RESEARCH
Platinum-Lithium Reaction Gives Catalyst New intermetallic compound has twice the catalytic activity of supported platinum oxide A simple way to make an active hydrogenation catalyst, and an unexpected intermetallic compound, LiPt 2 —these are the results of a laboratory accident that eventually led to a research project. Several years ago, Dr. Charles P. Nash, now at University of California, Davis, was heating a mixture of lithium and lithium hydride in a platinum crucible in a hydrogen atmosphere. The idea, he explains, was to reintroduce the hydrogen which is lost by the hydride on slow decomposition. The result was an explosion that destroyed a substantial part of the platinum crucible and deposited on the desk top a fiercely burning reaction mass that defied all attempts to extinguish it. Now, Dr. Nash, working with Dr. Lynn D. Whittig and Franklin M. Boyden at Davis, has taken up the problem of what caused the explosion and finds that hydrogen is not the real culprit. Platinum and molten lithium react violently at 540° ± 20° C , he finds, to form the previously unknown compound, LiPt 2 , in almost quantitative yield. Controlled Reaction. To carry out this reaction in a controlled way, Dr. Nash and his co-workers use a glass system which can either be evacuated or filled with argon. They place a small piece of freshly cut lithium in a molybdenum crucible (molybdenum is inert to molten alkali metals). The crucible then goes inside a glass tube where it is heated in a vacuum or in argon by a resistance furnace. When the metal melts, a strip of platinum fused to the end of a glass rod is lowered into it. And when the temperature reaches 540° ± 20° C , a violently exothermic reaction takes place. Removal of the excess lithium by hydrolysis leaves a brittle, metalliclooking solid which can easily be powdered and which analyzes as LiPt 2 , according to Dr. Nash. X-ray diffraction powder patterns show lines that are in good agreement with cal42
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culations based on an MgCu 2 cubic lattice. The product seems to be a true intermetallic compound, Dr. Nash says. The lithium is chemically bonded to the platinum and completely unreactive with water. Dr. Nash postulates a crystal structure like that of MgCu 2 . The lithium atoms are in a cubic lattice having the diamond structure, he believes. Inside each of these cubes are four tetrahedra made up of platinum atoms. Thus, in this unusual compound, each lithium atom has 12 platinum atoms around it and each platinum atom has six lithium atoms around it. The electrons are thinly spread. New Catalyst. In the course of this work, Dr. Nash and his team have found a simple way to make a very active hydrogenation catalyst. In fact, on a weight basis, he says it is about twice as active as a supported platinum oxide catalyst, although only about equal in activity on a contained platinum basis. But platinum hydrogenation catalysts are tricky and time consuming to make; the Davis group can make a laboratory quantity of the catalyst with reproducible, high activity in about 15 minutes. Molten lithium has a remarkable ability to penetrate the platinum lattice at temperatures well below those at which reaction occurs. Dr. Nash believes that lithium gives up its single valence electron to the partly filled conduction band of platinum. Then lithium ions diffuse into and break up the platinum lattice. To make the catalys^ Dr. Nash just barely melts the lithium at about 200° C , and lowers a platinum strip into it [JACS, 82, 6203 ( I 9 6 0 ) ] . In a few minutes, the end of the strip disintegrates. By using a continuous feed technique, several hundred milligrams of platinum can be assimilated in any run. When the reaction mass is thrown into water, the lithium hydrolyzes and the platinum forms a
microdispersion, the Davis chemist adds. This platinum, in the form of a very fine black powder, can be recovered by settling for several hours or by centrifugation, Dr. Nash says. It is a very active hydrogenation catalyst at room temperature. It is not, however, suitable for high temperature reactions, he notes. When it is heated to about 200° C , a perceptible rearrangement occurs, and the catalyst activity decreases by a factor of about four. At this temperature, the microcrystallites apparently rearrange into larger aggregates.
Muon Can Be Called a Heavy Electron, CERN Work Shows The muon (mu meson) can be called a heavy electron in spite of the remarkable difference in masses (207 to 1) between the two particles, according to physicists at European Organization for Nuclear Research (CERN) in Geneva. The conclusion is based on the results of their "g-2" experiment, a high precision measurement of one of the physical characteristics of the muon—its magnetic moment. The work also gives information about the lower limits of the muon's dimensions and of a fundamental length in physics. The CERN group looked at the problem this way. If the muon is a heavy electron and shows no interactions different from those of the electron, then quantum electrodynamics should allow calculating exactly the muon's magnetic moment. Deviations from the calculated value of magnetic moment would imply a real difference between the muon and the election. After two years of effort, CERN physicists under Dr. Gilberto Bernardini completed the experiment to find that the muon's magnetic moment is in agreement with theoretically predicted values (within 2 parts in 100,000). The CERN workers say: • Quantum electrodynamic laws are valid at very small distances; more precisely, down to 0.7 fermi (0.7 X 10~13 cm.). • The muon can be visualized as a pointlike particle or tiny sphere no bigger than 0.3 fermi (0.3 X 10" 13 cm.). • Any fundamental length which one may think of as a limit to the relativistic invariance of physics is less than 0.2 fermi (0.2 X 10~13 cm.).
Number 24 in Advances i n Chemistry Series edited by t h e staff of
The ACS Applied Publications
CHEMICAL MARKETING IN THE COMPETITIVE SIXTIES The chemical industry in the postwar period has moved with such large strides that many contemporary writers refer to this period as the "chemical age."
UV Removes Two Hydrogens from One Carbon Two hydrogen atoms come off a single carbon atom to form a molecule of hydrogen during the photolysis of ethane, according to a newly determined mechanism for this photolytic reaction. Formerly, it was thought that ultraviolet photolysis of ethane results in the removal of one hydrogen atom from each molecule, or that ethane splits into two methyl radicals. Chemists at National Bureau of Standards came up with the new theory during their work on elementary processes in chemical kinetics. Dr. H. Okabe (above) and Dr. J. R. McNesby of NBS provide the needed UV with a xenon source. UV is passed into partially deuterated ethane (CH3CD3) and into mixtures of ethane and completely deuterated ethane (C2D6) for various lengths of time—30 seconds to 200 minutes. After exposure, all products which volatilize at 77° K. were analyzed with a mass spectrometer; hydrogen and deuterium were the major hydrogen species detected in all cases, the NBS chemists say. Minor amounts of HD were also formed. Formation of some ethylidene, they note, suggests that the reactions which follow removal of hydrogen atoms are not controlled by free radicals, but by carbenes such as ethylidene. Some methane is also formed in the reaction.
BRIEF Over $400,000 in new agricultural research grants have been made in the U.S. and abroad for 1961. Grants from Corn Industries Research Foundation, Inc., totaling a quarter of a million dollars, go to 25 scientists for research in corn and its components, principally starch. Among the recipients are 18 universities. A four-year investigation of the mechanism of milk clotting during cheese manufacturing
will be supported by a $60,000 grant to National Institute of Agricultural Research, Paris, by the U.S. Department of Agriculture. A $57,000 grant from USDA to Institute for the Study of Applied Industrial Chemistry, Bologna, will finance a five-year investigation of the chemicals formed when cereal starch dextrins react with compounds derived from fats. The University of Milan will receive $58,000 for a four-year study of the fermentation conversion of glucose.
Wide diversification of products; increased competition between domestic and foreign producers; between different chemicals for the same end use; and between companies for their share of the markets for the same commodity point to the problems of the future. The solution requires over-all coordination of the sales organization with advertising and distribution—and concurrent assistance and guidance from those departments responsible for market research, technical service and application research. The challenges facing the chemical industry, while different for each segment—organic and inorganic, drugs, and agricultural chemicals—will likely have numerous similarities in their solution. With this in mind, the symposium was organized with leading marketing men of the industry presenting in 31 papers the broad challenges expected in the i960's. 147 pages-paper bound-$3,50
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