Preparation Of Eggshell-based Palladium Catalyst And Its Application In Selective Hydrogenation Of 1,3-butadiene

The selective hydrogenation of 1,3-butadiene has high industrial value which is often used as a molecular probe reaction to study the hydrogenation mechanism of unsaturated butenes.At present,as the most widely used catalyst with the best effect,Pd based catalyst has very high catalytic activity for 1,3-butadiene hydrogenation.However,due to the strong adsorption between Pd nanoparticles and alkenes,it often led to deep hydrogenation of 1,3-butadiene on its surface,resulting in the formation of the final product butane,which is a great waste of raw materials.This problem can be solved by adjusting the geometric structure and electronic structure of Pd via catalyst support modification.However,due to the complexity of modified carriers and the inevitable pollution to the environment,it has become a demand to utilize green and efficient modified carriers.In recent studies,as the public awareness of environmental protection is continuous growing,waste natural materials to prepare catalyst become the one of the most popular method.As a stable source of biological calcium carbonate with a large daily yield,eggshell has a potential advantage as a catalyst support due to its abundant groups and morphologies.Thus,by utilizing the surface group on the eggshell as a natural modified carrier,a high-performance hydrogenation catalyst can be obtained via the interaction between the surface group and Pd nanoparticles which affects the electronic properties of Pd.In this study,the waste eggshell was used as a support to load and regulate the spatial distribution of Pd and Ag nanoparticles.An efficient Pd-Ag/ES catalyst was successfully prepared,which was then used to catalyze the hydrogenation of 1,3-butadiene.Through a series of characteristics such as SEM,TEM,BET,XPS,FTIR,it was verified that the porous multi-layer structure of eggshell was beneficial to promote metal dispersion.At the same time,the inherent sulfonic groups on the eggshell surface was found to be strongly interact with Pd and Ag nanoparticles,leading to enhancement of butenes selectivity by Pd.The optimized Pd-Ag/ES catalyst was able to achieve butene selectivity of 95.8%and a 1,3-butadiene conversion rate of 95%at 45℃,with good stability in the continuous reaction for at least 30 h.Additionally,first-principle density functional theory(DFT)calculations and in-situ infrared techniques were used to explore the reaction mechanism of sulfonic groups that contribute to the enhanced catalytic performance of Pd nanoparticles.The results show that the sulfonate groups can effectively reduce the adsorption energy of 1-butene,cis-2-butene,trans-2-butene and 1,3-butadiene on the surface of Pd nanoparticles,and finally improve the selectivity of Pd particles to butenes.This study showed that waste containing sulfonic groups can be a good support material for selective hydrogenation of active metal nanoparticles.In order to further explore the potential of eggshell as a catalyst support,hydrochloric acid was used as the etching agent to acid etch a large number of mesopores on the surface of eggshell,which effectively changed the pore structure of eggshell and improved the defect of low specific surface area of eggshell(1.37 to 10.97 m2/g).After a series of optimization of etching temperature and loading capacity,the final etching catalyst Pd/ES-AR-58.8%can achieve 92%conversion rate and 90%selectivity of butenes.With the analysis of NH3-TPD,XPS,it was found that with the increase of acid etching degree,the medium and strong acid increased obviously.Through the analysis of BET,SEM,TEM,FTIR and TG,it was observed that the pore structure of eggshell contributes to the formation of Pd nanoparticles with small particle size.In addition,the different pore size of the porous etching support prepared at different temperatures has a great influence on the hydrogenation activity of the catalyst.Through comparative analysis,it is concluded that the large pore structure eggshell catalyst contributed to the improved mass transfer ability and hydrogenation activity of the catalyst.XPS and ICP analysis showed that with the increase in degree of acid etching,the content of sulfonic groups and the residual Cl elements in the eggshell increased as well as the number of pores.These additional electron-withdrawing groups will lead to the transformation of the electronic properties of Pd,which will alter the adsorption capacity of butenes,and ultimately affect the selectivity of the catalyst to the product.