Unsupported Thiolate-capped Palladium Nanoparticles as Selective Hydrogenation Catalysts PDF Download
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Author: Jie S. Zhu
Publisher:
ISBN: 9781085564441
Category : Alkenes
Languages : en
Pages : 45
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Book Description
Abstract: The reactions of palladium are invaluable to modern academic and industrial research, and nanotechnology is the foundation on which the next generation of materials is built upon. Unsupported thiolate-capped palladium nanoparticles were found to be highly substrate selective for alkene hydrogenation and isomerization. A modified Brust-Schiffrin reaction enabled the facile and convenient synthesis of a diverse set of ultra-small thiolate-capped nanoparticles. The physical properties of these nanoparticles were highly tunable due to the widespread availability of ligand precursors. Mechanistic evidence and insights reveal that steric and electronic effects from the ligand environment on the nanoparticle surface controlled reactivity by influencing alkene adsorption via [pi] bond coordination or di-[sigma] bond formation. Only alkenes close enough to the metal surface of the nanoparticles underwent reaction. Dienes with good overlapping p orbitals could overcome these steric effects on the deactivated palladium nanoparticle surfaces. A mechanistic model was built from these completed studies, and this model can be used to predict the selectivity of hydrogenation or isomerization in multiple classes of alkenes with varied substitution patterns. These palladium nanoparticles were also found to be capable of chemoselective alkene hydrogenation in the presence of functional groups that are known to be labile towards reduction by palladium.
Author: Jie S. Zhu
Publisher:
ISBN: 9781085564441
Category : Alkenes
Languages : en
Pages : 45
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Book Description
Abstract: The reactions of palladium are invaluable to modern academic and industrial research, and nanotechnology is the foundation on which the next generation of materials is built upon. Unsupported thiolate-capped palladium nanoparticles were found to be highly substrate selective for alkene hydrogenation and isomerization. A modified Brust-Schiffrin reaction enabled the facile and convenient synthesis of a diverse set of ultra-small thiolate-capped nanoparticles. The physical properties of these nanoparticles were highly tunable due to the widespread availability of ligand precursors. Mechanistic evidence and insights reveal that steric and electronic effects from the ligand environment on the nanoparticle surface controlled reactivity by influencing alkene adsorption via [pi] bond coordination or di-[sigma] bond formation. Only alkenes close enough to the metal surface of the nanoparticles underwent reaction. Dienes with good overlapping p orbitals could overcome these steric effects on the deactivated palladium nanoparticle surfaces. A mechanistic model was built from these completed studies, and this model can be used to predict the selectivity of hydrogenation or isomerization in multiple classes of alkenes with varied substitution patterns. These palladium nanoparticles were also found to be capable of chemoselective alkene hydrogenation in the presence of functional groups that are known to be labile towards reduction by palladium.
Author: Mohammed Mahdaly
Publisher:
ISBN: 9781085570886
Category : Alkenes
Languages : en
Pages : 47
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Book Description
This thesis presents the preparation and catalysis of octanethiolate-capped palladium nanoparticles (C8 PdNP) and phenylethanethiolate-capped palladium nanoparticles (PhC2 PdNP) for chemoselective catalytic hydrogenation reactions of alkene groups in the presence of other reducible functionalities. Kinetic studies are performed and analyzed by 1H NMR spectroscopy to obtain clearer understandings of the catalytic activity. The noncovalent interactions between surface phenyl ligands and aromatic substrates are found to hinder the hydrogenation activity of PhC2 PdNP. In comparison, the C8 PdNP is discovered to be highly active and selective for hydrogenating alkene and alkyne groups without the reduction of other reactive functional groups such as nitro, halo, carbonyls, etc. under the mild reaction condition (room temperature and atmospheric pressure).
Author: May Maung
Publisher:
ISBN: 9781339826233
Category : Allyl alcohol
Languages : en
Pages : 48
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Book Description
Abstract: This thesis presents the systematic evaluation of palladium nanoparticles functionalized with well-defined small organic ligands that can provide a spatial control in the surrounding environment of nanoparticle catalyst surfaces. Various thiolate ligand-capped palladium nanoparticles are produced by using different S-alkylthiosufate ligand precursors in a two-phase system composed of toluene and water. These palladium nanoparticles are then characterized using transmission electron microscopy, thermogravimetric analysis, NMR, FT-IR, and UV-vis spectroscopy. The catalysis studies on alkanethiolate-capped palladium nanoparticles with different ligand structures (linear alkyl vs cyclohexyl vs phenyl) show that the chemical and structural composition of a monolayer surrounding the palladium nanoparticles greatly influences the overall activity and selectivity of nanoparticle catalysts for the hydrogenation, isomerization, and hydrogenolysis of allylic alcohols. Especially, the effect of non-covalent interactions between surface ligands and incoming substrates in the near-surface environment is observed. Furthermore, the catalytic properties of & ohgr;-carboxylate-functionalized alkanethiolate-capped palladium nanoparticles are studied for the biphasic reactions of hydrophobic allylic alcohols that are immiscible in aqueous solution. The systematic investigations on the influence of pH and substrate size are performed to check the utility of structurally stable and water-soluble palladium nanoparticles as new micellar catalysts.
Author: Somnath Bhattacharjee
Publisher:
ISBN:
Category : Hydrogenation
Languages : en
Pages : 342
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Book Description
Author: David Gregory Vincent
Publisher:
ISBN:
Category : Catalysts
Languages : en
Pages : 80
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Book Description
Author: Renee Wai Ying Man
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author:
Publisher:
ISBN:
Category : Palladium
Languages : en
Pages : 150
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Book Description
A series of palladium catalysts with ca. 1 wt% palladium supported on mesoporous silica with different pore sizes (MCM-41, SBA-15, and MCF) were prepared by deposition of colloidal Pd nanoparticles (Pd/X_col) and Pd(II)acetate solution (Pd/X_imp). MCM-41 and SBA-15 showed the XRD characteristic peaks indicating highly ordered hexagonal pore structure while MCF consisted of spherical cell and frame structure with average pore size of 2.7, 3.9, and 7.8 nm, respectively. Sizes of the colloidal Pd nanoparticles were about 2.3 nm. The supports pore structure did not affect the Pd particle size of Pd/X_col catalysts. For the Pd/X_imp, the Pd particle size was increased with increasing pore diameter of the supports. However, the largest Pd particle size was obtained on Pd/SBA-15_imp since the Pd particles were formed in a long cylindrical shape similar to SBA-15. The Pd/SBA-15_col exhibited the best catalyst performance in the liquid-phase selective hydrogenation of phenylacetylene under mild conditions (40 degress celsius, H2 pressure = 1-5 bar, 30 min). The appropriated pore structure and pore size of SBA-15 could provide a better encapsulation of Pd particles so that high styrene selectivity was attained at complete conversion of phenylacetylene. All the Pd/X_col catalysts exhibited no change in the catalyst activities/selectivity during the recyclability test for four cycles while the Pd/X_imp showed an increase of catalyst activity and lower styrene selectivity in some cases.
Author: Takht Ravanchi Maryam
Publisher: LAP Lambert Academic Publishing
ISBN: 9783659779206
Category :
Languages : en
Pages : 188
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Book Description
The selective hydrogenation of multi-unsaturated hydrocarbons, especially in pyrolysis products, to corresponding mono-olefins is a widely exploited way for large-scale production of polymer-grade olefins and also upgrading of gasoline blending stocks. Thermodynamic and/or kinetic parameters could be responsible for directing the reaction network to a special product. This book deals with application of palladium-based catalysts in selective hydrogenation of alkynes and diens. It covers both fundamental and applied aspects of selective hydrogenation with special emphasis on the selectivity problem. The book is organized in rational way beginning with the electronic structure of palladium, followed by its catalytic properties, interaction with supports and transport limitations and commercial applications.
Author: Haeyoon Jung
Publisher:
ISBN:
Category : Nanoparticles
Languages : en
Pages : 210
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Book Description
Author: Khin Aye San
Publisher:
ISBN: 9780355097511
Category : Catalysis
Languages : en
Pages : 64
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Book Description
Abstract: Stable and isolable alkanethiolate-stabilized Pt nanoparticles (PtNP) were synthesized using the two-phase thiosulfate method with sodium S-alkylthiosulfate as ligand precursor. The mechanistic formation of octanethiolate-capped PtNP (Pt-SC8) from both sodium S-octylthiosulfate and 1-octanethiol ligands was investigated by using 1H NMR and UV-vis spectroscopy, which revealed the formation of different Pt complexes as the reaction intermediates. The partially poisoned PtNP with thiolate monolayer ligands was further investigated for the hydrogenation of various alkynes to understand the organic ligands-induced geometric and electronic surface properties of colloidal Pt nanoparticle catalysts. In addition, alkanethiolate-capped Pd nanoparticles (PdNP) were prepared using reversed thiosulfate addition method with S-octylthiosulfate as ligand precursor. Various synthetic conditions were applied to the modified two-phase method in order to control the average core size and surface ligand density. The obtained nanoparticles were characterized by 1H NMR, UV-vis spectroscopy, infrared spectroscopy (IR), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM).
