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Why can carbon monoxide and ethylene reduce the catalytic activity of platinum?

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nanoparticles: hydrogen peroxide — catalysis Nanoparticles of a gold-palladium (yellow-blue) alloy supported on acid-treated carbon (gray) directly catalyzing hydrogen peroxide formation from hydrogen (white) and oxygen (red) while shutting off unwanted hydrogen peroxide decomposition.

Carbon monoxide and ethylene can reduce the catalytic activity of platinum because they act as catalyst poisons.

In the context of catalysis, a catalyst poison is a substance that accumulates on the surface of a solid catalyst, thereby decreasing its effectiveness. These poisons often originate from the reacting substances or the products of the reaction itself. By occupying the active sites on the platinum surface, these molecules prevent the intended reactants from binding and undergoing the necessary chemical transformations.1

While platinum is highly effective in promoting reactions—such as the conversion of carbon monoxide and hydrocarbons in automotive exhaust systems—the accumulation of certain species on its surface can inhibit its performance. When the effectiveness of a catalyst drops due to such poisoning, it often becomes necessary to remove the accumulated substances or replenish the active catalyst component to restore its function.21