Energy efficient methane tri-reforming for synthesis gas production over highly coke resistant nanocrystalline Ni-ZrO₂ catalyst

We report the synthesis of nanocrystalline Ni-ZrO₂ catalyst for tri-reforming of methane (5CH₄ + O₂ + CO₂ + 2H₂O → 6CO + 12H₂) to produce synthesis gas with H₂/CO mole ratio ~2. Nanocrystalline Ni-ZrO₂ catalyst of size between 10 and 40 nm was prepared by hydrothermal method using cetyltrimethylammonium bromide (CTAB) as a surfactant. The prepared catalysts were characterized by N₂-physisorption studies, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature programmed reduction (TPR), H₂-chemisorpton, thermo-gravimetric analysis (TGA), Inductively coupled plasma atomic emission spectroscopy (ICP-AES) and X-ray photoelectron spectroscopy (XPS). The catalytic activity was monitored over temperature range between 500 and 800 °C. Different reaction parameters like temperature, Ni-loading, gas hourly space velocity (GHSV) and time on stream (TOS) were studied in detail. 4.8 wt% Ni loading for Ni-ZrO₂ catalyst was found to be the optimum Ni loading which showed the superior catalytic activity for methane tri-reforming. The catalyst was found to be stable for more than 100 h on time on stream with methane, carbon dioxide and steam conversion of ~95% at 800 °C. The H₂/CO ratio was almost constant to 1.9 throughout the time on stream experiment. Highly dispersed nickel and the presence of strong metal support interaction were found to be the key factor for the superior activity of the catalyst. The effect of O₂ and H₂O concentration on reactant conversions and H₂/CO ratios were also studied in detail.