Waste to Wealth: Discarded Cigarette Butt-Derived Metal-Free N-Rich Carbon Catalysts for the Selective Catalytic Oxidation of Hydrogen Sulfide to Sulfur

The selective catalytic oxidation of toxic gas H₂S to elemental sulfur (H₂S-SCO) is a promising desulfurization process known for its dual benefits of recovering valuable sulfur resources and mitigating environmental pollution. Nevertheless, developing cost-effective and efficient catalysts for H₂S-SCO remains a significant challenge. In this study, we synthesized a low-cost and metal-free nitrogen-rich carbon catalyst (NrCC) by copyrolyzing discarded cigarette butts (organic solid wastes that are difficult to degrade naturally) with urea for the continuous H₂S-SCO process at a relatively low temperature. The NrCC exhibited exceptional catalytic performance, achieving complete H₂S conversion to sulfur at 180 °C, and demonstrated excellent stability in humid (RH = 80%) and high CO₂ concentration environments. The catalyst succeeded due to its developed pore structure (specific surface area as high as 2267.77 m²·g^–1) and abundant pyridine-N sites. DFT calculations showed that the pyridine-N neighbor carbon sites were the active sites promoting H₂S adsorption and dissociation. This study presents a novel “waste control by waste” strategy that integrates the utilization of organic solid waste resources with air pollution control measures, showcasing the potential for sustainable environmental solutions.