Catalyst libraries take the strain

Choosing a catalyst for a process can be frustrating. Theory tells industrial chemists which metals and supports ought to catalyse a reaction, but the only way to confirm which actually work is to run test reactions.

Help may be at hand, however, thanks to a researcher who has used a technique known as combinatorial synthesis, to test many tiny samples of different catalysts simultaneously.

Combinatorial synthesis is a technique which prepares large 'libraries' of related compounds, explains Selim Senkan of the University of California, Los Angeles (Nature, vol 394, p350). A library starts off as a tray with a number of small wells, each containing a support coated with the same substance. Samples containing different substances are added to each well, causing a reaction and leaving a product. This could be used to make many salts of the same metal, for example.

The samples then have to be screened for catalytic activity. To help with this, Senkan's library trays are constructed in two layers. The top layer contains the wells of catalyst, which have perforated bases. The bottom layer contains a network of tubes, which carry a vapour mixture around the tray and allow it to bubble up through the catalyst mixtures (see diagram).

To detect this, Senkan uses a laser detector whose frequency is selected so that it will ionise one of the products that will be formed if the catalyst is active.

In this form, the system will test the activity of a catalyst; but using several lasers, each tuned to a different frequency, could also screen for selectivity, says Senkan.