“A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt 12 The D iscoverv and Early History j j j of Catalysis “ / have tried to produce these phenomena with various metals hut I have succeeded only with platinum and palladium. ” HUMPHRY DAVY The point had now been reached when the more important physical properties of platinum and some of its associated metals had become reasonably well understood and had formed the basis of several applications. One major property, and one that was later to make a most significant contribution to chemical industry, was, however, yet to be discovered. As is so often the case, this discovery came incidentally from a quite different investigation. A disastrous explosion in a coal mine in the North of England in 1812, shortly followed by a number of similar explosions, prompted an appeal for advice to Humphry Davy at the Royal Institution and resulted in his well- known researches on flame and his invention of the miner’s safety lamp. In a paper read to the Royal Society on January 23rd 1817 Davy described his experiments on the increase in the limits of combustibility of mixtures of coal gas and air with increasing temperature: “For this purpose, I introduced a small wire-gauze safe-lamp with some fine wire of platinum fixed above the flame, into a combustible mixture containing the maximum of coal gas, and when the inflammation had taken place in the wire-gauze cylinder, I threw in more coal gas, expecting that the heat acquired by the mixed gas in passing through the wire-gauze would prevent the excess from extinguishing the flame. The flame continued for two or three seconds after the coal gas was introduced; and when it was extinguished, that part of the wire of platinum which had been hottest remained ignited, and continued so for many minutes. It was immediately obvious that this was the result which I had hoped to attain by other methods, and that the oxygen and coal gas in contact with the wire combined without flame, and yet produced heat enough to preserve the wire ignited, and to keep up their own combustion. I proved the truth of this conclusion by making a similar mixture, heating a fine wire of platinum and introducing it into the mixture. It immediately became ignited nearly to whiteness, as if it had been itself in actual com­ bustion, and continued glowing for a long while, and when it was extinguished, the inflammability of the mixture was found entirely destroyed. 219 © 1982 Johnson Matthey “A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt The opening page of the manuscript of Sir Humphry Davy's paper read to the Koval Society on January 23rd. 1817. “Some new experiments and observations on the combination of gaseous mixtures, with an account of a method for keeping a continued light in mixtures of inflammable gases and air without flame". The paper goes on: **I had intended to expose fine platinum wires to oxygen and olefiant gas and to oxygen and hydrogen during their slow combination under different circumstances. when I was accidentally led to the discovery of a new and curious series of phenomena.** Davy had discovered heterogeneous catalytic oxidation but unfortunately he did not appreciate the significance of his fi n< lings By rourtes* of the Koval Institution I have tried to produce these phenomena with various metals; but I have succeeded only with platinum and palladium; with copper, silver, iron, gold and zinc, the effect is not produced. ” (1) Thus Davy discovered the phenomenon of heterogeneous catalytic oxidation and although he obtained the same results with ether and alcohol, obtaining an acidic product that Faraday and later Daniell identified as a mixture of ace- taldehyde and acetic acid, he did not carry further the study of this profoundly important effect. His mind was fully occupied with problems of combustion, he was by now fully satisfied with the safety-lamp and he tended to regard the phenomenon he had discovered, as he wrote to one of his colliery manager friends, as “more like magic than anything I have seen ... it depends upon a perfectly new principle in combustion” (2 ). The Researches of Edmund Davy Despite this Davy’s paper aroused great interest; it was translated into German and French and it also encouraged his cousin Edmund Davy to take up the matter. Edmund, seven years younger than Humphry, had been engaged as the 220 © 1982 Johnson Matthey “A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt Edmund Davy 1785-1857 A younger cousin of Humphry Davy. Edmund first assisted the latter at the Royal Institution and then held the chair of chemistrv at the Royal Cork Institution. Here he prepared finely divided platinum and found that it would oxidise alcohol vapour at room temperature, sufficient heat being generated to raise the metal to a white heat. Again. Edmund Davy failed to grasp the significance of his discovery, but it led immediately to the much more effective researches of Dobereiner From a portrait in the possession of ihe Ko\al Dublin Society latter’s assistant in 1804 and then in 1831 had secured an appointment as Professor of Chemistry at the Royal Cork Institution. While still at the Royal Institution in London he had made several studies in the chemistry of platinum and published long papers in The Philosophical Magazine (3). In 1817 he carried these researches further and presented a paper to the Royal Society on a new fulminating compound of platinum (4). He stood much in the shadow of Humphry, and when in 1820 he published a paper describing the preparation of finely divided platinum by reducing a solution of platinum sulphate with alcohol and its great activity at room temperature in the oxidation of a further quantity of alcohol, he merely wrote: “In this case the acid first noticed by Sir H. Davy (in his beautiful experiment of the ignited platinum wire, and since more fully examined by Mr. Daniell) is produced . This mode of igniting a metal seems to be quite a new fact in the history of chemistry, but the means of keeping it in a state of ignition is only another illustration of the facts previously pointed out by Sir H. Davy, in his late valuable researches.” (5) Johann Wolfgang Dobereiner Edmund Davy’s paper was reproduced in German in Schweigger’s Journal fiir Chemie in the spring of the following year and attracted the attention of Johann 221 © 1982 Johnson Matthey “A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt Wolfgang Döbereiner who was to open up a much more vigorous study of the phenomenon and to cause quite a sensation among his scientific contemporaries. Döbereiner, born the son of a coachman in 1780, first served an apprenticeship to an apothecary and then spent five years as an apothecary’s assistant in Karlsruhe and Strasburg, attending lectures on chemistry and mineralogy in his free time. Opening his own pharmaceutical manufacturing business, he began to contribute papers to Gehlen’s Neues Allgemeine Journal für Chemie but his business failed and he was left impoverished. In 1810, to his great surprise, Döbereiner was appointed to the Professorship of Chemistry in the University of Jena, the chair created by Carl August, Duke of Saxe-Weimar-Eisenach in 1789 and now left vacant by the death of its first holder, Johann Göttling. The appointment was made by the Duke, an enlightened patron of the arts and sciences, together with his Minister of State Goethe on the recommendation of Gehlen, and Döbereiner remained for the rest of his life most grateful for this opportunity, refusing several offers of chairs in other universities. An extraordinary friendship grew between Döbereiner, the Grand Duke (as he became in 1815) and Goethe, both interested in chemistry. By the August of 1821 he had not only repeated Edmund Davy’s experiments but had fully appreciated their significance, rightly regarding the important discovery as the activity of the platinum rather than, as had both the Davys, as the action upon it of the alcohol. He believed at the time that Edmund Davy’s product was a sub-oxide of platinum and he wrote: “The platinum sub-oxide moreover, does not undergo any change during this transformation of the alcohol and can immediately be used again to acidify fresh, perhaps limitless, quantities of alcohol ... a circumstance that permits its use for the large scale preparation of acetic acid. ” (7) In July 1823 he turned his attention to the metal itself, and prepared platinum in powder form by heating ammonium chloroplatinate. This he found would ignite a mixture of hydrogen and either air or oxygen even at room temperature or below: “There now followed in a few moments that strange reaction; the volume of the gases diminished and after ten minutes all the oxygen in the admitted air had con­ densed with the hydrogen to water. ” (8) He also gave some thought to the most suitable form to adopt for the platinum powder and made use of small moulded pellets of potter’s clay impreg­ nated with platinum - the first example of a supported catalyst. Döbereiner was quick to make his findings known. Two days after this experiment - which he repeated “ at least thirty times that day and always with the same result” — he wrote to Goethe: “ Permit me, your Excellency, to give you news of a discovery that seems to be important in the highest degree from the points of view of both physics and electrochemistry.” (9) He also wrote similarly to Lorenz Oken, the editor of a scientific journal Isis, 222 © 1982 Johnson Matthey “A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B.