Optimization of supported cobal catalysts for the Fischer-Tropsch Synthesis

Abstract

The Fischer-Tropsch synthesis is a process in which synthetic fuel can be produced from syngas. The interest of this fuel lies in its ability to foment a transition in hard to abate sectors such as aviation, heavy duty, and shipping. The main objective of this investigation is to foment and research about the sustainability of synthetic fuels, by optimizing the catalysts and by upcycling CO2 into fuels. These objectives were studied in 2 phases: The first phase focalized in the optimization of supported cobalt catalysts by varying their preparation technique and the cobalt loading, whilst for the second stage, cerium oxide is added to the optimized catalyst as promoter, for studying the effect of the cerium oxide on the conversion of CO/CO2/H2 mixtures. The obtained catalysts were characterized by TPR, N2 Adsorption, SEM, EDX, XRD, ICP-AES and CO chemisorption; and tested for Fischer Tropsch synthesis in a fixed-bed reactor at 2.0 MPa, 230 ºC and a H2/CO ratio of 2.Differences between the supported cobalt catalysts were observed and related to the preparation method. The impregnation of Co2+ and Ce3+ resulted in a uniform distribution on the catalyst pellets. Lower calcination temperatures and unique impregnation led to higher reducibility of the cobalt oxides, and enhanced properties (SBET, Metallic Surface Area, Dispersion, Particle Size) in comparison to the higher calcination temperature. The properties of the catalysts affected the catalytic performance of the catalysts Once selected the optimized catalyst, a new batch of catalysts impregnated with cerium are prepared in the same conditions. These catalysts were tested under 2 syngas mixtures, in which one syngas mixture was enriched with 25 vol% of CO2, and the other one had no CO2 in it. The reaction under a CO2-enriched mixture yields a lower productivity in comparison to the syngas these results are plausible because the CO2 is not as reactive as the CO. Nonetheless, CO2 conversion is detected at lower temperatures whilst for the highest temperature CO2 is produced. Cerium oxide improved the productivity obtained for the CO2-cointaining mixture in comparison to the non-promoted catalyst. Impregnation of the cobalt over the cerium oxide yields in higher CO2 concentrations than cerium oxide impregnated over cobalt