Steam reforming of tar derived from Fallopia Japonica stem over its own chars prepared at different conditions

[Display omitted] •Fallopia Japonica (FJ) showed an excellent gasification property.•Surface area and chemical compositions had great effect on char’s gasification property.•Promoting effect of char had strong relationship with its surface area and chemical compositions.•An optimum BET surface area existed for tar reforming on the char. In order to understand the promoting effect of char in different states on the steam reforming of biomass-derived tar during the gasification process, Fallopia Japonica stem (FJS) chars were prepared at different pyrolysis temperatures with different pyrolysis time, and used as the catalyst for the reforming of tar derived from FJS itself in a fixed-bed reactor. As-prepared FJS chars were characterized using Scanning Electron Microscope (SEM), Fourier Transform Infra Red spectroscopy (FT-IR), and Brunauer–Emmet–Teller (BET) surface area measurement for clarifying the relationship between the promoting effect and the physical and chemical structures of the char. It was found that BET surface area, chemical structure, and the contents of alkaline and alkaline earth metals (AAEM) in the char, which were obviously affected by pyrolysis temperature and time, had significant effect on char reactivity as well as the catalytic activity on tar reforming. The char obtained at lower temperature (