Study On Synergistic Catalytic Selective Hydrogenation Of Metal Pd And Semiconductor Hybrid Nanostructured Catalysts

Selective hydrogenation reactions lie at the heart of many chemical industrial processes.Among them,supported precious metal catalysts are widely used in selective hydrogenation.However,it is still a great challenge to achieve high conversion（100%）and high selectivity（≥95%）at the same time.In the past decade,single-atom catalysts have attracted more and more attention due to their excellent catalytic performance for selective hydrogenation because of the advantage of 100%single-metal atom dispersion.For the challenge of efficient selective hydrogenation,this thesis proposes a novel strategy:a novel metal Pd and semiconductor hybrid nanostructured catalyst is prepared by photochemical reduction.The semiconducting metal oxide is spread in the mesoporous molecular sieve SBA-15 channel according to the principle of spontaneous monolayer dispersion,and then the Pd nanoparticles are anchored on the monolayer dispersed semiconducting metal oxide film by the photochemical reduction method to prepare the metal Pd and semiconductor hybrid nanostructured catalyst.The main research contents and results are as follows:1.A novel metal Pd and semiconductor hybrid nanostructured catalyst Pd/@-Me Ox/SBA-15（Me:Zr,Ti）was prepared.The results of XRD and XPS confirmed that Zr O₂（Ti O₂）with 10%loading was coated in the pores of SBA-15 as a monolayer dispersed film;the results of XPS and H₂-TPR showed that there is strong electron transport between Pd nanoparticles and monolayer dispersed Zr O₂（Ti O₂）film,resulting in strong interfacial electronic effect;the results of selective hydrogenation reaction performance tests and comparative experiments show that there is a synergistic catalytic effect between Pd nanoparticles and the monolayer dispersed metal oxide film layer coated in the pores of SBA-15.2.The catalytic performance of Pd/@-Zr O₂/SBA-15 in the selective hydrogenation of nitrobenzene was systematically investigated.It was found that under the conditions of 0.12wt.%Pd,40℃,20 min,0.6 MPa,20 m L isopropanol,n（Pd）:n（nitrobenzene）=0.044%,nitrobenzene could be completely converted into aniline,and the turnover frequency（TOF）value of 23415 h^-1.Keeping other conditions unchanged,when the hydrogen pressure is 1 MPa,the TOF value is as high as 46654 h^-1.The activity of the catalyst did not decay after being used for 5 times,indicating that it has good stability.3.The catalytic performance of Pd/@-Zr O₂/SBA-15 in the selective hydrogenation of styrene was systematically investigated.It was found that under the conditions of 0.08wt.%Pd,30℃,20 min,0.4 MPa,20 m L isopropanol,n（Pd）:n（styrene）=0.013%,styrene can be completely converted to ethylbenzene,and TOF value as high as 69400 h^-1.The activity of the catalyst is much higher than that of the comparative samples Pd/Zr O₂and Pd/SBA-15.The TOF value is about 8 times higher than that of the single-atom catalyst Pd₁/Ti O₂-EG(TOF 8973 h^-1).The catalyst can be reused for at least 8 times without fading in activity,indicating good stability.4.The catalytic performance of Pd/@-Ti O₂/SBA-15 in the selective hydrogenation of benzaldehyde was systematically investigated.It was found that under the conditions of 0.23wt.%Pd,50℃,40 min,1 MPa,20 m L water,n（Pd）:n（benzaldehyde）=0.0637%,benzaldehyde can be completely converted to benzyl alcohol,and TOF value as high as 10144 h^-1.The activity of the catalyst is much higher than that of the comparative catalysts Pd/Zr O₂and Pd/SBA-15.The TOF value is about 10 times higher than that of the single-atom catalyst Pd₁/Ti O₂-EG(TOF 1002 h^-1).The catalyst can be reused for at least 6 times without fading in activity,indicating good stability.