Mechanism of coke formation and corresponding gas fraction characteristics in biochar-catalyzed tar reforming during Corn Straw Pyrolysis

Formation of coke deposition is the main problem that restricts the development of tar reforming and even biomass thermal conversion. Biochar, prepared from gasification at 800 °C, was used for the catalytic reforming of biomass pyrolysis tar at 650 °C, monitoring the syngas formation during coke deposition. The principal consequences and conclusions are as follows: the coke yield increases from 10.9% to 18.9%, and the tar removal efficiency decreases from 89.0% to 56.7% when the feeding time of biomass is extended (10–50 min). The number of O-containing groups on the biochar surface decreases, and the proportion of minor aromatic rings increases. Biochar is more efficient in the catalytic removal of aliphatic components from tar than aromatic components. Catalytic reforming leads to the development of tar in the direction of increased aromatization. The addition of biochar has essentially no effect on CO yield and CO2 yield, while the CH4 yield decreases and the H2 yield increases. In addition to tar reforming, CH4 cracking is one of the pathways for coke generation on the biochar surface. The number of physical adsorption sites (nN2) and adsorption equilibrium constant (b) of biochar are obtained based on the N2 adsorption test. [Display omitted] •During feeding (0–50 min), the coke yield on biochar increases without saturation.•Evaluating tar conversion rate over biochar based on N2 adsorption was developed.•Coke deposition leads to reduced surface reactivity of biochar catalyst.•Addition of biochar increases H2 yield but decreases CH4 yield in the gas.•Coke deposition comes from aromatics, long-chain alkanes and CH4 in pyrolysis gas.