Modified nickel-based catalysts for improved steam reforming of biomass tar: A critical review

The gasification of biomass produces a syngas that can be used for electricity generation and fuels/chemicals production. However, tar is generated along with the syngas as a by-product which causes problematic issues in the end-use of the syngas, such as blockages, plugging and corrosion. Catalytic steam reforming is a suitable option to convert tar into more syngas in the presence of nickel-based catalysts, as the preferred catalyst, mainly due to their activity and low cost. There has been considerable research reported in the literature on modified nickel-based catalysts for steam tar reforming. These modifications have been carried out in order to improve the performance of the Ni-based catalysts for tar reforming, mainly in terms of catalyst stability and activity. Such improvements are achieved by manipulating the properties of the catalyst. This paper therefore presents a critical assessment of these modifications on Ni-based catalysts available in the literature for improved tar reforming. The modifications considered in this review were categorised as: the addition of secondary metal (Fe, Co, Cu, Cr), the addition of noble metals (Pt, Pd, Rh, Au, Rh, Ir), addition of rare earth metals as promoters (Ce, La), alkali and alkaline earth metals (Sr, Ba, Ca, Mg,Ba) and modification of the support material. The paper aims at understanding the properties responsible for the improved performance of the modified Ni-based catalysts in comparison with unmodified Ni-based catalysts. The review paper will serve as a guide for further improvement of Ni-based catalysts for biomass tar reforming.