Enhanced stability of Co catalysts supported on phosphorus-modified Al₂O₃ for dry reforming of CH₄

Phosphorous-modified γ-Al₂O₃ support is used to prepare cobalt-based catalysts (CoP(x)Al, x = 0–4 wt%) for dry reforming of methane (DRM). From the studied catalysts, CoAl displays the highest conversions of CH₄ and CO₂ at the initial stage due to good cobalt dispersion. However, both conversions decrease significantly after 20 h on stream due to the formation of inactive CoAl₂O₄ phase through the reaction of oxidized CoO_x with the alumina surface. For the CoP(x)Al catalysts, although the initial CH₄ and CO₂ conversions decrease gradually as the phosphorus loadings increased, all catalysts show more stable catalytic activity than the CoAl catalyst. Formation of aluminum phosphate (AlPO₄) on the alumina surface can be achieved by the addition of phosphorus. The AlPO₄ phase has the capacity to suppress the formation of CoAl₂O₄ phase. Phosphorous loadings on alumina surface of up to 1–2 wt% exerted positive effect on catalyst stability, whereas loadings above this threshold exerted opposite effect.