The impregnation of sulfuric acid aqueous solution to silica is a traditional method to prepare the solid acid catalyst (SO42-/SiO2) via bonding of the SO4(2-) with surface atoms of silica to generate Bronsted acidic sites and Lewis acidic sites. The results in this study indicated the introduction of sulfuric acid could also impact the interaction between silica and subsequently loaded nickel species. The impregnation of sulfuric acid (i.e. 0.5 M) to Ni/SiO2 catalyst could enhance the dispersion of nickel via reducing nickel particle size, suppress sintering of nickel and increase abundance of the acidic sites with strong strength, which significantly enhanced the catalytic activity, stability and resistivity towards coking in steam reforming of guaiacol. The acidic sites with the strong strength aided the cracking of guaiacol to facilitate the subsequent reforming over metallic nickel sites. After impregnation of appropriate amount of sulfuric acid (i.e. 0.1 M or 0.5 M), the coke formed in amorphous form with low thermal stability was transformed into the coke in form of carbon nanotube with high thermal stability. The former type of coke induced rapid deactivation of the catalyst, while the latter type of coke did not. (C) 2020 Elsevier Ltd. All rights reserved.