Gasification is a process to transform solids, such as agricultural and municipal waste, into gaseous feedstock for making transportation fuels. The so-called coarse solid residue (CSR) that remains after this conversion process is currently discarded as a process solid residue. In the context of transitioning from a linear to a circular society, the feasibility of using the solid process residue from waste gasification as a solid catalyst for light olefin production from CO, CO , and H mixtures was investigated. This CSR-derived catalyst converted biomass-derived syngas, a H -poor mixture of CO, CO , H , and N , into methane (57 %) and C -C olefins (43 %) at 450 °C and 20 bar. The main active ingredient of CSR was Fe, and it was discovered with operando X-ray diffraction that metallic Fe, present after pre-reduction in H , transformed into an Fe carbide phase under reaction conditions. The increased formation of Fe carbides correlated with an increase in CO conversion and olefin selectivity. The presence of alkali elements, such as Na and K, in CSR-derived catalyst increased olefin production as well.