A new catalyst, composed of iron carbide nanoparticles (FeCNPs) and synthesized by plasma-spraying technology, was tested for Fischer-Tropsch synthesis (FTS) in a continuously stirred slurry reactor. The plasma-produced FeCNPs were core-matrix structures (FeC-rich core inside a graphitic carbon matrix) which protected air-sensitive carbides, preventing oxidation during their handling. The reactant used for FTS testing was simulated syngas with a composition similar to that obtained from air gasification of urban waste. This work reports the optimization of a new nanocatalyst reduction/activation protocol aimed at maximizing catalyst activity and a 100-h-long test performed to examine the catalyst's behavior over time. The catalyst was compared with Nanocat commercial nanoiron powder, and the results showed that its activity and robustness were higher. Conversion with the Nanocat catalyst was slightly but not statistically significantly lower than with the plasma-produced catalyst. However, 6% CH4 selectivity with the plasma-produced catalyst was significantly lower than the 10% obtained with Nanocat.