Effect of SiO_2-ZrO_2 supports prepared by a grafting method on hydrogen production by steam reforming of liquefied natural gas over Ni/SiO_2-ZrO_2 catalysts

摘要

SiO_2-ZrO_2 supports with various zirconium contents are prepared by grafting a zirconium precursor onto the surface of commercial Carbosil silica. Ni(20 wt.%)/SiO_2-ZrO_2 catalysts are then prepared by an impregnation method, and are applied to hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of SiO_2-ZrO_2 supports on the performance of the Ni(20wt.%)/SiO_2-ZrO_2 catalysts is investigated. SiO_2-ZrO_2 prepared by a grafting method serves as an efficient support for the nickel catalyst in the steam reforming of LNG. Zirconia enhances the resistance of silica to steam significantly and increases the interaction between nickel and the support, and furthermore, prevents the growth of nickel oxide species during the calcination process through the formation of a ZrO_2-SiO_2 composite structure. The crystalline structures and catalytic activities of the Ni(20 wt.%)/SiO_2-ZrO_2 catalysts are strongly influenced by the amount of zirconium grafted. The conversion of LNG and the yield of hydrogen show volcano-shaped curves with respect to zirconium content. Among the catalysts tested, the Ni(20 wt.%)/SiO_2-ZrO_2 (Zr/Si = 0.54) sample shows the best catalytic performance in terms of both LNG conversion and hydrogen yield. The well-developed and pure tetragonal phase of ZrO_2-SiO_2 (Zr/Si = 0.54) appears to play an important role in the adsorption of steam and subsequent spillover of steam from the support to the active nickel. The small particle size of the metallic nickel in the Ni(20 wt.%)/SiO_2-ZrO_2 (Zr/Si = 0.54) catalyst is also responsible for its high performance.