Highly active and stable Ni/γ-Al2O3 catalysts selectively deposited with CeO2 for CO methanation

Abstract

We report the preparation of highly active, coking- and sintering-resistant CeO₂-decorated Ni/γ-Al₂O₃ catalysts by an impregnation method followed by a modified deposition–precipitation (DP) of CeO₂. The samples were characterized by nitrogen adsorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, H₂ temperature-programmed reduction, H₂ temperature-programmed desorption and zeta potential analysis. The results revealed that compared with the Ni catalysts with a NiO loading of 40 wt% prepared by co-impregnation (CI) and sequential impregnation (SI) methods, the Ni catalyst synthesized by DP method showed enhanced catalytic performance for CO methanation at atmospheric pressure and an extremely high weight hourly space velocity (WHSV) of 240 000 mL g⁻¹ h⁻¹. In a 50 h high-pressure life-test, this catalyst showed a high resistance to both coking and sintering. It was found that CeO₂ nanoparticles were selectively deposited on the surface of NiO rather than on Al₂O₃ due to the electrostatic interaction during the DP process, effectively preventing Ni particles from sintering during the reduction and reaction at high temperatures, and inhibiting coke formation by increasing the supply of active oxygen species on the nickel surface. As a result, the formed CeO₂-decorated Ni/Al₂O₃ catalyst exhibited excellent catalytic performance and stability in CO methanation. This work demonstrated that catalytic properties could be much improved for a usual catalyst with a well-designed structure.