Pioneering studies

Paul Sabatier achieved a long series of studies that would eventually lead to a general method of direct hydrogenation by catalysis, and that would earn their originator the Nobel Prize in 1912.

Until then, hydrogenation methods had been limited to the use of nascent hydrogen or to catalysis by platinum.
This method is attractive for several reasons:
1- it is simple, using simple techniques and ordinary equipment, presents no danger and leads to good yields (Sabatier took out seven patents).
2- it renders possible certain very worthwhile reactions, and would eventually lead to a great number of industrial applications, in France and abroad.
3- it allows a theoretical interpretation, in which Sabatier proposed a reaction mechanism based on the hypothesis of intermediate combinations. Let us note that bi-dimensional chemical compounds of defined composition and structure, reaction intermediates (metallic formiates) inaccessible via kinetic methods, would be observed at the surface of catalysts, in the early 1960s.
“I acknowledge that hydrogen acts on the metal by very rapidly creating a combination on its surface. The hydride thus created is easily and rapidly dissociable, and if it is put into contact with materials able to use hydrogen, it releases the hydrogen to them while regenerating the metal, which, in turn, indefinitely has the same effect.”
This purely chemical explanation contrasted with the proposition of Moissan and Duclaux, who imagined a physical adsorption of reagents on the catalyst, an explanation which, emphasized Sabatier, would exclude all phenomena occurring in a homogeneous system. According to him, there must not exist “fundamental differences between the various types of catalysis.”
The method of direct hydrogenation led to an impressive number of applications, particularly abroad, to such a degree that B. Wojtkowiak identified Sabatier as the “leader of the modern school of heterogeneous catalysis.” [4] . A lively example merits special mention. In a patent registered in 1915, Sabatier and Maihle had identified a catalytic cracking process for hydrocarbons preferable to thermal cracking, and recommended the use of divided metals or of oxides capable of forming them, associated with an in situ catalyst revivification technique using water vapour. This method was of great industrial value in the United States and, in particular, permitted the fabrication of great quantities of gasoline for WWII aviation. The story must, however, be completed: only one French pharmacist showed interest in this process, and only one young industry man, who was interested in automobile racing, built a pilot unit in the suburbs of Paris and proved that a considerable increase in octane points was possible thereby. This installation, which elicited no interest from any petroleum company in France or Navarre, was reconstituted in the United States, and so the fixed-bed Houdry process was put into operation at the Paulsboro refinery, near Philadelphia. As of 1936, Sun Oil was therefore the first company in the world to operate a catalytic cracking unit.
In addition to the applications in the fuels industry, which evolved as we know starting around 1930, Sabatier’s hydrogenation method had an important impact on the industries of organic synthesis and of glycols, as well as on the industries derived from aniline (dyes and pharmaceuticals) and from methane. In 1944, H. S. Taylor saluted Sabatier as well as France: “Paul Sabatier’s glory lay in holding very high among nations the scientific renown of France. The hydrogenation of oils, methanol synthesis, catalytic etherification, the synthesis of amines and of thiols, the hydrogenation of olefins, all of the modern applications of catalysis to hydrocarbons come directly from the works of Sabatier and of his students.”
As Sabatier himself recognized, his explanation based on temporary unstable combinations took hypothetical products into account. It was nonetheless very fruitful, and allowed the prediction of a great number of phenomena. Is this not the attribute of a good theory?

At the beginning of the 20th century, catalysis progressed in an essentially empirical manner: BASF tested at least 2000 catalysts throughout 6000 experiments before retaining the iron catalyst that would permit the industrial fabrication of ammonia from atmospheric nitrogen. The comprehension of the phenomenon barely advanced, however: Sabatier’s theory of purely chemical mechanisms, which contrasted with Moissan’s theory of physical adsorption of the reagents, in which the reagents were compressed and heated in the pores of the catalyst mass, was criticized by Ostwald [5]. Soon after, Langmuir published a theory of chemisorption that took into account the physical conditions [6]. With none of these theories furnishing sufficient proof, it was barely possible to be taken seriously when one focused on catalysis. … Though most of the technical progress in industrial chemistry accomplished from the beginning to the century to this point was due to contact catalysis, progress in the knowledge of phenomena would be the result of advances in homogeneous catalysis.

Catalysis has had difficulty asserting itself as a specific field of scientific activity or as a teaching or research department. For catalysis is based essentially on the following constituent paradox: it involves numerous phenomena involving physics and multiple sectors of chemistry, and meanwhile, immense areas of chemical industry employ catalytic operations. This means that, at the foundation, catalysis will be better handled in industrial chemistry by the apprehension of processes than in treatises on physical chemistry.

Even though as early as 1927, Sabatier began to publish his Notes in the C.R. de l’Académie des Sciences under the heading Catalysis, and no longer under Organic Chemistry, it was only in the 1950s that catalysis was considered a true subject. At this time Paul H. Emmett edited a collective work entitled Catalysis, the first two volumes of which were dedicated to the fundamental principles and the theories of homogeneous and heterogeneous catalysis [7]. As he said in the opening, even if the importance and the number of catalytic processes employed by industry could, in and of themselves, be sufficient to justify the publication of a treatise on catalysis, it was, in fact, the progress in the understanding of catalysis that made it necessary to publish a current state of the art. Even though the scientific foundation of catalysis was not yet firmly established at that stage, the new progress in the field, in particular the establishment of a relationship between the activity and the electronic structure of a solid, made it possible to write a clear, intelligible summary of the theory and practice of catalysis.

2nd International Congress on Catalysis
The Second International Congress on Catalysis held in Paris in 1960 was an important event was organised in France and presided by Marcel Prettre. Nine hundred scientists from about thirty countries in the world were reunited in Paris. The Acts, published in 1961, would come to occupy almost 3000 pages. After evoking the two main categories of contributions to the advancement of the knowledge of the catalytic solid, Prettre pointed out that, despite certain disagreements between theory and experiment, it was important to continue to adapt solid state investigation techniques (electric measurements, infrared spectroscopy, calorimetry) to the special challenges of catalysis. It was also necessary to make efficient measurements and, during interpretation of results, to take into account the extreme variability of the process depending on the experimental domain. Though it was still far from possible to establish a general theory of contact catalysis, considerable progress had been made since the previous congress, particularly regarding the knowledge of the two-dimensional compounds of the intermediate step. Decidedly, despite its extreme complexity, heterogeneous catalysis was no longer very far removed from homogeneous catalysis, in terms of its representation of intermediate steps and of the state of its knowledge.