Influence of graphene surface chemistry on Ir-catalyzed hydrogenation of p-chloronitrobenzene and cinnamaldehyde: Weak molecule-support interactions

Abstract

Graphene is an ideal model support to investigate the influence of carbon surface chemistry on catalytic reactions. Here a mild hydrothermal method was developed to synthesize graphene-supported iridium nanocatalysts from graphene oxide. By simply varying the hydrothermal conditions, the physicochemical properties of catalysts can be tuned, which can further affect their catalytic performances. Catalysts obtained at higher H2 pressure during hydrothermal process performed higher catalytic activities for hydrogenation of both p-chloronitrobenzene and cinnamaldehyde, benefiting from their higher reduction degrees of iridium nanoparticles. Interestingly, catalysts obtained at lower hydrothermal temperature performed higher activities for p-chloronitrobenzene hydrogenation but lower activities for cinnamaldehyde hydrogenation, due to their distinct surface chemistry of graphene. Through systematic characterizations on 11 catalysts prepared under various conditions, we found that lower hydrothermal temperature endows graphene with larger lateral dimension and more in-plane oxygenated surface groups, which facilitates the accessibility of nitro groups to catalyst surface via H-bond interaction as confirmed by density functional theory calculations. This is not true for cinnamaldehyde, of which adsorption on graphene via π-π stacking interaction is favorable for its hydrogenation.