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

Abstract

Six products are formed from benzyl alcohol oxidation over Pd nanoparticles using O2 as the oxidant: benzaldehyde, toluene, benzyl ether, benzene, benzoic acid, and benzyl benzoate. Three experimental parameters were varied here: alcohol concentration, oxygen concentration, and temperature. Microkinetic modeling using a mechanism published recently with surface intermediates was able to produce all 18 trends observed experimentally with mostly quantitative agreement. Approximate analytical equations derived from the microkinetic model for isothermal conditions reproduced the isothermal trends and provided insight. The most important activation energies are Ea2=57.9 kJ mol−1, Ea5=129 kJ mol−1, and Ea6=175 kJ mol−1, which correspond to alcohol dissociation, alkyl hydrogenation, and the reaction of alkyl species with alkoxy species. Upper limits for other activation energies were identified. The concepts of a sticking coefficient and steric factor in solution were applied.

Selective Benzyl Alcohol Oxidation over Pd Catalysts

“…For example, for an alcohol/metal ratio of 500 mol/mol the resulting TOF is 1000 h −1 , 1100 h −1 , 700 h −1 and 700 h −1 for a BA concentration of 0.15 M, 0.30 M, 0.60 M and 1 M, respectively. The above results suggests that the surface is largely covered with adsorbates during reaction, which is consistent with the kinetic simulations in reference, where simulations suggested that adsorbed oxygen was the dominant species under most conditions [95].…”

“…Until recently, there was no published mechanism detailed enough for microkinetic modeling. However, Savara et al published a sufficiently complete mechanism and microkinetic model for benzylic alcohol oxidation over Pd/AC and AuPd/AC, [53,86,95] followed by a kinetic study by Galvanin et al [89].…”

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

“…We previously used microkinetic modeling (simulation+fitting) to validate and understand the mechanism for benzyl alcohol oxidation to various products (e.g., benzaldehyde, toluene, benzoic acid, etc.) over Pd/C . Herein, we apply the same microkinetic model based on the mechanism in Scheme to understand the differences in benzyl alcohol oxidation over AuPd/C relative to that over Pd/C and then use density functional theory calculations to validate the differences in the oxygen adsorption properties inferred from the microkinetic modeling.…”

“…The temperature and concentration conditions were the same as those in our previous study (Table S1, Supporting Information), and the same microkinetic model was also used (Table S2). The AuPd/C catalyst was prepared by following a two‐step procedure to produce homogenous‐alloyed AuPd nanoparticles .…”

Facile synthesis of crystalline nanoporous Mg3(PO4)2 and its application to aerobic oxidation of alcohols

“…Earlier, Au nano particle based catalysts were reported to exhibit effective oxidation property for this reaction [14][15][16]. Very recently, carbon supported Pd nano particles are also reported as low temperature active oxidation catalysts for this reaction [17,18]. The simple non-transitional metal based Mg 3 (PO4) 2 catalyst exhibiting promising oxidation property in solvent less conditions make the present study interesting.…”