Study On The Catalytic Transfer Hydrogenation Performance Of Formic Acid Over Gold Based Catalysts

In recent years,nano gold catalysts have become the research hotspot due to their unique selective hydrogenation properties.However,the low activity and harsh reaction conditions caused by the weak adsorption of hydrogen molecules on gold nanoparticles,which seriously restrict its practical application.Due to its mild reaction conditions,high molecular efficiency and cheap and easy hydrogen donors,hydrogen transfer has attracted more and more attention.Formic acid,as a promising hydrogen transfer agent,often requires the addition of alkali as an additive,which complicates the reaction system.Therefore,it is a challenging subject to study the catalytic hydrogenation of formic acid as a hydrogen transfer agent under the condition of no alkali.In this paper,we design Schiff base functionalized silica supported gold catalysts and build a non-alkali formic acid hydrogen transfer system.Then we investigated its hydrogenation performance.The main results presented in the dissertation have been summarized as follows:1.SiO₂ carrier containing the reducing functional group was synthesized by one pot aldimine condensation of?3-aminopropyl?-triethoxysilane?APTES?with formaldehyde.The Au/Schiff-SiO₂ catalyst was prepared by the method of liquid phase reduction of sodium borohydride.HAADF-STEM,XRD,FT–IR,UV – Vis and XPS characterization results indicated that the gold nanoparticles were highly dispersed over the Schiff-base modified silica support with an average size below 2 nm.Due to the strong electron donor capability of the Schiff base,metallic gold with weak electro negativity was observed on the Au@Schiff-SiO₂ catalyst.2.When formic acid is used as hydrogen transfer agent,Au/Schiff-SiO₂ catalyst showed excellent phenylacetylene half-hydrogenation activity.In mild conditions?60 0C?and without any additives,phenyl acetylene hydrogenation reaction conversion and selectivity were > 99%.The loss rate of styrene is less than 3 percent in solvent-free conditions of phenyl acetylene hydrogenation.Formic acid can be completely decomposed into carbon dioxide and hydrogen gas at the end of the reaction to become a green hydrogen transfer process.Due to the strong interaction between gold and Schiff base,the agglomeration and loss of gold nanoparticles were not occurred after the reaction.3.When formic acid is used as hydrogen transfer agent,Au/Schiff-SiO₂ catalyst exhibits good catalytic performance for imines synthesis with nitrobenzene and benzaldehyde.Under mild conditions?70 0C?,toluene as solvent,and without any additives,the yield of imines was 68% for 40 min.At the end of the reaction,formic acid can be completely decomposed into carbon dioxide and hydrogen gas.which provides a new route for the partial-hydrogenation in organic synthesis and fine-chemical synthesis.