Benzyl Alcohol Oxidation on Carbon‐Supported Pd Nanoparticles: Elucidating the Reaction Mechanism

Abstract

Experiments were conducted on the liquid‐phase oxidation of benzyl alcohol over Pd nanoparticles, with the aim of determining the operative chemical reaction. Experiments were conducted in a batch reactor with para‐xylene as the solvent and continuous gas purging of the headspace. The following experimental parameters were varied: the initial benzyl alcohol concentration, the oxygen partial pressure in the headspace, and the reactor temperature. From trends in the concentration profiles and integrated production of each product, it was determined that there are two primary reaction paths: A) an alkoxy pathway leading to toluene, benzaldehyde, and benzyl ether, and B) a carbonyloxyl pathway (“neutral carboxylate”) leading to benzoic acid, benzene, and benzyl benzoate. From the mechanism elucidated, it is clear that the coverages of atomic hydrogen, atomic oxygen, and surface hydroxyls must be accounted for to achieve a complete description of the quantitative kinetics.

Selectivity Control in Palladium-Catalyzed Alcohol Oxidation through Selective Blocking of Active Sites

“…1,11,[28][29][30] Possible side products (following the mechanism reported in ref. 31), which can greatly affect the selectivity of the reaction, are represented by benzoic acid, benzene, benzyl benzoate and toluene . 31 The selectivity toward each product appears to be related to the presence of specific active sites 24 and to the adsorption geometry and orientation of reactants and products.…”

“…31), which can greatly affect the selectivity of the reaction, are represented by benzoic acid, benzene, benzyl benzoate and toluene . 31 The selectivity toward each product appears to be related to the presence of specific active sites 24 and to the adsorption geometry and orientation of reactants and products. 33 In this paper, by using operando ATR-IR spectroscopy we have obtained a molecular view of the role of the protective molecule in controlling the selectivity of the palladium catalyzed benzyl alcohol oxidation.…”

Microkinetic Modeling of Benzyl Alcohol Oxidation on Carbon‐Supported Palladium Nanoparticles

“…As described elsewhere, this is considered a green process because O 2 (air) is readily available and the alcohol can be used directly in the reactor without additional solvents or prereactions. Although the main product of benzyl alcohol oxidation is benzaldehyde, five liquid‐phase minor byproducts have also been observed: benzene, toluene, benzoic acid, benzyl benzoate, and benzyl ether . Tentative partial mechanisms were proposed, and a mechanism with sufficient detail for microkinetic modeling has been published (Scheme ) …”

Nanoscale Pd supported on 3D porous carbon for enhanced selective oxidation of benzyl alcohol

“…As reported by Savara et al, there are two primary reaction pathways for the overall oxidation of benzyl alcohol to produce the desired benzaldehyde. 30 One pathway is oxidation and the other is the disproportionation of benzyl alcohol. In the latter reaction pathway, an equimolar amount of toluene, the main byproduct, is produced along with benzaldehyde.…”