How water reacts with solid catalysts.

Almost like magic, a good catalyst can provoke a slow-cooking chemical brew into a rapid-fire reaction. Stir the potion, sprinkle on a dash of catalytic powder, and off goes the chemical transformation.

In the petroleum industry, zeolites-porous solids used to refine crude oil into fuels-serve as the catalysts of choice. Zeolites have structures called acid sites on their surfaces that facilitate charge transfers between molecules, thereby accelerating chemical reactions. Anthony K. Cheetham, a chemist at the University of California, Santa Barbara, and his colleagues have now shown precisely how the acid sites accomplish this key proton transfer-at least among water molecules.

His team describes in the Feb. 9 Science results from an analysis of a synthetic solid catalyst, HSAPO-34, similar to the naturally occurring zeolitic mineral chabazite. The researchers used neutron diffraction and infrared spectroscopy. Their findings confirm the presence of two types of reactions. In the first, a water molecule forms a hydrogen bond with an acid site on the catalyst. In the second, a water molecule picks up a proton, creating a hydronium ion (H3O+). Computer models had predicted both reactions. "What's important here is that this is the first time that anyone has actually detected the proton being transferred to the water," says Antonio Redondo, a physical chemist at Los Alamos (N.M.) National Laboratory.

Cheetham speculates that deeper understanding of the catalytic mechanism might someday enable chemists to design catalysts with carefully tailored acidities, which would increase their effectiveness in particular chemical reactions. "Understanding the cooperation of the active site and its environment in tuning the acidity of the system is a fundamental chemical problem," says Joachim Sauer, a chemist at Germany's Humboldt University in Berlin.