Study On The Preparation Of Succinic Acid By Hydrogenation Of Maleic Anhydride In Aqueous Phase Using Pd-based Catalyst

Succinic acid is a binary carboxylic acid with significant industrial applications and is listed as one of the 12 most promising value-added chemicals by the US Department of Energy.Currently,it is mainly produced by catalytic hydrogenation of maleic anhydride.However,the acidic environment and leaching of active metals can lead to catalyst deactivation.Therefore,it is crucial to develop efficient and stable catalysts under acidic reaction conditions.Hydroxyapatite(HAP)has good thermal stability and metal anchoring and dispersion capabilities,and is widely used as a catalyst support.However,HAP is an alkaline support with a small number of weak acidic sites,which is not suitable for reactions in acidic systems.In fact,the inorganic components of bones are mainly composed of HAP.The protein and fat present in waste bone can be calcined in an inert atmosphere to generate NC species in situ,covering the surface of HAP,which is expected to obtain stable and efficient hydrogenation catalysts in acidic reaction systems.In Chapter 2 of this paper,a bone-based catalyst loaded with Pd was prepared using waste bones as raw materials,and a one-pot hydrogenation of maleic anhydride to succinic acid was carried out in aqueous solution.The effect of temperature,reaction time,and catalyst composition on the reaction was studied,and the stability of the catalyst was evaluated.It was found that Pd/nHAP@NC achieved complete conversion of maleic anhydride to succinic acid in a one-step reaction under mild conditions of 40℃ and 1 atm H2 in aqueous solution,with a maleic anhydride concentration as high as 19.6 wt%.Pd/nHAP@NC maintained high activity even after five cycles.Characterization revealed that the excellent performance of Pd/nHAP@NC is due to the small size of the metal particles in the catalyst,abundant mesoporous structure,and large surface area.The NC species formed in situ under a nitrogen atmosphere covered the catalyst and anchored the metal Pd,enhancing the activity and acid resistance of the catalyst.In chapter 3 of this article,in order to achieve controllable preparation and regulation of the nitrogen-carbon layer structure on the HAP surface,and to explore the effect of carbon layer thickness and nitrogen content on the catalyst,HAP@NC-X support was prepared by using L-lysine to coat HAP in different proportions(X represents the mass ratio of L-lysine to HAP,and Pd/HAP@NC-X catalyst was obtained after Pd was loaded.The catalyst was applied to the hydrogenation of maleic anhydride in water.The study found that when X was 0.5,Pd/HAP@NC-0.5 achieved complete transformation of maleic anhydride into succinic acid in water at 40℃ and 1 atm hydrogen pressure.The activity remained almost unchanged after five cycles.Characterization revealed that Pd was uniformly distributed on the support,and electrons transferred from HAP to the carbon surface,increasing the electron density on the carbon layer surface,promoting the activity of Pd on the carbon layer surface,and N anchored on the surface-dispersed Pd in the carbon layer,improving the stability of the catalyst in acidic environments.