What is a common example of a heterogeneous catalyst?

A common example of a heterogeneous catalyst is iron used in the Haber process. In this context, the iron catalyst is in a solid state, while the reactants (nitrogen and hydrogen gases) are in the gaseous state. This distinction between the phases—solid catalyst and gaseous reactants—highlights the key characteristic of a heterogeneous catalyst, which provides a surface for the reaction to occur without being consumed in the process.

Iron plays a crucial role in facilitating the synthesis of ammonia from nitrogen and hydrogen by lowering the activation energy needed for the reaction, thus increasing the rate at which ammonia is produced. The effectiveness of iron in this process exemplifies how solid catalysts can enhance reaction efficiencies in industrial applications, such as the production of fertilizers.

In contrast, other options like hydrogen peroxide in solution, ozone gas, and liquid sulfuric acid do not fit the criteria for heterogeneous catalysts. Hydrogen peroxide is a reactant rather than a catalyst in typical reactions, ozone is a gas that participates in reactions rather than catalyzing them, and sulfuric acid, while it can act as a catalyst, typically functions as a homogeneous catalyst when dissolved in solution.