H2-rich syngas production and tar removal over biochar-supported Ni-Fe bimetallic catalysts during catalytic pyrolysis-gasification of biomass

This study aims to develop an economically-viable biochar-based catalyst to improve H2-rich syngas production and simultaneously mitigate tar formation during catalytic pyrolysis-gasification of pine sawdust. Different biochar (BC@N2 and BC@CO2) and biochar-supported Ni-Fe bimetallic catalysts (Ni-Fe-BC@N2 and Ni-Fe-BC@CO2) were synthesized under N2 and CO2 atmospheres. A two-stage fixed-bed reactor was applied to evaluate their catalytic performance under varied temperatures. Ni-Fe-BC@N2 and Ni-Fe-BC@CO2 catalysts both had a porous structure with a Brunauer-Emmett-Teller (BET) surface area of around 330 m2/g, but Ni-Fe-BC@CO2 prepared under CO2 atmosphere exhibited additional meso-/macro-pores besides the micropores comparatively. With the addition of Ni-Fe-BC catalysts, the total gas yield increased greatly with a syngas content over 82 vol% when gasification temperature was higher than 700 °C. H2 was the dominated gas in the product gas instead of CO (compared with that without and with BC@N2 and BC@CO2 catalysts) possibly due to the enhanced water-gas shift (WGS) reaction by the Ni-Fe-BC catalysts. The total gas yield could achieve 3172.62 mL/g biomass at 750 °C, with a H2 yield of 1452.72 mL/g biomass and a CO yield of 1204.34 mL/g biomass. In comparison, Ni-Fe-BC@CO2 catalyst performed better than Ni-Fe-BC@N2 catalyst in terms of both H2-rich syngas production and tar removal.