial devices.