Study On Modification Of Palladium Based Catalyst And Selective Hydrogenation Of Isoprene

Nowadays,most ethylene is produced from thermal cracking of naphtha,and in this industrial process,more cracked gasoline is produced,which must continue to be processed and utilized.In industry,the one-stage hydrogenation process of pyrolysis gasoline aims to convert high content alkynes and diolefins to monolefins.The focus of its research and improvement is to design and synthesize selective hydrogenation catalysts with high activity and selectivity.Therefore,this paper intends to design and synthesize a catalyst for selective hydrogenation of pyrolysis gasoline with excellent performance from the two aspects of support and active component of catalyst,and uses isoprene selective hydrogenation as the probe reaction.The main contents of the study are as follows:In the aspect of support material design and synthesis,Al2O3 with wire(Al2O3-wire),leaf(Al2O3-leaf)and sheet(Al2O3-sheet)morphology were synthesized by the hydrothermal method.The three kinds of different morphologies of alumina and industrial alumina were used as the supports to prepare the Pd catalysts,investigating their performance in the hydrogenation of isoprene.The evaluation results showed that Pd/Al2O3-leaf catalyst had the highest isoprene conversion and monolefin selectivity,reaching 95%and 98%,respectively.Furthermore,the structure and properties of Pd/Al2O3-leaf catalyst were characterized and correlated with their catalytic performance.The characterization results showed that:(1)Al2O3-leaf support has a large specific surface area,which contributes to the high dispersion of metal component Pd particles,and thus forms more active sites;(2)There are many weak acid and basic sites on the surface,which enhance the interaction between the metal and the support,and promote the uniform distribution of active metal components on the surface in a relatively stable state;(3)The pore channels formed by the accumulation of sheet particles are more transparent and promote the diffusion of reactants.The synergistic effect of these factors makes the Pd/Al2O3-leaf catalyst exhibited the best performance in the selective hydrogenation of isoprene.In the aspect of active phase adjustment,Pd4S/Al2O3-leaf catalyst was prepared by high temperature reduction method.The corresponding characterization results prove the existence of Pd4S phase.The introduction of S atom makes the active site Pd atom relatively independent and the metal atom is not easy to coalesce.In addition,the lone pair electrons carried by S regulate the electronic structure of Pd atoms,enhance the adsorption of diolefin on the catalyst surface,and promote the desorption of single olefin,thus improving the selectivity of the reaction.Compared with the mono-metal Pd catalyst,the prepared Pd4S/Al2O3-leaf catalyst can still maintain high activity at 40℃,and the selectivity to mono-olefin is also maintained at more than 90%.Due to its excellent hydrogenation performance and relatively simple preparation process,Pd4S/Al2O3-leaf catalyst has a good prospect and great advantages in industrial application and popularization.