Hydrogenation Of Carbon Dioxide Into Formic Acid Catalyzed By MOF Supported Pd-based Catalyst

Carbon dioxide（CO₂）has negative influences on environment,but is also the most abundant carbon resource in the world.Rational utilization of CO₂ can effectively solve environmental problems and energy shortage problems.Among them,formic acid（FA）is the promising energy carrier for reversible chemical hydrogen storage and has a broad application prospect,which makes CO₂ hydrogenation into FA become a green route for CO₂ utilization.Many studies showed that Pd-based catalysts possess excellent performance for the hydrogenation of CO₂ into FA,and most importantly,the smaller nanoparticles（NPs）size and the electron-rich active sites of Pd can further improve the catalytic activity in general.Therefore,the main studies of this thesis were as follows:A series of Pd-based bimetallic catalysts were prepared by solution impregnation method with MIL-101-NH₂ as support,and the resulting catalysts were used to synthesize FA from the hydrogenation of CO₂.The effects of different second metal components on the catalytic performance of Pd/MIL-101-NH₂ catalysts were investigated and the results showed that there was the synergistic effect between Ag and Pd.Based on these results,we further studied on the loading amount of Ag and the loading sequence of Pd and Ag for the catalytic performance.The results showed that when the loading molar ratio of Pd and Ag was 1:1,the resulting catalyst Pd₁Ag₁/MIL-101-NH₂ obtained the turnover number（TON）of FA with 1220 under the optimal reaction conditions.The TEM and XPS analysis uncovered that the introducing Ag optimized the electronic states of Pd and dramatically facilitated the activation of hydrogen,thus improving the catalytic activity.Different organic amine（triethylenediamine,ethanediamine or N,N-dimethylethylenediamine）was used for achieving amine group functionalization in MIL-101-NH₂,then Pd Ag NPs were immobilized on the organic amine functionalized MIL-101-NH₂,and the resulting catalysts were investigated for the hydrogenation of CO₂ to FA.We came to the conclusion that Pd Ag NPs immobilized on TEDA functionalized MIL-101-NH₂ exhibited best catalytic performance with TON of 1500.The TEM and XPS results showed that TEDA on MOFs could increase the catalytic activity by dispersing Pd Ag NPs（1.6 nm）and forming rich-electron of Pd species.