A series of supported palladium catalysts have been prepared that are active for hydrogenation reactions in both gas and liquid phases. Infrared (diffuse reflectance and transmission) spectroscopy of chemisorbed carbon monoxide has been used to probe the morphology of the Pd crystallites. The catalytic performance of these catalysts have then been evaluated in a number of reactions and correlated with the structural characteristics attributed to each catalyst.

A representative test reaction is the hydrogenation of crotonaldehyde in the gas phase.

Some of our catalysts exhibit the expected behaviour of being 100% selective for formation of butyraldehyde, however, a number of catalysts also permit access to the 2^nd stage hydrogenation pathway, where butanol is formed. This difference in reaction characteristics is attributed to the presence of two distinct sites on the Pd crystallites: (i) a combination of Pd(111) and (100) planes and (ii) Pd edge atoms. First stage hydrogenation is attributed to the Pd(111) and Pd(100) planes, whereas second stage hydrogenation requires edge sites. In addition to hydrogenation pathways having a strong structural component, results indicate that chemical effects also play an important role in controlling the product distributions observed.

Collectively, this work defines catalyst specifications, with associated preparative procedures, for hydrogenation catalysts able to emphasise particular chemical pathways. Further work is required to see if generalisations suggested in these studies can be exploited in other, more complex, reactions.