Catalysts are substances that can be added to a reaction to increase the reaction rate without getting consumed in the process. They usually work by lowering the energy of the transition state, thus lowering the activation energy, and/or changing the mechanism of the reaction. This also changes the nature (and energy) of the transition state.

Nanoparticles catalysts can be used in the hydrogenolysis of C-Cl bonds such as polychlorinated biphenyls. Hydrogenation of halogenated aromatic amines is also important for the synthesis of herbicides and pesticides as well as diesel fuel. In organic chemistry, hydrogenation of a C-Cl bond with deuterium is used to selectively label the aromatic ring for use in experiments dealing with the kinetic isotope effect. These nanoparticles catalyzed the dehalogenation of aromatic compounds as well as the hydrogenation of benzene to cyclohexane.

Nanomaterial-based catalysts have to do with maximizing the effectiveness of the catalyst coating in fuel cells. Platinum is currently the most common catalyst for this application, however, it is expensive and rare. Gold nanoparticles also exhibit catalytic properties, despite the fact that bulk gold is unreactive.

TiO2 is regarded as the most efficient and environmentally benign photo catalyst and has been most widely used for photo degradation of various pollutants. TiO2 photo catalysts can also be used to kill bacteria, as has been carried out with E. coli suspensions. The strong oxidizing power of illuminated TiO2 can be used to kill tumor cells in cancer treatment.

Due to the quite high chemical stability and catalytic activity, Pt nanomaterials have been widely used in many fields, especially in catalysis. The chemical properties of Pt are inactive and stable in air and moisture. Their existing partially-full d orbit in the outer layer of Pt results in it being easy to form complexes and some intermediates with high activity.