Plasma-assisted Co/Zr-metal organic framework catalysis of CO₂ hydrogenation: influence of Co precursors

In this study, Co/Zr-metal organic framework (MOF) precursors were obtained by a room-temperature liquid-phase precipitation method and the equivalent-volume impregnation method, respectively, using a Zr-MOF as the support, and Co/Zr-MOF-M and Co/Zr-MOF-N catalysts were prepared after calcination in a hydrogen–argon mixture gases (${V}_{{\rm{Ar}}}:{V}_{{{\rm{H}}}_{{\rm{2}}}}=9:1$) at 350 °C for 2 h. The catalytic activities of the prepared samples for CO₂ methanation under atmospheric-pressure cold plasma were studied. The results showed that Co/Zr-MOF-M had a good synergistic effect with cold plasma. At a discharge power of 13.0 W, ${V}_{{{\rm{H}}}_{2}}:{V}_{{{\rm{CO}}}_{2}}=4:1$ and a gas flow rate of 30 mlmin⁻¹, the CO₂ conversion was 58.9% and the CH₄ selectivity reached 94.7%, which was higher than for Co/Zr-MOF-N under plasma (CO₂ conversion 24.8%, CH₄ selectivity 9.8%). X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N₂ adsorption and desorption (Brunauer–Emmett–Teller) and x-ray photoelectron spectroscopy analysis results showed that Co/Zr-MOF-M and Co/Zr-MOF-N retained a good Zr-MOF framework structure, and the Co oxide was uniformly dispersed on the surface of the Zr-MOF. Compared with Co/Zr-MOF-N, the Co/Zr-MOF-M catalyst has a larger specific surface area and higher Co²⁺/Cototal and Co/Zr ratios. Additionally, the Co oxide in Co/Zr-MOF-M is distributed on the surface of the Zr-MOF in the form of porous particles, which may be the main reason why the catalytic activity of Co/Zr-MOF-M is higher than that of Co/Zr-MOF-N.