University of Delaware
Office of Public Relations
UpDate - Vol. 16, No. 22, March 6
     
                         From fuel to medicine
            Zeolite has a variety of potential applications
     Anew material-characterized by a research team
including a University of Delaware faculty member-may some
day result in more efficient, less costly catalysts for
generating gasoline, medicines and other products.
     Raul F. Lobo, chemical engineering, recently helped
characterize a catalytic material with unusually large
atomic pores or "cages" that might prove useful for speeding
up, or catalyzing, reactions with the molecules in
hydrocarbon fuels and certain pharmaceuticals.
     Lobo and his colleagues at the University of Texas-
Dallas, the California Institute of Technology and the
University of Massachusetts are excited about the new
aluminosilicate "zeolite" because it features pores bounded
by 14 silicon and oxygen atoms-possibly the largest to date.
     The material also remains stable at temperatures up to
900 degrees Celsius (1650 degrees Fahrenheit), roughly two
times hotter than the temperatures required for industrial
catalysis, Lobo reported in the May 1996 issue of the
journal Nature.
     Researchers have previously made very large-pore
zeolites by combining alumina with phosphates (rather than
silicates), he added, but those materials tend to fall apart
as the temperature is raised above a few hundred degrees.
     "Some aluminophosphate zeolites have been made with
larger pores than aluminosilicate zeolites," he said, "but
these phosphate-based structures are thermally unstable. To
make a zeolite react, you have to heat it up."
     In Greek, the word zeolite means "boiling stone."
That's because "many zeolites appear in nature, and they're
full of water, which makes steam," Lobo explained. Engineers
now use synthetic zeolites, sometimes also described as
molecular sieves, to capture desirable molecules of a
certain size and to facilitate chemical reactions within
their pores.
     For this reason, zeolites are used for "cracking" the
large molecules in crude oil, to generate desirable products
such as gasoline from heavier-and cheaper-fractions of the
oil.
     "The size of the molecule you can crack depends on the
pore size of your zeolite," Lobo noted. "The market for high-
quality gasoline is much bigger than the market for diesel
fuel and kerosene, but existing catalysts produce larger
amounts of those lower-grade products."
     Rugged, thermally stable zeolites with larger pores
would make it easier and less expensive to produce high-
octane gas, he said. Other applications for the zeolites may
include pharmaceuticals based on very large molecules.
     The large-pore zeolite was prepared using a material
called bis-(pentamethyl-cyclopentadienyl)-cobalt(III)
hydroxide as a kind of "template." First, the template and
other components were heated to 175 degrees C in a sealed
vessel. The inorganic components organized around the
template to form the crystalline network that makes the
zeolite structure, Lobo said. In a final step, the template
inside the product was eliminated by exposing it to air at
550 degrees C. An evaluation of the resulting material,
based on X-ray diffraction patterns and other analyses,
revealed wide atomic rings.
     Before the material can be developed for use in an
industrial setting, the research team must still overcome
several technical hurdles, Lobo said.
     The template material is expensive, he said, and "we
can't reuse it because we're essentially burning it." Also,
researchers have "solved" most of the structure, meaning
that they understand what it looks like at the microscopic
level. But some aspects of the zeolite's structure remain a
mystery, and Lobo conceded that "it could take years" to
fully develop applications for the material.
     Lobo said he and his colleagues are optimistic about
the work, however. "Given the current price of the structure-
directing agent that we're using," he said, "this material
would probably be most useful in the pharmaceutical
industry, at least initially. Later, we hope it could be
developed for use in petrochemical applications."
                                          -Ginger Pinholster