Oxidation of Alcohols with Molecular Oxygen

Abstract

The sections in this article are Introduction Oxidation in the Gas Phase Metals Oxides Phosphates Zeolites Oxidation in the Liquid Phase Platinum‐Group Metals Gold Oxides Molecular Sieves Hydrotalcites Phosphates and Apatites Heterogenized Metal Complexes Summary

Dynamic Behavior of Pd/P4VP Catalyst during the Aerobic Oxidation of 2-Propanol: A Simultaneous SAXS/XAS/MS Operando Study

“…The two stages occur independently and in sequence. [1][2][3][4][5][6]18,19 According to this mechanism, molecular oxygen is not directly involved in the substrate oxidation, but has the double role of reoxidizing the Pd-hydrides (supported by the observation that O 2 can be replaced by a hydrogen acceptor), 20,21 and suppressing the decarbonylation of the oxidation products over metallic Pd. 1−5 Competing reactions may occur at specific surface sites 19 during the catalytic cycles (such as the decarbonylation or the overoxidation of the products, the overoxidation of the catalyst, and the aggregation of Pd species to inactive bulk metal), with a consequent decrease in selectivity and deactivation of the catalyst.…”

“…Selective aerobic oxidation of alcohols to their corresponding aldehydes over noble-metal-based catalysts is an environmentally benign process in fine chemistry, but also a reaction particularly demanding, because it requires the activation of molecular oxygen and C–O bonds in close proximity, at temperatures typically below 160 °C. − The economic and environmental advantages of molecular oxygen as a chemical oxidant are readily apparent: oxygen is abundant, inexpensive, and thermodynamically potent. However, effective solutions to this problem must overcome the intrinsic reactivity and selectivity challenges posed by the chemistry of O 2 : O 2 is a four-electron oxidant when it is reduced to water but most desired reactions are 2-electron oxidations, and partially reduced oxygen species are typically more reactive and potent oxidants than O 2 itself. − Both heterogeneous and homogeneous Pd-based catalysts are largely employed in selective alcohol oxidations, on account of the Pd ability to perform selective oxidations at temperatures typically between 60 and 160 °C and atmospheric oxygen pressure. − Albeit significant progress has been achieved in understanding the role of Pd-based catalysts by using in situ or operando spectroscopic − and microscopic , tools, the mechanism of the reaction is still a matter of discussion. − …”

“…It has long been accepted that the reaction proceeds following an oxidase-style mechanism consisting of two steps: (1) a Pd-mediated oxidation of the alcohol by dehydrogenation, with the formation of the corresponding aldehyde and of a Pd-hydride intermediate; and (2) the aerobic oxidation of the reduced catalyst. The two stages occur independently and in sequence. − ,, According to this mechanism, molecular oxygen is not directly involved in the substrate oxidation, but has the double role of reoxidizing the Pd-hydrides (supported by the observation that O 2 can be replaced by a hydrogen acceptor), , and suppressing the decarbonylation of the oxidation products over metallic Pd. − Competing reactions may occur at specific surface sites during the catalytic cycles (such as the decarbonylation or the overoxidation of the products, the overoxidation of the catalyst, and the aggregation of Pd species to inactive bulk metal), with a consequent decrease in selectivity and deactivation of the catalyst.…”