Ultrasmall Ni nanoparticles embedded in Zr-based MOFs provide high selectivity for CO2 hydrogenation to methane at low temperatures

Abstract

Of great significance from an energy-saving viewpoint is the direct use of CO₂ as a C1 source to mitigate the anthropogenic CO₂ emission into the earth's atmosphere and to produce methane that can be turned into chemicals and fuels. Herein, we report the use of UiO-66 metal–organic frameworks to anchor ultrasmall Ni nanoparticles (NPs), thus avoiding the sintering of Ni NPs protected by the frameworks. Transmission electron microscope images and EDX mappings show that Ni NPs with an average size of 2 nm are highly dispersed in UiO-66 (Ni@UiO-66). Moreover, the obtained catalyst with an optimal Ni loading of 20 wt% displays an outstanding activity (57.6% of CO₂ conversion) and high selectivity (100%) for methane in long-term stability tests up to 100 h at a reaction temperature as low as 300 °C. Compared with Ni/ZrO₂ and Ni/SiO₂, the good dispersion of ultrasmall Ni NPs and the low activation energy (E_a = 68.9 kJ mol⁻¹) facilitate a high catalytic activity, which makes Ni@UiO-66 a promising catalyst for CO₂ methanation.