Carbon Nanotubes Deposited on Mordenite Zeolite/NiAl-Layered Double Hydroxide Composites as Electrocatalysts for 2,5-Furandicarboxylic Acid Production from 5-Hydroxymethylfurfural

Abstract

The nanostructured free-standing NiAl-MOR-CNTs electrocatalysts containing carbon nanotubes (CNTs) deposited on mordenite (MOR) zeolite/NiAl-layered double hydroxide (NiAl-LDH) have been successfully fabricated. Initially, the core-shell NiAl-LDH-MOR with hierarchical structures was observed via an aqueous miscible organic solvent treatment process to deposit nanosized NiAl-LDH homogeneously on a zeolite surface. The synthesized NiAl-LDH-MOR composites were calcined to produce highly dispersed metal oxides catalyzing the CNTs formation via chemical vapor deposition using bioethanol as a feedstock, eventually producing the NiAl-MOR-CNTs composites. To illustrate the beneficial aspect of the prepared composite, they were mixed with Nafion as a binder and pressed into circular pellets used as free-standing electrodes for electrochemical oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA), an important renewable monomer of bioplastic. The prepared free-standing electrodes exhibited an excellent catalytic performance of 100% conversion of HMF with a high selectivity of FDCA up to 92% under ambient conditions. Moreover, the synthesized electrocatalysts can be recycled even after several consecutive cycles without any loss of catalytic activity, confirming a high stability of the synthesized electrodes. This work illustrates the design of electrocatalysts by using conductive CNTs grown on highly dispersed metal active sites on zeolite/LDH composites without using commercial conductive supports such as nickel foam or carbon fiber paper.