A two-step regeneration method for carbon-supported Ru catalysts deactivated by coke and sulfur during hydrothermal gasification

Abstract

Catalytic hydrothermal gasification (cHTG) offers a sustainable pathway for converting wet biomass into methane, but long-term operation is hindered by catalyst deactivation, particularly due to coke deposition and sulfur poisoning. Ruthenium on activated carbon (Ru/AC) is highly active for methane production but gradually loses performance during continuous gasification of biomass or wastes. Conventional high-temperature oxidative regeneration methods, which rely on combustion to remove coke, are unsuitable for carbon supports due to their poor stability in the presence of oxidizing agents. Here, a low-temperature aqueous regeneration strategy was explored using hydrogen peroxide (H 2 O 2 ) oxidation followed by subcritical water flushing. Effluent analysis and catalyst characterization reveal that coke is primarily oxidized and removed during H 2 O 2 oxidation (<120 °C), while sulfur species are oxidized to strongly adsorbed forms (sulfate) that require subsequent desorption via subcritical water flushing. Based on these insights, a two-step regeneration protocol was developed, consisting of two H 2 O 2 oxidation treatments (85–120 °C), each followed by subcritical water flushing (up to 320 °C). This approach achieves (97 ± 2) % sulfur removal while preserving carbon support integrity. The method enables efficient catalyst regeneration targeting both coking and sulfur fouling, offering a practical aqueous strategy to extend the operational lifetime of Ru/AC catalysts in cHTG and related catalytic systems without the need to remove the material from the catalytic reactor for regeneration. • Two-step aqueous regeneration restores Ruthenium catalyst activity. • Low-temperature H 2 O 2 oxidation removes coke and converts sulfur to oxidized forms. • Subcritical water flushing desorbs strongly bound sulfur species. • 97 ± 2% sulfur removal achieved without damaging carbon support. • Enables catalyst regeneration and lifetime extension without reactor disassembly.