New NiMo catalysts supported on sulfuric acid modified halloysite nanotubes for quinoline hydrodenitrogenation

Chemically modified halloysite nanotubes (HNTs) materials were prepared via sulfuric acid treatment of natural HNTs. The new NiMo catalysts for quinoline hydrodenitrogenation reaction were synthesized with the incipient wetness impregnation method using both natural and H2SO4-treated HNTs as supports. The materials were characterized by N2 adsorption-desorption, XRD, SEM, ICP-OES, H2-TPR, UV-vis DRS, NH3-TPD, Py-IR, XPS and TEM. Increasing the concentration of sulfuric acid treatment from 0 to 4.0 mol/L resulted in a significant rise in the specific surface area of HNTs, from 37 m2/g to 139 m2/g, along with an expansion in the pore volume. More importantly, sulfuric acid treatment of HNTs enhanced the concentration of both L and B acid sites, and effectively regulated the metal-support interaction in the corresponding oxidized NiMo catalysts. The sulfurized NiMo catalysts supported on H2SO4-treated HNTs (NiMo/HS-x) demonstrated a higher Mo sulfidation degree and a larger proportion of Ni-Mo-S active phases compared to that supported on untreated HNTs (NiMo/HNTs). Among all the synthesized catalysts, NiMo/HS-3, supported on HNTs treated with 3.0 mol/L H2SO4 solution, exhibited excellent catalytic performance, achieving a quinoline conversion of 95.0 % and a denitrogenation rate of 62.0 %. Essentially, this catalytic behavior was due to alterations in the support properties, particularly the metalsupport interaction and acidity. These changes influenced the formation of a large amount of Ni-Mo-S active phases and enhanced the C-N bond cleavage. This study on the NiMo catalyst supported on natural HNTs materials not only enhances the understanding of the acidity changes in HNTs following sulfuric acid treatment, but also broadens the range of available supports for HDN catalysts.