Catalytic Hydrogenation

Indian Journal of Chemical Technology Vol. 12, March 2005, pp. 232-243

Jaime Wisniak* Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel 84105

Development of catalytic hydrogenation is one of the most significant chapters in theoretical and applied chemistry, which led to the opening of a whole series of new industries, particularly in the petrochemical area. The mechanism for a catalytic reaction involving the presence of an intermediate complex formed by the catalysts and one of the reagents, which eventually led to our present understanding of the phenomenon was suggested by Paul Sabatier. For his achievements in the development of catalytic processes Sabatier was awarded the 1912 Nobel Prize of chemistry, together with Victor Grignard.

Catalytic hydrogenation—a new technique, was con- described for the first time a method for the prepara- tributed to science, by Paul Sabatier (1854-1941). The tion of aluminum sulphide pure and crystallized, by basic work of P Sabatier in this fundamental scientific reacting hydrogen sulphide with alumina heated to the and industrial subject forms the basis of our modern temperature of red in a carbon boat3. theories about catalysis and catalysts, as well as of the After moving to Toulouse he continued his studies processes for the thermal and catalytic cracking of the of sulphur and sulphides. Carl Wilhelm Scheele heavy fractions of petroleum, isomerisation and po- (1742-1786) had shown in 1777 that alkaline and al- lymerization of hydrocarbons, hydroforming, synthe- kaline-earth polysulphides treated with a diluted acid sis of ammonia, methane, methanol, a very large did not liberate hydrogen sulphide, like they did with number of intermediates and fine chemicals, hydro- the corresponding sulphides, but generated an oily genation of liquid fats, dye intermediates, and the liquid having an unpleasant smell, from which no Fischer-Tropsch process for the manufacture of syn- compound of definite composition could be separated. thetic fuels. Berthollet4 and Louis-Jacques Thénard (1777- Here, first the work of P Sabatier that led to the 1857)5,6, among others, had tried to determine the discovery of catalytic hydrogenation and the postula- composition of this substance that seemed to be com- tion of a mechanism for heterogeneous reactions, is posed by a mixture of hydrogen polysulphides, ac- being described and then some details about the life companied by hydrogen sulphide and sulphur, but the and career of P Sabatier, that will shed light on the analysis of these products had proven very difficult road that led him to the Nobel Prize is being given. because they decomposed easily in contact with many substances, particularly glass. Sabatier solved the Inorganic chemistry problem by distilling the oil under vacuum and isolat- During his doctoral thesis Sabatier prepared so- ing a liquid having a composition very close to hy- dium monosulphide (Na2S) anhydrous and hydrosul- drogen disulphide, H2S2, which he named persulphure phides in the pure state (NaSH, NaSH.2H20, d’hydrogène (hydrogen persulphide). The errors in NaSH.3H2O); he established the formula of a hy- relation to the theoretical composition were due to the drated potassium hydrosulphide and showed that a presence of a small amount of dissolved sulphur. Sa- number of alkaline polysulphides that had been de- batier studied the properties of the persulphide, in par- scribed as definite chemical species were actually ticular its ability to decompose violently under the mixtures containing free sulphur. He developed an action of light or the presence of substances that re- original method for the preparation of the sulphides of acted with it forming unstable combinations (eg, wa- calcium, barium, and strontium in the pure state based ter, alcohols, ethers and alkaline sulphides). In the on passing a stream of hydrogen over the correspond- presence of water it formed a rather unstable form of ing carbonates heated to live red (about 500°C). He amorphous sulphur, insoluble in carbon disulphide, while the action of ether led to the formation of crys- —————— talline variety of sulphur known as soufre nacre (pearl *E-mail: [email protected] sulphur) or soufre de Gerne3. EDUCATOR 233

Afterwards, he developed a new preparation lized into black crystals. His discoveries in this sub- method for silicon disulphide SiS2, which had been ject led to the development of the technique for de- synthetised before by Frémy: Treatment of crystalline tecting cupric compounds in the presence of hydrogen silicon heated to red with hydrogen sulphide. He bromide: they yield a purple coloration, easily ob- found the concurrent transport of amorphous and servable and having a characteristic wave length in crystalline silicon, observation that led him to assume the visible absorption spectra3. the simultaneous formation of a sublimable sub- In 1896, he observed that the reaction of all copper sulphide of silicon, SiS, stable only at high tempera- compounds with a nitro sulphuric solution (nitrosul- ture, and decomposing slowly on cooling. In fact, phuric acid), obtained by dissolving nitric acid in sul- rapid cooling of the vapours generated by the reaction phuric acid, yielded an intense blue purple solution allowed him to isolate this metastable sub-sulphide at due to the reduction of the nitric acid to a new acid, 3 room temperature and study its properties . which he named nitrosodisulphonic acid (today: nitro- By reacting hydrogen sulphide with boron at the sisulphonic acid). By studying the absorption spectra red temperature he was able to develop a new method he established that the colouration was not due to the of preparation of boron sulphide, B2S3, which he iso- copper but corresponded to the new acid formed. He lated in two amorphous forms, one white and opaque, also found that this reduction could be obtained with the other transparent and vitreous, and in a crystalline the help of other metallic reducing agents or with or- form obtained by sublimation at 200°C of the white ganic substances. He then proceeded to the direct syn- amorphous sulphide. The formation of a volatile bo- thesis of nitrosisulphonic dark blue, by the reaction ron sulphide was accompanied by that of sub- between nitric oxide, oxygen, and sulphur dioxide, in sulphide, to which Sabatier assigned the formula B4S, the presence of a small amount of water. He proved and that of a hydrosulphide of probable composition that nitrosisulphonic acid could produce several me- B(SH)3. He also obtained the sub-sulphide by the ac- tallic salts, particularly a blue cupric salt and a pink tion of hydrogen at red temperature on the normal ferric salt3. sulphide, and described its properties and its com- pounds3. Heterogeneous reactions He then went on to study selenides, He isolated for What makes Sabatier’s discoveries even more sen- the first time a silicon selenide, SiSe2, having a metal- sational is the simplicity of the equipment he built for lic aspect, unstable under the action of water, and a his studies of heterogeneous reactions: The reactor yellow boron selenide, B2Se3, sublimable, and de- consisted of a glass tube filled with catalyst and con- stroyed by water. In addition, he recognized the for- nected to a oxygen generator, a mechanism for adding mation of a sub-selenide of boron, non-volatile3. the reagents, and a receptacle for collecting the reac- From 1881 onwards he studied different hydrates tion products. The hydrogen generator, developed by of metallic chlorides, determining their heats of hy- Deville, operated continuously, and was based on the dration, stability, the possibility of their dehydration reaction between diluted hydrogen chloride over under cold, and their reaction with cold concentrated granulated zinc. The hydrogen generated was washed hydrogen chloride. In particular, he studied the hy- by passing it through caustic soda, sulphuric acid, and drates of ferric chloride and cupric chloride and the through tubes filled with copper turnings heated to conditions for their formation and dehydration. He about 500°C. The reaction tube had a diameter of 14- showed that the absorption of hydrogen chloride by a 18 mm and length 60 to 100 cm and was positioned solution of cupric chloride decreased the solubility of within a bed of fine sand to assure constant tempera- this salt yielding crystals of hydrated cupric chloride ture. The reactor was heated by either a gas burner or 8 that dissolved under the action of an additional an electrical heater . amount of hydrogen chloride, leading to the formation In 1890 Mond, Langer, and Quincke announced of complex hydrochlorides. Sabatier was one of the that by the direct action of carbon monoxide on very first to use spectroscopy of absorption to study hy- finely divided nickel, prepared by the reduction from 7 drates, particularly those of cupric bromide . Led by its oxide, they had obtained nickel carbonyl, Ni(CO)4, the indications of the absorption spectra of solutions a volatile compound resulting from the fixation of CO of cupric bromide in hydrogen bromide, he succeeded on the metal. They also reported that reduced iron in isolating a complex bromhydrate, which crystal- yielded a similar compound9. Their procedure was 234 INDIAN J. CHEM. TECHNOL., MARCH 2005

very simple: It involved passing a current of CO over it was not decomposed by cold hydrogen but on heat- finely divided metallic nickel at a temperature being to about 180°C, it generated ammonia and ammo- tween 350 and 450°C, yielding CO2 gas and a solid nium nitrite. Reduced cobalt, reduced nickel, and re- mixture of a black amorphous powder of nickel and duced iron gave similar reactions, but the products carbon. The composition of the powder varied widely were less stable12-15. with the temperature employed and still more with the Sabatier and Senderens decided now to repeat their time the reaction was carried on. In this manner they experiments, this time with ethylene and acetylene. obtained a product containing as much as 85 mass Then, in 1896 they learned that Moissan and Moureu percent of carbon and 15% nickel. When a finely di- had recently tried the fixation of acetylene on the vided nickel was obtained, for example, by reducing same metals16. They had passed a current of acetylene nickel oxide by hydrogen at about 400°C was allowed on slivers of iron, nickel, or cobalt freshly reduced to cool in a slow current of carbon monoxide, the gas from their oxides by hydrogen and chilled in this gas, was readily absorbed as soon as the temperature de- and observed a brilliant incandescence. The high tem- scended to about 100°C. If the current of CO was con- perature thus produced decomposed the greater part of tinued or was replaced by one of inert gases (such as the acetylene into hydrogen and a large amount of carbon dioxide, nitrogen, hydrogen, or even air), a carbon, which would eventually block the tube. The mixture of gases was obtained which contained up- remaining acetylene was converted into liquid hydro- wards of 30% mass of nickel-carbon oxide. Analysis carbons (such as benzene and styrene), which closely of the gas indicated that it corresponded to the for- resembled those obtained by Berthelot by heating mula Ni(CO)4. acetylene to dull redness inside a bell inverted over After Berthelot and Mond in 1891, independently, mercury. According to Moissan and Moureu “cette had also succeeded in making iron carbonyl, reaction est due à un phénomène physique” (this reac- 10,11 Fe(CO)5 , Sabatier and his doctoral student Ser- tions is due to a physical effect): reduced iron, nickel, endens speculated about the possibility that other un- or cobalt being extremely porous, absorbed the acety- saturated gaseous molecules such as nitric oxide, ni- lene with production of enough heat to cause its spon- trous oxide, nitrogen peroxide, acetylene, and ethyl- taneous destruction. The reaction being endothermic, ene could also be fixed on nickel or on reduced iron, incandescence was reached and maintained as long as giving well-defined, stable, and volatile products the acetylene entered. The incandescence also deter- comparable to nickel carbonyl. They first tried unsuc- mined the polymerization of the acetylene into liquid cessfully to fix nitric oxide (NO) on nickel, cobalt, products. However, Moissan and Moureu neglected to iron, and copper; at high temperatures nitric oxide analyze the free gas, which they judged to consist of was reduced to nitrogen, with formation of NiO, CoO, hydrogen, and examined the liquids only sufficiently FeO, and CuO. Similar results were obtained with to recognize the presence of benzene. Similar results 12 N2O, but when passing vapours of NO2 over copper were obtained with platinum black . freshly reduced from its oxide, they observed that at Sabatier made some discreet inquiries whether room temperature (25 to 30°C) there was a regular Moissan and Moureu would be continuing these ex- fixation leading to a definite compound, solid, black, periments, and after learning they would not, he and unstable, and nonvolatile, of nitrated copper, Cu2NO2. Senderens repeated the experiments but using ethyl- In all cases, the experimental technique involved re- ene instead of acetylene, a hydrocarbon less violent in ducing with a current of hydrogen the finely divided its reactions. The procedure the followed was similar metal oxide placed inside a heated glass tube and then to the one used before: They directed a current of eth- passing the unsaturated gas through the tube. Sabatier ylene upon slivers of reduced nickel and noticed that and Senderens made a detailed study of the properties this time no reaction occurred at room temperature. of the new compound: It was not altered by dry, cold Raising the temperature progressively, a brilliant in- air, but when heated in the presence of pure dry nitro- candescence of the metal took place at about 300°C, gen, it decomposed at about 90°C releasing NO2, NO, which disappeared in a voluminous deposit of black and N2. Carrying the reaction in a Faraday tube (a carbon, proving the destruction of ethylene. At around closed bent tube cooled at one end) it was possible to 300°C they, too, observed a blockage of the tube con- obtain liquid NO2. Nitrated copper was decomposed taining finely divided nickel, and the production of violently by water (or humid air) with release of NO; free hydrogen. The gases released did not react EDUCATOR 235

significantly with an aqueous solution of bromine or their results, but also the use of metals outside the with an ammonia solution of cupric chloride, which platinum family for catalysts. This result was com- showed that they did not contain measurable amounts pletely unexpected19. of ethylenic or acetylenic hydrocarbons. But they also The following year Sabatier and Senderens discov- found methane to be almost pure. Sabatier and ered that nickel is also capable of hydrogenating Senderens concluded that an unstable combination acetylene, but that reaction could be initiated at room between nickel and ethylene had formed, analogous to temperature20. Acetylene was first hydrogenated to nickel carbonyl, which doubled itself into carbon, ethylene and then to ethane, depending on if the react- methane, and nickel, C2H4 → C + CH4, which could ing mixtures contained the same or double the volume then repeat an identical process17. Pursuing this idea, of hydrogen. The reaction was very exothermic and the two tried the reduction of the finely divided nickel the temperature within the reactor could reach 100 to oxide at temperatures below 300°C, cooling the re- 150°C, depending on the length of the tube. Again, duced nickel first in a current of hydrogen and then of reduced cobalt, iron, and copper, as well as finely di- ethylene. After washing the gases leaving the reactor vided platinum sponge or black, slightly heated, led to with bromine to absorb any traces of ethylene, they an analogous but less energetic reaction. With freshly discovered that is was a mixture of ethane, formène (a reduced copper, for example, the composition of the mixture of equal volumes of ethane and hydrogen), exiting gas varied with the temperature; at about and hydrogen, with traces of hydrocarbons. Raising 130°C, it contained 11% volume of ethylene and the temperature above 325°C decomposed the ethane 178% ethane, and at 150°C, 331% ethylene, 20% eth- into methane and carbon and the formène into carbon ane, and 184% of higher unsaturated hydrocarbons21. and free hydrogen. The overall ratio between ethane Further work examined in more detail the hydro- and hydrogen formed varied with temperature, at genation of ethylene and acetylene using other met- 325°C it was 75% by volume ethane and 25% hydro- als22,23. gen and at around 390°C it was essentially pure for- After having studied in depth the hydrogenation of mene. Hydrogen could only be formed from hydro- unsaturated hydrocarbons Sabatier and Senderens genation of ethylene, and this hydrogenation had been turned to the next challenging problem: Hydrogena- provoked by the presence of nickel. In other words, it tion of benzene. This reaction had been attempted by seemed that reduced nickel had the property of hy- Berthelot using his universal agent of hydrogenation, drogenating ethylene. To test this possibility they re- a concentrated solution of hydrogen iodide in a sealed peated their experiments, this time directing a mixture tube heated to 250°C (under these conditions hydro- of equal volumes of ethylene and hydrogen upon a gen iodide decomposes into hydrogen and iodine), but bundle of thin slivers of freshly reduced nickel, instead of cyclohexane, which boils at 81°C, he had slightly heated at temperatures from 30 to 40°C. A only obtained its isomer, methylcyclopentane, which considerable increase in temperature was observed. boils at 69°C. Instead, Sabatier and Senderens tested The results confirmed their expectations: only one the possibility of using reduced nickel and excess hy- half of the volume of practically pure ethane was ob- drogen at 200°C. The gaseous mixture issuing from tained, and the reaction continued indefinitely without the reactor was sent to a U-tube surrounded by ice, the necessity of heating and without an appreciable within which the vapours of cyclohexane were ex- modification of the metal. At a higher temperature pected to condense to a liquid product. After boiling (150 to 180°C) the reaction was still very rapid and a the benzene for a rather short time, they noticed that catalyst bed of a few centimeters of metallic slivers the tube became clogged by colourless crystals, which was sufficient to accomplish it12. This result, they be- they assumed to be benzene, solidifying at 4°C, lieved, “doit être certainment attribuée à la formation whereas cyclohexane was reported in the literature to temporaire d’une combinaison directe et spécifique du crystallize at –11°C. On opening the U-tube they de- nickel et de l’éthylène” (ought certainly to be attrib- tected, instead of the odour of the original benzene, uted to the temporary formation of a direct and spe- the special intermediate odour between that of chloro- cific combination of nickel and ethylene)18. Cobalt, form and that of rose, which belongs to cyclohexane: iron, copper, and platinum black gave similar but less “It was from cyclohexane obtained practically pure at intense results. It was not only the easy hydrogenation the first attempt, the fusion of which is in reality of ethylene and acetylene that was extraordinary in 65°C…that hour was one of the greatest joy in my 236 INDIAN J. CHEM. TECHNOL., MARCH 2005

life”. The transformation of benzene had been com- and Persoz studied in detail the transformation of plete14,24. starch into dextrin and then into sugar by the action of In the following three years, Sabatier and Sender- diastase and proved how starch, once rendered solu- ens hydrogenated unsaturated ethylenic or acetylenic ble, went from one tissue to another, as much as to carbides into saturated carbides, nitro compounds and accumulate again, as much as to bind in strong aggre- nitriles into amines, aldehydes and ketones into the gation and participate in this form in the formation of corresponding alcohols, unsaturated hydrocarbons of cellular membranes in the tissue. cyclic nuclei, homologous with benzene (polyphenyls, In 1823, Johann Wolfgang Döbereiner (1780-1849) naphthalene, anthracene, etc) into the corresponding obtained a spongy platinum material by calcinating saturated hydrocarbons, the phenols into the cyclo- ammonium chloroplatinate32. This material was hexanic alcohols, and aniline into cylohexylamine. shown to be able to absorb hydrogen at room condi- They also found that they could produce the major tions and on heating up to ignite a stream of air di- types of natural petroleum by modifying conditions of rected to it. Water was formed as a result without the 1,14 the hydrogenation of ethylene . They also realized spongy mass changing its aspect or its weight, and the synthesis of methane by hydrogenating carbon being capable of repeating the process after cooling. 25,26 dioxide or carbon monoxide . In those days, when there was no simple way to pro- With Mailhe, another doctoral student, Sabatier duce fire, Döbereiner’s discovery led immediately to found that some metal oxides were catalysts not for its application, the hydroplatinic lamp, also called hydrogenation and dehydrogenation, but instead for briquet à hydrogene (hydrogen lighter). hydration and dehydration. While ordinary alcohols Platinum did not behave in this manner only when directed at 250°C on reduced copper split into hydro- made as a sponge; it did also when finely divided as gen and aldehyde, the same vapour directed on fine filings, wire, or turnings, as long as it was first heated 27,28 alumina or thoria split into water and aldehyde . slightly. Many experiments led to think that this activ- They also observed that amorphous oxides were more ity increased the more the platinum was divided; it active catalysts for dehydrogenation or dehydration even increased more if before calcination the aqueous 28,29 than the crystalline oxides ones . Calcination of the solution of chloroplatinate was boiled with a little of latter at temperatures higher than 500°C led to a nota- sodium carbonate and sugar. The chloroplatinate was ble agglomeration. The calcinations reduced the ac- completely decomposed and the metal precipitated as tive surface by modifying the nature and distribution a black powder. This powder was much more active of the active centers. This was the first example of the than the sponge; it absorbed hydrogen rapidly and the sintering effects, which were later used to graduate smallest particle led to the instantaneous ignition of a the activity of catalysts. mixture of hydrogen and air. Thénard then found that black platinum decomposed hydrogen peroxide rap- Catalysis idly and with violence into oxygen and water, without Catalysis is a phenomenon known from very an- absorbing the gas releasing or losing its activity33. By cient times, although not its theory or characteristics. 1900 this property of platinum was found also in other By the nineteenth century, enough experimental in- metals (such as copper and iron), metallic oxides formation began to accumulate to call the attention of (such as manganese dioxide), carbon, certain acids, scientists. In 1811, Sigismund Constantin Kirchhoff etc. The only difference with platinum was that these (1764-1833) discovered that mineral acids upon heat- additional materials had to be heated, sometimes to ing changed starch into dextrin and sugar, without red temperature34. themselves being modified by the reaction30. In 1833 In his 1836 Annual Survey35, Jöns Jacob Berzelius Anselme Payen (1795-1871) and Jean-François Per- (1779-1848) summarized the findings of different soz (1805-1868)31 found that the transformation of scientists on the formation of ether from alcohols; on starch discovered by Kirchhoff was attributable to the the enhanced conversion of starch to sugar by acids; action of a special substance, which they called dia- the hastening of gas combustion by platinum, the stase (amylase), which can be extracted from germi- stability of hydrogen peroxide in acid solution but its nated barley by water and purified by repeated pre- decomposition in the presence of alkali and such cipitation with ethyl alcohol; they had also found that metals as manganese, silver, platinum, and gold; and the activity is eliminated by heating to 100°C. Payen the observation that the oxidation of alcohol to acetic EDUCATOR 237

acid was accomplished in the presence of finely ence of the metal, but also bringing them into more divided platinum. In a brilliant stroke, he was able to favourable states for union by abstracting a part of understand that all these processes, although that power (upon which depends their elasticity) seemingly different, had a common denominator, which elsewhere in the mass is opposing their combi- which he called catalysis (either catalysis of inorganic nation. The consequence of their combination is the reactions by metals or of biological reactions by production of the vapour of water and an elevation of enzymes). In the Annual Survey he wrote: ”In temperature. But as the attraction of the platina for the inorganic nature when compounds arise through the water formed is not greater than for the gases, if so interaction of several substances, the available great (for the metal is scarcely hygrometric), the va- combining units strive for a state of better satisfaction. pour is quickly diffused through the remaining gases. Thus, the substances endowed with strong affinities The platina is not considered as causing combination combine readily on the one hand, while those weakly of any particles with itself but only associating them endowed form combinations among themselves on closely around it and the compressed gases are as free the other. The agent causing the conversion of to move from the platina being replaced by other par- substances does not participate in the new compounds ticles as a portion of dense air upon the surface of the formed but remains unchanged, thus operating by globe or at the bottom of a deep mine is free to move means of an internal power, the nature of which is still by the slightest impulse into the upper and rarer parts unknown, although it was in this way that it revealed of the atmosphere”. its existence. Thus, it is certain that substances, both Berzelius argued that the catalytic force acted on simple and compounds, in solid form as well as in the polarity of atoms through some phenomenon of solution, have the property of exerting an effect on temperature elevation. compound bodies which is quite different from The physical theory was supported by the work of ordinary affinity in that they promote the conversion Jacques Duclaux (1877-1978) and Moissan on the without necessarily participating in the process. This absorption of gases by finely divided metals36,37. is a new power to produce chemical activity Wilhelm Ostwald (1853-1932; 1909 Nobel Prize belonging to both inorganic and organic natures. It for Chemistry) and others had also assumed that cata- will also make it easier for us to refer to it if it lyzed gas reactions resulted from the absorption of possesses a name of its own I shall call it the catalytic gases in the cavities of the porous metal, where com- power of substances, and decomposition by means of pression and local temperature elevation led to chemi- this power catalysis“(καταλγω from the Greek kata-, cal combination. Ostwald believed that a catalyst did "down" and lyein "loosen”). not induce a reaction but rather accelerated it but not

Mechanism of catalysis with formation of intermediate compounds. He argued When Sabatier commenced his investigations on it was necessary to prove that the succession of as- catalysis there were two theories of heterogeneous sumed reactions required less time than the direct re- catalysis, a physical and a chemical one. In 1833, af- action itself. 38 ter studying the data on the catalytic combination of William Charles Henry (1774-1836) in 1824 and 39 hydrogen and oxygen on the surface of platinum, August de la Rive (1801-1873) in 1828 proposed a Faraday suggested a physical theory in which one or chemical theory where intermediate compounds, for more of the reacting gases were condensed by attrac- example, oxides of metals, were formed and decom- tion on the surface of the metal. He wrote: “The posed. course of events when platinum acts upon and com- Sabatier did not accept this purely physical view of bines oxygen and hydrogen may be stated according the function of the catalyst, remarking that if it was to these principles as follows. From the influences of true then charcoal should be almost a universal cata- the circumstances mentioned, ie, the deficiency of lyst, whereas it proved to be somewhat mediocre ex- elastic power and the attraction of the metal for the cept for the formation of carbonyl chloride40. While gases, the latter, when they are in association with the finely divided metals were able to absorb substantial former, are so condensed as to be brought within the quantities of gas, these absorptions were somewhat action of their mutual affinities at the existing tem- specific, being “characterized by a sort of selective perature, the deficiency of their elastic power not only affinity”. Not only that, some catalytic reactions were subjecting them more closely to the attractive influ- extremely specific, for example, zinc oxide decom- 238 INDIAN J. CHEM. TECHNOL., MARCH 2005

posed formic acid into hydrogen and carbon dioxide, vide a free ion for a reaction which simply would not but at the same temperature titania gave carbon mon- occur otherwise. Thus, hydrogen peroxide solutions oxide and water. The idea that absorption of gases decompose relatively slowly in the cold the same as facilitated their liquefaction could not be true since solutions of chromic acid do, but when the two solu- the easily absorbable hydrogen was very difficult to tions are mixed there is a rapid decomposition with liquefy. The physical theory was unable to explain the brisk evolution of oxygen and appearance of an in- development of high local pressure and temperature in tense blue colouration (reciprocal catalysis). The col- the cases where the catalyst was held in suspension, our is due to the unstable combination and did not account for the specificity of catalysts and 3H2O2.2H2CrO4, which can be isolated by shaking the remarkable diversity of effects they produced, de- with ether and evaporating the ether1. 1,40 pending on the particular metal or oxide used . Sabatier also addressed himself to the problem of Sabatier and his students observed that an extended orientation and specificity of the catalyst and claimed surface was not necessarily a synonym of catalytic that they strongly supported the chemical theory. He activity. For example, colloidal nickel, contrary to showed that different contact masses produced differ- palladium and nickel, was essentially inert. The activ- ent reactions: At 350°C amyl alcohol in the presence ity of the catalyst depended particularly of the surface of copper yielded valeric aldehyde and hydrogen; at structure; this was the reason why it was preferable to the same temperature but in the presence of some tho- use a chemical method of preparation instead of me- ria as catalyst it yielded amylene and water. Chromic chanical ones. Sabatier demonstrated that the manner oxide acted both in oxidation and in dehydrogenation by which the reducible oxide was prepared played a and dehydration reactions and heated alumina decom- critical role, and searched which were the best deriva- posed alcohol into ethylene and steam, while metallic tives to prepare the reduced metal. He also showed molybdenum and zinc oxide decomposed it into acet- that these metallic catalysts were extremely fragile aldehyde and hydrogen. He attributed the orientation and that they became stronger when using high reac- of the reaction to the metallic or nonmetallic character tion temperatures. Higher temperatures led to an irre- of the catalyst or, in other words, to the intervention versible decrease of the catalytic activity; the activity of different electrical contact forces. He understood was not recovered if the operating temperature was that this differentiation was not valid in every case. lowered8. He wrote: “J’ai trouvé avec M Mailhe que les vapeurs Sabatier then formulated a chemical theory of ca- d’acide formique en présence d’oxyde de zinc à talysis involving the formation of unstable chemical 250°C, donnent de l’anhydride carbonique et de compounds as intermediate stages, which determined l’hydrogène, en presence d’oxyde titanique elles se the direction and rate of the reaction. He assumed that détruisent exclusivement en eau et oxyde de carbone in hydrogenation various nickel hydrides were in- Ici les deux oxides n’ont aucune dissemblance physi- volved, whose composition depended on the activity que et l’intervention d’affinité chimique spéciale of the nickel. Carefully prepared nickel resulted in the s’exerçant à la surface de ces catalyseurs est seule very active NiH2, which would operate on benzene, capabe d’expliquer une inversion aussi complete du while impure nickel or nickel prepared at too high phénomène…” (I have found with M Mailhe that va- temperature gave an impoverished hydride, Ni2H2, pours of formic acid in the presence of zinc oxide at which is inactive with benzene, but works with the 250°C yield carbon dioxide and hydrogen, in the ethylenic carbides or nitrate derivatives. Sabatier ar- presence of titania they decompose only into water gued that the formation and decomposition of inter- and carbon monoxide. Here, the two oxides do not mediate compounds usually corresponds to a diminu- have any physical resemblance and the intervention of tion of the Gibbs energy of the system. This reduction a special chemical affinity that is exerted at the sur- is accomplished in several steps and this process is face of the catalyst is capable of explaining such a frequently much easier than an immediate and direct complete inversion of the phenomenon)8. decrease of Gibbs energy, just as the use of a staircase Sabatier postulated the formation of different in- facilitates a descent1. He argued that while the pres- termediate compounds, each with its own mode of ence of catalyst might indeed lower the temperature decomposition, and he also clearly established that required by a reaction, the catalyst’s greatest asset some organic reactions are reversible. In cases where was in reacting with a molecular gas in order to pro- the intermediate compounds could not be isolated, he EDUCATOR 239

assumed the formation of surface compounds, a phe- according to which a gas adsorbed over a catalyst was nomenon, which he named fixation, thus linking the fixed thanks to its unsaturated valences yielding a 41 physical, and the chemical theories of catalysis . For gas-metal compound of the type MxGy, where x is a example, in the catalytic oxidation of organic com- function of the mass of the catalyst and y varies ac- pounds with the aid or copper, or the decomposition cording to the specific surface and physical conditions of carbon monoxide on nickel, the intermediaries, of pressure and temperature44,45. This theory was con- copper oxide and nickel carbonyl, respectively, can be trary to Sabatier’s hypothesis of distinct, individual isolated and identified. On his studies of the hydro- intermediates and allowed more importance to physi- genation of ethylene, Sabatier suggested the fixation cal conditions19. Although Langmuir’s theory retained of hydrogen by the nickel as the intermediary com- the concept of fixation of the reagents on the surface plex. In the case of acetylene, however, he remarked of the catalysts, it assigned a predominant importance that it was adsorbed more energetically than hydro- to the physical conditions that Sabatier had purpos- gen, thus indicating the possibility of organometallic edly ignored. For a time, Langmuir’s theory of the compounds playing a role in heterogeneous cataly- fixation of a monomolecular layer on the catalyst sis42. During his acceptance speech at Stockholm Sa- gave it a certain advantage because it permitted to batier said43: “J’admets que l’hydrogène agit sur le address quantitatively the problem of heterogeneous métal en donnant très rapidement sur sa surface une catalysis and played a considerable role in experimen- combinaison L’hydrure ainsi engendré est facilement tal studies8. Langmuir’s theory became particularly et rapidement dissociable, et s’il est mis en présence important because it permits a first quantitative analy- de matières capables d’utiliser de l’hydrogène, il le sis of the possible mechanism of a reaction. leur cede, en régénérant le métal, qui recommence Poisoning indéfiniment le même effect La distinction que j’ai faite entre plusieurs sortes de’activité du metal The catalysts sensitivity to poisons, discovered by conduirait à admettre qu’il existe plusieurs stades de the work of Rudolph Knietsh (1854-1906) on cata- combinaison” (I admit that hydrogen acting on the lysts used for the synthesis of sulphur trioxide (was metal produces rapidly on its surface a combination. shown to be a general phenomenon, which could be The hydride thus generated is easily and rapidly dis- used to control catalytic reactions Sabatier, when sociated; put in contact with substances capable of comparing catalysts to ferments, described poisoning using hydrogen, gives it to them, regenerating the in the following words: “Comme les ferments or- metal and restarting indefinitely the process)8. ganisés qui sont tués par des doses infinitésimales de certains toxiques, le ferment minéral qu’est le métal Sabatier summarized his views in respect to the 1,40 est tué par des traces de chlore, de brome, d’iode, de mechanism of catalytic action as follows : “As far soufre, d’arsenic, soit qu’elles lui viennent par as I am concerned, this idea of temporary unstable l’hydrogène soit qu’elles lui soient apportées par la intermediate compounds has been the beacon light substance qui doit subir l’hydrogenation…le nickel un that has guided all my works on catalysis; its light peu intoxiqué ne pourrait fournir qu’un premier hy- may perhaps be dimmed by the glare of light as yet drure, comparable à celui du cuivre, et capable d’agir unsuspected which will rise in the better explored sur les groupes nitrés ou sur la double liason éthylé- fields of chemical knowledge. Actually, such as it is, nique; seul le nickel sain pourrait fournir un hydrure in spite of its imperfections and gaps, the theory ap- capable d’hydrogéner le noyau aromatique” (In the pears to us good because it is fertile and permits us in same way that organized ferments are killed by infini- a useful way to foresee reactions”. tesimal amounts of certain toxins, the mineral ferment We must note that Sabatier was the first to demon- which is the metal is killed by traces of chlorine, bro- strate, the reversibility of the reaction alco- mine, iodine, sulphur, or arsenic that are carried by hol⇔aldehyde−hydrogen, which gave place to a large the hydrogen or by the substance to be hydrogen- number of thermodynamic and statistical investiga- ated…nickel, a little poisoned, can only provide a first tions on the Gibbs energy changes of organic reac- hydride, similar to that of copper and capable of act- tions. ing over the nitro groups or on the ethylenic double During the Second World War Irving Langmuir’s bond, only nickel cannot provide a hydride able to (1881-1957; 1952 Nobel Prize for Chemistry) pub- completely hydrogenate the aromatic ring)1,8. lished a rival theory called “theory of chemisorption”, Sabatier and Espil46 made the interesting discovery 240 INDIAN J. CHEM. TECHNOL., MARCH 2005

Three years later (1877), Sabatier received the license de physique and the license de mathématiques at the École Normale and joined the local school at Nîmes as professor of physics. In 1878, he was rec- ommended as normalien to the laboratory of Marcelin Berthelot (1827-1907), then at the Collége de France. At that time, Berthelot was the most outstanding chemist of France and was well connected to the high ranks of the academic and political establishment. Sabatier took advantage of his stay at the Collége de France to successfully prepare for his doctorate, receiving the degree of Docteur ès Sciences (Doctor of Sciences) in 1880 with a thesis on the thermochemis- try of sulphur and metallic sulphides48. The fact that Sabatier had been raised at home on a religious and conservative atmosphere soon led to strong divergences of opinion with Berthelot on political and philosophical grounds. This inflexible position explains why Berthelot forced Sabatier to use in his thesis the notation of equivalents (as seen in all the tables), instead of the atomic one. Nevertheless, at various points in his thesis Sabatier mentions that his Paul Sabatier (1854-1941) experiments confirm Berthelot’s principles or predic- 8,1 that after being used to hydrogenate nitrobenzene, tions . nickel poisoned by chlorine recovers its ability to hy- These divergences affected profoundly Sabatier’s drogenate benzene1. career In 1880, after receiving his doctorate Berthelot Discussion on the life and scientific career of Sa- led him to understand that he should look for a posi- batier, in the following paras will give an overall view tion in the provinces. In France of that time this of the background that led to this major contribution. statement was equivalent to academic exile. Berthelot was known to punish in this harsh manner those who Life and career criticized his theories and opposed his ideas. One of the most famous scientists thus penalized was Pierre Paul Sabatier (Fig. 1) was born on November 5, 49 1854, at Carcassonne, Southern France, one of the Maurice Duhem (1861-1916) . His choices to start an seven children of Alexis Sabatier and Pauline Guil- academic career were now limited to three universi- hem. He received his first education at the primary ties: Algiers, Bordeaux, or Lyon. Berthelot recom- school and the local Lycée in Carcassonne. In 1868, mended Sabatier for the position at Bordeaux, where he entered the Lycée at Toulouse and a year later he stayed for one year as Maître de conferences in joined the Collège Saint-Marie. In June 1872, after physics. Eventually Sabatier’s personality and bril- receiving his diplomas of bachelier ès sciences liant scientific achievements overcame the ideological (bachelor of sciences) and bachelier ès letter (bache- barrier and on December 1905 he became Doyen lor of humanities), he departed for Paris to prepare for (dean) of the Faculty of Sciences at Toulouse, a posi- the entrance examinations to the Grand Écoles (École tion he occupied for the next twenty-five years. Polytechnique and École Normale Supérieure). Al- Sabatier remained faithful to Toulouse for all his though he placed highly in the entrance competitions life, turning down many offers of respectful positions for both Ècoles, he chose the latter, where his brother elsewhere. In 1907, he was offered Henri Moissan’s Théodore has preceded him19,47. At the École Normale (1852-1907; 1906 Nobel Prize for Chemistry) chair at he took the courses given by Henry Sainte-Claire De- the Sorbonne and that of Berthelot at the Collège de ville (1818-1881), Charles Friedel (1832-1899), Jean France (ironies of life!). Although he realized that all Gaston Darboux (1842-1917), and Pierre Auguste candidates for the Académie des Sciences were re- Bertin (1818-1884)8. quired to be residents of Paris, he nevertheless chose EDUCATOR 241

to remain at Toulouse. He retired from his professor- less violent reaction of ethylene and reduced nickel ship in 1930 after nearly fifty years of uninterrupted and found that the reaction product was mainly ethane service in the Faculty of Science. with a little of hydrogen. Discovery of this hydro- In 1913, he became the first scientist elected to one genation reaction opened a new world of chemical of six chairs newly created by the Académie for pro- synthesis, which was intensively researched by Sabat- vincial members. ier and his students. He promptly demonstrated the Sabatier’s initial researches were in the field of in- general applicability of his method to the hydrogena- organic and physical chemistry, within the framework tion of unsaturated and aromatic carbides, ketones, of Berthelot’s laboratory. His thesis, which sought to aldehydes, phenols, nitriles, nitrate derivatives, carbon complete the study of sulphides, included accounts of monoxide and carbon dioxide, and liquid fats. He also the preparation of various metal and nonmetal, espe- showed that certain metallic oxides, particularly man- cially alkali and alkaline-earth sulphides and polysul- ganous oxide, behave analogously to metals in hydro- phides, with determinations of their heat of reaction genation and dehydrogenation, although at slower and solution. As described below, Sabatier ap- rates; and that powdered oxides such as thoria, alu- proached the problem from a variety of possibilities. mina, and silica possess hydration and dehydration In the 1879-1897 period, he performed analyses of properties. His work revealed also the general in- metallic and alkaline earth sulphides, chlorides, crease in catalytic activity arising from the dispersal chromates, and notably of copper compounds7, the of the active material on suitable supports. preparation of hydrogen disulphide by vacuum distil- Sabatier’s discoveries lay at the root of most of the lation, the isolation of selenides of boron and silicon, giant chemical industries of today (petroleum, petro- the definition of basic cupric salts containing four chemicals, chemical synthesis, synthetic fuels, fat hy- copper atoms, and preparation of the deep blue nitro- drogenation, etc), nevertheless, like Claude-Louis sodisulphonic acid and the basic mixed argentocupric Berthollet (1748-1822) and Michael Faraday (1791- salts. He studied the partition of a base between two 1867) before him, he pursued science only and did not acids, using the spectrophotometric change of colour- seek the commercial benefits of his inventions, pat- ation of chromates and dichromates, as an indicator of enting very few of them. acidity50,51, and analyzed the velocity of transforma- Sabatier passed away in Toulouse on August 1941, tion of metaphosphoric acid52. From 1896 to 1899, he at the age of 87. made some in-depth studies of the oxides of nitro- The scientific work of Sabatier was very extensive; 12,53-55 gen and of nitrosodisulphonic acid and its in addition to a large number of speeches, reports, and 3,55-58 salts . eight patents, he published over 250 scientific mem- Sabatier himself has described how his interest in oirs, his famous book La Catalyse en Chimie Or- the field of catalysis arose12. In 1890, after learning ganique 1 (1913), as well as Leçons Élémentaires de that Ludwig Mond (1839-1909), Carl Langer, and Chimie Agricole2 (1890), and collaborated in major Friedrich Quincke had succeeded in preparing nickel works such as Edmond Frémy’s (1814-1894) carbonyl13, a volatile compound, by the direct action L’Encyclopédie. Charles-Adolph Würtz’s (1817- of carbon monoxide on finely divided nickel he de- 1884) Dictionnaire de Chimie, and Moissans’s book cided to investigate the possibility that other “incom- Chimie Minérale. plete” (unsaturated) gaseous molecules would behave La Catalyse en Chimie Organique was first pub- in the same manner, giving well-defined, stable, and lished in 1913; this book on catalysis marks a mile- volatile products comparable to nickel carbonyl. In stone in the evolution of modern chemistry and still collaboration with his doctoral student Jean Baptiste continues to be quoted extensively. Senderens (1856-1937) they succeeded in preparing nitrated copper, Cu2NO2, by reacting NO2 with re- Honors and Positions 15 duced copper at room temperature . Sabatier received many honours for his contribu- Sabatier and Senderens were about to try to fix tion to science, industry, and the Nation. He became acetylene on several metals (copper, cobalt, iron, and Correspondent Member of the Académie and was nickel) when they learned that Moissan and François nominated to the Légion d'Honneur. He was awarded Charles Léon Moureu (1863-1929) had failed to the degree of Doctor of Science, Honoris Causa, by achieve it16. Sabatier and Senderens tried instead the several foreign universities and elected member or 242 INDIAN J. CHEM. TECHNOL., MARCH 2005

honorary member of many foreign scientific societies. most brilliant of crowns”. In 1897, the Académie des Sciences awarded him the Lacaze prize and in 1905 the Jecker prize, jointly with References Senderens. The Royal Society of London awarded 1 Sabatier P, La Catalyse en Chimie Organique, C, Béranger, him the Davy Medal (1915) and the Royal Medal Paris,1913. (1918), the Royal Society of Arts the Albert Medal 2 Sabatier P, Leçons Élémentaires de Chimie Agricole, Mason, Paris, 1890. (1926), and the Franklin Institute the Franklin Medal 3 Champetier G, Bull Soc Chim Fr, 3 (1955) 469. (1933). 4 Berthollet C L, Ann Chim, 25 (1798) 233. The maximum award came in 1912 when Sabatier 5 Thenard L J, Ann Chim, 85 (1812) 132. was awarded the Nobel Prize of Chemistry for his 6 Thenard L J, Ann Chim, 93 (1831) 79. method of hydrogenating organic compounds in the 7 Sabatier P, Compt Rendus, 106 (1888) 1724; 107 (1888) 40. presence of finely divided metals. He shared the prize 8 Wojtkowiak B, Paul Sabatier Un Chimiste Ind?pendant with Victor Grignard (1871-1935), who received it on (1854-1941), Jonas Editeur, Argueil, 1989. account of his discovery of the so-called Grignard 9 Mond L, Langer C & Quincke F, J Chem Soc, 57 (1890) 749. reagent. 10 Mond L & Quincke F, J Chem Soc, 57 (1890) 604. 11 Berthelot M, Compt Rendus, 112 (1891) 1343. Interesting enough, the road of both Sabatier and 12 Sabatier P & Senderens J B, Compt Rendus, 114 (1892) Grignard to the Nobel Prize of Chemistry was deter- 1429. mined by a twist of destiny. As mentioned before, 13 Mond L, Langer C & Quincke F, J Chem Soc, 57 (1890) 749. Sabatier went to become a chemist and not an engi- 14 Sabatier P, Ind Eng Chem, 18, (1926) 1005. neer because his acceptance to the École Polytech- 15 Sabatier P & Senderens, J B, Bull Soc Chim Fr, 9 (1893) nique was arrived several days after that to the École 669. Normale Supérieure. In 1887, Grignard graduated 16 Moissan H & Moureu, Compt Rendus, 122 (1896) 1240. with honours the lycée at Cherbourg. At that time the 17 Sabatier P & Senderens J B, Compt Rendus, 124 (1897) 616. 18 Sabatier P & Senderens J B, Compt Rendus, 124 (1897) city of Paris offered scholarships to brilliant graduates 1358. from the secondary schools in the provinces, to pre- 19 Nye M J, Isis, 68 (1977) 375. pare for the entrance examinations to one of her uni- 20 Sabatier P & Senderens J B, Compt Rendus, 128 (1899) versities. The Cherbourg lycée had received a promise 1173. that Grignard would be awarded one of those scholar- 21 Sabatier P & Senderens J B, Compt Rendus, 130 (1900) ships in order to prepare for the entrance examina- 1559. tions to the École Normale Supérieure in Paris, to 22 Sabatier P & Senderens J B, Compt Rendus, 130 (1900) 1761. study mathematics. Unfortunately, because of the ex- 23 Sabatier P & Senderens J B, Compt Rendus, 131 (1900) 40. penses involved in the preparation of the 1889 World 24 Sabatier P & Senderens J B, Compt Rendus, 132 (1901) 210. Exposition (that would see the inauguration of the 25 Sabatier P & Senderens J B, Compt Rendus, 134 (1902) 514. Eiffel Tower) no scholarships were offered at the time 26 Sabatier P & Senderens J B, Compt Rendus, 134 (1902) 689. of Grignard’s graduation from high school. 27 Sabatier P & Mailhe A, Ann Chim Phys, 20 (1910) 289. Whoever took the decisions that affected the ca- 28 Sabatier P & Mailhe A, Compt Rendus, 150 (1911) 823. reers of Sabatier and Grignard, could have hardly 29 Sabatier P & Mailhe A, Compt Rendus, 152 (1911) 1212. guessed the tremendous impact they would have in 30 Kirchhoff S C, Bull Neusten Wiss Naturwiss, 10 (1811) 88. the development of modern organic chemistry. 31 Payen A & Persoz J F, Ann Chim, 53 (1933) 73. 32 Döbereiner J W, Edinburgh Phil J, 10 (1824), 153. Epilogue 33 Thenard L J, Ann Chim, 9 (1818-1819) 441. 34 Bertrand G, Bull Chim Fr, 473 (1955) 475. Sabatier ended his speech at the Nobel Prize award 43 35 Berzelius J J, Jahresbericht 1836, 15, 237, 243. ceremony saying : “Theories cannot be indestructi- 36 Moissan H, Traité de Chimie Minérale, Masson, Paris, 1904. ble. They are only the plough, which the ploughman 37 Duclaux J, Compt Rendus, 152 (1911) 1176. uses to draw his furrow and which he has every right 38 Henry W C, Phil Trans, 114 (1824) 266. to discard for another one, of improved design, after 39 De la Rive A, Ann Chim Phys [2], 39 (1828) 297. the harvest. To be this ploughman, to see my labours 40 Sabatier P, Compt Rendus, 152 (1911) 1176. result in the furtherance of scientific progress, was the 41 Partington J R, Nature, 174 (1954) 859. height of my ambition, and now the Swedish Acad- 42 Rideal E K, J Chem Soc, Abstracts, (1951) 1640. emy of Sciences has come, at this harvest, to add the 43 Anonymous, Nobel Lectures – Chemistry 1901-1921, Novel EDUCATOR 243

Foundation, Elsevier, Amsterdam, 1966; pp 216-231. 51 Sabatier P, Compt Rendus, 103 (1886) 49. 44 Langmuir I, J Am Chem Soc, 38 (1916) 2221. 52 Sabatier P, Compt Rendus, 103 (1866) 138. 45 Langmuir I, J Am Chem Soc, 40 (1918) 1361. 53 Sabatier P, Compt Rendus, 106 (1888), 63: 108 (1888) 738. 46 Sabatier P & Espil L, Compt Rendus, 158 (1914) 668. 54 Sabatier P, Compt Rendus, 114 (1892) 1476. 47 Chamichel C, Bull Soc Chim Fr, (1955) 466. 55 Sabatier P, Compt Rendus, 115 (1892) 236. 48 Sabatier P, Recherches Thermiques Sur les Sulphures, Thèse 56 Sabatier P, Compt Rendus, 114 (1892) 1429. de Doctorat, #445, Sorbonne, Paris, 1880. 57 Sabatier P, Compt Rendus, 122 (1896) 1479. 49 Wisniak J, Chem Educator, 5 (2000) 156. 58 Sabatier P, Compt Rendus, 122 (1896) 1537. 50 Sabatier P, Compt Rendus, 106 (1888) 1724; 107 (1888) 40. 59 Sabatier P, Compt Rendus, 123 (1896) 255.