Roles of AAEMs in catalytic reforming of biomass pyrolysis tar and coke accumulation characteristics over biochar surface for H2 production

Coke formation is a significant challenge in catalytic tar reforming. AAEMs are essential in the conversion and decomposition of tar catalyzed by biochar. In this paper, four biochar catalysts with different K and Ca contents were prepared by acid washing and loading, and the coke accumulation characteristics in catalytic tar reforming at 650 degrees C were investigated using a single-stage reaction system. The gas-liquid-solid products were characterized by GC-MS, Raman, N2 adsorption, FTIR and TG. The results suggest that K-loaded biochar has a maximum tar reforming capacity of 94.9%, while H-form biochar has a tar removal ef-ficiency of only 27.8%. The micropore area in biochar is considerably reduced and the average pore size is increased after coke deposition. While K-loaded biochar retains the highest micropore area, it also exhibits a smaller increase in average pore size. The loading of K/Ca affects the growth structure of the coke, resulting in an increased number of O -containing structures in it. The coke on the Raw biochar surface is mainly small aromatic ring structures and aliphatic structures, thus increasing the intensity of the vibrational peaks corresponding to aromatic = C-H and aliphatic C-H on it. The coke on K-loaded biochar has a large proportion of aliphatic structures, which also contributes to the reduced graphitization of it after reforming. The AAEMs-free biochar surface preferentially removes tar components carrying O-containing groups. K-loaded biochar preferentially catalyzes the reforming of mono-aromatic ring components in tar. Ca-loaded biochar preferentially removes the mono-aromatic ring components, while being less selective for the removal of tar components containing hydroxyl groups and polyaromatic ring com-ponents. The loading of K/Ca promotes the dehydrogenation of the tar fraction during reforming, while only K catalyzes the deoxygenation of tar components. H-form biochar has no appreciable catalytic activity on CH4 cracking. AAEMs have a catalytic activity on CH4 cracking. K is particularly effective in improving tar conversion and hydrogen pro-duction of biochar.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

This paper investigates the coke accumulation characteristics in catalytic tar reforming using different K and Ca-loaded biochar catalysts. The results indicate that K-loaded biochar exhibits a higher tar conversion capacity, while H-form biochar has a lower tar removal efficiency. The loading of K/Ca affects the growth structure of the coke, with K-loaded biochar retaining a higher micropore area and experiencing a smaller increase in average pore size. Furthermore, the loading of K promotes the dehydrogenation of tar components, while only K catalyzes the deoxygenation of tar components. These findings are important for improving the efficiency and selectivity of tar reforming.