Hydrogen production from spent coffee grounds in alkaline conditions using NiFe/Al2O3 as a catalyst

Abstract

This study explores an innovative approach to sustainable hydrogen production from spent coffee grounds (SCG) via alkaline thermal treatment (ATT) utilizing NiFe/Al₂O₃ as a catalyst. A series of single-factor experiments were conducted to examine the impact of key ATT parameters on hydrogen and methane yields. Subsequently, process optimization was achieved using a Box-Behnken Design (BBD) model. The optimal operational conditions were 600 °C, a sodium hydroxide concentration (SHC) of 33 %, a sodium hydroxide solution volume to SCG mass (RSSC) ratio of 4 mL/g, and a catalyst to biomass (RCB) ratio of 0.23:1 g/g. Hydrogen and methane yields of 19.27 and 2.31 mmol/g were obtained upon this condition and were experimentally confirmed. The fresh and spent NiFe/Al₂O₃ were characterized using Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), temperature programmed reduction (H₂-TPR), and field emission scanning electron microscopy (FE-SEM). The XRD results of NaOH-solution treated SCG revealed a transition from a crystalline structure to a more amorphous structure, which facilitates the scission of hydrocarbon chains and enhances hydrogen release. In addition, the presence of Ni in Fe-based catalysts enhances the cracking of hydrocarbon chain and thus hydrogen production. The elucidation of enhanced hydrogen generation through nickel incorporation into the catalyst and NaOH solution treatment provide valuable insights into a viable route for producing hydrogen from SCG.