Fe-containing nanoparticles used as effective catalysts of lignin reforming to syngas and hydrogen assisted by microwave irradiation

Active iron-containing nanosized components have been formed on the lignin surface. The metal was deposited on the lignin from an ethanol solution of Fe(acac)₃ and from a colloid solution of iron metal particles obtained beforehand by metal vapor synthesis. These active components are able to absorb microwave radiation and are suitable for microwave-assisted high-rate dehydrogenation and dry reforming of lignin without addition of a carbon adsorbent, as a supplementary radiation absorbing material, to the feedstock. The dependence of the solid lignin heating dynamics on the concentration of supported iron particles was investigated. The threshold Fe concentration equal to 0.5 wt.%, providing the highest rate of sample heating up to the reforming and plasma generation temperature was identified. The microstructure and magnetic properties of iron-containing nanoparticles supported on lignin were studied before and after the reforming. The Fe₃O₄ nanoparticles and also core-shell Fe₃O₄@γ-Fe-С nanostructures are formed during the reforming of lignin samples. The catalytic performance of iron-based nanoparticles toward the lignin conversion is manifested as increasing selectivity to hydrogen and syngas, which reaches 94% at the Fe concentration of 2 wt.%. It was found that with microwave irradiation under argon, hydrogen predominates in the gas. In the СО₂ atmosphere, dry reforming takes place to give syngas with the СО/Н₂ ratio of ~ 0.9. In both cases, the degree of hydrogen recovery from lignin reaches 90–94%.