Comparative Study on the Effect of La ₂ O ₃ , CeO ₂ , Nd ₂ O ₃ , and Sm ₂ O ₃ on Ni–SiO ₂ for Dry Reforming of Methane

Four lanthanide-oxide-modified Ni–SiO 2 catalysts were prepared via the β-cyclodextrin-assisted impregnation method and were comparatively evaluated for dry reforming of methane (DRM) under the severe conditions of 750 °C, CH 4 /CO 2 molar ratio of 1, and GHSV of 84 000 mL g –1 h –1 . The addition of lanthanide oxide improves the Ni dispersion, the promotional effect of which is related to the type of lanthanide oxide used. The lanthanide oxide enhances the anti-sintering capacity of the modified catalysts, attributable to the confinement effect of the formed Ni–lanthanide oxide interface, which is dependent on the lanthanide oxide dispersion. All of the modified catalysts display a higher CH 4 activity than that of Ni–SiO 2 (145.1–248.7 mmol min –1 g –1 of Ni vs 61.6 mmol min –1 g –1 of Ni). However, Ni–La–SiO 2 and Ni–Ce–SiO 2 encounter rapid deactivation with k d values of 0.095 and 0.051 h –1 compared to Ni–SiO 2 ( k d = 0.058 h –1 ), which is assigned to extreme loss of active Ni sites caused by serious sintering and/or an extensive decrease in the surface area. The catalytic stability of Ni–Nd–SiO 2 ( k d = 0.025 h –1 ) and Ni–Sm–SiO 2 ( k d = 0.004 h –1 ) is significantly improved compared to Ni–La–SiO 2, Ni–Ce–SiO 2, and Ni–SiO 2, and the best stability with a TOS of 70 h is achieved over Ni–Sm–SiO 2, which can be well-explained as the enhanced anti-sintering and anti-coking capacities as well as the stable textural property. The consecutive CH 4 /CO 2 -TPSR results vigorously prove that the addition of Sm 2 O 3 simultaneously enhances the CH 4 decomposition and CO 2 dissociation while reducing the temperature difference of the two reactions, which results in a better balance between carbon generation and total gasification processes, and hence, the high activity and superior anti-coking capacity are achieved over Ni–Sm–SiO 2 . The above understanding provides an important guidance for modulating the CH 4 and CO 2 activation to achieve the balance between carbon generation and gasification processes.