Controlling the Duality of the Mechanism in Liquid‐Phase Oxidation of Benzyl Alcohol Catalysed by Supported Au–Pd Nanoparticles

Abstract

In the solvent-free oxidation of benzyl alcohol to benzaldehyde using supported gold-palladium nanoparticles as catalysts, two pathways have been identified as the sources of the principal product, benzaldehyde. One is the direct catalytic oxidation of benzyl alcohol to benzaldehyde by O(2), whereas the second is the disproportionation of two molecules of benzyl alcohol to give equal amounts of benzaldehyde and toluene. Herein we report that by changing the metal oxide used to support the metal-nanoparticles catalyst from titania or niobium oxide to magnesium oxide or zinc oxide, it is possible to switch off the disproportionation reaction and thereby completely stop the toluene formation. It has been observed that the presence of O(2) increases the turnover number of this disproportionation reaction as compared to reactions in a helium atmosphere, implying that there are two catalytic pathways leading to toluene.

The benzaldehyde oxidation paradox explained by the interception of peroxy radical by benzyl alcohol

“…The oxidation of pure benzaldehyde was conducted under conditions analogous to those employed in our previous studies of the aerobic benzyl alcohol oxidation 17,29 . Benzaldehyde was oxidized under solvent-less conditions without a catalyst at 353 K in a glass reactor under 1 atm pressure of O 2 .…”

Deactivation studies of bimetallic AuPd nanoparticles supported on MgO during selective aerobic oxidation of alcohols

“…13,[18][19][20][21] However, during this reaction, toluene, benzoic acid, benzyl benzoate and benzene are formed as by-products lowering the selectivity to benzaldehyde. [22][23][24] Typically, benzoic acid, benzylbenzoate, and benzene are formed in smaller quantities (ca <5%). During this reaction, toluene is also formed in a substantial amount (ca 20%).…”

“…22,25 We have further demonstrated that by tuning this metal-support interface, using basic supports such as MgO or ZnO, we can switchoff the disproportionation reaction and thereby the toluene production. 23, 25 The basicity of MgO in supported metal catalysts has been exploited for the homogeneous base-free oxidation of bioderived polyols.…”

“…39 The metalsupport interfacial sites have been tuned by choosing different supports thereby enhancing the selectivity during aerobic oxidation of benzyl alcohol. 23 Here, we attempt to optimise the support properties for the AuPd/MgO catalyst and study its effects on the resultant catalytic activity and stability. In order to achieve that, we prepared a variety of MgO materials from different precursors and used them as supports for 1%AuPd/MgO catalyst.…”

The Study on Activity Enhancement of Gold and Palladium Alloy Nanoparticles in Comparison with Monometallic Catalysts

“…Aldehydes are largely acquired as they are valuable intermediates for the pharmaceuticals and agrochemicals industries [5]. Interest in catalytic oxidation of alcohols by supported gold and gold-palladium alloy nanoparticles has expanded dramatically [6].…”