Cucurbit[6]uril as a co-catalyst for hydrogen production from formic acid

Abstract

Cucurbiturils are organic macrocycles, which are only rarely used for catalytic reactions. We studied a composite comprising of single-walled carbon nanotubes (SWCNTs), cucurbit[6]uril (CB6) and Au species and demonstrated that CB6 is a co-catalyst for hydrogen production from formic acid. Thus, insertion of CB6 into SWCNTs with open tips provides a decrease of the reaction temperatures by 60 K as compared to those over pure SWCNTs. This indicates that CB6 is a metal-free catalyst for this reaction. The use of CB6 during the synthesis of Au catalysts supported on SWCNTs leads to even a stronger decrease of the reaction temperature by 110 K as compared to the Au/SWCNTs catalyst. Density functional theory (DFT) calculations show that these effects could be explained by abstraction of the hydrogen atom from the hydroxyl group of the formic acid molecule on the basic carbonyl portal of the CB6 molecule with the formation of the formate containing adduct. Unusual sandwich-like structures of Au were formed inside the SWCNTs channels due to the interaction of Au with CB6. The results create a base for the development of catalysts containing cucurbiturils for the energy related reactions taking place through the hydrogen abstraction from reactant molecules.