Effect of reflux digestion treatment on the catalytic performance of Ni–CaO–ZrO2 nanocomposite catalysts for CO2 reforming of CH4

• Reflux digestion is beneficial to from a mixed oxide with very small nanoparticles.
• Stronger metal–support interaction is found in refluxed Ni–CaO–ZrO2 nanocomposites.
• Ni is partially covered by ZrO2 after reduction of Ni–CaO–ZrO2.
• Higher stability and less coke formation in CO2–CH4 reforming on refluxed catalysts.

Ni–CaO–ZrO2 nanocomposite catalysts with high activity and low coke formation for CO2 reforming of CH4 are developed by the co-precipitation method followed by a reflux digestion (aging) process. The effects of hot water treatment of the Ni–Ca–Zr containing precipitates on the structures and catalytic performance of the catalysts are systematically investigated. Results indicated that reflux temperature and time dramatically affect the textural properties, crystal phases, metal dispersion, and the metal–support interaction of the catalysts as indicated by the N2 adsorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), chemisorption, and temperature programmed reduction (TPR) results. The reflux digestion with a higher temperature and a longer time substantially increases the surface areas of the catalyst, decreases the particle size in the mixed oxides, and also enhances the metal–support interaction, thus giving a higher activity and stability of the catalyst. The Ni–CaO–ZrO2 nanocomposite catalyst refluxed at 100 °C for 24 h exhibits a stable activity over 800 h without deactivation at a GHSV of 79,000 ml/(h g) at 850 °C due to the restriction of Ni particle sintering and less coke formation. The relationship between the reflux treatment and catalytic performance is discussed.

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