Steam reforming of acetic acid over Ni/biochar of low metal-loading: Involvement of biochar in tailoring reaction intermediates renders superior catalytic performance

Abstract

Biochar is a reactive carrier as it may be partially gasified with steam in steam reforming, which could influence the formation of reaction intermediates and modify catalytic behaviors. Herein, the Ni/biochar as well as two comparative catalysts, Ni/Al2O3 and Ni/SiO2, with low nickel loading (2% (mass)) was conducted to probe involvement of the varied carriers in the steam reforming. The results indicated that the Ni/biochar performed excellent catalytic activity than Ni/SiO2 and Ni/Al2O3, as the biochar carrier facilitated quick conversion of the —OH from dissociation of steam to gasify the oxygen-rich carbonaceous intermediates like C ═ O and C—O—C, resulting in low coverage while high exposure of nickel species for maintaining the superior catalytic performance. In converse, strong adsorption of aliphatic intermediates over Ni/Al2O3 and Ni/SiO2 induced serious coking with polymeric coke as the main type (21.5% and 32.1%, respectively), which was significantly higher than that over Ni/biochar (3.9%). The coke over Ni/biochar was mainly aromatic or catalytic type with nanotube morphology and high crystallinity. The high resistivity of Ni/biochar towards coking was due to the balance between formation of coke and gasification of coke and partially biochar with steam, which created developed mesopores in spent Ni/biochar while the coke blocked pores in Ni/Al2O3 and Ni/SiO2 catalysts.