SCIENCE/TECHNOLOGY
No Organics Needed To Synthesize Aluminophosphate Molecular Sieves Georgia Tech researchers' new route eliminates need for costly amine, coincidentally solving mystery triggered by French chemist 30 years ago Researchers at Georgia Institute of Technology have demonstrated for the first time that microporous molecular sieve aluminophosphates of h i g h purity can be synthesized without the use of organics. This is a major advance, says team leader Rosemarie Szostak, because earlier recipes for aluminophosphates call for an organic amine—an expensive ingredient everyone has assumed is required for the synthesis. Eliminating the amine could substantially cut the cost of preparing these industrially important catalysts because the other ingredients—aluminum and phosphoric acid—are cheap. In making this discovery, Szostak's team also has solved a 30-yearold mystery triggered by a French chemist named Ferdinand D'Yvoire. In a 1961 paper, D'Yvoire reported the synthesis of a new aluminophosphate called H I . Because it could not be isolated as a p u r e material, D'Yvoire was unable to characterize it in detail. His synthesis procedure, which involved only inorganic ingredients, was repeated by several groups, none of which succeeded in preparing HI as a pure phase. Then, in 1982, Union Carbide researchers reported making the first microporous aluminophosphates using an amine. The amine appeared to be necessary to promote crystallization and formation of the microscopic network of pores and tunnels in these materials. This discovery "touched off an explosion of new
molecular sieve structures and compositions extending beyond the known zeolite [aluminosilicate] molecular s i e v e s / ' Szostak notes. Using the amine methodology, Mark E. Davis and coworkers at Virginia Polytechnic Institute & State University prepared a new molecular sieve called VPI5, which has pores the size of 18-member rings—the largest pore size yet achieved. Today's petroleum-cracking catalysts use zeolite molecular sieves with 12-memberring pores. But refiners are always on the lookout for larger pore structures because these can accommodate and crack larger crude oil molecules, yielding high-grade fuels. In any case, Szostak, an inorganic chemist at Georgia Tech Research Institute (GTRI), noticed—as had other scientists—that the x-ray powder diffraction pattern of VPI-5 is similar to that of D'Yvoire's mysterious HI. If VPI-5 and HI are indeed one and the same, she thought, then perhaps this unique aluminophosphate could be prepared in pure form without the use of an amine. As Szostak told attendees of the Materials Research Society meeting in Boston two weeks ago, she asked an undergraduate student, Bryan Duncan, to repeat D'Yvoire's work with the objective of making HI as a single pure phase. Duncan, however, was not fully aware of the project's background and possible link to VPI5. He simply followed Szostak's directions and reacted aluminum hydroxide and phosphoric acid in water under modified conditions. When Duncan identified his product as VPI-5, he couldn't understand what was wrong—why he wasn't getting
Szostak: vindicated
hunch
HI. But when Szostak finally learned of Duncan's results, it was immediate vindication of her hunch. T w o k e y m o d i f i c a t i o n s of D'Yvoire's synthetic reaction led to the Georgians' success. One was the addition of hydrochloric acid, a common impurity in early alumina synthesis but one not present in today's higher purity alumina sources, according to Szostak. The other change involved enriching the aluminum content of the reaction mixture relative to phosphorus. Duncan's product, dubbed Hl(GTRI), gives an x-ray powder diffraction pattern and infrared spectrum identical to those of VPI-5. The product was characterized by Kristin Sorby, a visiting graduate student from the University of Oslo, and Judith Ulan, an electron microscopist at the University of California, Berkeley. The critical experiment centered on the thermal behavior of Hl(GTRI). When VPI-5 is heated to 100 °C, it is transformed into a n o t h e r a l u m i n o p h o s p h a t e called AIPO4-8 that has 14-memberring pores. The Georgia Tech researchers observed that, under similar conditions, HI (GTRI) also undergoes this solid-state transformation. The transformation, h o w e v e r , December 10, 1990 C&EN
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Science/Technology generates faults in the crystal structure that serve to block the pores. Since heating cannot be avoided during catalytic cracking, Hl(GTRI)type materials probably won't be used to crack large hydrocarbon molecules anytime soon. But Szostak hopes to refine the Hl(GTRI) synthesis so as to produce heat-stable material. She is confident that the new organic-free synthesis process will soon yield similar molecular sieves with very large pores. The Hl(GTRI) work, to be published in Catalysis Letters, was supported by a consortium of companies involved in the manufacture and use of molecular sieves. As for D'Yvoire, Szostak points
out that he did pioneering work in a l u m i n o p h o s p h a t e s but has not been g i v e n credit for it. What Szostak has done is to confirm, three decades after the fact, that the French chemist actually was the first to report the synthesis of VPI-5, albeit in impure form. As it turns out, hydrochloric acid may not have been a contaminant of D'Yvoire's reaction mixture, Szostak now thinks. But that just goes to show that making molecular sieves is largely a matter of trial and error—and luck. And the joy of studying these materials, she suggests, is not unlike the fun kids have running amok in a candy store. Ron Dagani
Consortium forms to use 'fastest" supercomputer A supercomputer to be installed next spring at California Institute of Technology, which is being called "the world's fastest computer," will form the basis for a new consortium of research institutions, the Concurrent Supercomputing Consortium. Many of the applications anticipated for the supercomputer are chemistry-related. The consortium, composed of 14 member institutions, is acquiring the Touchstone Delta system, a parallel supercomputer made by Intel Corp. The system has 528 numeric processors that work in parallel to provide a peak computational speed of 32 gigaFLOPS (32 billion floatingpoint operations per second). In
comparison, a Cray Y-MP supercomputer is rated at 2.7 gigaFLOPS, and a four-processor NEC SX-3 currently in development claims a peak rate of 22 gigaFLOPS. The members of the consortium are Argonne National Laboratory, Battelle Pacific Northwest Laboratories, Caltech, Caltech's Jet Propulsion Laboratory, the Center for Research in Parallel Computation (a National Science Foundation Science & Technology Center), the Defense Advanced Research Projects Agency, Intel, Lawrence Livermore National Laboratory, Los Alamos National Laboratory, the National Aeronautics & Space Administration, the National Science Founda-
tion (programs in computational science and engineering), Oak Ridge National Laboratory, Purdue University, and Sandia National Laboratories. Researchers from nonmember institutions can gain access to the s u p e r c o m p u t e r by w o r k i n g through consortium members. Problems that members of the consortium are planning to study on the Caltech supercomputer include several that are chemistry-related. Among them: • Calculating the rates of chemical reactions using ab-initio quantum chemistry techniques. • Pattern recognition of DNA sequences within the human genome. • "Engineering" enzymes for enhanced biodégradation. • Modeling of molecular processes in natural and contaminated systems to better understand the behavior of contaminants in the environment. • Modeling and simulations of global climate change. For example, Battelle's molecular science research center will use the computer to help modify an enzyme for enhanced biodégradation. According to Battelle associate director Thorn Dunning, "It takes our current supercomputer one hour to model one trillionth of one second of the enzyme's activity. While we still won't be able to model the whole process with the massively parallel computer, we can get a more accurate picture of what is happening more quickly." Stu Borman
Dynamical structure of proteins studied
Intel officials with company's Touchstone Delta supercomputer 20
December 10, 1990 C&EN
A team of theoretical chemists has developed a supercomputer-based method for probing the internal motion of proteins. The method, which is used to figure out how distant and seemingly unrelated parts of large proteins exert an influence on each other, has already led to a better understanding of HIV-1 protease, an essential enzyme in the replication of human immunodeficiency virus. The method, developed by S. Swaminathan and David L. Beveridge of Wesleyan University, Middletown,
