Stabilizing Supported Ni Catalysts for Dry Reforming of Methane by Combined La Doping and Al Overcoating Using Atomic Layer Deposition

Deposition of La₂O₃ and Al₂O₃ on Al₂O₃-supported Ni catalysts was performed to study their effects on heterogeneous catalysts for the dry reforming of methane (DRM) reaction. An alumina-supported Ni catalyst (Ni/Al₂O₃, 2 wt % of Ni), synthesized via incipient wetness impregnation, loses ∼87% of its initial activity within 45 h under DRM conditions. While overcoating of Al₂O₃ on this catalyst via atomic layer deposition (ALD) helps stabilize the catalytic activity in long time-on-stream (TOS) tests, this overcoated catalyst is ca. 40 times less active than the uncoated catalyst at peak activity. This Al₂O₃-overcoated Ni/Al₂O₃ catalyst also exhibits a long induction period (∼20 h) due to the slow reduction of Ni²⁺ within the catalytically inactive nickel aluminate (NiAl₂O₄) phase, formed by the interaction of metallic Ni with the Al₂O₃ overcoat during pre-DRM treatment at the 700 °C reaction temperature. Here, we report that, while doping small amounts of La (∼0.03 wt %) into the Ni/Al₂O₃ catalyst does not significantly affect the catalytic activity or stability by itself, the addition of ALD-Al₂O₃ on top of the La₂O₃-promoted Ni catalysts significantly suppresses the long TOS deactivation, helps recover the peak activity of uncoated Ni/Al₂O₃, and eliminates the DRM induction period. This strategy obtains the stabilization benefits of Al₂O₃ overcoating on Ni/Al₂O₃ while, at the same time, avoiding the formation of undesirable NiAl₂O₄ species.