Impact of Promoter Addition on the Regeneration of Ni/Al₂O₃ Dry Reforming Catalysts

Industrial-scale reforming of methane is typically carried out with an excess of oxidant to suppress coking of the catalyst. On the other hand, many academic studies on dry reforming employ a CO₂/CH₄ ratio of unity to quickly observe coking which can be reduced by adding a catalyst promoter. In this work, Ni/Al₂O₃ catalysts were tested for dry reforming of methane (CO₂/CH₄=1) with additional regeneration steps to test the resistance against an oxidation treatment. Thereby, we wanted to evaluate catalyst stability for industrial relevance. The effects of three promoters, Cr, Mn and Fe, that differ in their degree of CO₂ interaction, are compared. A higher iron loading on Ni/Al₂O₃ leads to higher stability in dry reforming with lower coke formation. However, the higher the concentration of a promoter with high CO₂ affinity, the quicker the catalyst is oxidized during regeneration with CO₂. Subsequent reduction of a catalyst oxidized with CO₂ leads to considerable sintering in all cases. This sintering induces formation of more coke during dry reforming. On such sintered samples only highly effective promoters in large concentrations still have a noticeable effect compared to unpromoted Ni/Al₂O₃.