Kinetics of model tar decomposition over activated biochar from a heavy metal-contaminated area

Abstract

This study explores the catalytic potential of activated biochar derived from heavy metal (HM)-contaminated biomass for tar decomposition, presenting a dual-benefit approach that merges waste valorization with phytoremediation. The growing interest in utilizing HM-laden biomass stems from its ability to contribute to environmental remediation while aligning with circular economy principles. The central rationale of this work is to develop a sustainable pathway for transforming contaminated biomass into high-value catalytic materials for tar decomposition, thereby addressing critical challenges in HM-contamination management and clean energy production. Biochar samples were obtained from both heavy-metal (HM)-polluted and HM-free sites. Gasification was performed with a 50/50vol% CO<inf>2</inf>/H<inf>2</inf>O mixture. Toluene was used for tar conversion tests to represent the most refractory tar compounds. Condensable reaction products were collected every 20 min to measure toluene conversion as function of time. Kinetic parameters for toluene decomposition were determined using a first-order reaction model, while biochar deactivation due to coke deposition was evaluated via an activity function. Physicochemical properties of the biochars were characterized using SEM, XRD, thermogravimetric analysis, and gas adsorption techniques. HM retention analysed via ICP-OES. Thermal stability of biochar structure was also addressed by high temperature treatment. Gas adsorption techniques showed no significant structural differences between contaminated and uncontaminated biochars. Both types were highly microporous and thermally stable. The results revealed similar toluene conversion rates for both biochars, suggesting that toluene decomposition was primarily influenced by biochar's structural properties, with no significant effect of HM presence on toluene decomposition.