Fundamentals and applications of char in biomass tar reforming

In the last few decades, the production of value-added chemicals from biomass has become a key research focus. Biomass gasification into syngas and further for methane, methanol, and C2+ alcohols production has already proved to be promising for utilization of renewable energy. Therefore, heterogeneous catalyst design and optimization are extremely significant for solving the issues of tar formation during biomass gasification. Apart from alkali metals, natural minerals, and synthetic catalysts, char and char supported catalysts prepared from residual biomass or coal have been already proved to be effective for tar reforming due to their relative chemical inertness, cheap price, excellent pore structures, etc. Advantageously, bio−/coal char could be modified and/or functionalized with heteroatoms doping and metal addition to improve activity in tar reforming. In this review, we systematically discussed the preparation, modification, and application of char catalysts in the reforming of biomass tar and tar model compounds. After that, we reviewed and compared the activity of char catalysts in tar reforming, and then we gave corresponding reactions and deactivation mechanisms over char catalysts in biomass tar reforming. Finally, we proposed existed challenges and shared our perspectives regarding future needs in char catalysts design for accelerating fuel sustainability and green development. [Display omitted] •A comprehensive review of biomass tar reforming over char catalysts.•Preparation and activity comparison of char catalysts for gasification are given.•Recent cases in tar reforming over char catalysts are well discussed.•Possible challenges and perspectives of char in gasification are proposed.