Controlled Preparation Of Pd-based Alloy Nanocatalysts And Performance Study In Olefin Hydrogenation Reactions

With the booming development of petrochemical industry in China,the application of loaded metal nanocatalysts in hydrogenation reactions has become more widespread.At present,industrial research on Pd catalysts mainly focuses on carrier modification and addition of additives,with less research on the application of Pd nanoparticle size regulation and alloying.Therefore,in this work,the size regulation,binary alloys and ternary alloys of Pd nanocatalysts were explored by experiments,which provides reference for the industrial applications of selective hydrogenation of olefins.The main research contents as follows:（1）The size of Pd particles on the catalyst surface is adjusted by changing the conditions of PVP addition,p H values of the impregnating solution and roasting temperature.It was found that there is a close relationship between hydrogenation performance and catalyst particle size in the hydrogenation of isoprene and styrene.The performance tests showed that the styrene conversion was higher when the Pd particle size was in the range of 4.5-8.5 nm,and the highest monoolefins yield was achieved when the Pd particle size was in the range of 5.5-8.5 nm.The results showed that the hydrogenation effect reached the best level when the average particle size of Pd particles was between 5.5 and 8.5 nm.（2）The addition of metal Ni to the Pd catalyst was used to investigate the effect on the catalytic performance of Pd.It was found that the Pd Ni alloy catalysts prepared by stepwise impregnation had high styrene conversion and monoolefins yield.The styrene conversion of hydrogenation reaction was close to 100%and the monoolefins yield was greater than 90%when the Pd Ni molar ratio was 1:2,the reaction temperature was 90°C,the reaction pressure was 1 MPa and the reaction space velocity was 12 h^-1.From the characterization analysis,it can be concluded that the surface active components of the Pd Ni alloy catalyst have a high dispersion degree and an alloy structure,which is favorable for both styrene hydrogenation conversion and monoolefins selectivity.In addition,the main reason for the excellent hydrogenation performance of this catalyst was the modulation of the Pd⁰/Pd²⁺atomic ratio by the Ni on its surface.（3）The Pd Ag Cu ternary alloy nanocatalyst were successfully synthesized by adding Ag and Cu to the Pd catalyst,and their performance was tested in the selective hydrogenation of isoprene.The performance tests showed that the Pd Ag Cu ternary alloy nanocatalysts showed the maximum isoprene conversion and monoolefins yield of 98%and 92%,respectively,in the isoprene selective hydrogenation reaction when the Pd Ag Cu molar ratio was 3:2:3.Characterisation analysis showed that the Pd atoms acted as the active center,while Ag and Cu acted as promoters.The presence of a moderate Pd⁰/Pd²⁺atomic ratio on the catalyst surface,which effectively enhanced the selectivity of monoolefins in the isoprene hydrogenation reaction,meanwhile maintains the hydrogenation activity.In addition,the catalytic activity and monoolefins yield were superimposed as the fourth dimension on the ternary phase diagram,which helped to identify more clearly the optimal ternary alloy composition for this reaction.