Catalytic conversion of bioethanol over cobalt and nickel-doped HZSM-5 zeolite catalysts

This study focuses on the use of H-ZSM-5 catalyst modified with transition metals for the conversion of ethanol into liquid fuel hydrocarbons. The HZSM-5 catalyst was synthesized hydrothermally, and the transition metal (0.5 wt%) was incorporated by the incipient wetness impregnation method. The synthesized catalysts were tested in a fixed-bed reactor at varying weight hourly space velocities (WHSVs) and temperatures to investigate their effects on the selectivity of the liquid hydrocarbon product. The pure and metal-doped catalysts were characterized using XRD, FTIR, SEM-EDX, PSD, BET, N-2 adsorption-desorption, and NH3-TPD. The metal species were evenly dispersed on the catalyst support without affecting the porous framework significantly. The modification did not alter the morphology of the catalyst; however, the particle size was altered slightly. The pore distribution plot confirms the hierarchical porous framework of the catalyst. This unique feature facilitates internal diffusion and accelerates mass transfer, improving the selectivity and distribution of the liquid product. The catalytic evaluation showed ethanol conversion of more than 97% for all catalysts tested. A low space velocity (5 h(-1)) favored gaseous (C-1-C-4) hydrocarbons, but more liquid products (C-5+) were generated at 12 h(-1) (at 350 and 400 degrees C), with metal-doped catalysts showing higher selectivity (> 79%). In comparison with the unmodified catalysts, the metal-doped catalysts enhanced the production of aromatics (benzene), with Ni/HZSM-5 showing higher selectivity (> 4%). This study showed that the synthesized catalysts are active in the selective production of liquid hydrocarbon and improve the transformation of ethanol to fuel-range hydrocarbons.