Heterogeneous Catalysis - American Chemical Society

33 Catalysis at Princeton University Chemistry Department

Downloaded by CORNELL UNIV on August 22, 2016 | http://pubs.acs.org Publication Date: June 3, 1983 | doi: 10.1021/bk-1983-0222.ch033

JOHN TURKEVICH Princeton University, Chemistry Department, Princeton, NJ 08544

Catalysis started at Princeton in 1919 when Taylor(1) came from England to join the Chemistry Department. Turkevich came as a graduate student of Taylor's in 1931. Except for one year at Leipzig and Cambridge Universities, Turkevich remained at Princeton since that time. Taylor assumed the deanship of the Graduate School in 1948 and retired in 1958. Turkevich retired from teaching in 1975 and is s t i l l active in catalytic research. Steven Bernasek joined the faculty in 1976 and Jeffrey Schwartz in 1970. Both are active: one in surface chemistry and the other in catalysis. The work in the Chemistry Department has been complemented by that in the Department of Chemical Engineering by Richard Wilhelm (1934-65), Leon Lapidus (1954-1977), Michel Boudart (1953-1962) and David Ollis (1969-1980). For sixty-three years there has been a continuity of research in catalysis at Princeton University: continuity in basic ideas expressed by novel techniques. There was close association between the research activity and training of undergraduates, graduate students, postdoctoral research associates and visiting professors. The students carried out and are still carrying out the Princeton tradition throughout the world.

0097-6156/83/0222-0463$07.75/0 © 1983 American Chemical Society

Davis and Hettinger; Heterogeneous Catalysis ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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Hugh S. Taylor and Chemical

Physics

The founder and leader f o r many decades of the P r i n ceton School of c a t a l y s i s was S i r Hugh T a y l o r . A student of H. Bassett, J r . and F. W. G. Donnan, at L i v e r p o o l U n i v e r s i t y , Taylor d i d research work with Svante Arrhenius at the Nobel I n s t i t u t e i n Stockholm and with Max Bodenstein at the Technische Hochschule at Hanover, Germany. Bodenstein had a strong i n f l u e n c e on T a y l o r . He spurred him to t r a v e l i n k i n e t i c s along the path of c a t a l y s i s and h i s steed was to be chemistry p h y s i c s — the molecular s t r u c t u r e approach to Chemistry. During World War I Hugh Taylor worked with E r i c R i d e a l f o r the B r i t i s h Munitions Board on ammonia synthesis and the water gas s h i f t r e a c t i o n . During t h i s p e r i o d he wrote with E r i c R i d e a l " C a t a l y s i s i n Theory and P r a c t i c e " (1919). On h i s r e t u r n to P r i n c e t o n i n 1919 (where he had been f o r a short time i n 1915) Taylor organ i z e d the f i r s t center of c a t a l y s i s i n the United S t a t e s . Phys i c a l chemistry was i n i t s infancy and was dominated by concepts of e q u i l i b r i u m . Thermodynamics was king and e l e c t r o c h e m i s t r y , queen. T a y l o r was i n f l u e n c e d by h i s work on homogeneous react i o n s at the Arrhenius l a b o r a t o r y , by h i s research of gaseous k i n e t i c s i n Bodenstein's i n s t i t u t e and by h i s experience i n heterogeneous c a t a l y s i s i n B r i t a i n . In Princeton he turned to k i n e t i c s of heterogeneous c a t a l y t i c r e a c t i o n s with a s s o c i a t e d i n t e r e s t s i n photochemistry, discharge tube chemistry, alpha p a r t i c l e induced r e a c t i o n s . The i n i t i a l approaches were m a c r o s c o p i c — c h a r a c t e r i s t i c of p h y s i c a l chemistry. Taylor however went beyond that, h e l p i n g to e s t a b l i s h the d i s c i p l i n e of chemical p h y s i c s . This motivated the P r i n c e t o n school of c a t a l y s i s f o r a h a l f a century. Atomic and molecular theory of matter, quantum mechanics, s t a t i s t i c a l mechanics were i n explosive development at the time. The Physics Department of the U n i v e r s i t y and the I n s t i t u t e of Advanced Studies at P r i n c e t o n were centers of t h i s development. A l b e r t E i n s t e i n , N i e l s Bohr, Wolfang P a u l i , J . von Neumann, E. U. Condon, Eugene Wigner, P. A. M. D i r a c were at Princeton at that time. On the experimental side spectroscopy was p r a c t i c e d at a high l e v e l by Alan Shenstone. A general-use i n f r a - r e d spectrometer was b u i l t by Bowling Barnes and mass spectroscopy was developed and s t u d i e d by Walker Bleakney. Chemical p h y s i c s - i n v e s t i g a t i o n of d i v e r s e chemical species and t h e i r r e a c t i o n s at the atomic and molecular l e v e l , became the p r i n c i p a l theme of the Princeton scene. Not only d i d T a y l o r use i t as a bridge between the Chemistry and Physics Departments, but he a l s o b u i l t up t h i s d i s c i p l i n e w i t h i n the Chemistry Department. In 1927 he a t t r a c t e d G. Kistiakowsky from the Bodenstein Laboratory to P r i n c e t o n . Unfortunately f o r P r i n c e t o n Kistiakowsky moved to Harvard where he, together with another P r i n c e t o n i a n , E. B r i g h t Wilson, i n i t i a t e d a s i m i l a r program of chemical physics. T a y l o r countered with the appoint-



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ment of Henry E y r i n g as the f i r s t t h e o r e t i c a l chemist. Interact i o n between Chemisty and Physics was f u r t h e r strengthened by frequent short v i s i t s to P r i n c e t o n by Linus P a u l i n g , I r v i n g Langmuir, Harold Urey, Joseph Mayer, J . H. Van Vleck, J . S l a t e r and longer stays of A. T i s e l i u s , M. G. Evans, B. Topley, Lord Wynne-Jones and J . Kirkwood. Communal l i v i n g at the Graduate School brought chemists i n contact with such p h y s i c i s t s as John Bardeen, Robert Hofstadter, F r e d e r i c k S e i t z , Joseph H i r s c h f e l d e r . At the same time Taylor organized a p p l i e d c a t a l y s i s s t u d i e s i n the Engineering School. Richard Wilhelm came to P r i n c e t o n i n 1933 to carry out research on c a t a l y t i c r e a c t o r design and mass and heat t r a n s f e r i n c a t a l y t i c systems. The P r i n c e t o n branch of the R o c k e f e l l e r I n s t i t u t e f o r Medical Research served as a l i n k with biochemistry. Such prominent personages as John Northrup, Wendel Stanley, M. Anson, M. Kuntiz with t h e i r colleagues, attended seminars i n p h y s i c a l chemisty. One product of a post-seminar d i s c u s s i o n of Rene Dubos, George Wald and Dean Burk was the work on hydrocarbon metabolizing bact e r i a by Turkevich, Goodale and F. Johnson.(2)

Taylor's Concepts- A c t i v a t e d Adsorption T a y l o r developed three concepts which were made more p r e c i s e by the work of h i s students i n many c o u n t r i e s and by h i s successor Turkevich at P r i n c e t o n . The f i r s t was the concept of a c t i v a t e d a d s o r p t i o n . I t was known from the time of Michael Faraday, that heterogeneous c a t a l y t i c r e a c t i o n s took place on the surface of the s o l i d . The f i r s t attempt to e x p l a i n the increase i n r e a c t i v i t y by mere increase i n concentration of reactants on the c a t a l y s t surface was abandoned. P h y s i c a l a b s o r p t i o n could not e x p l a i n the s p e c i f i c i t y of c a t a l y t i c a c t i v i t y . P h y s i c a l adsorption was e x t e n s i v e l y studied during World War I on c h a r c o a l , s i l i c a and other high surface m a t e r i a l s as part of the gas mask war e f f o r t . A f t e r World War I new c a t a l y s t m a t e r i a l s came i n t o i n d u s t r i a l use i n hydrogénation of f a t s , ammonia synthesis and methanol production. These c a t a l y s t s cons i s t e d of metals, metals on supports, oxides of t r a n s i t i o n e l e ments and z i n c oxide. At the same time novel techniques were a v a i l a b l e f o r experimental s t u d i e s : Pyrex glass handling systems, mechanical fore pumps, mercury high vacuum pumps, McCleod gauges, Dewar f l a s k s with Dry Ice or l i q u i d a i r . These T a y l o r and h i s students used to study the adsorption of gases on i n d u s t r i a l l y important c a t a l y s i s . I t was found that there were at l e a s t two types of adsorption. One was a r a p i d low temperature a d s o r p t i o n — p h y s i c a l i n type, a s s o c i a t e d with van der Waals forces and decreasing with r i s e i n temperature. This was u t i l i z e d e f f e c t i v e l y l a t e r by Brunauer, Emmett and T e l l e r f o r the determination of the t o t a l surface area of a f i n e l y d i v i d e d



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s o l i d . ( 3 ) In a d d i t i o n , on many metals and oxides there was another slow adsorption process increased i n extent with temperature, went through a maximum and then decreased. Since t h i s was a slow process, i n v o l v i n g a temperature c o e f f i c i e n t , Taylor c a l l e d i t a c t i v a t e d adsorption(4) and attempted to c o r r e l a t e i t with the a c t i v a t i o n of the adsorbed r e a c t a n t s . T h i s provoked considerable controversy—was i t r e a c t i o n with the s u r f a c e , was i t s o l u b i l i t y i n the s o l i d , was i t a d i f f u s i o n c o n t r o l l e d process, was i t displacement of a poison from the surface? Many systems were s t u d i e d by R. M. Burns,(5) A. W. Gauger,(6) R. A. Beebe,(7) W. A. Dew,(8) G. B. Kistiakowsky,(9) E. W. F l o s d o r f , ( 1 0 ) A. T. Williamson,(11-12) P. V. Kinney,(13) D.V. Sickman,(14) A. Sherman,(15) A. J . Gould,(16) J . Pace,(17) J.Turkevich,(18) R. L. Burwell, Jr.(19-20). A c r i t i c a l i n v e s t i g a t i o n was the adsorption of hydrogen on z i n c oxide. In 1934 C. 0. Strother(21) found two types of a c t i v a t e d a d s o r p t i o n while i n 1938 E. A. Smith and Taylor(22) showed that the r e a c t i o n between hydrogen and deuterium which involved a c t i v a t i o n of hydrogen went at a much f a s t e r rate than e i t h e r a c t i v a t e d a d s o r p t i o n of hydrogen gas. Gradually the emphasis s h i f t e d from a c t i v a t e d adsorption to chemisorption as a method of determining the number of r e a c t i v e s i t e s . ( 2 3 ) Elegant techniques f o r determining the number of a c t i v e s i t e s by chemisorption were developed by Emmett and h i s group and by students of T a y l o r : Benson and Boudart.(24) The r e l a t i o n between the numbers of centers which chemisorb reactants and the number of centers which are c a t a l y t i c a l l y a c t i v e came l a t e r from the Turkevich group. Active

Centers

Another important concept introduced by Taylor was that of heterogeneity of s u r f a c e - a c t i v e centers.(25-26) This stemmed from observation of R. N. Pease that minute amounts of carbon monoxide, much smaller than the amount necessary to cover the s u r f a c e , were s u f f i c i e n t to poison the surface of a copper c a t a lyst. T a y l o r proposed that there were a c t i v e centers on the surface while others argued that n i c k e l i m p u r i t i e s segregated p r e f e r e n t i a l l y on the surface and acted as c a t a l y s t . The v a r i a t i o n of the heats of adsorption with surface coverage as determined by R. Beebe was used as evidence supporting the concept of a c t i v e centers. In s p i t e of the c o n t r a d i c t o r y i n t e r p r e t a t i o n of the same experimental data, the concept of a c t i v e centers has been a f r u i t f u l one. I t i n s p i r e d imaginative research i n the f i e l d of metal and oxide c a t a l y s i s and has i t s present day expression i n s o p h i s t i c a t e d surface physics s t u d i e s . Subsequent work by coworkers of Turkevich at P r i n c e t o n r e f i n e d the nature of a c t i v e centers i n monodisperse metal p a r t i c l e s and c r y s t a l l i n e oxide c a t a l y s t s .


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Model Reactions The t h i r d important concept introduced by Taylor was the use of model r e a c t i o n s , "yard s t i c k s " to determine the mode of a c t i v a t i o n of molecules by surfaces. For hydrogen a c t i v a t i o n , Taylor(15) proposed the conversion of ortho to para hydrogen as a measure of the c a t a l y t i c a c t i v i t y of a s u r f a c e . This turned out to be more complicated than was f i r s t r e a l i z e d . A p h y s i c a l magnetic e f f e c t was a l s o operative as was shown among others by Diamond and Taylor(27) f o r the case of rare earths and by Turkevich and Selwood.(25) Later Laroche and Turkevich(29) used magnetic resonance to quantify the c a t a l y t i c e f f e c t of charcoal and to d i f f e r e n t i a t e i t from d i s s o c i a t i v e process. The discovery of deuterium opened up the use of i s o tope exchange r e a c t i o n s as d e l i c a t e "model r e a c t i o n s " f o r e l u c i d a t i o n of the a c t i v a t i o n of molecules. Immediately a f t e r H. Urey announced the discovery of heavy water i n 1932, Taylor(30) r e a l i z e d i t s p o t e n t i a l as a t o o l i n c a t a l y t i c research and engaged i n a massive production i n P r i n c e t o n of heavy water. Soon hydrogen-deuterium gas exchange was studied on a v a r i e t y of c a t a l y s t s and a l s o exchange between proteum and deuterium compounds. The methods of a n a l y s i s were those using thermal cond u c t i v i t y and i n f r a - r e d spectroscopy. D e t a i l e d d i s t r i b u t i o n of deuterium among v a r i o u s molecules and d i f f e r e n t s i t e s i n the same molecule d i d not come u n t i l a f t e r World War I I by Turkevich. Pioneer work was c a r r i e d out by Taylor, Morikawa, and Benedict(32-35) on the hydrogenolysis of hydrocarbons as compared to deuterium exchange. I t was shown that on n i c k e l the exchange r e a c t i o n took place at 373 to 403°K while hydrogenolys i s to methane took place at 90° higher. Thus the a c t i v a t i o n of a hydrogen-carbon bond was more f a c i l e than that of the carboncarbon bond. Morikawa went from P r i n c e t o n to work f o r the Japanese government i n Manchuria. A f t e r World War I I he became Dean of the Tokyo I n s t i t u t e of Technology and f a c i l i t a t e d the flow of Japanese post-doctorates to P r i n c e t o n . Dehydrocyclization During the t h i r t i e s , the p a l l of economic depression hung over the academic scene. There were few p o s i t i o n s f o r graduate students and post doctorates i n the chemical industry or the u n i v e r s i t i e s . Taylor went to New York to the M. W. K e l l o g g Company to obtain funds f o r an i n d u s t r i a l f e l l o w s h i p . I t s v i c e president P. D. K e i t h , J r . s a i d that money was a v a i l a b l e f o r the production of hydrogen from hydrocarbons. T a y l o r had intended t h i s f e l l o w s h i p f o r one of the unemployed i n s t r u c t o r s , b u t i n the meantime the l a t t e r had accepted a p o s i t i o n with the DuPont Company. Taylor c a l l e d i n Turkevich to take on the p r o j e c t . Turkevich had studied i n h i s d o c t o r a l t h e s i s



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the adsorption of hydrocarbons on oxide c a t a l y s t s , p a r t i c u l a r l y chromium oxide. This oxide was chosen as the c a t a l y s t . However no pure hydrocarbons higher than C3 were a v a i l a b l e at that time. Turkevich heard that pure normal heptane could be obtained as a sap from a pine tree growing on the shores of Lake Tahoe i n C a l i f o r n i a . T h i s was chosen as the s t a r t i n g m a t e r i a l . A s p e c i a l apparatus f o r a c a t a l y t i c flow system i n which the s t a r t i n g m a t e r i a l was a l i q u i d and the product l i q u i d and gas was constructed. I t c o n s i s t e d of a mercury l e v e l i n g device whose bulb was l i f t e d by an e l e c t r i c clock f i t t e d with gears and c o n t a i n i n g η heptane i n the other arm. The product c o l l e c t i n g system had a l i q u i d trap and two large carboys, one f i l l e d with s a l t water and the other empty. A mercury mano meter with an e l e c t r i c contact was attached to the t r a p . As the pressure increased i n the c o l l e c t i n g t r a p , an e l e c t r i c r e l a y allowed s a l t water to syphon from one carboy to the other c o l l e c t i n g the gas evolved. When the r e a c t i o n was c a r r i e d out i n the Spring of 1935, copious amounts of gas were produced at tmperatures above 400°C. This gas analyzed as 90% hydrogen. The l i q u i d i n the trap was toluene. Thus not only a f i n e source of hydrogen was discovered but a process was found f o r reforming i n one step heptane of octane number one to toluene of octane number one hundred and ten. The m a t e r i a l so produced was very u s e f u l i n World War I I i n g i v i n g to the B r i t i s h A i r Force a higher c e i l i n g than the Luftwaffe and to the munitions works, toluene f o r production of TNT. Further t h i s dehydroc y c l i z a t i o n process became the f i r s t bridge between a l i p h a t i c and aromatic chemistry. Various forms of chromium oxide were t r i e d and d i f f e r e n t types of alumina. The black form of chro mium oxide was found to be a c t i v e while the green form was "dead". Gamma alumina was a good support f o r chromia while alpha i n a c t i v a t e d the chromia.(36) Turkevich spent the academic year of 1935-1936 a t Cambridge U n i v e r s i t y with S i r John Lennard Jones(37) and at L e i p z i g U n i v e r s i t y with K a r l Bonhoeffer working on quantum chemistry. This was a c o n t i n u a t i o n of h i s t h e o r e t i c a l s t u d i e s with Henry Eyring(38) which r e s u l t e d i n a paper on one of the a p p l i c a t i o n s of group theory to the e l e c t r o n s t r u c t u r e of symmetric molecules. During T u r k e v i c h s absence from P r i n ceton, work on d e h y d r o c y c l i z a t i o n was c a r r i e d out by S. Goldwasser(39), Harold Fehrer and Donovan Salley.(40-44) On h i s r e t u r n from Europe Turkevich was appointed i n s t r u c t o r i n che m i s t r y and resumed h i s studies on aromatization of saturated hydrocarbons on various molybdenum c a t a l y s t s . ( 4 5 ) Molybdena on alumina, phosphomolybdic a c i d were found to be e x c e l l e n t aroma t i z a t i o n c a t a l y s t s while molybdena alone was poor, a c t i n g as a cracking catalyst. In a d d i t i o n , the r e l a t i o n between i s o m e r i z a t i o n and aromatization was i n v e s t i g a t e d by c o n t r a s t i n g the aromatization behavior of 223 t r i m e t h y l pentane with that of normal heptane. An attempt was made to extend the aromatiza1


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t i o n process to the production of h e t e r o c y c l i c compounds. Charles H. K l i n e passed amyl amine over aromatizing c a t a l y s t s i n hope of making pyridine.(46) The d i s a p p o i n t i n g product was amyl isocyanide, a h i g h l y t o x i c m a t e r i a l . This approach was promptly abandoned and p y r i d i n e was synthesized c a t a l y t i c a l l y from f u r f u r a l . As a by-product of t h i s i n v e s t i g a t i o n the i n f r a - r e d spectra of p y r i d i n e was measured(47) and a group t h e o r e t i c a l a n a l y s i s ( 4 8 ) made of i t s normal v i b r a t i o n a l modes.


War

Research

War had f l a r e d up i n the Far East. The Japanese had cut o f f the supply on n a t u r a l rubber. The s y n t h e t i c rubber program organized by the government required large amounts of butadiene. With the support of the U.S. Rubber Reserve Board, Turkevich organized a group c o n s i s t i n g of A. S a f f e r , J . Arnold, W. McCarthy and R. Woodbridge to develop a steam i n s e n s i t i v e c a t a l y s t f o r the thermodynamically d i f f i c u l t dehydrogenation of butane to butadiene. Temperatures of over 900K were required and steam was necessary to s a t i s f y the thermodynamic conditions. In the s p r i n g of 1941 Taylor e n l i s t e d Turkevich i n the atomic weapon p r o j e c t . Hahn and Strassman had c a r r i e d out t h e i r famous experiment of uranium f i s s i o n the preceding year. T a y l o r , a B r i t i s h subject, was working f o r the B r i t i s h Canadian group before the American e f f o r t was organized i n t o the Manhattan P r o j e c t . The f i r s t task was to make deuterium by c a t a l y t i c exchange with water. This process was to be used at the T r a i l , B r i t i s h Columbia plant where deuterium was to be a byproduct of ammonia s y n t h e s i s . This deuterium was to be used as a moderator i n the Canadian p i l e . George J o r i s , a Belgium post-doctorate and Walter Moore, J r . joined the group that studied t h i s c a t a l y t i c exchange process. The a n a l y s i s f o r deuterium was the d i f f i c u l t aspect of the p r o j e c t . J o r i s and Turkevich b u i l t a mass spectrometer while Turkevich worked on the thermal c o n d u c t i v i t y method. Late i n 1942, the Taylor group on deuterium production and T u r k e v i c h s butadiene p r o j e c t were incorporated i n t o the newly organized Manhattan P r o j e c t . The o b j e c t i v e was the production of enriched uranium-235 from n a t u r a l uranium by d i f f e r e n t i a l d i f f u s i o n of h i g h l y r e a c t i v e uranium h e x a f l u o r i d e through a porous membrane. A number of surface chemistry problems r e l a t e d to c a t a l y s i s had to be solved. The work at Princeton was i n support of the main e f f o r t at the SAM Laboratories of Columbia U n i v e r s i t y . Aside from production of the d i f f u s i o n b a r r i e r , the task was to c h a r a c t e r i z e i t s pore d i s t r i b u t i o n and s t a b i l i z e i t from c o r r o s i o n . Taylor was a s s o c i a t e d i r e c t o r of the SAM L a b o r a t o r i e s , spending h i s days i n New York and evenings and weekends at Princeton. Turkevich, i n a d d i t i o n to teaching both at Princeton 1



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and at Newark f o r the War Manpower Commission, brought the i n f r a - r e d spectrometer back i n t o working c o n d i t i o n . I t had been abandoned when Bowling Barnes l e f t the P h y s i c s Department to j o i n American Cyanamid Company. Together with P. C. Stevenson, he measured the i n f r a - r e d spectrum of uranium h e x a f l u o r i d e ( 4 9 ) which with the Raman spectrum measured by Professor Duncan of Brown permitted the c a l c u l a t i o n of the t h e r modynamic p r o p e r t i e s of the uranium hexafluoride so necessary f o r the d i f f u s i o n process. In the meantime the RCA Laboratories moved to P r i n ceton. Turkevich became t h e i r chemical consultant spending a h a l f a day each week at t h e i r l a b o r a t o r i e s . He became part i c u l a r l y i n t e r e s t e d i n the a p p l i c a t i o n of e l e c t r o n microscopy to c a t a l y s t s and s u r f a c e s . With James H i l l i e r he surveyed the texture of many t y p i c a l c a t a l y s t s , presenting a paper on t h e i r work at the Gibson I s l a n d Conference on C a t a l y s i s . ( 5 0 ) With the help of s e v e r a l engineers at RCA, he obtained r e p l i c a e l e c t r o n micrographs of the pores of the b a r r i e r m a t e r i a l s . These gave a d e t a i l e d view of the s i z e , shape, surface c o n d i t i o n of the pores which p r e v i o u s l y had been deduced i n d i r e c t l y by p o r o s i t y measurements. T a y l o r i n Post War

I I Period

In the post World War I I period Hugh Taylor became Dean of the Graduate School at Princeton r e t a i n i n g f o r a p e r i o d h i s chairmanship of the Chemistry Department. He kept up h i s i n t e r e s t i n c a t a l y t i c research, p a r t i c u l a r l y i n hydrogenolysis of hydrodrocarbons, mechanism of ammonia synthesis and the a p p l i c a t i o n of semiconductor theory to c a t a l y s i s . He was joined i n these researches by J . Polanyi, C. Kemball(51) and F. S. Stone(52) from England and P. J . Fensham(53) from A u s t r a l i a , A. Ozaki(58), A. Amano (56) and K. Tamaru(55) from Japan, A. Cimino(57) and G. Parravano(58) from I t a l y and J . P. McGeer(59) and M. M. Wright(60) from Canada. Among the graduate students were A. A l e i , H. Benesi, J . F. Black, L. C. Bostian, M i c h e l Boudart,(61) G. D. Halsey,Jr.(62) E. J . Mikovsky,(63) Thor Rodin, H. Sadek(64) and S. C. Liang.(65) Turkevich's Program i n Post-War Period 1

T u r k e v i c h s research program during the post World War I I period of t h i r t y - f i v e years followed the guide l i n e s f o r mulated by Hugh T a y l o r . What i s the r e l a t i o n of adsorption to c a t a l y s i s ? What i s the nature of a c t i v e c a t a l y t i c centers? In a d d i t i o n two new l i n e s were e s t a b l i s h e d : What i s the nature of a c t i v a t i o n of the adsorbed molecule by the a c t i v e center and a l s o what i s the r e l a t i o n of c a t a l y s i s i n such d i v e r s e systems as gas phase, s o l u t i o n s , enzymatic r e a c t i o n s and medical t r e a t ment such as cancer therapy?


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Turkevich's T r a i n i n g i n Chemistry Turkevich's t r a i n i n g i n chemistry and c a t a l y s i s arose i n the f o l l o w i n g way. He attended from 1919 to 1924, Columbia Grammar School i n New York where he r e c e i v e d a c l a s s i c a l education with a strong blend of mathematics. Chemistry was introduced h i s senior year as the f i r s t science subject i n t h i s o l d secondary school once a s s o c i a t e d with Columbia College. In c o n t r a s t to the other teachers, the chemistry teacher was p r i m a r i l y an a t h l e t i c coach and was a poor che m i s t r y teacher. He was so poor that Turkevich s t a r t e d to study chemistry on h i s own using c o l l e g e textbooks, p a r t i c u l a r l y the one w r i t t e n by Deming. He became f a s c i n a t e d by the s u b j e c t . On h i s m a t r i c u l a t i o n at Dartmouth College where he obtained a s c h o l a r s h i p and work f o r board due to the e f f o r t s of F r e d e r i c k Alden, the headmaster, President Hopkins asked Turkevich what subject he would choose as a major. On hearing that i t was chemistry, President Hopkins suggested that Turkevich see the Chemistry Professor, Leon B. Richardson. Not knowing that Richardson was c a l l e d " c h e e r l e s s " by the undergraduates, Turke v i c h went to get h i s advice, saying that he wanted to become a chemist. Richardson's r e t o r t was "there are too many bad che mists i n the United States and there was no need f o r more." This remark f u r t h e r motivated Turkevich to o b t a i n a p e r f e c t score i n Richardson's General Chemistry course. It i s i n t e r e s t i n g to note that during World War I Richardson worked with Arthur Lamb, subsequently a professor at Harvard, on a d s o r p t i o n of gases on c h a r c o a l . The teachers at Dartmouth: A. J . S c a r l e t t , L. B. Richardson, F. Low, J . Amsden, C. B o i s e r , Ε. Β. Hartshorn, were superb; a t t r a c t i n g to chemistry i n Turkevich's c l a s s such future chemists as G. Wheland of C h i cago, Harry Scherp of Rochester and A l b e r t o Thompson of Minnesota. On graduation, Turkevich was r e t a i n e d as an i n s t r u c t o r f o r two years. He was i n charge of the l a b o r a t o r y i n Richardson's course and gave an o c c a s i o n a l l e c t u r e . The only research a c t i v i t y i n the department was that of Hartshorn, an organic student of Lauder Jones of Chicago. For h i s master's t h e s i s under Hartshorn, Turkevich developed a method of using 30% hydrogen peroxide to make amine oxides. In the summer of 1930 Hartshorn obtained from h i s f r i e n d Dr. Peck, a summer job f o r Turkevich at the Standard O i l of New Jersey r e f i n e r y i n Bayway. The new research d i r e c t o r , Per K. F r o l i c h , an expert on c a t a l y t i c synthesis of methanol, assigned Turke v i c h a c a t a l y t i c process of converting methane using poisonous phosgene to a c e t y l c h l o r i d e . Methane was p l e n t i f u l and a c e t y l c h l o r i d e was i n high demand f o r "safe" photographic f i l m . Because of the poisonous nature of the p r o j e c t , the work was set up i n a shed outside the l a b o r a t o r y b u i l d i n g . Monitoring t e s t s f o r phosgene had to be developed and a flow system had to



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be constructed. By the end of the summer the system was operat i o n a l and a small y i e l d of a c e t y l c h l o r i d e was obtained. F r o l i c h suggested that Turkevich apply f o r graduate study at Princeton to work with Hugh Taylor on c a t a l y s i s and then do postdoctorate work at MIT with Professor Lewis, the leading chemical engineer of that time and F r o l i c h ' s mentor. A f t e r two years of teaching general chemistry at Dartmouth, Turkevich was asked to remain f o r another year to replace Hartshorn who was on s a b b a t i c a l leave. Turkevich was i n charge of the laboratory work i n organic chemistry and taught advanced organic chem i s t r y . One of h i s students was Frank Westheimer, now Prof e s s o r of Organic Chemistry at Harvard, who d i d h i s f i r s t independent p r o j e c t i n organic chemistry f o r Turkevich. Wheland, Scherp and Thompson and subsequently Westheimer went to Harvard to do graduate work with James Conant. The Dartmouth group wanted Turkevich to go to Yale to work i n organic chem i s t r y . However the summer with F r o l i c h persuaded Turkevich to go i n 1931 to P r i n c e t o n to work with T a y l o r . Adsorption Process By the end of World War I I i t was w e l l e s t a b l i s h e d that Van der Waals p h y s i c a l adsorption as determined by techniques of p h y s i c a l chemistry (volume-pressure measurements) could under BET c o n d i t i o n s measure the extent of surface. This i s a c l a s s i c a l experiment i n p h y s i c a l chemistry. J . Clarkson and Turkevich(65)showed how p h y s i c a l adsorption of oxygen on porous Vycor glass could be determined by spectroscopic methods of chemical physics. An oxygen gas molecule has a number of strong sharp l i n e s i n the e l e c t r o n paramagnetic resonance spectrum. The pressure of oxygen i n the pores could be determined from the width of oxygen l i n e s rather than from the manometer reading. This method was extended by E. Angelescu(67) from Rumania to the determination of chemisorbed O2" on palladium, gold and palladium gold a l l o y s on s i l i c a . Oxygen adsorbed as O 2 " has a c h a r a c t e r i s t i c EPR spectrum while oxygen gas shows sharp l i n e s i n another region of EPR. Catal y s t s were t r e a t e d with oxygen gas at various temperatures and then t h e i r temperature was lowered to that of Dry Ice. The excess oxygen was pumped o f f and then the c a t a l y s t was lowered to l i q u i d n i t r o g e n temperature. The i n t e n s i t y of the O2"" s i g n a l was measured. I t was shown that the number of cent e r s increased on a l l o y i n g palladium with gold and that chemis o r p t i o n to produce 02~ occurred. Furthermore when ethylene was admitted to a non-reacting palladium c a t a l y s t loaded with 02~ the O2" s i g n a l disappeared and oxygen gas s i g n a l s appeared. Thus ethylene d i s p l a c e d oxygen from i t s adsorbed s t a t e without r e a c t i n g with i t . On the other hand, on an a c t i v e palladium-gold a l l o y a d d i t i o n of ethylene to an



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O2" loaded s u r f a c e , lowers the O2"" s i g n a l but _no_ oxygen gas s i g n a l appears. The oxygen does not d e s o r b — i t r e a c t s . Another example of the a p p l i c a t i o n of s p e c t r o s c o p i c techniques to the study of chemisorption was the work of Sato(68) and Turkevich on the adsorption of oxygen on m e t a l l i c sodium f i l m s . Pores of Vycor glass were f i l l e d with a s o l u t i o n of sodium i n l i q u i d ammonia. The s o l u t i o n was then evaporated to give a m e t a l l i c f i l m of sodium. The process was r e a d i l y followed by EPR with the sharp l i n e of sodium i n l i q u i d ammonia becoming the broad l i n e c h a r a c t e r i s t i c of the c o n d u c t i v i t y e l e c t r o n s of sodium metal. On admission of oxygen gas the decrease i n the c o n d u c t i v i t y e l e c t r o n s and the i n c r e a s e i n the 0 2 " s i g n a l could be measured independently as e l e c t r o n s were t r a n s f e r r e d from the surface to the adsorbed gas. Adsorbed CH3I d i d not react with the sodium f i l m . However on i l l u m i n a t i o n with v i s i b l e l i g h t f a c i l i t a t e d e l e c t r o n t r a n s f e r to produce a s i g n a l c h a r a c t e r i s t i c of the methyl r a d i c a l . Titration for Catalytic Sites It has been t a c i t l y assumed that the number of c a t a l y t i c a l l y a c t i v e s i t e s was the number of chemisorption s i t e s . An elegant extension of the method of determining the number of chemisorbed s i t e s f o r hydrogen on platinum c a t a l y s t s present i n small q u a n t i t i e s on supports was introduced by Benson and Boudart,(24) both students of Hugh T a y l o r . The Turkevich group developed a poisoning t i t r a t i o n technique f o r determining the number of c a t a l y t i c a l l y a c t i v e centers.(69-74) In i t the EmmettKokes microreactor was modified i n the f o l l o w i n g way. A flow of a c a r r i e r gas (e.g. hydrogen) was passed over the c a t a l y s t , through a gas chromatographic column and i n t o a d e t e c t o r . A pulse of an i n d i c a t o r substance (ethylene) was introduced i n t o the gas stream and i t s conversion product (ethane) measured. A pulse of the t i t r a n t poison (carbon d i s u l f i d e ) was then i n t r o duced. This was adsorbed and was not detected. Another pulse of the i n d i c a t o r (ethylene) was introduced. The conversion was again noted. The cycle of i n d i c a t o r and t i t r a n t was repeated. A f t e r a c e r t a i n number of pulses of the poison the conversion decreased and became zero. The number of a c t i v e c a t a l y t i c cent e r s was then determined from the number of poison molecules j u s t necessary to decrease the c a t a l y t i c a c t i v i t y to zero. This technique was f i r s t used with cumene as an i n d i c a t o r f o r the c r a c k i n g r e a c t i o n and q u i n o l i n e as a t i t r a n t f o r determination of the number of a c t i v e centers on alumnia s i l i c a g e l and z e o l i t e c r a c k i n g c a t a l y s t s . The number of a c t i v e centers was found to be p r o p o r t i o n a l to the number of acid s i t e s and i n the case of z e o l i t e s with c r y s t a l l o g r a p h i c a l l y i d e n t i f i e d aluminum atoms. In order to e f f e c t i v e l y extend t h i s method to metals, to determine the number of a c t i v e centers and the v a r i a t i o n of



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a c t i v i t y of these centers with p a r t i c l e s i z e , a program had to be i n s t i t u t e d f o r preparing monodisperse p a r t i c l e s of p a l l a dium, platinum, and a l l o y s of palladium platinum and gold p l a tinum. The d e s c r i p t i o n of t h i s program w i l l be presented i n a l a t e r s e c t i o n of t h i s account. Kim t i t r a t e d monodisperse palladium(71) c a t a l y s t s (of diameters greater than 75 Â) with carbon monoxide using ethylene hydrogénation as an i n d i c a t o r . The surface atoms of the c a t a l y s t were determined from e l e c t r o n microscopic s i z e determination. Kim and Turkevich showed that a l l the atoms on the surface of the palladium p a r t i c l e s of diameter greater than 74 A were equally a c t i v e . Gonzales, A i k a , Namba and Turkevich(72) used t h i s method to determine the number of c a t a l y t i c s i t e s on monodisperse platinum of v a r i o u s s i z e s and found that i n general a l l surface atoms were c a t a l y t i c a l l y a c t i v e f o r double bond hydrogénation i n ethylene, propylene, butene, cyclohexene. I t was the same f o r hydrogen-deuterium exchange. The number was d i s t i n c t l y smaller f o r the hydrogénation of benzene. Furthermore while the number of hydrogen chemisorbed centers i s u s u a l l y the same as that obtained from poison t i t r a t i o n , the l a t t e r technique permits determination of centers f o r d i f f e r e n t hydrogénation r e a c t i o n s . The d i s c r e p a n c i e s between the two techniques found i n c e r t a i n cases give an experimental approach to hydrogen s p i l l - o v e r and carbon poisoning of the c a t a l y s t . In o l e f i n hydrogénation over platinum, the turn-over number was found to be constant as the p a r t i c l e diameter decreased to 19 Â. Enhanced a c t i v i t y of z e o l i t e s with respect to alumina s i l i c a g e l type of c a t a l y s t s was a s c r i b e d to the enhanced mobil i t y of the protons i n the c r y s t a l l i n e z e o l i t e b r i n g i n g about increased a c i d strength.(73) Thus,though i n d i v i d u a l c a t a l y t i c s i t e s may be e q u i v a l e n t , t h e i r ensembles of d i f f e r e n t s i z e would have d i f f e r e n t c a t a l y t i c a c t i v i t y . ( 7 5 ) Furthermore C-13 n u c l e a r magnetic resonance of adsorbed molecules showed that strong e l e c t r i c forces present i n the regular pores of c r y s t a l l i n e z e o l i t e s p o l a r i z e and a c t i v a t e adsorbed molecules (155). Laser Raman Spectroscopy was used by Buechler and Turkevich (76) to study the nature of a d s o r p t i o n of benzene and water vapor on porous Vycor g l a s s . Unfortunately p h o t o c a t a l y s i s producing f l u o r e s c e n t m a t e r i a l s l i m i t e d the usefulness of t h i s approach to c a t a l y t i c a l l y - a c t i v e s u r f a c e s . As we s h a l l see l a t e r C-13 NMR was found to be an i n c i s i v e t o o l f o r the study of adsorption of hydrocarbons on c a t a l y t i c surfaces. Use of Isotopes as Tracers The discovery of deuterium i n 1932 by Urey and t r i t i u m i n 1939 by Alvarez and Corning opened up new techniques f o r c a t a l y t i c s t u d i e s . As p r e v i o u s l y stated T a y l o r organized the production of heavy water and used the deuterium so obtained to


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study the a c t i v a t i o n of molecules by c a t a l y s t s . Exchange react i o n s of deuterium with hydrogen, deuterium with hydrocarbons, heavy water with benzene, heavy ammonia with l i g h t ammonia, were i n v e s t i g a t e d . O v e r a l l exchange was determined using changes i n index of r e f r a c t i o n , thermal c o n d u c t i v i t y , and i n f r a - r e d . There was l i m i t e d use of mass spectroscopy. The d e t a i l e d i n v e s t i g a t i o n of the isotope d i s t r i b u t i o n between d i f f e r e n t p o s i t i o n s i n the molecule and among the d i f f e r e n t molecules was introduced and developed a f t e r the war by Turkevich.


T r i t i u m as Tracer T r i t i u m was f i r s t used by Smith and Turkevich i n studying the mechanism of double bond migration i n the normal butènes. At that time a n a l y t i c a l techniques using i n f r a - r e d spectroscopy permitted a n a l y s i s f o r the two isomers.(77) Phosphoric a c i d , s u l f u r i c a c i d , a l u m i n a - s i l i c a s were good c a t a l y s t s f o r t h i s transformation. T r i t i u m oxide obtained from E. 0. Lawrence of the R a d i a t i o n Laboratory at Berkeley, C a l i f o r n i a was used to make t r i t i a t e d phosphoric a c i d . When t h i s was used to c a t a l y z e the double bond migration,(78) i t was found that t r i t i u m i n t r o d u c t i o n took place at the same rate (with c o r r e c t i o n f o r isotope e f f e c t ) as the double bond migration. Since i t was known that acids such as h y d r o c h l o r i c d i d not c a t a l y z e the double bond migration i n the butene, the "hydrogen switch" mechanism was proposed: f o r c a t a l y s i s a c t i v e i n double bond migration, a concerted atomic a c t i o n must take place with hydrogen from the Bronsted a c i d of the c a t a l y s t adding to the f i r s t carbon atom of butene-1 and a hydrogen atom being removed from the t h i r d carbon atom to the Bronsted base of the c a t a l y s t molec u l e . The c a t a l y s t must have a Bronsted a c i d s i t e (ΡΟΗ) and a Bronsted base s i t e (P=0) separated by 3.2 Â. This c o n d i t i o n i s a l s o s a t i s f i e d by the a l u m i n a - s i l i c a c a t a l y s t s . The hydrogen switch mechanism was extended to polymerization and c r a c k i n g of olefins.(79) A s s o c i a t i o n with groups outside the U n i v e r s i t y were i n v a l u a b l e f o r c a t a l y t i c research at P r i n c e t o n . As a r e s u l t of succ e s s f u l experiment on d e h y d r o c y c l i z a t i o n Turkevich became a consultant to M. W. K e l l o g g Company attending f o r many years t h e i r s t a f f meetings. During the War years c a t a l y t i c c r a c k i n g was the process of i n t e r e s t . Mass spectrometers graduated from "home made" apparatus to s o p h i s t i c a t e d equipment b u i l t by Cons o l i d a t e d Engineering Company. This was used at the K e l l o g g Company i n the pioneering s t u d i e s of determining p o s i t i o n and number of t r a c e r atoms i n various i s o t o p i c isomers. As a r e s u l t of the establishment of the RCA Research L a b o r a t o r i e s at P r i n c e t o n , Turkevich became t h e i r chemical consultant i n e l e c t r o n microscopy, microwave spectroscopy and s o l i d state phys i c s ( e s p e c i a l l y luminescence). Another f r u i t f u l a s s o c i a t i o n


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developed a f t e r the War, when the U.S. Atomic Energy Commission e s t a b l i s h e d the Brookhaven N a t i o n a l Laboratory near h i s summer place on the North Shore of Long I s l a n d . Together with Prof e s s o r R. W. Dodson of Columbia U n i v e r s i t y , Turkevich organized, s t a f f e d and equipped the chemistry department of t h i s l a b o r a tory.


Carbon-14 as Tracer The f i r s t i n v e s t i g a t i o n c a r r i e d out with the study with F r a n c i s Brown of the r e a c t i o n of CO2 with carbon to produce CO.(80) Radioactive C-14 carbon dioxide was allowed to c i r c u l a t e i n a closed loop over a bed of heated c h a r c o a l . I t was essent i a l that the amount of carbon dioxide gas be smaller than the number of carbon atoms on the surface. The course of r e a c t i o n was followed by change i n pressure, by an i n t e r n a l Geiger M i l l e r counter and by the r a t i o of CO2 to CO. The r e a c t i o n was found to procède i n two s t e p s — a rapid disappearance of a l l the CO2 to produce CO with the same s p e c i f i c a c t i v i t y as that of the i n i t i a l CO2 and a slow build-up of the pressure of non-radiative CO. The mechanism proposed f o r t h i s simple r e a c t i o n was that i n the f i r s t step, the CO2 molecule on c o l l i s i o n with the carbon surface l o s t one oxygen atom making CO and an oxygenated carbon s u r f a c e . In the second step, a unimolecular decomposition of the oxygenated surface l i b e r a t e d the second molecule of non-radioactive carbon monoxide. This l i b e r a t i o n took place by two exponential r a t e s . Amick and Turkevich(81) extended t h i s i n v e s t i g a t i o n to the r e a c t i o n of steam with hot carbon to produce by an analogous process hydrogen f i r s t and then carbon monoxide. No f u r t h e r work was c a r r i e d out on the use of r a d i o a c t i v e C-14 as a t r a c e r i n c a t a l y t i c work. Deuterium as T r a c e r A t t e n t i o n was then turned to the use of deuterium with s p e c i a l emphasis on where the deuterium was l o c a t e d i n the molec u l e . Model deuterated compounds such as the methanes, ethanes, propanes, toluenes, i s o p r o p y l a l c o h o l s , were synthesized.(82-84) The f i r s t approach f o r a n a l y s i s was the use of i n f r a r e d spectra. The Brookhaven Chemistry Department had acquired an e x c e l l e n t spectrometer making the home-made one at P r i n c e t o n obsolete. However i t was decided that mass spectrometry o f f e r e d a more i n c i s i v e determination of the number of v a r i o u s i s o t o p i c molecules and the p o s i t i o n s of the t r a c e r atoms i n these molecules. During the war years, the Chemistry Department at P r i n c e t o n U n i v e r s i t y had an a l l glass spectrometer made by Lee H a r r i s , the glassblower of the Physics Department and placed i n t o operation by G. J o r i s with the help of Turkevich. I t was used p r i m a r i l y f o r hydrogen-deuterium a n a l y -



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sis. I t was f r a g i l e and i t s e l e c t r o n i c s f i c k l e . During t h i s p e r i o d the Consolidated Engineering Company put on the market a rugged r e l i a b l e but expensive mass spectrometer. I t was used by petroleum companies to analyze hydrocarbon gas and l i q u i d s . Any given hydrocarbon gave under standardized c o n d i t i o n s on e l e c t r o n impact, a c h a r a c t e r i s t i c spectrum of i o n products whose masses and abundances could be determined. Turkevich decided to apply t h i s technique to a n a l y s i s of deuterated compounds. Together with Lewis Friedman, a number of deuterated hydrocarbons were synthesized and a new m e t a l l i c spectrometer was b u i l t i n P r i n c e t o n . Turkevich e n l i s t e d Ernest Solomon and F r a n c i s Wrightson of the M. W. K e l l o g g Company to determine on t h e i r Consolidated mass spectrometer the e l e c t r o n impact spectra of those hydrocarbons. This c o l l a b o r a t i o n r e s u l t e d i n a landmark paper on "Determination of P o s i t i o n of Tracer Atoms i n a Molecule: Mass Spectra of Some Deuterated Hydrocarbons" published i n 1948,(85) and another presented i n 1951(86,87) at Discussions of the Farady Society. With S c h i s s l e r and I r s a , Turkevich(88) made a d e t a i l e d study of the i n t e r a c t i o n of ethylene and deuterium. With Thompson and I r s a the study of the F i s c h e r Tropsch synthes i s using deuterium gas,(89,90) with Lewis Friedman on r e d u c t i o n of acetone,(91,92) with G. C. Bond, the r e a c t i o n of propylene(93) and cyclopropane(94) with deuterium. Using the ethylene-deuterium r e a c t i o n as an example,(98) the mass s p e c t r o s c o p i c approach permitted a n a l y s i s of each of the f i v e ethylenes and seven ethanes at the same time and showed, among other i n t e r e s t i n g data, that the f i r s t product of the r e a c t i o n between deuterium and ethylene was an ethane c o n t a i n i n g no deuterium. Another example of the power of t h i s method was i t s a p p l i c a t i o n to the F i s c h e r Tropsch(90) s y n t h e s i s . This r e a c t i o n was f i r s t run with CO and H2 u n t i l a steady state was a t t a i n e d . The r e a c t i v e gases were flushed o f f with helium and deuterium was then i n t r o duced. The hydrocarbons produced were a l l completely deuterated suggesting that the a c t i v e intermediate on the surface was c a r bon. The deuterium t r a c e r work was c a r r i e d out e x t e n s i v e l y i n England by C. Kemball and G. C. Bond and i n the United States by R. L. Burwell, J r . C a t a l y s t Synthesis In the pre-Worid War II days there was l i t t l e work done at Princeton on synthesis of c a t a l y s t s . Copper c a t a l y s t s were made by r e d u c t i o n of Kahlbaum copper oxide, the i r o n ammonia c a t a l y s t s were obtained from the Fixed Nitrogen Laboratory through the courtesy of Dr. Paul Emmett, the n i c k e l on k i e s e l g u h r c a t a l y s t was obtained from DuPont. Platinum on asbestos was made i n the laboratory by soaking asbestos with c h l o r o p l a t i n i c a c i d and then i g n i t i n g i t , mixed chromite c a t a l y s t s were p r e c i p i t a t e d and c a l c i n e d and a study was made,




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p a r t i c u l a r l y by R. L. Burwell, of the p r e c i p i t a t i o n of an " a c t i v e " chromium oxide g e l . During the war and e s p e c i a l l y a f t e r the war, the synthesis of c a t a l y s t s and t h e i r supports has been the preoccupation of the Turkevich group. The main d i a g n o s t i c t o o l used i n t h i s work was the e l e c t r o n microscope. In 1942 the r e s o l u t i o n of the microscope i n the hands of James H i l l i e r of the RCA L a b o r a t o r i e s was 20 Â. Now i n the hands of Joseph H. Wall of the Brookhaven N a t i o n a l Laboratory i t i s 2.5 Â permitting v i s u a l i z a t i o n of the i n d i v i d u a l platinum atoms. A survey of c a t a l y s t s made with the e l e c t r o n microscope i n 1942(95) showed a d i v e r s i t y of s i z e , shape and texture of c a t a l y t i c substances. Many of the precious metals were large and consequently not very e f f i c i e n t — o n l y a very small f r a c t i o n of the atoms were a v a i l a b l e f o r surface r e a c t i o n s . However many of them were of c o l l o i d a l size,(96) i . e . of one dimension at most of 2000Â. The usual method of making the c a t a l y s t was to soak the support with a s o l u t i o n of the s a l t of the precious metal and then subject i t to thermal treatment. The complex topochem i c a l r e a c t i o n s that take place are d i f f i c u l t to c o n t r o l to o b t a i n monodisperse p a r t i c l e s of optimum s i z e . Two questions arose i n the 40 s and 5 0 s . What i s the dependence of c a t a l y t i c a c t i v i t y on p a r t i c l e size? Is there a p a r t i c l e s i z e below which there i s no c a t a l y t i c a c t i v i t y ? I t was proposed to synthesize the metal p a r t i c l e s i n s o l u t i o n i n c o l l o i d a l form; check t h e i r p r o p e r t i e s , both p h y s i c a l and chemical i n s o l u t i o n ; then mount them on a s u i t a b l e support to study t h e i r a c t i v i t y i n heterogeneous c a t a l y t i c r e a c t i o n s . However, the c o l l o i d a l chemistry of platinum and palladium was complex, poorly understood and d i f f i c u l t to reproduce. f

f

Monodisperse Metal Studies Stevenson, H i l l i e r and Turkevich (97) turned to study the synthesis and p r o p e r t i e s of the most stable of c o l l o i d a l metal s y s t e m s — g o l d . An e l e c t r o n microscope examination was made of a l l c l a s s i c a l preparations of t h i s metal i n the search of one producing the most uniform p a r t i c l e s . The preparation based on the r e d u c t i o n of gold s a l t s with sodium c i t r a t e was found to y i e l d monodisperse p a r t i c l e s . The d i s t r i b u t i o n of part i c l e s i z e was c o r r e l a t e d with the r a t e of n u c l e a t i o n , growth and c o a g u l a t i o n of p a r t i c l e s . Together with a "pure growth" r e a c t i o n , monodisperse p a r t i c l e s of diameters from 50 to 1200Â could be synthesized. The Mie theory of the dependence of c o l o r of c o l l o i d a l gold on p a r t i c l e s i z e was experimentally confirmed(98) as was a l s o the G u i n i e r theory of small angle X-ray scattering,(99-100) Smoluchowski k i n e t i c s f o r formation of dimers, t r i m e r s , e t c . , the Verwey Overbeek theory of f a s t and slow coagulation.(101-102) The l a t t e r permitted determination of the u n i v e r s a l Van der Waals (Hamaker) constant.(103) Coagulation of



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small p a r t i c l e s to f l a t c r y s t a l l i n e p l a t e s with a growth s p i r a l was also studied.(104) Furthermore the adherence of c o l l o i d gold p a r t i c l e s to surface and supports was investigated.(105) A s o l i d experimental and t h e o r e t i c a l basis was produced f o r the preparat i o n of monodisperse c a t a l y s t s . Unfortunately gold i s not a c a t a l y s t f o r most r e a c t i o n s of i n t e r e s t . The knowledge of the c o l l o i d a l chemistry of gold was used by Kim and Turkevich(106) to prepare monodisperse palladium p a r t i c l e s i n diameter greater than 75 Â. The number of surface atoms determined by e l e c t r o n microscopy was found to be equal to the number of c a t a l y t i c centers determined by poison t i t r a t i o n f o r the ethylene hydrogénation r e a c t i o n . The surface of the palladium c a t a l y s t was homogenous. The v e l o c i t y of the c a t a l y t i c r e a c t i o n was found to be p r o p o r t i o n a l to the number of surface atoms. A l l surface atoms were a c t i v e . A p p l i c a t i o n of these t h e o r e t i c a l and experimental techniques to platinum c a t a l y s t s had to await s i g n i f i c a n t advances i n e l e c t r o n microscopy. The r e s o l u t i o n of the RCA e l e c t r o n microscope at the Chemistry Department of the U n i v e r s i t y was only 20 A while the platinum p a r t i c l e s produced under standard preparation c o n d i t i o n s were at most 30 Â i n diameter. However i n t e r e s t i n g f i n d i n g s were found even with t h i s l i m i t e d r e s o l u t i o n . A smooth platinum f o i l was used as a c a t a l y s t i n the Ostwald process of ammonia o x i d a t i o n . I t was known from o p t i c a l observations that the surface became rough and t a r n i s h e d . In 1953 Garton and Turkevich(107) a p p l i e d the r e p l i c a technique, developed during the war f o r the d i f f u s i o n b a r r i e r , to observe with the e l e c t r o n microscope what was described as the " c a t a l y t i c e t c h " . During the course of ammonia o x i d a t i o n , the amorphous B e i l b y l a y e r produced on the platinum surface during manufacture of the f o i l rearranged to become a b e a u t i f u l c r y s t a l l i n e surface w i t h t e r r a c e s , corners, r e g u l a r etch p i t s . The c a t a l y s t surf a c e , even of high melting platinum, i s not s t a t i c during a c a t a l y t i c r e a c t i o n . While the surface area d i d not change a p p r e c i a b l y , the number of edges, s l i p planes and corners increased enormously. Nevertheless the c a t a l y t i c a c t i v i t y of the f o i l f o r hydrogen peroxide decomposition d i d not change a f t e r " c a t a l y t i c etch". Thus, no s p e c i a l enhanced a c t i v i t y can be a s c r i b e d to various c r y s t a l l o g r a p h i c l o c i — e d g e s , corners, etch p i t s of an a c t i v e c a t a l y s t . C o n t r o l l e d synthesis of platinum p a r t i c l e s was made p o s s i b l e i n the l a t e s i x t i e s and seventies by s i g n i f i c a n t advances i n e l e c t r o n microscopy. L a z l o L. Ban of the C i t i e s Service L a b o r a t o r i e s i n nearby Hightstown was able to obtain l a t t i c e imaging with a r e s o l u t i o n of 0.05 A while Joseph Wall at the Brookhaven N a t i o n a l Laboratory constructed a scanning transmission e l e c t r o n microscope with a r e s o l u t i o n of 2.5 Â perm i t t i n g v i s u a l i z a t i o n of i n d i v i d u a l platinum atoms. These techniques together with the use of the u l t r a c e n t r i f u g e of Barbara



480


Bamman of the U n i v e r s i t y Biology Department were a p p l i e d to the platinum system. P a r t i c u l a r a s s i s t a n c e i n t h i s program was given by S e i t e r o Namba and R. S. Miner, Jr.(72) The synthesis of monodisperse platinum(108,109,110),and a l s o of i t s a l l o y s with gold and palladium was studied.(112) I t was found that only c e r t a i n platinum compounds formed platinum p a r t i c l e s . This served as an i n s i g h t i n t o the e f f i c a c y of c e r t a i n platinum compounds as antitumor drugs i n cancer therapy.(113) E l e c t r o n microscopy was used to f o l l o w p a r t i c l e formation from atoms i n the s t a r t i n g m a t e r i a l . The l a t t i c e parameters of i n d i v i d u a l p a r t i c l e s were determined. In s o l u t i o n i t was found that a minimal diameter of 12 Â had to be exceeded i n order to o b t a i n c a t a l y t i c a c t i v i t y f o r hydrogen peroxide decomposition. T h i s l i m i t a t i o n was not found f o r the hydrogénation of ethylene on platinum p a r t i c l e s supported on alumina. A l l surface atoms of a 32 Â diameter part i c l e were found to be a c t i v e . Thus the main o b j e c t i v e s of a synthesis program i n i t i a t e d three decades ago, were a t t a i n e d . Alumina supports f o r metal p a r t i c l e s were synthesized i n the form of f i b e r s and t h i n p l a t e s s u i t a b l e both f o r c a t a l y s t s t u d i e s and e l e c t r o n microscopic examination.(106) L i g h t s c a t t e r i n g , proton resonance, v i s c o s i t y measurements, were used to study the formation of s i l i c a gels and monodisperse sols.(114) The same techniques were used to study synthesis of z e o l i t e s . Magnetic Resonance « I n t e r e s t at Princeton i n magnetic phenomena r e l a t e d to c a t a l y s i s goes back to 1931 when P. W. Selwood came to Princeton as a post-doctorate f e l l o w from the U n i v e r s i t y of I l l i n o i s where he worked with Professor Hopkins on the magnetic p r o p e r t i e s of rare earth. His help was i n v a l u a b l e to Taylor and Diamond i n t h e i r work on the e f f e c t of rare earths on the ortho-para hydrogen conversion. At Princeton, Selwood b u i l t a Gouy balance f o r measuring s t a t i c s u s c e p t i b i l i t y using a magnet borrowed from the Physics Department. Turkevich, a new graduate student from Dartmouth College, where he taught organic chemistry suggested to Selwood that they measure the magnetism of the s t a b l e free r a d i c a l a l p h a , a l p h a - d i p h e n y l - j e t a - p i c r y l hydrazyl (DPPH), which he made f o r t h i s purpose by a four step s y n t h e s i s . I t was found to have the expected s p i n due to one unpaired electron.(115) DPPH was f u r t h e r used by Selwood and Turkevich as a c a t a l y s t f o r ortho-para hydrogen conversion. In a d d i t i o n C. P. Smyth, D. Oesper and Turkevich measured the e l e c t r i c s u s c e p t i b i l i t y of DPPH and showed that the unpaired e l e c t r o n was not l o c a l i z e d on the n i t r o g e n but resonated to other parts of the molecule.(116) A f t e r Selwood l e f t f o r Northwestern s t a t i c magnetic s u s c e p t i b i l i t y work was continued at P r i n c e t o n on chromic oxide c a t a l y s t s and on the r e l a t i o n of luminescence to the magnetic c h a r a c t e r i s t i c s of manganese i n z i n c s u l f i d e phosphors. During the summer of 1950 a t lunch at the Brookhaven N a t i o n a l Laboratory, Turkevich learned from



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Charles H. Townes that he was using the very uniform magnetic f i e l d of the uncompleted c y c l o t r o n to c o n s t r u c t an e l e c t r o n paramagnetic resonance (EPR) spectrometer. Turkevich persuaded Townes to measure the EPR of DPPH. Townes(117) found a very sharp resonance i n the r a d i c a l , so sharpened by exchange narrowing, that i t has been used ever since i t s d i s c o v e r y , as a standard i n EPR measurements. This opened up the a p p l i c a t i o n of EPR not only to free r a d i c a l research(118) but a l s o to the whole f i e l d of c a t a l y s i s . Unfortunately the equipment f o r t h i s work, part i c u l a r l y a homogeneous f i e l d magnet, was expensive. T h i s l i m i t a t i o n was circumvented when Pastor and Turkevich b u i l t at Princeton a rather inexpensive low magnetic f i e l d spectrometer using Helmholtz c o i l s . I t was s u i t a b l e f o r measuring narrow lines. Charcoal as C a t a l y s t On the basis of the Bonhoeffer work on the ortho-para hydrogen conversion, i t was concluded that charcoal showed surface magnetism and was a s u i t a b l e system f o r EPR studies.(119-120) Glucose was carbonized to v a r i o u s temperatures. A broad EPR s i g n a l appeared at 350°C, increased i n i n t e n s i t y and decreased i n width as the temperature of c a r b o n i z a t i o n was r a i s e d . The s i g n a l reached i t s maximum i n t e n s i t y and minimum width on heat treatment at 605°C. At higher temperature t r e a t ment, the l i n e broadened, decreased i n i n t e n s i t y and the charc o a l specimen became " l o s s y " due to e l e c t r i c c o n d u c t i v i t y . These observations were c o r r e l a t e d by Laroche and Turkevich(29) w i t h the c a t a l y s i s of ortho-para conversion at l i q u i d n i t r o g e n temperature and hydrogen-deuterium e q u i l i b r a t i o n a t room temperature. On heating glucose, water and CO were evolved producing on the surface free r a d i c a l s . As these increased i n c o n c e n t r a t i o n , they showed exchange narrowing and intense magnetic f i e l d s . These f i e l d s c a t a l y z e the ortho-para hydrogen conversion at l i q u i d n i t r o g e n temperatures but did not c a t a l y z e hydrogen-deuterium e q u i l i b r a t i o n at room temperatures. As the temperature i s r a i s e d above 600°C hydrocarbons and CO are evolved from the c h a r c o a l and the spins begin to p a i r o f f to form a n t i - f e r r o m a g n e t i c domains, the surface magnetism drops and the a b i l i t y of the surface to c a t a l y z e the ortho-para hydrogen conversion at l i q u i d n i t r o g e n i s lowered. On the other hand the H2-D2 r e a c t i o n and a l s o the ortho-para r e a c t i o n i s c a t a l y z e d a t room temperature. On f u r t h e r heat treatment, as a n t i f e r r o magnetic domains grow i n t o g r a p h i t i c sheets, they lose t h e i r a b i l i t y to c a t a l y z e the H2-D2 r e a c t i o n . Previous studies(124) on EPR of potassium complexes of aromatic r i n g systems gave an i n s i g h t i n t o the s i z e of pools of a n t i f e r r o m a g n e t i c e l e c t r o n s which can serve as sources or r e c i p i e n t s of e l e c t r o n s a c t i v e i n c a t a l y t i c processes. Since that i n v e s t i g a t i o n EPR work was


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HETEROGENEOUS

CATALYSIS

c a r r i e d out on carbon black used f o r t i r e reinforcement, carbon from c i g a r e t t e s , carbon i n lungs of c o a l miners and c i t y dwellers. The l a s t i n v e s t i g a t i o n on carbon took place i n 1980 when the l a t e P r o f e s s o r S. Krzyzanowksi studied i t s formation i n a ZSM-5 z e o l i t e c a t a l y s t during petroleum synthesis from methanol.


Other C a t a l y s t Systems As p r e v i o u s l y noted Sato and Turkevich(68) studied the t r a n s f e r of c o n d u c t i v i t y e l e c t r o n s from surface sodium f i l m s to adsorbed species. Clarkson and Turkevich(66) studied by EPR the p h y s i c a l a d s o r p t i o n of oxygen on s i l i c a , Angelescu and Turkevich(67) the t r a n s f e r of e l e c t r o n s from metals to adsorbed oxygen and Vanderspurt, Che and Turkevich studied chemisorption of oxygen and ferrocene on s i l i c a observing not only 02~ with i t s t r i p l e t gx, gy, gz, but a l s o each having a super h y p e r f i n e s t r u c t u r e of s i x l i n e s corresponding to the f i v e hydrogen atoms i n the cyclopentadiene complex—a m o l e c u l e - s t r u c t u r a l i n t e r p r e t a t i o n of the a c t i v e a d s o r p t i o n center. In the s i x t i e s the generous support from the Exxon Research Corporation and equipment grant from the U. S. Atomic Energy Commission permitted the purchase of commercially b u i l t EPR spectrometers at 9.3 and 35 G and a broad l i n e nuclear magnetic spectrometer. In 1964 a short i n v e s t i g a t i o n was made of EPR s i g n a l s of platinum on alumina by F. Nozaki, D. Stamires and Turkevich.(70) The r e l a t i o n of c a t a l y t i c a c t i v i t y of t r a n s i t i o n metal oxides to t h e i r EPR p r o p e r t i e s was studied. Thus i n 1967 Kazanski i n v e s t i g a t e d the chromium oxide on s i l i c a and i t s a b i l i t y to carry out low temperature p o l y m e r i z a t i o n of ethylene. A s e r i e s of papers were devoted to the T1O2, i t s decomposition products and i t s i n t e r a c t i o n with oxygen. The r e s u l t s so obtained were compared with the behavior of T i ( I I I ) ( 1 2 9 ) compound with hydrogen peroxide i n s o l u t i o n using fast-mixing flow techniques. The a c t i v e species was i d e n t i f i e d by EPR as an o c t a h e d r a l complex of T i ( I V ) with OH, substrate and oxygen l i g a n d s . Zinc oxide, a m a t e r i a l studied by Taylor and h i s students, an i n t e r e s t i n g semiconductor and a c t i v e p r i n c i p l e i n xerography, was i n v e s t i g a t e d by Turkevich. (130,131,132) Methyl r a d i c a l s were produced on s i l i c a surfaces of porous Vycor glass by p h o t o l y s i s of methyl iodide.(75) The ESR c h a r a c t e r i s t i c of the proteum, deuterium and C-13 compound showed extensive m o b i l i t y of the r a d i c a l on the surface, i t s planar s t r u c t u r e and i t s s t a b i l i t y f o r days at room temperature. I t s r e a c t i v i t y with gases was studied under d i f f u s i o n c o n t r o l c o n d i t i o n s . Thus the goal of the organic chemists of the middle nineteenth century was a t t a i n e d — u n d e r proper c o n d i t i o n s methyl r a d i c a l s can be produced and used as chemical reagents. F u r t h e r more t h e i r s t a b i l i t y at room temperature i n d i c a t e d that they can


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be important intermediates i n c a t a l y t i c hydrocarbon r e a c t i o n s . The s t r u c t u r e and behavior of methyl r a d i c a l s on surfaces was compared with that i n aqueous s o l u t i o n . Methyl r a d i c a l s were produced and c h a r a c t e r i z e d by EPR i n a fast-mixing flow system of T i ( I I I ) with t e r t i a r y b u t y l hydroperoxide.(133) As a side i n v e s t i g a t i o n , the r e a c t i o n of methyl r a d i c a l s with oxygen d i s s o l v e d i n water was monitored not only by EPR but by chemiluminescence using an e l e c t r o n i c image i n t e n s i f i e r . ( 1 3 4 ) Under appropriate experimental conditions a " c o l d flame" could be produced by t h i s r e a c t i o n i n water.


Magnetic Resonance i n Z e o l i t e s For a number of years (1961-1981) the main thrust of the EPR work was the i n v e s t i g a t i o n of z e o l i t e s . The f i r s t i n v e s t i g a t i o n of these m a t e r i a l s at P r i n c e t o n was c a r r i e d out i n 1933 by the Swedish chemist Arne T i s e l i u s ( 1 3 5 ) who brought with him samples which he p e r s o n a l l y c o l l e c t e d i n the Orkney Islands. C. 0. Strother, a P r i n c e t o n i a n who was the d i r e c t o r of the Linde Research Laboratory of the Union Carbide Company at Tonowanda, New York sent samples of NaX z e o l i t e s f o r surface s t u d i e s . Unfortunately the hydrogen (acid) form i s not s t a b l e and the sodium form i s i n a c t i v e . However, the NaY form has a s t a b l e hydrogen form and t h i s opened a comprehensive research program i n the s y n t h e s i s , p h y s i c a l examination and chemical r e a c t i o n s of zeolites.(70,136-144) These materials when free of i r o n impurit i e s show no EPR s i g n a l s . However a f t e r a v a r i e t y of t r e a t ments, EPR s i g n a l s are produced which are d i a g n o s t i c of the molecular environment of the a c t i v e a c i d centers: replacement of sodium ions by Cu(II) by Nikula, Stamires,(145) Ono, Soria;(146) by r a r e earths by L. Iton;(147) e l e c t r o n t r a n s f e r to and from adsorbed molecules ( t r i n i t r o b e n z e n e and triphenylamine) from Lewis acids by Stamires, Nozaki and 0no(139-148) and trapping of e l e c t r o n s by Lewis a c i d s i t e s on gamma i r r a d i a t i o n s . ( 1 3 8 - 1 5 0 ) The behavior of hydrogen atoms trapped i n the l a t t i c e of calcium f l u o r i d e was compared to that of hydrogen atoms adsorbed i n c a v i t i e s of z e o l i t e s . ( 1 5 2 ) These researches were continued i n Japan by Professors Y. Ono, Y. F u j i t a , S. Namba, I. Okura; i n Spain by X. S o r i a , i n France by M. Che and J.E. Védrine; i n the United States by R. Clarkson and L. Iton. Proton resonance of charcoals prepared by heat treatment of dextrose at various temperatures was studied before and a f t e r hydrogen treatment by Turkevich, Mackey and Thomas.(136) This was followed by a p r e l i m i n a r y study of double (electron-proton) resonance by Turkevich and Derouane(153) of benzene adsorbed on c h a r c o a l . This i n v e s t i g a t i o n was completed r e c e n t l y by M. Che and J . L. Vendrine.(154) The status of water i n pores of z e o l i t e s was examined by proton resonance by Mackey, Thomas and Turkevich.(136) The water


HETEROGENEOUS


484

CATALYSIS

hydrated the c a t i o n which moved f r e e l y i n the c a v i t y . On dehydration the c a t i o n was l o c a l i z e d on aluminum centers i n the c a v i t y . L. Meecham studied water i n glass which had uniform pores.1^1 D i f f e r e n t c h a r a c t e r i s t i c s were found f o r water conf i n e d i n pores of diameter l e s s than 200 Â. The behavior of A l and Na i n the z e o l i t e as a f u n c t i o n of water content was i n v e s t i g a t e d by NMR of these nuclei.(141) A thorough i n v e s t i g a t i o n of C-13 n u c l e a r resonance of hydrocarbons adsorbed by z e o l i t e s was c a r r i e d out i n c o l l a b o r a t i o n with Dorothy Denney of Rutgers U n i v e r s i t y , S. M a r t i k h i n of the I n s t i t u t e of C a t a l y s i s , USSR, S. Namba of Tokyo I n s t i t u t e of Technology.(156) The chemical s h i f t , the coupling constants, the r e l a x a t i o n times of the i n d i v i d u a l carbons i n the adsorbed molec u l e s i n d i c a t e d not only the presence of strong e l e c t r i c f i e l d i n the pores of the z e o l i t e but a l s o permitted e v a l u a t i o n of the p o l a r i z a t i o n of i n d i v i d u a l carbon atoms i n the molecule.

Conclusion Thus over the course of h a l f a century, the b a s i c concepts of a c t i v a t e d adsorption and a c t i v e centers were made more p r e c i s e by a p p l i c a t i o n of novel techniques. In a d d i t i o n to the d i r e c t l i n e work on c a t a l y s i s , many s c i e n t i f i c side l i n e s were pursued: photochemistry, discharge tube chemistry, r a d i a t i o n induced transformation, s o l i d s t a t e chemical physics, and chemotherapy of cancer. (113)

Acknowle dgment s Support f o r these i n v e s t i g a t i o n s of the Taylor and Turkevich groups came from the U n i v e r s i t y Research Fund, the Higgins Fund, the M.W. Kellogg Company, the Chevron Research Fund, the S h e l l Company Grant, the U.S. Atomic Energy Commission, U.S. Deptartment of Energy and the N a t i o n a l Science Foundation. These are g r a t e f u l l y acknowledged.


33.

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33.

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489

Turkevich, J., Demirci, S., and Skvir, D. J., Croatica Chemica Acta, 1972, 45, 85. Kim, G. and Turkevich, J., Science, 1970, 169, 873. Garton, G. and Turkevich, J., J. Chem. Phys.,1954, 51, 516. Turkevich, J., Aika, K., Bann, L. L., Okura, I . , Namba, S. J. Res. Inst. Catalysis, Hokkaido University, 1976, 24, 34. Turkevich, J., Bann, L. L. and Wall,, J. Η., Perspectives in Catalysis (Larssen, ed.), 1980, 59. Turkevich, J., Miner, R. S.,Jr., Okura, I., Namba, S., Zacharina, Ν., Perspectives in Catalysis (Larssen, ed. ) 1980, 111. Miner,R. S., J r . , Namba, S., and Turkevich, J., Proc. 7th. Int. Gong. Catal., Tokyo, 1980, 160. Turkevich, J., Plenary Lecture,VIII, Ibero-American Symp. on Catalysis, La Rabida, Spain, July 1982. Burchenal, J., Lokys, L., Turkevich, J., and Gale, G., in Cis Platin,(Prestayko, W. S., Crooke, S. T. and Carter, S. Κ., eds.) Academic Press, New York, 1951, 113. Turkevich, J . and Bartholin, Μ., Proc. IV Simposio IberoAmericano de Catalysis, Mexico City, 1976. Turkevich, J . and Selwood, P. W., J . Am. Chem. Soc., 1941, 63, 1077. Oesper, P., Smyth, C. P. and Turkevich, J., J. Am. Chem. Soc., 1942, 64, 1179. Townes, C. H. and Turkevich, J., Phys. Rev., 1950, 77, 148. Cohen, V. W., Kikuchi, and Turkevich, J., Phys. Rev., 1952, 85, 379. Pastor, R. Α., Weil, J. Α., Brown, T. H. and Turkevich, J., Phys. Rev., 1956, 102, 918. Pastor, R. C . , Weil, J . Α., Brown, T. H. ,and Turkevich, J . , Adv. in Catalysis, 1957, 9, 1078. Brown, T. H. and Turkevich, J., J. Phys. Chem., 1957, 61, 1452. Brown, Τ. Η., and Turkevich, J., Proc. of 1957 Conf. on Carbon, 1957, Pergamon Press, London. Turkevich, J., and Laroche, J., Zeit fur Physik Chemie,N.F., 1956, 15; 399. Pastor, R. C. and Turkevich, J., J. Chem. Phys., 1955, 23, 1731. Vanderspurt, Τ. Η., Turkevich, J., Che, Μ., and Buchler, E. J. of Catalysis, 1974, 32, 127. Kazanski, V. Β., and Turkevich, J., J. of Catalysis, 1967, 8, 231. Iyengar, R. D. Codell, M., Karra, J . S. and Turkevich, J., J. Am. Chem. Soc., 1967, 88, 5055. Iyengar, R. D.., Codell, M. and Turkevich, J., J. of Catalysis, 1967, 9 305. Chiang, Y. S., Craddock, J., Mickewitch, D., and Turkevich, J., J. Phys. Chem., 1966, 70, 3509.


HETEROGENEOUS

490


130. Larach, S. and Turkevich, J., J. Phys. Chem. Solids, 1968, 29, 1519. 131. Larach, S., and Turkevich, J., Applied Optics, 1968. 132. Larach, S., and Turkevich, J., Surface Science, 1970, 20, 192. 133. Mickewich, D. and Turkevich, J. J. Phys. Chem., 1968, 72, 2703. 134. Turkevich, J., Mickewich, D., and Reynolds, G. T., Zeit fur Phys. Chem., NF, 1972, 82, 185. 135. Tiselius, A. Zeit.Phys. Chem. A, 1935, 174, 401. 136. Turkevich, J., and Mackey, J. H., Jr., Thomas, W. Η., Acte du Deuxieme Congres International de Catalyse, Ed. Tech. , Paris, 1961, 1815. 137. Murakami, Y., Nozaki, F., and Turkevich, J., Shokubai, (J. Catalysis in Japan), 1963, 5, 262· 138. Turkevich, J., and Ciborowski, S., J. Phys. Chem., 1967, 71, 3208. 139. Turkevich, J., Murakami, Y., Nozaki, F. and Ciborowski, S., Chem. Eng. Progress, Symposium Series, 1967, 63, 75. 140. Turkevich, J. Catalysis Reviews, 1967, 1, 1. 141. Turkevich, J., and Ono, Y., Advances in Catalysis, Academic Press, New York, 1969, 20, 135. 142. Turkevich, J., and Ono, Υ., Advances in Chemistry, 1971, 102, 315. 143. Buechler, E. and Turkevich, J., J. Phys. Chem., 1972, 76, 2325. 144. Miner, R. S., Ione, K. G., Namba, S., and Turkevich, J., J. Phys. Chem., 1978, 82, 214. 145. Nikula, Α., Stamires, D. and Turkevich, J., J. Chem. Phys. 1965, 42, 3684; Rev. Roum. Phys., 1964, 9, 613. 146. Turkevich, J., Ono, Υ., and Soria, X., J. of Catalysis, 1972, 25, 44. 147. Iton, L.E., and Turkevich, J., J. Phys. Chem., 1977, 81, 435. 148. Stamires, D. N. and Turkevich, J., J. Am. Chem. Soc., 1964, 86, 749. 149. Stamires, D. N. and Turkevich, J., J. Am. Chem. Soc., 1964, 86, 757. 150. Haul, R., Karra, J., and Turkevich, J., J. Am. Chem. Soc., 1965, 87, 2092. 151. Turkevich, J., Shokubai (J. of Catalysis in Japan), 1965, 7, 328. 152. Iton, L. E. and Turkevich, J., J. Phys. Chem., 1978, 82, 200. 153. Derouane, Ε., and Turkevich, J., unpublished. 154. Che, M. and Vendrine, J. C., in press. 155. Denney, D., Mastikhin, V. Μ., Namba, S., and Turkevich, J., J. Phys. Chem., 1978, 82, 1752. RECEIVED February 1,

1983


CATALYSIS

Heterogeneous Catalysis - American Chemical Society

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