A review of CaO based catalysts for tar removal during biomass gasification

Tar, among the most difficult contaminants to be removed, is the major technical barrier for the development and application of advanced biomass gasification technology. Catalytic cracking of tar, with the advantages of energy recovery from tar, quality increase of product gas and no secondary pollution, has become the main focus currently for tar removal. Among various types of catalysts, CaO based catalysts, including the naturally available calcined limestone/dolomite, the single-/multi-metal active components (Ni, Fe, Mg, etc.) and CaO composite catalysts, and the synthetic CaO based catalysts, have been demonstrated to be effective and economically viable for tar removal. Meanwhile, CaO is also being used in some novel CaO-looping gasification processes as a CO2 absorbent in recent years. Therefore, the CaO derived from different precursors, the in-situ and ex-situ applications of CaO catalysts and the tar removal under different operation conditions have been studied in this review. The tar cracking mechanism over CaO catalysts has been summarized. The single-/multi-metal doped CaO based catalysts for tar removal are also discussed. The use of CaO catalysts in some novel gasification processes and their tar removal efficiency have been also investigated. Finally, the main drawbacks and future perspectives of CaO based catalysts are discussed. (C)& nbsp;2022 Elsevier Ltd. All rights reserved.