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Emmett, Paul Hugh

EMMETT, PAUL HUGH

(b. Portland, Oregon, 22 September 1900;

d. Portland, 22 April 1985), chemistry, catalysis.

Emmett devoted sixty years of research to unraveling the myriad complexities and subtleties of chemical catalysis. After the turn of the twentieth century, industrial chemists were increasingly employing metal catalysts to make chemical reactions fast and efficient. However, the scientific understanding of catalysis lagged far behind its technical importance throughout the first half of the century. Emmett was one of a small group of chemists, beginning in the 1920s, who were undaunted by the complexity of the phenomena they were investigating. His most important contribution was his research in the mid-1930s on determining the surface area of catalyst particles. Before this work, researchers could not distinguish between catalysts that very efficiently expedited chemical reactions and those that reacted molecules more slowly over a very large surface area. In order to investigate the actual mechanism of catalysis, it was critical to normalize experiments by accounting for differences in surface area. Working with a colleague, Stephen Brunauer, and physicist Edward Teller, Emmett developed a straightforward experimental method for determining the surface area of a catalyst particle. Their classic paper, “Adsorption of Gases in Multimolecular Layers,” was published in 1938; their surface area formula soon became known as the BET (Brunauer-Emmett-Teller) equation.

Over his long, productive career, Emmett published 164 papers and edited 8 books. Perhaps reflecting the scientific ethos of his formative years—the 1920s—his approach to research was to investigate what were deemed at the time the “fundamentals” of catalysis—that is, to explain the various physical and chemical properties that determined how a particular catalyst worked. The goal of this work, of course, was to develop a more general understanding of the phenomena involved. His methodology can be characterized as scientific puzzle solving. Emmett became highly skilled at designing experiments and interpreting the data they yielded. His extensive study of catalysts used to make ammonia was cited by catalysis pioneer Hugh S. Taylor as a model for others to emulate. In recognition of his stature in catalysis, Emmett was elected to the National Academy of Sciences in 1955.

Childhood and Education . Emmett was born in Portland, Oregon, on 22 September 1900, to John Hugh and Vina (Hutchens). His father worked for a railroad and had become an expert on explosives. In high school, Emmett took no science classes until his senior year, when a guidance counselor suggested that he take chemistry and physics. His chemistry teacher, William Green, inspired him to continue studying chemistry in college. Green apparently had a similar effect on another young man, Linus Pauling. Emmett, who was a friend of Pauling, followed him to the Oregon Agricultural College (now Oregon State University) at Corvallis and then for graduate school to the new California Institute of Technology (Caltech) in 1922. (They would publish a paper together in 1925, “The Crystal Structure of Barite,” on the crystal structure of barium sulfate.) Emmett was attracted to Caltech because of its eminent faculty members, including Arthur A. Noyes in chemistry and Robert Millikan in physics, and the fact that its graduate stipends were double those of other schools. At Caltech, Emmett worked with Arthur F. Benton, who had been a student of Hugh S. Taylor at Princeton University in New Jersey. Benton was an accomplished experimentalist working on the role of adsorption in catalysis. For his thesis, Emmett studied a number of metal oxide systems to determine whether during reduction with hydrogen, the reduced metal atoms became catalytic sites that accelerated the reaction rate. This was his initiation into the emerging science of catalysis.

The BET Equation After earning his doctorate at Caltech in 1925, Emmett taught for one year at his undergraduate alma mater before joining the Fixed Nitrogen Research Laboratory (FNRL) in Washington, D.C., during 1926. The FNRL had been founded in 1919 as a continuation of wartime efforts to develop an American “fixed” nitrogen industry for the production of synthetic ammonia. At the outbreak of World War I, most of the world’s supply of nitrates, an essential ingredient in explosives and fertilizer, came from mines in Chile. Germany, which had stockpiled only enough nitrates for a short war, came to rely on the new Haber-Bosch process that produced ammonia from the high-pressure catalytic reaction of nitrogen and hydrogen. In the early 1920s the FNRL developed its own ammonia process, a key component of which was an effective catalyst.

When Emmett joined the FNRL, located at American University, he was assigned to work on the iron catalyst used in the process. As part of his extensive studies on ammonia catalysts, he realized that it would be important to know the surface area of catalyst particles; his research on this matter led to the famous BET equation. The scientific challenge was to correlate what could be measured, which in this case was curves of the mass of gas adsorbed on a catalyst surface as a function of pressure at a constant temperature. Emmett’s mentor, Benton, had conducted experiments with nitrogen that showed several kinks in this curve. Benton had hypothesized that these kinks might signal the completion of the first and then additional layers of gas molecules surrounding the catalyst surface. However, Emmett determined that the kinks could be accounted for by deviations from the ideal gas law. Upon further study of these curves, Emmett surmised that the beginning of the linear section might indicate the completion of a monolayer and the beginning of a second layer of adsorbed molecules. Using a number of different gases and catalysts, Emmett became convinced that his hypothesis was correct. At this point, in 1937, Brunauer, who was doing the experimental work and also had helped analyze the curves, told a former teacher and fellow Hungarian, Teller, about this research. Teller had left Hungary in 1935 and taken a position in the Physics Department at George Washington University in Washington, D.C. Starting with the earlier work of Irving Langmuir on adsorbed monolayers, Teller developed a theory of multilayer adsorption, which included the equation for calculating surface area from adsorption data.

In his eleven years at the FNRL and—after 1927—its successor, the U.S. Department of Agriculture’s Bureau of Chemistry and Soils, Emmett also developed methods for determining the surface composition of multicomponent catalysts. (The ammonia catalyst was a three-component one.) One of Emmett’s favorite projects was one which showed that an anomaly in the predicted and measured equilibrium constant in the important water gas reaction (H20 + CO= H2 + CO2) was the result of thermal diffusion effects in standard apparatus.

Mellon Institute and Johns Hopkins . In 1937 Emmett moved to Johns Hopkins University, where he became the first head of its Department of Chemical Engineering. He later noted that during the late 1930s and early 1940s, it was very difficult to find money to finance basic research. In 1943 Emmett left Hopkins and joined the Manhattan Project, where he did mostly administrative work before moving on the following year to the Mellon Institute in Pittsburgh to work on research sponsored by Gulf Oil, which had its headquarters there. His research at the Mellon Institute focused on sorting out the complex set of reactions occurring in the Fischer-Tropsch process that produced gasoline from carbon monoxide and hydrogen. This process had been commercialized in Germany, and American oil companies saw it as a potential alternative to processes based on petroleum should supplies of it become scarce and expensive. To follow the complex path of reactions, Emmett used molecules that were tagged with radioactive carbon-14 atoms. As concerns about the future supply of oil faded in the 1950s, Emmett shifted to studying catalytic cracking of petroleum fractions to make gasoline. Catalytic cracking, which had been developed by Eugene Houdry in the 1930s, produced high-octane gasoline, but chemists did not understand how the mixture of molecules in petroleum were broken up and reformed. To comprehend this, he developed a microcatalytic pulse reactor that could be put in the gas stream of a gas chromatograph. This allowed him to analyze the compounds that are produced by reactions on the surface of the catalyst. His research on catalytic cracking demonstrated that the larger molecules in gasoline were built up by reactions of smaller molecules generated by cracking.

In 1955 Emmett left the Mellon Institute and returned to Johns Hopkins, this time as the W. R. Grace Professor in the Chemistry Department. He continued his research on catalytic cracking and did more general studies to investigate the nature of catalysis. After retiring from Johns Hopkins in 1971, he returned to his native Oregon where he served as visiting research professor at Portland State University until his death on 22 April 1985.

Encyclopedist of Catalysis . In addition to his research, Emmett was widely recognized for his encyclopedic knowledge of the catalysis literature and his willingness to share his information with others. His expertise, in part, resulted from his editing of seven volumes on catalysis between 1954 and 1960. In 1965 he coauthored a text titled Catalysis Then and Now. Emmett wrote Part 1, which was a general survey of catalysis, with emphasis on his areas of expertise. Part 2 was a reprint of a translation of catalyst pioneer Paul Sabatier’s 1913 treatise, La catalyse en chimie organique(translated as Catalysis in Organic Chemistry). It is rather unusual in science that a general survey of a field, like Emmett’s contribution to Catalysis Then and Now, would still be relevant over forty years after its publication. But catalysis had always been a highly empirical art, so the careful experimental results of early investigators were never completely replaced by later investigations or more general theoretical treatments. It was perhaps the hallmark of Emmett’s career that his work has held up to the test of time in spite of advances in the field, especially in instrumentation, which has allowed much more intimate examination of chemical reactions on catalyst surfaces.

BIBLIOGRAPHY

Emmett’s papers are at Oregon State University in Corvallis, Oregon. (See http://osulibrary.oregonstate.edu/specialcollections/coll/emmett/index.html) “Publications by Professor Paul H. Emmett,” in Journal of Physical Chemistry 90 (1986): 4706–4710, provides a complete bibliography of Emmett’s published works.

WORKS BY EMMETT

With Linus Pauling. “The Crystal Structure of Barite.” Journal of the American Chemical Society46 (1925): 1026–1030.

With Stephen Brunauer and Edward Teller. “Adsorption of Gases in Multimolecular Layers.” Journal of the American Chemical Society 60 (1938): 309–319.

Editor. Catalysis. 7 vols. New York: Reinhold, 1954–1960.

With Paul Sabatier. Catalysis Then and Now. Englewood Cliffs, NJ: Franklin Publishing, 1965. Emmett wrote Part 1, A Survey of the Advances in Catalysis.

“The Fixed Nitrogen Research Laboratory.” In Heterogeneous Catalysis: Selected American Histories, edited by Burtron H. Davis and William P. Hettinger Jr. Washington, DC: American Chemical Society, 1983.

OTHER SOURCES

Brasted, Robert C., and Peter Farago, eds. “Interview with Paul H. Emmett.” Journal of Chemical Education 55, no. 4 (April 1978): 248–252.

Davis, Burtron H. “Paul H. Emmett (1900–1985): Six Decades of Catalysis.” Journal of Physical Chemistry90, no. 20 (1986): 4701–4706. This article is in the Emmett Memorial Issue of the journal.

Garten, Robert L. “Paul H. Emmett: Six Decades of Contributions to Catalysis.” In Heterogeneous Catalysis: Selected American Histories, edited by Burtron H. Davis and William P. Hettinger Jr. Washington, DC: American Chemical Society, 1983.

Koski, Walter S. “Paul Hugh Emmett, September 22, 1900–April 22, 1985.” Biographical Memoirs of the National Academy of Sciences 67 (1995): 118–129. Also available from http://www.nap.edu/readingroom/books/biomems/pemmett.pdf

John K. Smith

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