Heterogeneous Catalysis Before 1934

ROBERT L. BURWELL, JR. Northwestern University, The Ipatieff Catalytic Laboratory, Department of Chemistry, Evanston, IL 60201

This ar t i c l e was prepared as an introduction to this symposium. Its aim was to provide a br ie f survey of heterogeneous catalysis before American contributions began. It makes no pretence to any contribution to scholarship (1).

We shal l then go back to some suitably remote time in the past and proceed to the terminal date rather rapidly. Ingoing back in time, let us, how­ever, make a stop at 1909. In his Nobel Award ad­dress of that year, Wilhelm Ostwald said: "The employment of the concept of catalysis has served hitherto as an indication of s c i ent i f i c backward­ness."

We may hope that this i s no longer true and presumably Ostwald f e l t that he had made catalysis respectable. But what led Ostwald to make this statement?

During the nineteenth century, a l l kinds of interpretations of catalysis were advanced and most had a closer relationship with metaphysics than with science. Here i s a example from Stohmann in 1894 (2).

"Catalysis i s a process involving the motion of atoms in molecules of lab i le compounds which results from the presence of a force emitted by another compound and which leads to the formation of a more stable compound and the l iberat ion of energy." (Emphasis added).

In the same year Ostwald gave a def init ion of catalysis which looks rather better (3): "Catal­ysis i s the acceleration of a slow reaction by the presence of a foreign material."

0097-6156/83/0222-0003$06.00/0 © 1983 American Chemical Society

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4 H E T E R O G E N E O U S C A T A L Y S I S

Let us now see what led to some of the curious theories of catalysis, although we should keep in mind that even theories of uncatalyzed reactions were necessarily very inadequate and sometimes rather metaphysical.

The philosophers 1 stone of the alchemist was of course a catalyst and i t was not u n t i l nearly 1800 that chemical theory - the ideas of chemical elements and the nature of chemical change - made transmutation suspect. The lingering idea of the philosophers' stone may have influenced the develop­ment of the idea of catalysis. The following clearly describes a catalytic experiment although the text i s unclear as to whether the experiment involves homogeneous or heterogeneous catalysis (4).

"Paracelsus sent his waiting man to deliver a piece of paper containing a small amount of a blood-red powder with the command that i t be poured into molten lead and stirred well.... The master of the mint paid several thousand guilders for the resulting gold."

The experiment was not reproducible, but we have no record that the work was formally withdrawn.

During the eighteenth century various reports of what we would c a l l transmutations appeared in the literature. But, in the absence of the theory of chemical elements, there was no way to d i s t i n ­guish between what we would now c a l l a chemical change and a transmutation. Although most educated people came to believe that most alchemists were charlatans, there was no s c i e n t i f i c reason why trans­mutation was impossible and another master of the mint, Sir Isaac Newton, took i t seriously. But, in the nineteenth century, alchemy disappeared from the s c i e n t i f i c literature. The discovery of radio­active transmutations revivified "alchemy" for a short period in the earlier 1900's and the philos­ophers 1 stone made i t s last appearance in the form of a Pd/asbestos catalyst.

In the Berichte der Deutschen Chemisches Gesellshaft for 1926 (59B, 2039), the eminent radio-chemist F r i t z Paneth and K. Peters published a paper entitled "On the Transmutation (Verwandlung) of Hydrogen Into Helium." Paneth had developed a method for the measurement of very small quantities of helium. In this paper, he reported that 1 g

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1. B U R W E L L Heterogeneous Catalysis Before 1934 5

of a 50% Pd/asbestos led to the formation of 10-7 cm3 of helium per day. The authors were well aware of the energetics of the process. Certainly, this was the most significant heterogeneous catalytic reaction ever to be reported. Unfortu­nately, the authors had to withdraw the paper very shortly after i t s appearance. Despite the state­ments of the authors in the communications with­drawing the work, my suspicion i s that the helium collected had diffused through the glass walls of the apparatus.

In the second half of the eighteenth century there were various reports of what we would recog­nize today as catalytic reactions. However, the idea of a catalytic reaction could not have been understood before chemical elements and chemical change had appeared. This early work i s a histor­i c a l curiosity which had no influence on the devel­opment of catalysis. The idea of catalysis can be taken as starting in 1814 when Kirchoff published his work on the hydrolysis of starch to glucose by acids. A number of people had investigated the hydrolysis, but Kirchoff was the f i r s t clearly to understand what was going on.

The second event in the development of catal­ysis came in 1817 when Sir Humphry Davy discovered that the introduction of a hot platinum wire into a mixture of air and coal gas led the platinum to become white hot. Davy considered that there was oxidation but no flame and that the platinum was unchanged.

His cousin, Edmund Davy, continued the work and in 1820 he discovered that the platinum could be introduced at room temperature provided that i t was finely divided. Dobereiner continued this work and in 1823, he found that, in the presence of platinum, vapors of ethanol reacted with oxygen to form acetic acid. Work on selective oxidation continues to this day but Dobereiner did i t f i r s t . He also noticed, in line with the work of Edmund Davy, that divided platinum became red hot in the presence of hydrogen and oxygen. Dobereiner did more than notice. He developed Dobereiner 1 s Tinder Box (Dôbereiners Feuerzeug) (5). This involved a small Kipp generator containing zinc and dilute sulfuric acid. When a valve was opened a jet of hydrogen emerged, the acid rose into the zinc and the jet continued. The jet f e l l upon spongy plat­inum and burst into flame. One then lighted his f i r e or his pipe. Over a million Tinder Boxes were

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6 H E T E R O G E N E O U S C A T A L Y S I S

sold. Dobereiner 1s Tinder Box represented the f i r s t technological application of heterogeneous catal­ysis .

In 1824, Henry reported the f i r s t example of poisoning. Ethylene inhibited the reaction between hydrogen and oxygen on platinum. He also noted selective oxidation in the reaction between oxygen and a mixture of hydrogen, carbon monoxide, and methane.

Continuing the line of catalytic oxidation on platinum, Peregrine Philips (1831, British Patent No. 6096) patented the oxidation of S O 2 to S O 3 on platinum, but he must have died before the f i r s t contact process plant for the production of sulfuric acid went on stream. And f i n a l l y , along this line of work, Schweigger in the same year discovered that hydrogen sulfide poisoned platinum.

Another line of catalytic work was started by Thenard (1818). He discovered hydrogen peroxide and he who discovers H 2 O 2 i s apt also to discover i t s catalytic decomposition. Thenard did, and he inves­tigated the matter carefully using both homogeneous and heterogeneous catalysts.

Today, someone might possibly write an annual review of the coordination chemistry of chromium. But, Baron Jacob Berzelius, the "Mr. Chemistry" of his day, wrote an annual review of chemistry every year for twenty-eight years. In 1835, he surveyed K i r c h o f f s work on acid hydrolysis, the catalytic oxidations on platinum and Thenard1 s work on the decomposition of H 2 0 2 . He discerned a phenomenon common to the three areas, and he invented catalysis and catalyst. Unfortunately, he coined another term, catalytic force (6).

"Catalytic force actually means that substances are able to awaken a f f i n i t i e s which are asleep at this temperature by their mere presence and not by their own a f f i n i t y . " (Emphasis added).

During the rest of the century, much fruitless effort was devoted to trying to develop explanations for catalytic force. It was this that gave catal­ysis something of a bad reputation and led to Ostwald 1s unfriendly remark. However, a l l through the century there were those who advanced chemical theories of catalysis. For example, de l a Rive (7) in 1838 proposed that platinum catalyzed the oxida­tion of hydrogen by a cycle of alternate oxidations of platinum followed by reduction of the surface oxide. He said:

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1. B U R W E L L Heterogeneous Catalysis Before 1934 7

"Ce n'est pas nécessaire de recourir a une force mystérieuse t e l l e que celle que Berzelius a admise sous le nom de force catalytique. [It i s unnecessary to resort to a mysterious force like that which Berzelius has proposed under the name, catalytic force]." However, believers in a chemical explanation

were in the minority up into the twentieth century. Berzelius did not refer to Faraday's paper of 1834 (8), but we should. It was an excellent study of the catalytic characteristics of platinum f o i l s for the oxidation of hydrogen: effect of pretreat-ment, rates of reaction in a primitive fashion, deactivation, reactivation and poisoning. For exam­ple, ethylene inhibited the reaction of a H 2 + O 2 mixture, but after some hours vigorous action com­menced. H 2 S and P H 3 were, however, permanent poi­sons . It would be interesting to rewrite Faraday * s ar t i c l e in modern form and terminology, to add a few imaginary experiments with XPS and EXAFS, and to submit the result to J.Catal. It would not be wise, however, to insert Faraday's mechanism in such a paper. He thought that hydrogen and oxygen were con­densed (one might say, physisorbed) on the surface of the platinum and that reaction to form water resulted from the mere proximity of H 2 and 0 2 .

"The platinum i s not considered as causing the combination of any particles with i t s e l f , but only by associating them closely around i t . "

One cannot fault Faraday for not inventing dissociative chemisorption. Hydrogen and oxygen were not known to be diatomic in 1834. Anyway, Faraday did not believe in atoms and assigned such ideas to metaphysics.

The concept of atoms "did not afford me the least help in my endeavour to form an idea of a particle of matter...with experience, I outgrew the idea of atoms.... Such ideas are mere hindrance to the progress of science (9)."

Following Faraday, there was a long, rather dry spell in academic heterogeneous catalysis. Most of the earlier work involved catalysis of oxidations or the l i k e . The world was not ready for the oxidation of naphthalene to phthalic anhydride - either academ­i c a l l y or technologically. Organic heterogeneous catalysis remained unexplored for many years after 1834. However, the beginning of the technology of heterogeneous catalysis came in this period ( s t i l l oxidations). The Deacon process was developed in

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8 H E T E R O G E N E O U S C A T A L Y S I S

the I860's - the oxidation of hydrogen chloride to chlorine on copper chloride - and Messel started the f i r s t plant for the oxidation of sulfur dioxide to sulfur trioxide in 1875, 44 years after the Peregrine Philips patent.

Things began to pick up towards the end of the century. In 1888, Ludwig Mond discovered steam reforming of hydrocarbons on nickel/pumice to give carbon monoxide and hydrogen. Sir James Dewar noted that oxygen adsorbed in large amounts on charcoal at the temperature of li q u i d a i r and that i t desorbed as such on warming. However, oxygen adsorbed at 250C could be desorbed only at high temperatures and as oxides of carbon. These observations can be taken as the beginning of physisorption and chemi-sorption.

The development of thermodynamics led to the recognition that a catalyst could only promote a rate in the direction of the position of equilibrium and that a catalyst could not change the position of equilibrium. Further, starting with Nernst, i t be­came l i k e l y that one would need to worry about d i f -fusional problems in heterogeneous catalysis.

In 1909, Ostwald was awarded the Nobel Prize in chemistry for his work in catalysis. My suspicion i s that the committee decided to award him the prize - he was the "Mr. Physical Chemistry" of his day -and they chose his work in catalysis as providing as good a basis as any other. In fact, not much of his career had been devoted to catalysis. In 1884, he reported a study of the acid-catalyzed hydrolysis of methyl acetate which introduced kinetics, in the modern sense, into catalysis. He also tied the concept of catalytic activity to rate. Both of these items were important. Then in 1901-1904 he and his former student, Brauer, developed the Ostwald process for the oxidation on platinum of ammonia to n i t r i c oxide. The f i r s t plant went on stream in Bochum in 1906 at a level of 300 kg of n i t r i c acid per day. In 1908, the production was 3000 kg per day. The process actually goes back to Kuhlmann in 1838, but there had been no industrial interest in such a process, because C h i l i saltpeter was cheaper source of n i t r i c acid than ammonia. How­ever, at the beginning of the twentieth century, the ease with which the British fleet could sever the sea lane between C h i l i and Germany had become a stimulus to the development of the Ostwald process.

German writers tend to make Ostwald the giant of catalysis as the following quotation (1) from G.-M. Schwab ill u s t r a t e s .

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1. B U R W E L L Heterogeneous Catalysis Before 1934 9

"It i s a very wide ranging undertaking to talk on Ostwald's work on catalysis. It i s similar to that which would be involved in talking on Newton's contributions to mechanics or Planck's to quantum theory." I doubt that many French, English, Russian or

American workers would write so strongly. Person­al l y , I would put the influence of Sabatier who did not get the Nobel Prize u n t i l three years after Ostwald; Ipatieff who never got i t , and perhaps Haber and Mittasch as great or greater.

However, in the years after Ostwald, his former students and collaborators dominated catalysis in Germany. We can mention Bodenstein who put the study of the kinetics of heterogeneous catalysis essentially in i t s modern state. The Ostwald school made l i t t l e contribution to mechanism, but i t adhered to a view surprisingly close to that of Faraday. The famous paper of Bodenstein and Fink of 1907 interpreted the kinetics of the oxidation of sulfur dioxide on platinum in terms of the diffusion of sulfur dioxide or oxygen through a polymolecular layer of adsorbed material. In extreme cases, accord with the observed inhibition by sulfur t r i -oxide would have required adsorbed layers so thick that they could have been pared with a razor.

Langmuir's work put a f i n a l quietus to such ideas, but independently support for chemical theories of catalysis came from such workers as Ipatieff and Sabatier. The latter said in an a r t i ­cle written at the end of his career (10):

"Like my il l u s t r i o u s master, Marcellin Berthelot, I always assumed that the fund­amental cause of a l l types of catalysis i s the formation of a temporary and very rap­i d combination (he meant a chemical combi­nation) of one of the reactants with a body called the catalyst.... This theory has been much discussed. Other theories more or less complex and based on modern concepts of the atom, have been proposed. I have tenaciously held to my theory of a temporary combination. It has guided my work both in hydrogénations and in dehydra­tions . "

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He had won the battle completely, but he was s t i l l rather defensive.

By 1934, the only remaining trace of catalytic force lay in the low temperature catalysis of the interconversion of the newly discovered ortho- and parahydrogen by paramagnetic surface sites.

Starting about 1900, Sabatier (10) and Ipatieff opened up the area of organic heterogeneous catal­ysis. The impact of Sabatier*s work was more immediate. Anyone, in a day or two could set up the apparatus needed to duplicate Sabatier's discovery of the hydrogénation of olefins and benzene. Further, before Sabatier, the conversion of an alkene to an alkane was an operation of such d i f ­f i c u l t y and of such low yi e l d that i t was rarely carried out. Sabatier's discovery created something of a sensation. Furthermore, i t was rapidly put to hydrogenating vegetable o i l s to make margarine.

As an a r t i l l e r y officer, Ipatieff started with autoclaves and high pressures. His work was not so readily applied i n the usual laboratory. In the long run, however, I p a t i e f f s work was as i n f l u ­ential as Sabatier ' s and i t was more important in technological applications of catalysis to the modern industries of petroleum refining and the production of petroleum-based chemicals. Further, as w i l l have been noticed, catalysts before Ipatieff were largely Group VIII metals. He introduced oxides like alumina into the catalytic repertory. Overall, the work of Sabatier and Ipatieff led to the development of organic heterogeneous catalysis, an area which had hardly existed in the nineteenth century and which was to provide a powerful stimulus to heterogeneous catalysis both academically, and industrially.

The work of Haber and Mittasch during the f i r s t decade of the twentieth century in developing the synthesis of ammonia by the hydrogénation of nitro­gen was of major importance although more limited in scope. The industrial application of heterogeneous catalysis was further extended by the development of the commercial hydrogénation of carbon monoxide to methanol by the Badische Ani l i n - und Soda-fabrik. Commercial production started at Merseburg in 1923 and the plant was producing 10-20 tons of methanol per day at the end of that year (11). The catalyst was not a Group VIII metal (we now know that they could have used palladium) but ZnO«Cr203.

Finally, I should note that the early t h i r t i e s saw the beginnings of detailed mechanistic proposals

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based on the intermediate compound theory but in advance of the rather vague ideas of Ipatieff and Sabatier. The f i r s t two mechanistic proposals i n the modern sense were the Bonhoeffer-Farkas (12) and the Horiuti-Polanyi (13) mechanisms. In the Bonhoeffer-Farkas mechanism (1931), the ortho- para-hydrogen conversion at high temperatures was assumed to proceed via dissociative adsorption of hydrogen followed by associative desorption and the mechanism could be immediately extended to H 2 + E>2 —^ 2HD. The Horiuti-Polanyi mechanism (1934) for the hydrogén­ation of ethylene could also be readily extended to other hydrogénation reactions. Both mechanisms are s t i l l in use.

We have now reached into the period in which American work in catalysis had started and we have mentioned the European work of two scientists whose work continued in the United States, V.N. Ipatieff and A. Farkas.

Industrial applications of heterogeneous catal­ysis were well underway in the chemical industry: The contact process for sulfuric acid, the Haber process for the synthesis of ammonia, the BASF process for the synthesis of methanol, the catalytic hydrogénation of vegetable o i l s , and the catalytic water-gas shi f t process for producing the hydrogen needed in the preceding processes. The applications of heterogeneous catalysis to the petroleum industry had hardly begun. That was a development which was largely to occur in the United States. Acknowl edgment

This a r t i c l e was written while the author was enjoying the hospitality of Prof. J. Fraissard and the Laboratoire de Chimie des Surfaces of the Université Pierre et Marie Curie, Paris. Literature Cited

1. The art ic les on W. Ostwald by G.-M. Schwab, Z. f ü r Elektrochem. (1953) 25, 878, and by W. Schirmer, Sitzungsber. Akad. Wiss. DDR, Math., Naturwiss. Tech. (1979) 33, (13N) were part icu lar ly helpful to the author and he wishes to thank Professors Schwab and Schirmer for providing him with copies of their papers. Among other secondary sources, the work on Berzelius by J.E. Jorpes ("Jac. Berzelius, His Life and Work," Uppsala, 1966) and the excel–

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12 HETEROGENEOUS CATALYSIS

lent art ic les by W.D. Mogerman in the Inco Reporter for 1965 should receive part icular mention.

2. Stohmann, Z. Bio l . (1894), 31, 364. 3. Ostwald, W., Z. physik. Chem. (1894) 15, 705. 4. Schwab, G . - M . , "Catalysis", translated by

Taylor, H .S . , and Spence, R., van Nostrand, New York, NY, (1937).

5. Co l l ins , P . , Educ. Chem., (1977) 14, 14. 6. Jorpes, J . E . "Jac. Berzelius, His Life and

Work", Uppsala, 1966, p. 112. "Power in Jorpes has been changed to "force".

7. de la Rive, Compt. rend. (1838) 7, 1061. 8. Faraday, Μ., P h i l . Trans. Roy. Soc. (1834) 124,

55. 9. Mogerman, W.D., Inco Reporter, (1965) No. 5,

July. 10. Sabatier, P . , B u l l . Soc. Chim. France (1939) V6,

1261. This paper provides a fascinating account of how Sabatier came to discover hydrogenation.

11. Lormand, C., Ind. Eng. Chem. (1925) 17, 430. 12. Farkas, Α . , Ζ. physik. Chem. (1931), B14, 371. 13. Horiut i , J., and Polanyi, Μ., Trans. Faraday

Soc. (1934) 30, 1164.

Received November 17, 1982

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