Influence of temperature during pyrolysis of Fe-alginate: Unravelling the pathway towards highly active Fe/C catalysts

Transition metals supported on carbons play an important role in catalysis and energy storage. By pyrolysis of metal alginate, highly active catalysts for the Fischer-Tropsch synthesis (FTS) can be produced. However, the evolution of the carbon (alginate) and transition metal (Fe3+) during pyrolysis remains largely unknown and was herein corroborated with several advanced in situ techniques. Initially, Fe3+ was reduced to Fe2+, while bound to alginate. FeO nucleated above 300 °C, destabilizing the alginate functional groups. Increasing temperatures improved carbonization of the carbon support, which facilitated reduction of FeO to α-Fe at 630 °C. Catalysts were produced by pyrolysis between 400 and 700 °C, where the highest FTS activity (612 µmolCO gFe-1 s-1) was achieved for the sample pyrolyzed at low temperature. Lower metal loading, due to less decomposition of alginate, moderated sintering and yielded larger catalytic surface areas. The results provide valuable knowledge for rational design of metal-alginate-based materials. [Display omitted] •FeO nucleates above 300 °C, while the reduction of FeO to α-Fe occurred around 630 °C.•Pyrolysis between 400 and 700 °C yielded Fe nanoparticles with average sizes from 2.8 to 7.1nm.•Higher pyrolysis temperature yielded more reduced iron, i.e., metallic or carbide iron phases.•Alginate-derived carbon facilitates reduction to α-Fe and carburization at high temperatures.•Lower pyrolysis temperature is beneficial for catalytic activity in FTS.