Tailoring novel hierarchical HZSM-5 catalysts for high-selectivity ethanol valorisation to transportation fuels: transition metal doping, process optimisation, and coke formation

• All catalysts showed >95 % ethanol conversion across operating conditions. • 1 %Ni/HZSM-5 overall performance with 77.8 % jet fuel selectivity, 92.6 % LHC yield. • 1 %Co and %Fe attained 71.1 % gasoline and 31.1% benzene selectivity, respectively. • Ni showed highest coke mass: 1.59 mg (7.84 %) vs Co & Fe: 1.43 mg (∼7.0 %) • Surface area dropped 72–84 % in spent catalysts with 5 wt% metal doping. This study investigates the single-step catalytic valorisation of ethanol to liquid fuels over newly developed hierarchical ZSM–5 modified with Ni, Fe, or Co (0.5–5 wt%). The catalysts were evaluated under varying operating conditions (350–400 °C, 5–12 h −1 ) and subjected to post–reaction coke analysis. Comprehensive characterisation using XRD, XRF, SEM, EDS, FT-IR, N 2 adsorption, PSD, and NH 3 -TPD confirmed the incorporation of transition metals without compromising the MFI framework. The addition of metal altered porosity, surface area, acidity, and morphology, indicating improved tunability of the catalyst microstructure. Catalytic results showed that metal-doped catalysts achieved ethanol conversion >95 % across operating conditions. Product selectivity was strongly influenced by space velocity, with lower values favouring gaseous hydrocarbons and higher values promoting liquid fuel production. Temperature shifts affected product distribution but had minimal impact on gaseous hydrocarbon selectivity. The Ni‑doped catalyst system exhibited superior performance, with 1 wt% Ni achieving the highest jet fuel selectivity (77.8 %) and liquid hydrocarbon yield (92.6 %). For gasoline, Co‑doped showed a clear preference, with 1 wt% Co being most effective, reaching 71.1 % selectivity. Fe‑doped catalysts enhanced aromatic formation, with 1 wt% Fe increasing benzene selectivity from 26.9 % to 31.1 %. Overall, 1 wt% metal‑doped HZSM‑5 catalysts offer a compelling balance of activity, selectivity, and operational stability. Post-reaction thermogravimetric analysis revealed coke accumulation increased with metal loading, with Ni-doped catalysts showing the highest deposition (1.59 mg, 7.84 wt%) compared to Co– and Fe-doped systems (1.43 mg, ∼7.0 wt%), indicating enhanced resistance to carbon deposition. Coke formation also increases with increasing temperature and WHSV. Spent catalyst analysis showed preserved framework but reduced surface area (72–84 %) for high metal loadings (5 wt%). These results highlight the need for precise control of catalyst composition and reaction parameters to minimise coke and optimize fuel selectivity in bioethanol upgrading.