High-throughput experimentation as a tool in catalyst design for the reductive amination of benzaldehyde

Abstract

A combinatorial library of 24 carbon-supported noble metal catalysts is screened for reductive amination of benzaldehyde in the presence of ammonia. Gas chromatography is used to rapidly quantify the product yields and selectivities obtained with the different candidates. The results show that the catalytic activity is strongly influenced by, both, the nature of the support and the nature of the metal. The activity is higher when the parent support, SX1G, has been treated by oxidation and subsequent sodium-exchange. With regard to the metal, the activity decreases in the order of Ru, Pd, Pt. Surprisingly, Ru-based catalysts, which do not rank among the most commonly used for reductive amination processes, show the highest activity. The selectivity to a particular amine is controlled essentially by the nature of the metal. Benzylamine is the major product obtained over Ru-based catalysts, while dibenzylamine is formed preferentially over Pd-based catalysts. Conventional methods are in complete agreement with the trends observed by high-throughput techniques. Consequently, high-throughput experimentation allows the discovery of new catalysts for a given reaction by shortening considerably the catalyst optimisation time.