Mesoporous zeolite LTA-encapsulated Ni(II)-Schiff base complex: an efficient heterogeneous catalyst for electrocatalytic oxidation of methanol in alkaline media

A series of Ni(II)-Schiff base complexes were encapsulated in mesoporous zeolite LTA (denoted as NiL/LTA with L = salen, salpn, salbn, salphen, and (t)Bu(4)salen) and showed superior electrocatalytic activities for methanol oxidation in alkaline media. Different performances for methanol oxidation were due to the existence of different type of ligand that may originate from different steric and electronic effects exerted by the substituents present on the backbone of the salen ligands and/or by the different lengths of diamine bridge. The use of mesoporous zeolite LTA with nano-cages of 3 nm makes possible the interaction between the partially coordinated Ni(salen) in adjacent or appropriate sites in a nano-cage through the zeolite lattice oxygen, leading to the formation of new electrochemically accessible active sites and a great improvement in the electrocatalytic activities. A possible mechanism was proposed that electrocatalytic oxidation of methanol on NiL/LTA/GCEs was done by reaction with Ni(III)LO(OH) and also direct electro-oxidation reaction.