Indian Journal of Chemical Technology Vol. 12, March 2005, pp. 232-243 Catalytic Hydrogenation 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 be- ing 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.