Rice Husk Biochar for Tar Cracking: Critical Role of Minerals and Textural Properties

Abstract

This study investigates rice husk biochar for catalytic cracking of toluene - a tar model compound - in a fixed-bed reactor. The rice husk biochar was physically activated to about 25% conversion in either a H2O or CO2 atmosphere. The activated biochars were then employed as catalysts for toluene decomposition at 850 °C in a laboratory-scale fixed-bed reactor. Catalytic performance evaluation of the raw rice husk biochar indicates poor activity in toluene cracking due to its low surface area and porosity. With physical activation, BET surface area increases significantly from 17 m²/g to 440 m²/g under CO₂ and 426 m²/g under H₂O. These morphological changes lead to better catalytic activity, particularly for the steam-activated char. It achieved about 71% toluene conversion and a longer activity span of about 20 min than the CO₂-activated char, before total deactivation. This improved performance is attributed to the presence of surface mesoporosity, which slows deactivation. Silicon oxide constituted approximately 94 % of the inorganic content, which rendered the active metal species less effective in the process.