Beneficial Role of Oxygen in CO and Propylene Oxidation over a Pt–Pd-Based Wiremesh Catalyst as a Retrofit Emission Control Device for Four-Stroke Gasoline Spark-Ignited Motorcycles
Alireza Lotfollahzade Moghaddam, Tayebeh Hamzehlouyan, Vahid Hosseini, Andreas Mayer
Abstract
Over 200 million motorcycles in use worldwide account for a substantial portion of global mobile source total hydrocarbons (THC) and carbon monoxide (CO) emissions. In Tehran, capital of Iran, ultrarich inefficient combustion in gasoline-fueled motorcycles results in significantly high CO and THC emissions. Motorcycle catalysts can reduce CO and C3H6 (as a representative hydrocarbon) emission factors by 60–80%. In the present work, CO and propylene oxidation over a commercial Pt–Pd-based wiremesh catalyst is studied in a flow reactor setup under simulated conditions relevant to 125 cc four-stroke gasoline carburetor motorcycles. Steady-state individual and co-oxidation tests for CO and C3H6 oxidation under rich, stoichiometric, and lean conditions indicated that increasing oxygen concentration shifted the light-off profile toward lower temperatures. Kinetics of CO and C3H6 oxidation were studied. For co-oxidation of CO and C3H6, the apparent activation energies of CO and C3H6 oxidation were decreased by increasing oxygen concentration, indicating the positive role of oxygen in the reaction progress. The obtained reaction orders indicated the self- and mutual-inhibition effects of CO and C3H6. The highly positive order for O2 confirmed the beneficial effect of oxygen. Our results suggest that injecting secondary air in the motorcycle exhaust gas can be used as a practical technique for enhancing CO and hydrocarbon oxidation efficiency over a Pt–Pd/CeO2–ZrO2–Al2O3 wiremesh catalyst.