Mechanism of K/Ni Etching for Biochar-H₂O Gasification

Biomass-H₂O gasification is a complex thermochemical reaction, including three processes of volatile removal: homogeneous/heterogeneous reforming, biochar gasification and etching. The rate-determining step is biochar-H₂O gasification and etching so the DFT is carried out to see the catalytic role of different metal elements(K/Ni) in the zigzag biochar model. The calculation results show that the gasification of biochar-H₂O needs to go through four processes: dissociative adsorption of water, hydrogen transfer (hydrogen desorption, hydrogen atom transfer), carbon dissolution and CO desorption. The energy barrier indicated that the most significant step in reducing the activation energy of K is reflected in the hydrogen transfer step, which is reduced from 374.14 kJ/mol to 152.41 kJ/mol; the catalytic effect of Ni is mainly reflected in the carbon dissolution step, which is reduced from 122.34 kJ/mol to 84.8 kJ/mol. The existence of K causes the edge to have a stronger attraction to H and does not destroy the 仔 bonds of biochar molecules. The destruction of 仔 bonds is mainly due to the role of H free radicals, while the destruction of 仔 bonds will lead to easier C-C bond rupture. Ni shows a strong attraction to O in OH, which forms strong Ni-O chemical bonds. Ni can also destroy the aromatic structure directly, making the gasification easier to happen. This study explored the catalytic mechanism of K/Ni on the biochar-H₂O gasification at the molecular level and looked forward to the potential synergy of K/Ni, laying a foundation for experimental research and catalyst design.