Molecular Origin of the Selectivity Differences between Palladium and Gold–Palladium in Benzyl Alcohol Oxidation: Different Oxygen Adsorption Properties

Savara, Aditya; Chan‐Thaw, Carine E.; Sutton, Jonathan E.; Wang, Di; Prati, Laura; Villa, Alberto

doi:10.1002/cctc.201601295

Cited by 35 publications

(36 citation statements)

References 26 publications

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“…Moreover, in the study by Baiker, the AuPd ratio has an influence on the selectivity to benzaldehyde, which decreased by increasing the Au content, probably due to the formation of benzoic acid. The decrease in activity and selectivity observed by Baiker are consistent with results by Villa et al [53]. Clearly, the composition of AuPd particles are not the only factor.…”

Section: Bimetallic Catalystssupporting

confidence: 91%

Selective Benzyl Alcohol Oxidation over Pd Catalysts

2018

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In the last decades, the selective liquid phase oxidation of alcohols to the corresponding carbonyl compounds has been a subject of growing interest. Research has focused on green methods that use “clean” oxidants such as O2 in combination with supported metal nanoparticles as the catalyst. Among the alcohols, benzyl alcohol is one of the most studied substrates. Indeed, benzyl alcohol can be converted to benzaldehyde, largely for use in the pharmaceutical and agricultural industries. This conversion serves as model reaction in testing new potential catalysts, that can then be applied to other systems. Pd based catalysts have been extensively studied as active catalytic metals for alcohol oxidation for their high activity and selectivity to the corresponding aldehyde. Several catalytic materials obtained by careful control of the morphology of Pd nanoparticles, (including bimetallic systems) and by tuning the support properties have been developed. Moreover, reaction conditions, including solvent, temperature, pressure and alcohol concentration have been investigated to tune the selectivity to the desired products. Different reaction mechanisms and microkinetic models have been proposed. The aim of this review is to provide a critical description of the recent advances on Pd catalyzed benzyl alcohol oxidation.

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Section: Bimetallic Catalystssupporting

confidence: 91%

Selective Benzyl Alcohol Oxidation over Pd Catalysts

2018

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“…However, considering that high pressure favors the benzyl benzoate production and that low pressures produce benzaldehyde, we believe that the O 2 concentration may lead to different reaction mechanism for the formation of both products. It has been proposed that the differences in the selectivity for Au−Pd systems can be explained by a decrease in oxygen adsorption on their surfaces …”

Section: Resultsmentioning

confidence: 99%

“…The coordinated substrate forms a carbonyloxyl intermediate ( IV ). The next step counts with the interaction of a new benzyl alcohol molecule with a neighbor basic site, producing the benzoate ( V ), and restoring the catalyst …”

Section: Resultsmentioning

confidence: 99%

“…It has been proposed that the differences in the selectivity for AuÀ Pd systems can be explained by a decrease in oxygen adsorption on their surfaces. [45] In light of the foregoing, we can comment on the reaction mechanism on the basis of the experimental data we have presented. Figure 5 shows the reaction mechanism for the benzaldehyde formation, illustrating that the reaction proceeds with synergy between the AuÀ Pd NPs and the basic sites on the surface of the SrCO 3 (I).…”

Section: Mechanistic Considerationsmentioning

confidence: 98%

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Au−Pd Selectivity‐switchable Alcohol‐oxidation Catalyst: Controlling the Duality of the Mechanism using a Multivariate Approach

et al. 2019

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Supported gold‐palladium nanoparticles are highly selective catalysts for the oxidation of alcohols. However, little is known about how integrated reaction conditions can affect the chemoselectivity of a specific catalytic system. Herein, a novel Au−Pd selectivity‐switchable catalyst supported on SrCO3 is reported; and a multivariate optimization was suggested as the key process to better understand the formation of the products. The optimization approach considered temperature, pressure, time of reaction, and Au : Pd molar ratio, and settled that the temperature and Au : Pd molar ratio showed an important effect on the ester yield, while just the metal molar ratio significantly influenced the selectivity for the aldehyde. Thus, taking into consideration the experimental data and optimized conditions, we were able to efficiently switch the selectivity by just changing the pressure of the system in a benzyl alcohol oxidation reaction. In addition, we proposed that the presence of O2 implies that there are two catalytic pathways, which leads to different selectivity, allowing us to bring some mechanistic insights dealing with the duality of the mechanism. Such outcomes are based on dense experimental results and characterizations (FT‐IR, Rietveld refinement, XPS, H2‐TPR, and EDS‐STEM). The catalyst was also very stable, presenting activity up to 6 runs without loss of activity and selectivity, under certain reaction conditions.

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“…The catalytic mechanism of selective oxidation of benzyl alcohol catalyzed by Pd or other noble metal species generally involves the following steps: (I) the oxygen adsorption onto the Pd surface to form surface oxygen, which reacts with the alcohol proton, yielding alkoxy species; (II) β-H elimination of the alkoxy intermediates and transformation into aldehyde; step (II) is regarded as the rate-determining step in the overall catalytic oxidation of alcohol [36,37]. For Pd/NH 2 -LDH-NS catalyst, benzyl alcohol can be adsorbed onto basic sites (MgOH) on the LDH surface which is beneficial to the formation of alkoxy intermediates [38], while the -NH 2 groups implanted on LDH nanosheets can strength the basicity of the catalysts, which is in favor of the β-H elimination of the alkoxy intermediates, thereby greatly promoting the activity of supported Pd NPs.…”

Section: Plausible Mechanism Of Enhancementmentioning

confidence: 99%

Pd Nanoparticles Supported on Amine-Functionalized MgAl Layered Double Hydroxides for Solvent-Free Aerobic Oxidation of Benzyl Alcohol

et al. 2019

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Pd nanoparticles (NPs) supported on amine-functionalized layered double hydroxides (LDHs) (Pd/NH2-LDH-NS) were successfully obtained by implanting aminopropyltriethoxysilane (APTS) on MgAl LDH nanosheets (LDH-NS), followed by impregnating [Pd(NH3)4]Cl2 and reduction with NaBH4. The physicochemical characteristics of the obtained Pd/NH2-LDH-NS were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR),, N2 adsorption–desorption, inductive coupled plasma (ICP), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy(XPS), and their catalytic performance was tested in the selective oxidation of benzyl alcohol with molecular oxygen under solvent-free and base-free conditions. The results showed that the implanted –NH2 groups can promote the dispersion of the supported Pd NPs via complexation of the implanted –NH2 groups to Pd NPs, and they can increase the surface basicity of the catalysts, thus enhancing the catalytic activity and selectivity to benzylaldehyde. Pd/NH2-LDH-NS exhibited enhanced catalytic activity (31.6%) and selectivity (>98%) compared to the corresponding Pd/LDH-NS, Pd/LDH, Pd/SiO2, and Pd/Al2O3. Moreover, Pd/NH2-LDH-NS was remarkably stable and could be reused at least four times without a significant loss in activity and selectivity.

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Molecular Origin of the Selectivity Differences between Palladium and Gold–Palladium in Benzyl Alcohol Oxidation: Different Oxygen Adsorption Properties

Cited by 35 publications

References 26 publications

Selective Benzyl Alcohol Oxidation over Pd Catalysts

Selective Benzyl Alcohol Oxidation over Pd Catalysts

Au−Pd Selectivity‐switchable Alcohol‐oxidation Catalyst: Controlling the Duality of the Mechanism using a Multivariate Approach

Pd Nanoparticles Supported on Amine-Functionalized MgAl Layered Double Hydroxides for Solvent-Free Aerobic Oxidation of Benzyl Alcohol

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