Supercritical-assisted Preparation Of MOFs Materials And Its Catalytic Performance Of CO₂ Conversion

In order to reduce the negative impact of CO₂ emissions on global warming,researchers have proposed tremendous routes to convert CO₂ into high-value chemicals.Among the potential routes,CO₂ methanation has attracted much attention in recent years.As a new type of porous materials with regular pore structure and multiple active centers,Metal-Organic Frameworks（MOFs）are widely employed for CO₂ capture and chemical conversion.In this study,CO₂ methanation was used as the target reaction,and the supercritical preparation method and performance of precious metal-supported catalysts were investigated.By comparing the Pd particles size and the Pd dispersion of the catalyst prepared by the inorganic metal precursor salt and the organic metal precursor salt,Na₂Pd Cl₄ was selected as the suitable Pd precursor salt for supercritical fluid deposition on UiO-66.Three co-solvents systems including ethanol,acetone,and ethanol/DMF（20%）were added to improve the solubility of the precursor in the supercritical fluid.It was preferable to select ethanol/DMF（20%）as a suitable co-solvent.By analyzing the Pd metal size and dispersion of the Pd/UiO-66 catalyst prepared at different deposition temperatures,deposition pressures,and deposition times,suitable preparation conditions were optimized in the process of preparation of Pd loading on UiO-66.The characterization and evaluation results of Pd/UiO-66catalysts with different loading amount showed that loading amount of Pd had great influence on the catalyst’s CO₂ methanation catalytic performance,4%Pd/UiO-66catalyst had the best catalytic activity and selectivity,with a CO₂conversion of 53%and a methane selectivity of 95%.Compared with the sol-gel method,Pd/UiO-66prepared by supercritical deposition method used less precious metals when the same activity was obtained,indicating that the supercritical fluid deposition method had a better effect on the dispersion of metal nanoparticles on the UiO-66 carrier,and the amount of precious metals used was 40% compared to sol-gel method.