Performance of carbon nanomaterial (nanotubes and nanofibres) supported platinum and palladium catalysts for the hydrogenation of cinnamaldehyde and of 1-octyne

Abstract

Within this work, different carbon nanomaterials, multi-walled nanotubes (MW-CNT) as well was herringbone (HB-CNF) and platelet nanofibres (PL-CNF), were synthesised and loaded with the active metal (platinum or palladium) by means of selected functionalisation techniques. As loading methods conventional techniques (wetness impregnation (WI), ion adsorption (IA), homogeneous deposition precipitation (HDP)) as well as a very young method, the colloidal microwave process (CMP), were applied. For comparison, a conventional activated charcoal (Fluka, Norit) was loaded by the CMP. In addition, commercial catalysts such as Pt- and Pd-catalysts on activated charcoal (Fluka) as well as the industrially well-established Lindlar catalyst (Fluka) and a Pt/alumina material (Aldrich) were employed. In order to evaluate the catalytic performance of the materials, two different hydrogenation reactions were carried out. The platinum materials were tested for the hydrogenation of cinnamaldehyde and the palladium catalysts were applied in the hydrogenation of 1-octyne. Regarding the hydrogenation of cinnamaldehyde, the materials produced via the CMP showed the best results in terms of activity and selectivity towards the desired intermediate cinnamyl alcohol in comparison to the commercial materials. It was also shown that not only the functionalisation technique (CMP) but also the support material is crucial concerning catalyst performance. Thus, with the herringbone nanofibre supported Pt-catalyst (CMP) the most promising results were obtained with respect to activity and selectivity. Within the hydrogenation of 1-octyne the CMP-loaded Pt/platelet-nanofibre catalyst showed similar characteristics in activity and selectivity compared to the commercial Lindlar catalyst. However, in long term experiments the nanofibre material featured much higher stability. A commercial Pt/activated charcoal material was most active but least selective towards the favoured intermediate 1-octene. The presented results indicate a strong influence of carbon nanomaterials as a support and of the functionalisation technique on the performance of hydrogenation catalysts.