Activity study of NiO-based oxygen carriers in chemical looping steam methane reforming

• Metallic Ni on ZrO2, Al2O3 and NiAl2O4 is active and stable in reforming.
• Use of SiO2 and TiO2 support results in fast catalyst deactivation.
• Ni on TiO2 easily reoxidizes to NiO during reforming conditions.
• NiO/ZrO2 shows excellent activity and stability in chemical looping steam reforming.

This study evaluates the performance of NiO-based oxygen carriers supported on ZrO2, TiO2, SiO2, Al2O3 and NiAl2O4 as conventional reforming catalysts at low temperature (650 °C) as well as oxygen transfer materials (OTMs) for chemical looping steam methane reforming. Conventional reforming experiments with pre-reduced OTMs demonstrated satisfactory performance of NiO/Al2O3, NiO/ZrO2 and NiO/NiAl2O4 at 650 °C, with less than 8% relative decrease in conversion after 10 h time-on-stream. On the other hand, NiO/SiO2 and NiO/TiO2 were found to have low activity (<50% initial CH4 conversion) and deactivated rapidly, eventually dropping to less than 10% CH4 conversion after 2 h on stream. The three most promising materials were tested under chemical looping steam methane reforming conditions for twenty consecutive redox cycles in a fixed bed flow unit. NiO/ZrO2 exhibited good activity with initial CH4 conversion higher than 80% and had very good stability. Deactivation was minimal after 20 consecutive redox cycles, corresponding to 20 h exposure to CH4/steam. NiO/Al2O3 and NiO/NiAl2O4 demonstrated similar high initial activity, but also high deactivation, leading to methane conversion of 59 and 63% conversion respectively at the end of the test.

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