The presence of tars in syngas is a major technological constraint for upscaling biomass gasification to produce heat, power, and other value-added chemicals such as biofuels. At the same time, the solid remains from biomass gasification i.e. char and ashes, have capabilities to catalyse the reforming of gasification tars. This work presents a comprehensive analysis of the relevance of gasification chars and ashes as catalysts for tar reforming. A description of the solid products from biomass gasification, their formation, chemical characteristics and potential applications is given. Additionally, a review of the state of the art of the uses of regular char, activated carbon and ashes as a catalyst for tar reforming is presented. Further, kinetics reported in literature, and the homogeneous and heterogeneous mechanisms for tar reforming over char are discussed and explained. From reviewing literature it was found that activated chars exhibit the best reforming capabilities, followed by regular char and ashes. Knowing the role of the interactions between the char and the tars is a key factor for optimization of char catalysts. Ultimately, this work provides guidance for understanding the uses of biomass solids as catalysts for tar reforming, and aid in future research to increase the economic feasibility of biomass gasification.

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