Nanostructured Ceria-zirconia Supported Ni Catalysts for High Performance CO2 Methanation: Phase and morphology effect on activity

Abstract

BackgroundHydrogenation of CO2 to produce value-added chemicals through thermochemical or electrochemical routes is considered as a promising approach for CO2 utilization and mitigation. Highly efficient Ni-based catalysts supported on nanostructured CexZr1-xO2 composite with advanced performances towards CO2 methanation have been developed. MethodsIn this research, nanostructured CZ composite supports of different phases and morphology were prepared by varying cerium/zirconium molar ratio from 0.9:0.1 to 0.1:0.9 and hydrothermal temperature from 110°C to 180°C by a modified hydrothermal precipitation method. The Ni supported catalysts were prepared by incipient wetness impregnation method. The as-prepared catalysts were characterized by XRD, Raman, XPS, H2-TPR, H2-TPD, CO2-TPD, HR-TEM, SEM-EDX, etc. to explore the detail mechanism of the CZ on promoting effect of Ni/CZ catalyst for CO2 methanation. Significant FindingsThe current study explored the structure-activity relationship of pure c-CeO2, t-ZrO2 and composite CexZr1-xO2 (CZ) supported Ni catalysts for CO2 methanation. It was found that the Ni/CZ catalysts exhibited much higher low-temperature activity than Ni/c-CeO2 or Ni/t-ZrO2, getting CO2 conversion as high as 85.6% and nearly 100 % selectivity to CH4 at 325°C. The Ni/Ce0.9Zr0.1O2 catalyst exhibited higher activity towards CO2 methanation than Ni/Ce0.1Zr0.9O2 catalyst. The characterization results demonstrated that the ceria-rich phase (c) could disperse nickel species more effectively and resulted stronger interaction with nickel than the zirconia-rich (t) phase. Furthermore, the synergistic interaction of nickel with ceria-rich phase promoted the reduction of nickel species and oxygen vacancy on the surface of catalyst, as well as the activation of adsorbed CO2 species. Among different morphological CZ supported Ni catalysts, the nano-polyhedral CZ supported Ni catalyst achieved significantly higher CO2 methanation performance than nanospherical and nanocubic CZ due to better nickel dispersion, higher reducibility, more moderate basic sites, more adsorbed surface oxygen and oxygen vacancies associated with the highly reactive exposed CeO2 (100) and CeO2 (110) planes.