Tandem reactions on phase separated MnO2 and C to enhance formaldehyde conversion to hydrogen

Abstract

Hydrogen production from formaldehyde aqueous solution at room temperature shows a unique advantage regarding the bi-functional reaction route. MnO2 was reported to be an active catalytic material for this process, especially after coating with carbon composite for improved active site distribution. Here, we unravel that the conversion of formaldehyde can be treated as two tandem half-reactions: the oxidative dehydrogenation (ODH) of formaldehyde and the hydrogen evolution reaction (HER). β-MnO2 in a physical mixture with carbon (i.e., XC-72R, graphene) enhances both formaldehyde conversion (from 13% to 19.5%) and hydrogen productivity (from 22.35 μmol mg−1 h−1 to 33.86 μmol mg−1 h−1) by a synergistic effect of the phase separation catalyst in terms of electron redistribution and transport over the active sites. The catalyst examination supported by DFT calculation shows relatively low activation energy and band gap of β-MnO2 + C with a density of states spanning the Fermi level. The discovery of this novel synergistic catalytic effect: a phase separation catalyst with cooperative enhancement, provides new insight into the area of tandem catalysis.