Oxygen oxides CO to CO₂ on a supported metal catalyst in an isothermal plug flow reactor. Use buttons to select plots of "partial pressures" (P), "surface coverages" (θ), or "reaction rate" as a function of distance down the reactor. Use sliders to vary the "temperature", the "CO feed partial pressure", and the "O₂ feed partial pressure". Because the rate-determining step is the reaction of adsorbed CO and adsorbed O, and because CO adsorbs more strongly than O₂, increasing the CO feed partial pressure can decrease the rate of C₂ formation. This happens when the CO surface coverage becomes much higher than the O surface coverage.