Computational methods are helping chemists unravel the complexities of inorganic catalysts with possible implications for ozone depletion and the automotive industry.

Chabazite is a rare mineral with a beauty that makes it a rock collectors’ favorite. Creamy colored or pinkish with a vitreous sheen, it is pressed into nearly cubic crystals when volcanic rocks are subjected to the heat and pressures of metamorphosis.

Although chabazite looks impressively solid sitting on a coffee table, on the atomic level it has properties possessed by all zeolites—it’s full of holes. Zeolites, a class of natural and synthetic minerals possessing large, vacant spaces in their crystalline structure, provide tunnels and hideouts for such atoms as potassium, sodium, and calcium and even for molecules like water and ammonia. This property makes zeolites useful for things such as water purification and softening, removing radioactivity from spent nuclear fuel, and controlling kitty litter odor.

The cavities in a zeolite’s structure also help explain its effectiveness as a catalyst. A catalyst is a substance, in this case an acidic solid, that facilitates chemical reactions without itself being changed. Not much is currently known about these zeolite caves on the atomic level, including how they interact with the atoms that enter their passages. Successful spelunking here could have ramifications far beyond the contentment of the household cat.

“Zeolites are rather large, complex systems. They’re analogous to enzymes,” says David White, a chemistry professor at the University of Pennsylvania. “The big question is: What kind of chemistry goes on in small cavities—just like what you have in cells?” Because cells also contain complex networks of cavities, a better understanding of the chemistry of zeolites could reveal much about the chemistry of biological systems.

	The Trout research group in front of MIT's Killian Court.

Bernhardt Trout, professor of chemical engineering at the Massachusetts Institute of Technology, White, and other collaborators are using the Alliance’s SGI Origin2000 supercomputer at NCSA to simulate catalysis computationally. They chose chabazite as their archetype zeolite because it’s used in industry to convert methanol to olefins. Despite having rather complex zeolitic systems, chabazite is small enough (only 36 atoms) to be successfully modeled by supercomputers, yet big enough to yield important information.

Trout is also using the Origin2000 to study both catalytic behavior relevant to the automotive catalysts used in catalytic converters and the chemistry of ice crystals. Understanding how ice in the stratosphere reacts with other compounds could offer insights into ozone depletion and how to prevent it.

Access Online | Posted 12-11-2001