Press-fit chemistry

Many catalysts provide a passive surface or cavity on which reacting molecules can sit in the right position to react together. Daedalus is now dreaming up a more active type of catalyst.

He recalls the catalytic zeolites, which are riddled with molecular-scale cavities, within which entering molecules can react. Sometimes the cavities actually expand when molecules enter them. So, says Daedalus, imagine an elastic porous catalyst, perhaps a piezoelectric zeolite or microporous silica, expanding and contracting under external control. In its expanded state, it allows reacting molecules to enter its cavities freely. Then it contracts, squashing them together in a way that forces them to react. On the next expansion, the product molecule can escape, to be replaced by new reagents. The cycle could be repeated at megahertz rates.

DREADCO chemists are now trying it. They are combining the skills of the piezoelectric quartz crystal and silica-based catalyst industries to study the effects of setting such catalysts into intense vibration. With luck, the chemical yields of standard test reactions should increase dramatically. Even better, a piezoelectric catalyst could be ‘tuned’ electronically by setting it into different vibrational modes. A mode which elongated its molecular sites or cavities would give linear molecules; one which flattened them would encourage planar ones. A single catalyst could generate a wide range of products under perfect control.

But the real goal of the project is to find entirely new reactions, yielding hitherto unknown products. Imagine, says Daedalus, a piezoelectric porous catalyst whose cavities can expand to accept three dinitrogen molecules arranged as a hexagon. When such a cavity contracts, the molecules will be squashed together to form the hitherto unknown hexagonal molecule N₆. Being isoelectronic with benzene, it could well be stable. On the next expansion, it would be released, and more dinitrogen taken up. O₆, tetrahedrane (dimerized from acetylene) and many other unknown molecules, could be made in the same way.

N₆ would probably be a powerful high explosive, O₆ a ferocious oxidizing agent, and tetrahedrane an energetic rocket fuel. But they are just the start of a new era of chemical synthesis. A whole bonanza of weird, warped, incredible molecules could pour from the new cornucopia of piezoelectric catalysis.