Preparation And Selective Hydrogenation Performance Of Confinement Catalysts With Zeolite Encapsulating On Noble Metal Nanoparticles

Encapsulation of metal catalysts with redox property within zeolite forming confinement M@Zeo can boost the catalytic performances in many ways.The rigid zeolitic framework can improve the activity,anti-sintering or anti-leaching property of metal nanoparticles due to the confinement effect.In the meanwhile,the zeolitic microchannel also endows shape-selectivity to the M@Zeo.Moreover,the synergetic metal-acid catalyst,where metal nanoparticles are in proximity with acid sites,is promising for tandem catalysis.The pivotal tenet of the academic research on M@Zeo is that the synthetic methods need to be further optimized and extended for improving catalytic performances.In this thesis,highly dispersed Pd,Pt and Rh nanoparticles are encapsulated within silicalite-1（S-1）or L zeolite to enhance the catalytic performances in hydroformylation,selectiveɑ,β-unsaturated hydrogenation and phenol hydrogenation.Also,the inproved catalytic performances over M@Zeo are tentatively discussed.The main content is as follow:（1）Highly dispersed Rh₂O₃ nanoparticles are encapsulated within S-1 with hydrothermal seeds-induced method（Rh₂O₃@S-1）.The surface of S-1 seeds is chemically modified by MPTMS and then anchored with metal ions,which are the prerequisites for preventing the agglomeration and even precipitation of metal species during the synthesis process.In addition,the Rh₂O₃@S-1 is further used for secondary epitaxial growth,during which the average crystal size increases from 400 nm to 700 nm（Rh₂O₃@S-1-Ⅱ）.The regioselectivity of terminal alkene hydroformylation can be effectively improved over Rh₂O₃@S-1 compared with that over Rh₂O₃/S-1.Moreover,increasing the chain length from C₆ to C₁₀ or the sheath thickness of S-1 are conducive for the n/iso ratio of aldehyde products.For example,Rh₂O₃@S-1-Ⅱgives the conversion of 99.3%,meanwhile the aldehyde yield of 93.6%and n/iso ratio of 6.65 in the hydroformylation of 1-decene.The results from product distribution studies and in-situ FT-IR experiments reveal that the confinement of S-1 not only restricts the formation of intermediate internal alkenes to some extent,but also fosters faster diffusion of n-aldehydes than that of iso-aldehydes,thus boosting the resulting n/iso ratio during the hydroformylation process.（2）Highly dispersed Pt nanoparticles are also encapsulated within S-1 zeolite（Pt@S-1）with hydrothermal seeds-induced method.For comparison,poorly dispersed Pt nanoparticles with larger size are encapsulated within S-1 as well via in-situ hydrothermal synthesis（Pt@S-1-is）.Comprehensive characterizations indicate that though the crystalline and porous structures between Pt@S-1 and Pt@S-1-is are similar,the size distribution and encapsulation properties of Pt nanoparticles are obviously different,in which Pt nanoparticles of 1.36 nm are homogeneously dispersed within S-1 matrix of Pt@S-1,whereas larger nanoparticle of 5.75 nm are sparsely embedded within the central of Pt@S-1-is.It has been proved that the catalytic performances are enhanced in the cinnamaldehyde and furfural hydrogenation over Pt@S-1.For example,Pt@S-1 gives conversion of 99.8%and meanwhile cinnamal alcohol selectivity of 98.7%in the cinnamaldehyde hydrogenation,whereas only cinnamal alcohol selectivity of31.9%and 0.1%are obtained over Pt@S-1-is and Pt/S-1,respectively.As for smaller3-methyl-2-butenal,besides confinement effect,electronic effect is also introduced by doping Fe species to further improve the catalytic performance and thus 3-methyl-2-butenal conversion of 64.5%and 3-methyl-2-butenol selectivity of 83.7%are attained.Hydrogenation of cinnamal alcohol/hydrocinnamaldehyde in separate or mixed reaction systems combined with in-situ FT-IR experiments demonstrate that Pt@S-1 are prone to preferential C=O hydrogenation compared with Pt@S-1-is and Pt/S-1.Moreover,C=O adsorbed on Pt sites of Pt@S-1 via on-topη₁mode is the key to enhancing the selectivities of unsaturated alcohols.（3）Highly dispersed Pd and Rh nanoparticles are encapsulated within K-type L zeolite（KL）with in-situ hydrothermal method（Pd@KL/Rh@KL）to investigate the effect of zeolitic microenvironments and metal locations on the phenol hydrogenation.KL zeolite are modulated to Na-type（Pd@Na KL）or H-type（Pd@HKL）via ion-exchange and the average size of Pd nanoparticles of～2 nm remains unchanged.From the FT-IR spectra,the decreased peak intensity and the red-shift of relevant peak reveal the chemisorption of phenol on the KL,while the weak basicity of KL is beneficial for increasing cyclohexanone selectivity.In the selective phenol hydrogenation,conversion of 99.2%and cyclohexanone selectivity 94.8%are attained over Pd@KL.Product distribution studies and TPD experiments show that though the phenol is facilitated to convert over Pd@Na KL,the over-hydrogenation of cyclohexanone and intermolecular dehydration of cyclohexanol occur.In addition,the strongly acidic microenvironment of Pd@HKL hinders the chemisorption and conversion of phenol,thus resulting in phenol conversion of less than 10%after the reaction time of 14 h.The locations of Rh nanoparticles are tailored under different H₂reduction temperatures.Systematic characterizations reveal that Rh nanoparticles gradually migrate from the central KL channel to the pore mouth with the increasing of reduction temperature,during which the nanoparticle size maintains～1.1 nm.In combination with XPS,CO-adsorption FT-IR and kinetic studies,it has been proved that Rh species have interactions with the K⁺of the cation sites and thus are inclined to be in the electron-enriched state,which positively influences the activity.The TOF value over Rh@KL reduced at 300℃is as high as 155 h^-1,which is twice than that of Rh/KL even under mild reaction conditions,i.e.,30℃and 1 atm H₂.