How does a catalyst provide a reaction mechanism with a lower activation energy? Although inorganic and metallic catalysts have been used for decades in the chemical and petroleum industries, we are in the rather odd position of knowing more of the details of catalytic mechanisms for enzymes than for these simpler catalysts, mainly because of recent x-ray crystallographic structure analyses of enzyme molecules.

Nevertheless, we can find a simple explanation of why platinum, nickel, or other clean metal surfaces are effective accelerators for reactions involving hydrogenation. Many hydrogenation reactions, such as the following, are catalyzed by metal surfaces:

It would be difficult to give these molecules enough kinetic energy in the gas phase to cause them to react upon colliding. The metal surface assists by adsorbing H₂ molecules and pulling them apart into hydrogen atoms, which bind to metal atoms at the surface.(opposite)