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Competitive adsorption 2026-10-18

Competitive adsorption occurs when different chemical species seek the same adsorption sites. For intact molecules

A

and

B

, retain identical adsorption sites and no interactions, but replace the vacant fraction by

1 - θ_{A} - θ_{B}

. The same equilibrium balance gives

θ_{A} = \frac{b _{A} P _{A}}{1 + b _{A} P _{A} + b _{B} P _{B}}, θ_{B} = \frac{b _{B} P _{B}}{1 + b _{A} P _{A} + b _{B} P _{B}} .

Here

P_{A}

and

P_{B}

are partial pressures, not total pressure. Increasing

P_{B}

can reduce

θ_{A}

at unchanged

P_{A}

: replacing

P_{A}

by total pressure in a single-species Langmuir isotherm loses this competition.

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