Synthesis and characterization of different activated biochar catalysts for removal of biomass pyrolysis tar

The use of low-cost and high-efficiency catalysts is a promising approach to remove tar and increase the gas yield in the catalytic reforming of biomass pyrolysis volatiles. In this study, using rice husk biochar (RHC) as a precursor, four typical activated biochar catalysts were prepared using both chemical (H3PO4 and KOH) and physical (CO2 and H2O) activators. The experiments demonstrated that high surface areas were obtained upon activation. The chemical activators introduced inorganic elements in the biochar, while physical activators were beneficial to the formation of high micropore volume. The effects of varying the catalyst type, catalyst to feedstock ratio, and catalytic cracking temperature on the tar decomposition efficiency and gas yield were studied. The results showed that maximum tar decomposition efficiency (91.75%) and gas yield (704.85 mL/g) were achieved using the RHC-KOH catalyst at a catalytic cracking temperature of 800 °C and a catalyst to feedstock ratio of 2:1. The introduction of the catalysts changed the gas composition, and the yield of H2/CO increased significantly. The increase in catalytic cracking temperature promoted the secondary cracking reaction of tar and the biochar self-gasification reaction in addition to facilitating the cyclopolymerization of some tar components.