Catalysts
It is fairly easy to see how a heterogeneous catalyst works. Two reacting gases, e.g. hydrogen and ethene, adsorb onto the surface of a transition metal such as nickel or palladium. This brings the two reactants close together and with the right orientation producing an alternative pathway with a lower activation energy than the uncatalysed reaction. Once the product has formed, it is then desorbed. It is less easy...