Coffee grounds derived porous nitrogen-rich biochar as a metal-free catalyst for efficient selective oxidation of hydrogen sulfide to sulfur

Abstract

The development of metal-free catalysts for efficient selective catalytic oxidation of hydrogen sulfide (H2S-SCO) to elemental sulfur represents a sustainable solution for toxic gas purification. Herein, we synthesized a regenerable metal-free catalyst through facile activation and pyrolysis of coffee grounds. The optimized catalyst demonstrated exceptional H2S-SCO performance at 180 ℃, achieving > 99% H2S conversion with near-perfect sulfur selectivity (~ 100%) while maintaining remarkable stability under humid conditions and high CO2 concentrations. These superior properties originate from the synergistic effects of elevated nitrogen doping (17.33 at.%), abundant defect edge sites, and hierarchical porosity. Density functional theory (DFT) calculations revealed that carbon atoms adjacent to pyridine-N configurations serve as dual-active sites, facilitating H2S adsorption/dissociation and O2 activation through optimized electron redistribution. A plausible reaction mechanism was established based on experimental and theoretical analyses. This work provides fundamental insights into designing cost-effective, biomass-derived carbon catalysts for industrial gas purification while addressing agricultural waste valorization.