Graphene oxide as superior catalyst support for heterogeneous catalysis

Abstract

Graphene oxide (GO) offers appealing features such as their 2D structure and the presence of oxygen functional groups for its use as support for heterogeneous catalysis. In this work we show that GO offers superior catalyst support performance when compared to a variety of carbon supports (single-walled and multi-walled carbon nanotubes, graphite, graphitic cones, nanodiamond, ordered mesoporous carbon, carbon xerogel, carbon black, activated carbon, and laser-ablation produced carbon foam). We show that these carbon materials could be efficiently used as supports for gold nanoparticle (AuNP)- based catalysts for the hydroamination of phenylacetylene with aniline. Carbon supports were decorated with AuNPs synthesized by in situ reduction of chloroauric acid (H[AuCl4]) in water. The synthesized gold-carbon hybrids worked remarkably well as catalysts for the targeted reaction. Conversion values as high as 79% were achieved by suitably adjusting the gold:carbon support w/w ratios. Our results indicate that the catalytic activity strongly depends on gold:carbon support w/w ratios and on the structure and textural properties and dispersibility of the carbon supports used. The best gold-carbon catalyst performance in terms of conversion values and low carbon support content has been achieved when using GO as well as supports (carbon black, carbon nanotubes, and nanodiamond) that combine high BET surface areas, well-developed mesoporosity, and good dispersibility in water during the GNP decoration process. GO, that exhibits high microporosity, behaves differently probably because the microporosity present in the dry solid drastically decreased when the material was highly exfoliated in water, leading to a huge surface area available for the GNP deposition. Moreover, the large number of oxygen functional groups (hydroxyl, carbonyl, phenol, and epoxide groups, 44.9 wt.% O content) of GO allowed a good GO dispersibility in water. The presence of these oxygen-containing functional groups in GO may also assist the GNP deposition and, eventually, may favor the gold-carbon hybrid/reactants interaction, so they may also further account for the superior catalytic performance of the Au-GO hybrids.