Study On Ru Catalytic Hydrogenation Of Carbon Dioxide For Direct Synthesis Of Formic Acid In Consecutive Reaction

Although carbon dioxide is one of the main greenhouse gases result to global warming, it is the most abundant carbon resources in the world. The reaction of CO2 hydrogenation direct to formic acid is an atomic economic reaction, therefore, the research and development of an appropriate reaction system for formic acid synthesis from CO2 become a meaningful hot task now. This thesis mainly studied the reaction of CO2 hydrogenation to formic acid on Ru Catalyst which were immobilized on the functional support in miniature fixed bed.Three inorganic oxide materials include y-Al2O3,SiO2 and artificial zeolite which are rich in hydroxyl in their surface were chosed as the supporters, and then the Ruthenium complex which actived highly in homogeneous reaction was immobilized on the founctional supports. The surface functional groups microstructures of the supporters, the founctionalized supporters and Ru catalysts on the founctionalized supporter were characterized by BET, fourier transform infrared spectra(FT-IR), X-ray diffraction powder(XRD), scanning electron microscope techniques(SEM), and so on. Based on the experimental determination about the structure and activity test of the catalysts under different reaction conditions we studied the activity influence rules in micro reaction, and the possible reaction mechanism of CO2 hydrogenation to formic acid in miniature fixed bed was discussed.The results of thermodynamic calculations for CO2 hydrogenation to formic acid showed that:the CO2 equilibrium conversion increases along with the increasing of temperature, pressure and the mole ratio of H2 and CO2. The selectivity and yield of formic acid showed an rising tendency when the temperature, pressure increased and the ratio of H2 and CO2 decline.For the three type of immobilized ruthenium catalysts, the one supported on artificial zeolite had high activity and more stable. Besides, this catalyst with a maximum load of Ru at 0.5 wt% among the catalysts which prepared under the same condition.The optimization of reaction conditions and components of the catalyst were carried out in the system of carbon dioxide hydrogenation to formic acid with immobilized catalyst. Experiential rules obtained showed that when the mass ratio of coupling agent and carrier is 1.25:1,n(PPh3)/n(Ru) was 3:1, under the condition ofp=10MPa, T=673.15K, GHSV=3000 h-1,n(H2)/n(CO2)= 4, n(PPh3)/n(Ru)=3:1, Ru content as 0.5 wt%, the selectivity and the yield of the target product HCOOH became the highest-level, moreover, the conversion rate of CO2 maintained at a high level. When the n(Ru):n(La/Ce) was 5:3, the catalysts modified by rare earth gave higher loading of Ru and activity. And it was helpful to enhance the stability of the catalyst, for which the prmotion of La is better than Ce.Proposed that the activation of carbon dioxide was resulted from the interaction of reverse water gas reaction and carbon dioxide abnormol insertion into an M-H bond. In the reaction of CO2 hydrogenation to formic acid, a phosphine ligand in the immobilization Ruthenium hydride complexes is replaced by H2O created from water gas reverse reaction and generates circulation active substances. And then, CO2 anti-insert into Ru-H generating formic acid ester complexes, finally, the bond of Ru-CO2H in complexes was hydrogenolysis into active substances again, completing catalytic cycle.