Catalyst and Catalysis

Humans used the process known as catalysis long before, they understood what took place in that process. For example, soap-making, the fermentation of wine to vinegar, and the leavening of bread are all processes that involve catalysis. Ordinary people were using these procedures in their everyday lives without knowing that catalysis was involved.

The term catalysis was proposed in 1835 by the Swedish chemist Jons Berzelius. The term comes from the Greek words for down, kata, and loosen, lyein. Berzelius explained that he meant by the term catalysis the property of exerting on other bodies an action which is very different from chemical affinity. By means of this action, they produce decomposition in bodies, and form new compounds into the composition of which they do not enter.

One of the examples of catalysis familiar to Berzelius was the conversion of starch to sugar in the presence of strong acids. In 1812, the Russian chemist Gottlieb Sigismund Constantin Kirchhof had studied this reaction. He found that when a water suspension of starch is boiled, no change occurs in the starch.

However, when a few drops of concentrated sulfuric acid are added to the same suspension before boiling, the starch breaks down into a simple sugar called glucose. The acid can be recovered unchanged from the reaction. Kirchhof concluded that it had played a helping role in the breakdown of the starch, without itself having undergone any change.

Berzelius had been able to draw on many other examples of catalysis. For example, both Humphry Davy and Johann Dîbereiner had studied the effect of platinum metal on certain organic reactions. They had concluded that the metal increased the rate at which these reactions occurred without undergoing any change itself. Davy's most famous protégé, Michael Faraday, also demonstrated the ability of platinum to bring about the recombination of hydrogen and oxygen that had been obtained by the electrolysis of water.

When Berzelius first defined catalysis, he had in mind some kind of power or force by which an agent (the catalyst) acted on a reaction. He imagined, for example, that platinum might exert an electrical force on gases with which it came into contact in order to bring about a change in reaction rates.

This kind of explanation works well for heterogeneous catalysis, in which the catalyst and the reaction are in different phases. In a platinum catalyzed reaction, for example the platinum is in a solid state and the reaction in a gaseous or liquid state.

Homogeneous catalysis, in which catalyst and reaction are in the same state, requires a different explanation. How does sulfuric acid in the liquid state, for example, bring about the conversion of a starch suspension with which it is intermixed?

The solution to this problem came in the early 1850s. Alexander William Williamson was carrying out research on the preparation of ethers from alcohol. Chemists knew that concentrated sulfuric acid was an effective catalyst for this reaction, but they did not know why. Williamson was able to demonstrate that the catalyst does break down in the first stage of this reaction, but is regenerated in its original form at the conclusion of the reaction.

The role of catalysts in living systems was first recognized in 1833. Anselme Payen and Jean François Persoz isolated a material from malt that accelerated the conversion of starch to sugar. Payen called the substance diastase. A half century later, the German physiologist, Willy Kahne, suggested the name enzyme for catalysts that occur in living systems.

Toward the end of the nineteenth century, catalysts rapidly became important in a variety of industrial applications. The synthesis of indigo became a commercial possibility in 1897 when mercury was accidentally found to catalyze the reaction by which indigo was produced. Catalysis also made possible the commercial production of ammonia from its elements (the Haber-Bosch process), of nitric acid from ammonia (the Ostwald process) and of sulfuric acid from sulfur oxides (the contact process).