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What happens when multiple catalysts work together as promoters?

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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.

When multiple catalysts are present simultaneously and produce a combined effect greater than the sum of their individual contributions, this is referred to as promoter action.1

In these instances, it is generally assumed that each catalyst acts by activating a specific reactant involved in the process. For example, in the reaction between hydrogen peroxide and iodine, iron ions are used to fortify the catalytic action of copper ions.1

More broadly, a promoter is a substance added to a solid catalyst to enhance its performance, even though the promoter itself typically has little or no catalytic effect on its own. Promoters can improve a catalyst's efficiency by:2
* Extending the effective surface area of the catalyst.3
* Increasing the quality of the surface for a specific reaction.3
* Altering the electronic or crystal structures of the active solid component through interaction.2