In-situ study on structure evolution and gasification reactivity of biomass char with K and Ca catalysts at carbon dioxide atmosphere

The structural evolution and gasification reactivity of biochar prepared from the pyrolysis of wheat straw were investigated by in-situ Raman spectroscopy and thermogravimetric analysis. The Raman spectra consisted of a combination of four Lorentzian bands (D1, D2, D4, G) and one Gaussian band (D3) in the first-order region. The experimental results showed that the addition of catalysts or the presence of ash could improve the CO₂ gasification reactivity of biochar and result in a larger I_D1/I_G ratio and a lower I_G/I_ALL ratio, meaning that the carbon structure was less ordered, and there were also more active sites such as amorphous carbon and cross-linked structures; Ca-based catalysts and K-based catalysts changed the evolution of biochar structure in a different way in CO₂ atmosphere, the I_D3/I_D1 of Ca-based biochar was close to the value of non-catalyst biochar and decreased slowly, indicating that the Ca-based catalysts can stabilize the aromatic rings, while the I_G/I_ALL of K-based biochar decreases significantly and the I_D3/I_D1 increased significantly, indicating the increase of carbon structure defects and the cracking of large aromatic rings in bio-char into small ones; a scheme of K and Ca reaction with biochar in CO₂ gasification process was proposed.