Design And Preparation Of High Efficiency Solid Catalysts Applied In Formic Acid Dehydrogenation And Catalytic Transfer Hydrogenation

Hydrogen?H₂?as the simplest chemical energy carrier has attracted particular interest for replacing fossil fuels because of its efficient transformation into chemical energy with water as a byproduct.However,the safe,economical,and controlled storage and transport of H₂remains a difficult issue in achieving successful hydrogen economy.In view of this,several concepts based on the use of hydrogen-rich liquid or solid compounds have been proposed for hydrogen storage and release.Formic acid?FA?,a natural biomass-derivative and which is accessible via CO₂ reduction,has been identified as a promising liquid hydrogen storage medium with high hydrogen capacity?4.4 wt%?,low toxicity,and excellent stability.Complementary to the direct hydrogenation,FA has also received considerable interest as a liquid hydrogen carrier for catalytic transfer hydrogenation,which is a fundamental and important transformation for organic synthesis.What's more,catalytic transfer hydrogenation has the characteristics of mild reaction conditions,safe and controllable reaction process,and high atomic economy.Heterogeneous catalysts are easy to separate from the reaction system and can be recycled,in line with the current development trend of green chemistry.The research mainly focuses on supported noble metal catalysts,and their catalytic performance is greatly affected by the support with poor stability.The rare non-noble metal catalysts applied in catalytic transfer hydrogenation generally have the problems of harsh reaction conditions and poor catalytic activity.In this dissertation,with the goal of efficient utilization of formic acid,a series of green and economical novel solid catalysts are designed and prepared for dehydrogenation of formic acid and catalytic transfer hydrogenation to reveal the influence of catalyst composition and structure on catalyst performance.The specific research contents are as follows:?1?A novel type of support was designed and prepared to promote the catalytic performance of Pd nanoparticles,while the catalytic performance of Pd-based heterogeneous catalyst is remarkedly dependent on the nature of the support.The composites,designated Pd/NC_t@WO₃,were fabricated by combining a wet self-assembly approach with F127 as the template,surface adsorption of dicyandiamide?DCA?,then pyrolysis treatment and Pd nanoparticles loading.The obtained catalysts were fully characterized by BET,TEM and XPS and their catalytic activity for FA dehydrogenation was investigated under mild conditions.The unique composite structure and strong electronic regulation ability of NC_t@WO₃ enabled it to efficiently stabilize the small Pd NPs and improve their catalytic activity.The resulting catalyst Pd/NC₄₀₀@WO₃ exhibited good catalytic activity and durability for dehydrogenation of FA.?2?From environmental and economic viewpoints,a novel type of transition metal cobalt-based catalyst was designed and prepared to supersede noble metal catalysts for formic acid dehydrogenation and the corresponding transfer hydrogenation reactions under additive-free reaction conditions.A simple and feasible melamine-assisted pyrolysis strategy was developed for preparating the catalysts?Co-N?_n@NC.It was realized by chelation of Co²⁺and hyper-cross-linked polypyrrole?HPPY?to form a hybrid Co-HPPY,and then melamine was mixed with Co-HPPY by mechanochemical method.The mixture?Co-HPPY/Mel?was subsequently carbonized at 900°C to afford?Co-N?_n@NC.The obtained catalysts were fully characterized by BET,XRD,HAADF-STEM,Raman,XPS and XANES.Systematic investigation reveals that the target catalyst?Co-N?_n@NC in which atomic cobalt-nitrogen?Co-N?-anchored mesoporous carbon with high metal loading?>6.8 wt%?and high specific surface area(750 m² g^-1).The obtained samples?Co-N?_n@NC were demonstrated to be highly efficient and robust catalysts for FA dehydrogenation and formylation of quinolines through transfer hydrogenation.?3?An environmentally friendly N-doped porous carbon coating cobalt nano catalysts were prepared by a simple mechanical assembly and carbonization procedure,using renewable tannin,accessible g-C₃N₄ and Co?OAc?₂ as precursors.The obtained catalysts Co@NC-n were successfully applied in both hydrogenation of nitroarenes and one-pot reductive amination of nitroarenes and aldehydes with formic acid as the hydrogen donor.The target catalyst Co@NC-2 exhibited optimal activity,applicability and also can be reused for at least six times with good stability.A strong electron interaction between Co and rich basic N sites in NC was detected by Raman,XPS and CO₂-TPD analysis,which was demonstrated to contribute the excellent catalytic performance.