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Construction Of Pt Catalysts Supported On Metal-organic Frameworks And Their Derivatives For Liquid Phase Hydrogenation

Posted on:2024-05-15Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q P YangFull Text:PDF
GTID:1521306938450024Subject:Chemical Engineering and Technology
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The selective hydrogenation ofα,β-unsaturated aldehydes to unsaturated alcohols is an important process for the production of fine chemicals such as flavors,fragrances,drugs and food additives.Metal-organic frames(MOFs)and their derivatives due to their ultra-high specific surface area,porosity and diverse structures make them carriers of noble metal nanoparticles for enhancing the activity and selectivity ofα,β-unsaturated aldehyde hydrogenation.Therefore,the construction of noble metal-based catalysts based on MOFs and their derivatives are of great significance for the development of hydrogenation catalysts with high catalytic activity,high catalytic selectivity and high stability.This thesis aims to synthesize efficientα,β-unsaturated aldehyde selective hydrogenation catalysts,prepare a variety of Pt/MOFs and their derivatives,investigate the relationship between catalyst structure and performance by various characterization means,elucidate the reaction mechanism,and provide new ideas for the construction of efficient selective hydrogenation catalysts.The main research of this thesis is as follows:(1)Deposition of Pt clusters onto MOFs-derived CeO2by ALD for selective hydrogenation of furfuralThe selective hydrogenation of furfural(FAL)to furfuryl alcohol(FOL)in liquid phase has drawn tremendous attention,while designing and preparing efficient catalysts with satisfied selectivity remains a challenge due to the coexistence of two conjugated C=O and C=C groups within FAL molecule.This work has depicted a simple-yet-effective strategy to load small sized Pt(<2 nm)onto MOFs-derived CeO2via atomic layer deposition(ALD)technique.Special aberration-corrected scanning transmission electron microscopy(AC-STEM)confirmed the dominant presence of Pt nanoclusters.Physicochemical properties of Pt/M-CeO2were investigated by a various of characterizations,inclusive of XRD,SEM,TEM,BET,XPS,Raman,CO-DRIFTS and FAL-DRIFTS.In comparison to Pt/commercial CeO2(Pt/C-CeO2),the Pt/M-CeO2one displayed the superior catalytic activity,yielding 100%conversion of FAL and 98%selectivity to FOL.The high catalytic activity of Pt/M-CeO2can be reasonably assigned to Pt clusters with clean surface,strongly interacting between Pt and M-CeO2,and rich oxygen vacancy/porous structure of the M-CeO2support.This work highlights an effective approach towards deposition of noble metal clusters onto MOFs-derived metal oxides,offering an alternative way to reasonable design highly efficient catalyst in selective hydrogenation reactions.(2)Highly dispersed Pt on partial deligandation of Ce-MOFs for furfural selective hydrogenationMOFs have been extensively investigated as noble metal nanoparticle supports for selective hydrogenations.However,because of small-sized micropores and organic ligands present in MOFs,interactions between inorganic nodes and noble metals are normally weak and the accessibility of active sites is seriously limited.To address these problems,in this study,a partial deligandation strategy is proposed where Pt/CeO2-270 is obtained by a partial decomposition of Ce-MOFs at 270°C,then the Pt nanoparticles are deposited by ALD method.In comparison with the full deligandation of Ce-MOFs at 600°C(CeO2-600),the CeO2-270catalyst with residual organic ligands exhibits larger surface area,extensive porous structure,abundant Ce3+and oxygen vacancy,which stabilize the highly dispersed small Pt nanopartciles.These unique structural features enable the Pt/CeO2-270 catalyst to display different furfural(FAL)adsorption configuration,and show excellent FAL conversion(100%)and high selectivity(97.3%)for furfuryl alcohol(FOL).This work provides a strategy to support highly dispersed Pt nanoparticles on MOFs-derived porous materials prepared by partial deligandation strategy,achieving excellent catalytic performance and chemoselectivity for selective hydrogenation reactions.(3)Construction of ZIF-67@Pt@MOF-74-T sandwich structure catalysts by ligand exchange strategy for selective hydrogenation performance studyThe construction of MOFs and nanoparticle composites is a very effective method,but the weak interaction between MOFs and noble metal nanoparticles inevitably leads to noble metal loss and agglomeration problems.Therefore,how to improve their stability remains a considerable challenge.In this work,ZIF-67@Pt@MOF-74-T with sandwich structure was prepared for the selective hydrogenation of furfural using ligand exchange strategy.The ZIF-67 core can be used as an effective carrier for Pt nanoparticles,and the MOF-74-T shell can prevent the leaching and oxidation of Pt nanoparticles.Various properties of ZIF-67@Pt@MOF-74-T were investigated by XRD,SEM,TEM,BET,XPS,Raman,CO-DRIFTS and FAL-DRIFTS.Compared with Pt/MOF-74,Pt/MOF-74-C and Pt/ZIF-67catalysts,ZIF-67@Pt@MOF-74-T exhibited higher activity and selectivity in the selective hydrogenation reaction of furfural.(4)Carrier dilution effect in the promotion of Pt/CeO2-catalyzed furfural hydrogenation reactionImproving the efficiency of multiphase catalytic reactions is essential to increase the production efficiency of furfural conversion to biofuels and biochemicals.As a feedstock for the synthesis of biochemicals,furfural is extracted from lignocellulosic biomass and converted into high value-added furfuryl alcohol by selective hydrogenation over Pt-based catalysts.In this study,Pt/M-CeO2catalysts were prepared by loading Pt on Ce-MOFs-derived CeO2support and applied to the liquid-phase hydrogenation of furfural.When CeO2was physically mixed with Pt/M-CeO2catalyst as an additive,the conversion of Pt/M-CeO2catalyst in the selective hydrogenation reaction of furfural was increased by 23%.From various characterization analyses,it was concluded that CeO2could absorb more spilled active hydrogen from Pt and exhibit excellent adsorption ability on the reaction substrate compared to diluent AC and Ce-MOFs,thus providing additional catalytic active sites.The catalytic activity of Pt/M-CeO2catalyst was significantly improved by the simple strategy of adding CeO2,which provides a new idea to improve the production efficiency of furfuryl alcohol.
Keywords/Search Tags:MOFs, MOFs-derived, Pt, selective hydrogenation, furfural
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