Investigating deposition sequence during synthesis of Pd/Al<sub>2</sub>O<sub>3</sub> catalysts modified with organic monolayers

Blanchette, Zachary; Zhang, Jing; Yazdi, Sadegh; Griffin, Michael B.; Schwartz, Daniel K.; Medlin, J. Will

doi:10.1039/d1cy02131a

Cited by 7 publications

(9 citation statements)

References 52 publications

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“…Differences in ligand coverage have been shown to provide different levels of site modification for phosphonic acid-modified Pd/Al 2 O 3 catalysts. 23 As shown in Figure 7, liquid-phase hydrogenation was also performed using 2-phenyl-2-butanol as the reactant. This molecule is analogous to benzyl alcohol; however, the alcohol group is more sterically hindered.…”

Section: Effect Of Sams On Liquid Phase Reactionsmentioning

confidence: 99%

“…Ligands for heterogeneous catalyst modification are often in the form of SAMs, which, in general, are dense and highly ordered. For this reason, improvements in selectivity are often accompanied by losses in overall activity due to significant site blocking. , Therefore, it is of considerable interest to generate ligand-modified catalysts with controlled surface densities in order to free active sites and restore activity while still gaining selectivity benefits from any of the mechanisms discussed above. Indeed, there are some examples in the literature that have addressed this issue.…”

Section: Introductionmentioning

confidence: 99%

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Directing Reaction Pathways on Supported Metal Catalysts with Low-Density Self-Assembled Monolayers

Blanchette

Schwartz

Medlin

2023

ACS Appl. Nano Mater.

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Controlling reactant adsorption on catalyst surfaces is crucial to reaction activity and selectivity. One method for improving selectivity is by imposing steric constraints to bias the reactant binding orientation. In this study, thiol self-assembled monolayers (SAMs) were deposited onto Pt/Al2O3 catalysts as a method for controlling activity and selectivity via steric effects. In addition to a full monolayer, a low-density SAM-coated catalyst was employed. A number of characterization techniques demonstrated the successful deposition of homogeneous low-density SAMs on the metal surface with reduced site-blocking compared to a full high-density monolayer. Reaction kinetic studies showed increased benzyl alcohol hydrodeoxygenation (HDO) selectivity for both SAM-modified catalysts. This was attributed to the inability of the reactant to adsorb on the catalyst with the aromatic ring parallel to the surface, thus preventing decarbonylation and ring hydrogenation reaction pathways. Additionally, SAM density influenced reaction activity significantly, with the low-density-modified SAM catalyst being more active than the catalyst coated with a full monolayer. Moreover, liquid-phase hydrogenation reactions were used to investigate the relationship between SAM density and reactivity for reactant molecules of various sizes. In all cases, the low-density SAM improved reaction rates relative to dense SAMs. The effect of controlling ligand density depended on the type of reaction: high ligand densities greatly diminished ring hydrogenation, while HDO was largely unaffected, suggesting a potential strategy for size-selective reaction rate and selectivity control.

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Section: Effect Of Sams On Liquid Phase Reactionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Directing Reaction Pathways on Supported Metal Catalysts with Low-Density Self-Assembled Monolayers

Blanchette

Schwartz

Medlin

2023

ACS Appl. Nano Mater.

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“…TPP-modified Rh nanoparticles supported on graphene oxide have higher selectivity to aldehyde products when compared to Rh that has been modified with ethylene glycol or hydrazine . Medlin et al have published numerous articles using organic ligand self-assembled monolayers on metallic and metal-oxide surfaces to enhance the reaction rates and to direct selectivity to the desired products. − In one recent example, they compare phosphonic acid and thiol-modified Pd/Al 2 O 3 catalysts where the thiol serves as only a site blocking agent, while phosphonic acid enhances the rate of furfuryl alcohol ring hydrogenation . Medlin and Nikolla et al also observe that when they test a variety of surface ligands such as thiols, phosphines, amines, and alcohols, which are bound to supported Pd nanoparticles, the selectivity for H 2 O 2 formation is altered depending on the ligand that is bound to Pd.…”

Section: Introductionmentioning

confidence: 99%

Electronic Tuning of Gold Nanoparticle Active Sites for Reduction Catalysis

Sufyan

Devener

Perez

et al. 2022

ACS Appl. Mater. Interfaces

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Electronic tuning of active sites in heterogeneous catalysis with organic ligands remains challenging since the ligands are often bound to the most active sites on the catalysts’ surfaces. In this work, gold nanoparticles, which are on average less than 2 nm in diameter, are synthesized with strongly binding thiol and phosphine ligands and have measurable quantities of accessible sites on their surfaces in both cases. Triphenylphosphine (TPP) is used as the phosphine ligand, while triphenylmethyl mercaptan (TPMT) serves as the thiol ligand. Phosphines are chosen because they are electron-donating ligands when bound to Au, and thiols are selected because they are electron-withdrawing on the Au surface. X-ray photoelectron spectroscopy (XPS) results show differences in the Au 4f binding energies between the TPP- and TPMT-bound Au nanoparticles. Fourier transform infrared spectroscopy (FTIR) measurements of bound CO indicate that the TPP-bound Au nanoparticles are more electron-rich than the TPMT-bound Au nanoparticles. The number of binding sites on the surface is quantified using 2-naphthalenethiol titration experiments. It is observed that the number of binding sites on the thiol and phosphine-bound Au nanoparticles is similar in both cases. The Au nanoparticles are used for three different reactions: resazurin reduction, CO oxidation, and benzyl alcohol oxidation. For both CO oxidation and benzyl alcohol oxidation, which are performed with the ligands attached, TPP- and TPMT-bound nanoparticles are both catalytically active. However, for resazurin reduction, the TPMT-bound Au nanoparticles are not active, while the TPP-bound Au nanoparticles are catalytically active. These results illustrate that the catalytic activity can be tuned using bound organic ligands with different electronic properties for reduction reactions using Au nanoparticle catalysts.

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“…Considering the wide versatility of PA-grafted materials, the exploration and use of PAs bearing an additional functional moiety such as amine, thiol, or carboxylic groups has received considerable attention. , In particular, most studies in this field have been devoted to the grafting with aliphatic PAs containing terminal amine functional groups given the wide-stretched application perspectives. This is evidenced by the grafting of various metal oxides including Fe 3 O 4 , − TiO 2 , − Al 2 O 3 , , and ZnO, targeted for applications in supported metal catalysis, , enzyme immobilization, metal scavenging, and hybrid (photo)electric devices. , …”

Section: Introductionmentioning

confidence: 99%

“… 32 , 33 In particular, most studies in this field have been devoted to the grafting with aliphatic PAs containing terminal amine functional groups given the wide-stretched application perspectives. This is evidenced by the grafting of various metal oxides including Fe 3 O 4 , 34 − 39 TiO 2 , 40 − 46 Al 2 O 3 , 47 , 48 and ZnO, 49 targeted for applications in supported metal catalysis, 50 , 51 enzyme immobilization, 52 metal scavenging, 42 and hybrid (photo)electric devices. 43 , 53 …”

Section: Introductionmentioning

confidence: 99%

Amino-Alkylphosphonate-Grafted TiO₂: How the Alkyl Chain Length Impacts the Surface Properties and the Adsorption Efficiency for Pd

Gys

Pawlak

et al. 2022

ACS Omega

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Amino-alkylphosphonic acid-grafted TiO2 materials are of increasing interest in a variety of applications such as metal sorption, heterogeneous catalysis, CO2 capture, and enzyme immobilization. To date, systematic insights into the synthesis–properties–performance correlation are missing for such materials, albeit giving important know-how towards their applicability and limitations. In this work, the impact of the chain length and modification conditions (concentration and temperature) of amino-alkylphosphonic acid-grafted TiO2 on the surface properties and adsorption performance of palladium is studied. Via grafting with aminomethyl-, 3-aminopropyl-, and 6-aminohexylphosphonic acid, combined with the spectroscopic techniques (DRIFT, 31P NMR, XPS) and zeta potential measurements, differences in surface properties between the C1, C3, and C6 chains are revealed. The modification degree decreases with increasing chain length under the same synthesis conditions, indicative of folded grafted groups that sterically shield an increasing area of binding sites with increasing chain length. Next, all techniques confirm the different surface interactions of a C1 chain compared to a C3 or C6 chain. This is in line with palladium adsorption experiments, where only for a C1 chain, the adsorption efficiency is affected by the precursor concentration used for modification. The absence of a straightforward correlation between the number of free NH2 groups and the adsorption capacity for the different chain lengths indicates that other chain-length-specific surface interactions are controlling the adsorption performance. The increasing pH stability in the order of C1 < C3 < C6 can possibly be associated to a higher fraction of inaccessible hydrophilic sites due to the presence of folded structures. Lastly, the comparison of adsorption performance and pH stability with 3-aminopropyl(triethoxysilane)-grafted TiO2 reveals the applicability of both grafting methods depending on the envisaged pH during sorption.

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Investigating deposition sequence during synthesis of Pd/Al₂O₃ catalysts modified with organic monolayers

Abstract: Modification of supported metal catalysts with self-assembled monolayers (SAMs) has been shown to improve selectivity and turnover frequencies (TOFs) for many catalytic reactions. However, these benefits are often accompanied by...

Cited by 7 publications

References 52 publications

Directing Reaction Pathways on Supported Metal Catalysts with Low-Density Self-Assembled Monolayers

Directing Reaction Pathways on Supported Metal Catalysts with Low-Density Self-Assembled Monolayers

Electronic Tuning of Gold Nanoparticle Active Sites for Reduction Catalysis

Amino-Alkylphosphonate-Grafted TiO₂: How the Alkyl Chain Length Impacts the Surface Properties and the Adsorption Efficiency for Pd

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Investigating deposition sequence during synthesis of Pd/Al2O3 catalysts modified with organic monolayers

Abstract: Modification of supported metal catalysts with self-assembled monolayers (SAMs) has been shown to improve selectivity and turnover frequencies (TOFs) for many catalytic reactions. However, these benefits are often accompanied by...

Cited by 7 publications

References 52 publications

Directing Reaction Pathways on Supported Metal Catalysts with Low-Density Self-Assembled Monolayers

Directing Reaction Pathways on Supported Metal Catalysts with Low-Density Self-Assembled Monolayers

Electronic Tuning of Gold Nanoparticle Active Sites for Reduction Catalysis

Amino-Alkylphosphonate-Grafted TiO2: How the Alkyl Chain Length Impacts the Surface Properties and the Adsorption Efficiency for Pd

Contact Info

Product

Resources

About

Investigating deposition sequence during synthesis of Pd/Al₂O₃ catalysts modified with organic monolayers

Amino-Alkylphosphonate-Grafted TiO₂: How the Alkyl Chain Length Impacts the Surface Properties and the Adsorption Efficiency for Pd