Nano-Fe/SiO2 catalysts prepared by facile colloidal deposition: Enhanced durability in Fischer-Tropsch synthesis

Abstract

Nano-iron catalysts exhibit good performances in the Fischer–Tropsch synthesis to lower olefins (FTO), however, there is still a lack of simple methods for their preparation. In this work, we introduced a facile colloidal deposition (CD) method to fabricate silica-supported Fe2O3 nanoparticles using a colloidal solution readily prepared from ferric hydroxide. With increasing the Fe loading from 16.3 % to 31.6 %, the Fe2O3 particle size increased from 1.3 to 6.1 nm. The catalytic performances in FTO were tested at a H2/CO molar ratio of 1. At a Fe loading of 30.4 %, the catalyst having a particle size of 4.7 nm showed the highest lower olefin selectivity and the lowest CO2 selectivity, outperforming analogs prepared by impregnation method. Furthermore, this catalyst showed good stability in a 200-hour durability test, while the impregnated analogue quickly deactivated due to serious coking. Presumably, the effective contact areas between the nanoparticles and the generated carbon sheets are geometrically small, which results in weak van der Waals forces between them, preventing the former from being heavily covered by the latter. Besides, from the point of view of the carbide decomposition mechanism of coking, due to the relatively low volume to surface area ratios of the intermediate carbide nanoparticles, the surface concentrations of carbon atoms released from them are low, which delays the coke formation. This study may provide a simple method to fabricate supported nano-iron catalysts, and cast some light on understanding catalyst durability in FTO.