Evolution characteristics of different types of coke deposition during catalytic removal of biomass tar

Abstract

The evolutions of different types of coke deposition, including amorphous carbon, carbon networks (CNWs) and carbon nanotubes (CNTs), were clarified on Ni-based catalyst during catalytic cracking and reforming of biomass tar. Different from the changing of total coke, the amount of amorphous carbon gradually increased at the decreasing rate, while the amount of graphite carbon (CNWs and CNTs) firstly increased and then decreased after 60min reactions. The formation of amorphous carbon was prior to that of graphite carbon, and it was proved that a part of amorphous carbon converted to graphite carbon. After the 60min reaction, the proportion of graphite carbon and graphitization degree of coke decreased. The graphite carbon underwent the aging process in which the graphite structure would be destroyed to amorphous carbon. In cracking reaction, CNWs was the main type of graphite carbon which encapsulated the Ni particles with graphitic layers. After the addition of steam, the toluene conversion and coke amount remarkably increased in reforming reaction. Plenty of CNTs grew on the surface of catalysts and the amount of CNTs reached the maximum of about 200mg/g-cata at 60min. These research results are important for understanding the formation mechanism of coke and optimization the produced CNTs.