John Sinfelt: Removal of lead from gasoline with bimetallics

John Sinfelt

John Sinfelt

Use of lead alkyls, primarily in the form of tetraethyllead, to enhance the octane number and performance of U.S. motor gasolines nearly doubled from 235,000 tons in 1955 to 445,000 in 1975. As the harmful health effects of tailpipe-exhausted lead compounds became increasingly apparent, legislative initiatives, beginning in 1975, mandated the complete removal of lead additives from U.S. motor fuels by year-end 1991. Dr. Sinfelt’s research on alternate petroleum conversion chemistries allowed refiners to remove lead alkyls from gasoline years before the mandated deadline. Application of novel, highly active and selective bimetallic cluster catalyst systems he invented and championed made it possible to produce high-octane motor gasoline without the use of lead additives.

Dr. Sinfelt’s distinctive research methodology emphasized entirely new concepts in the understanding and use of catalyst materials containing bimetallic clusters. Earlier work on metal alloys emphasized the relation between catalytic performance of a metal and its electron band structure. However, little attention had been paid to the possibility of catalytically influencing the selectivity of chemical transformations (product selectivities). One of Dr. Sinfelt’s most important discoveries, achieved through in-depth studies on bimetallic catalysts, concerns control of chemical reaction selectivity. He discovered that it is, in fact, possible to catalyze one type of chemical reaction in preference to other reactions that are themselves thermodynamically favorable. He clearly showed that bimetallic catalysts could be tailored to effectively reduce undesirable competing reactions, and thus control the kinetic specificity of surface reactions. This made possible the economical conversion of low octane number molecules to ones with high octane numbers. The public benefited greatly from the environmental improvements due to lead-free gasoline, and motorists did not pay a hugh price for it.

While Dr. Sinfelt’s research has made far-reaching contributions to our understanding of hydrocarbon conversion processes, the practical benefits of his research are equally profound. The application of bimetallic catalysts in petroleum refining was crucial to making high-octane “lead-free” motor fuels widely available. Today, bimetallic catalysts have replaced traditional catalysts in catalytic reforming (the major commercial process used in increasing the octane rating of motor fuels) allowing thereby elimination of lead-based, octane improving additives. Dr. Sinfelt is the inventor both of a Pt-Ir catalyst that has been widely used in catalytic reforming and of a staged reforming process that has also found wide application. The latter uses two different bimetallic catalysts in separate reactors to optimize performance. The classic work of Sinfelt on the kinetics of catalytic reforming reactions in the late 1950’s and early 1960’s provided the foundation for these important industrial advances.

In addition to eliminating the hazard of lead in gasoline, Sinfelt’s work enabled the development and application of multi-metallic catalysts for the exhaust systems of automobiles to decrease the emission of pollutants such as carbon monoxide, unburned hydrocarbons and nitrogen oxides. The catalysts commonly used today contain a combination of metals; i.e., they are bi-metallic or tri-metallic. These catalysts, like reforming catalysts, perform better when more than one metallic element is present. Current exhaust catalyst systems are based on Sinfelt’s ground breaking discoveries. Finally, since these catalysts are poisoned by lead, its removal from gasoline made the application of auto exhaust catalysts technically feasible.

The basic studies of Dr. Sinfelt on bimetallic catalysts generated much interest in the field and called attention to their importance for catalytic reforming and for the production of lead-free gasoline. The discovery was first reported in two U. S. Patents to Sinfelt et al. (3,442,973, which issued in 1969 and 3,617,518, which issued in 1971) and in two papers in the Journal of Catalysis 24, 283 (1972) and 29, 308 (1973). These early publications stimulated much interest in bimetallic catalysts as a major area of research that is still flourishing. For these contributions to the lead phase-down in the United States, Dr. Sinfelt was awarded the National Medal of Science by the President of the United States in 1979 and the prestigious Perkin Medal in 1984. His is among the most important contributions enabling the worldwide reduction of environmental lead and the elimination of the associated risks to human health.

In a tribute to John Sinfelt in I&EC, 42 (2003) 1537, Professor Michel Boudart comments, “His impact has been uniquely important because John combined the inventiveness required for scientific discovery with the ability to engineer his work to many successful applications in industry. John succeeded though repeated scientific discoveries and engineering applications, without ever preaching … John managed to become a role model to those who practice catalytic science, not only in the secretive industrial environment but also in universities worldwide … The legacy of John Sinfelt is his unshakable belief in chemical kinetics to advance catalytic science and engineering. John’s impact on the field exceeds by much the impact of his own scientific and engineering contributions.”
Contributed by Gary McVicker and John Armor