Visualising Co nanoparticle aggregation and encapsulation in Co/TiO2 catalysts and its mitigation through surfactant residues

Due to the reducible nature of TiO₂, the encapsulation of cobalt nanoparticles (CoNPs) by reduced TiO_2-x is often reported to decrease their catalytic performance in reactions such as Fisher-Tropsch synthesis (FTS). Here, we show using HAADF-STEM imaging and electron energy loss spectroscopy (EELS) that a residual C₁₂E₄ surfactant used to prepare the CoNPs, remains on the surface of a TiO₂ rutile support, preventing the formation of Ti³⁺/Ti²⁺ oxides and therefore TiO_2-x migration. Furthermore, the presence of these surfactant residues prevents the coalescence and aggregation of CoNPs during catalyst preparation, maintaining the dispersion of CoNPs. As such, using C₁₂E₄ in the preparation of Co/TiO₂ can be considered beneficial for producing a catalyst with a greater number of active Co species.