3D honeycomb monoliths with interconnected channels for the sustainable production of dihydroxybenzenes: towards the intensification of selective oxidation processes

Abstract

Novel 3D Fe/SiC honeycomb monolithic reactors with different morphologies (i.e. cell geometry, cell density and interconnected channel pattern) have been conceptually designed, digitally prototyped and manufactured by robocasting. Square, tronco-conical and triangular cell geometries with parallel channels presenting staggered or faced interconnections have been tested in the phenol hydroxylation reaction with hydrogen peroxide to produce dihydroxybenzenes, such as catechol and hydroquinone. The analysis of the valence state of iron in the monoliths by Mössbauer spectroscopy identified iron silicides, viz. Fe3Si and α-FeSi2, as the iron catalytic species.The results demonstrate that an increased macro-channel tortuosity, favoured by a high density cell and a high number of not-facing inter-connected channels, facilitates the selectivity to the dihydroxybenzenes. In particular, 3D Fe/SiC monoliths with triangular cells provide an outstanding improvement with respect to the commercial process, not only because of their superior performance (SDHBZ=99.1% and YDHBZ=29.6% at 80 ºC) and stability (over 8 days on stream) but also in sustainability (i.e. operation in flow-reactor, no need of catalyst filtration, water as unique solvent). The additive manufacturing has allowed the smart integration of the catalytic phase into the monolithic structure, enabling, by this way, to architecture the reactor independently on its chemical composition.