Chemical route to prepare nickel supported on intermetallic Ti ₆ Si ₇ Ni ₁₆ nanoparticles catalyzing CO methanation

In this study, ternary intermetallic nickel silicide, Ti₆Si₇Ni₁₆, nanoparticles with a high surface area of 37.5 m² g^-1 were chemically prepared from SiO₂-impregnated oxide precursors, which were reduced at as low as 600 °C by a CaH₂ reducing agent in molten LiCl, resulting in the formation of single-phase Ti₆Si₇Ni₁₆ with a nanosized morphology. The intermetallic Ti₆Si₇Ni₁₆ phase in the nanoparticles was stabilized in air by surface passive oxide layers of TiO_x-SiO_y, which facilitated the handling of the nanoparticles. Considering our previous successful work of preparing single-phase LaNi₂Si₂ (39.3 m² g^-1) and YNi₂Si₂ (27.0 m² g^-1) nanoparticles in a similar manner, the proposed chemical method showed to be a versatile approach in preparing ternary silicide nanoparticles. In this study, we applied the obtained Ti₆Si₇Ni₁₆ nanoparticles as catalyst supports in CO methanation. The supported nickel catalyst showed an activation energy of 56 kJ mol^-1, which is half as low as that of common TiO₂-supported nickel catalysts. Also, Ni/Ti₆Si₇Ni₁₆ provided the lower activation energy more than any previous Ni-based catalyst. Since the measured work function of Ti₆Si₇Ni₁₆ (4.5 eV) was lower than that of nickel (5.15 eV), it was suggested that the Ti₆Si₇Ni₁₆ support can accelerate the rate-determining step of C-O bond dissociation in CO methanation due to its good electron donation capacity.