Unlocking the potential of biochar derived from coffee husk and khat stem for catalytic tar cracking during biomass pyrolysis: characterization and evaluation

Biochar has the potential to catalyze and accelerate the decomposition process during biomass pyrolysis and tar cracking. However, limited research has been done so far on its suitability as a catalyst. This study aims to characterize the properties of biochar produced from coffee husks (BCH) and khat stems (BKS) at various pyrolysis temperatures (350 °C, 450 °C, 550 °C, and 700 °C) and evaluate their potential application as catalyst for tar cracking in biofuel production. Coffee husk (CH) and khat stem (KS) were selected as feedstocks due to their high potential availability in Ethiopia. The physicochemical characteristics of the biochar materials were analyzed using a range of techniques, including thermogravimetry analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), and Fourier transform infrared (FTIR). The findings revealed that the yield of biochar decreased as the pyrolysis temperature increased for both CH and KS. The biochar exhibited a microstructure with a large specific surface area (SSA) and a porous structure rich in functional groups (O–H, C-H, C = C, C-O, and C–O–C), as well as the presence of inorganic minerals (Na, Cl, Mg, P, Fe, Al, K, and Ca). The XRD and TGA results indicated that the biochar samples were amorphous and thermally stable. The SEM and BET analysis showed changes in surface area and porosity with varying temperatures. In view of this, the present work suggests that biochar with diverse characteristics can be produced by adjusting the pyrolysis environment to suit the intended applications. Hence, CH and KS can be converted into biochar to increase the economic benefits and improve biochar-based catalyst properties for commercial purposes.