Recent advances in the heterogeneously catalysed aerobic selective oxidation of alcohols

Abstract

The heterogeneously catalysed selective aerobic oxidation of alcohols is an important tool for the synthesis of valuable chemical intermediates and a hot topic within both academic and industrial arenas. In this mini-review, selected aspects of catalyst formulation, process operating conditions, and progress in identifying the active sites and surface reaction mechanisms notably through the application of synchrotron radiation, are highlighted.

Tunable Pt nanocatalysts for the aerobic selox of cinnamyl alcohol

“…However, the cinnamaldehyde product is unstable with respect to decarbonylation (to styrene) and hydrogenation (to 3-phenylpropionaldehyde), leaving only 22 % of reactively formed cinnamaldehyde intact. [3][4][5][6][7][8][9][10][11][12][13][14][15] phenylpropionaldehyde intermediate is itself extremely unstable with respect to subsequent oxidation to the corresponding 3-phenylpropanoic acid. Interestingly, reactively-formed cinnamaldehyde does not undergo over-oxidation to cinnamic acid under our conditions, presumably because surface hydrogen 20 co-liberated during its formation from cinnamyl alcohol promotes competing hydrogenolysis/hydrogenation pathways.…”

“…Historically stoichiometric amounts of hazardous 20 oxidants were employed to effect such oxidations, with final product selectivity often poor and generated significant quantities of harmful waste. 3 Heterogeneous catalysts capable of such chemoselective aerobic oxidation (selox) have thus attracted great interest, 4 wherein the co-existence of reactive H 2 C-OH and C=C 25 moieties is a challenge to high aldehyde selectivity. 5,6 Consequently, a fundamental understanding of the active site and reaction network is pivotal for improving catalyst design.…”

“…[7][8][9] Palladium has been extensively studied for the selective oxidation of allylic alcohols, 4,[10][11][12] wherein sophisticated in-situ/operando spectroscopic and kinetic measurements have identified surface PdO as the active site responsible for crotyl and cinnamyl alcohol. 13 22 is also effective towards allylic alcohol selox.…”

Alcohol Oxidation at Platinum–Gas and Platinum–Liquid Interfaces: The Effect of Platinum Nanoparticle Size, Water Coadsorption, and Alcohol Concentration

“…[1][2][3] Although there are variable ways to carry out the oxidation reactions, using transition metal catalyst with molecular oxygen is one of the promising systems to achieve productivity and low environmental impact. [4][5][6][7][8] Alcohol oxidation reaction processes with heterogeneous catalysts occur in the gas-solid and liquid-solid interfaces. The reaction rate and product selectivity are significantly affected by the phase 9 and we have studied alcohol oxidation by using size controlled platinum nanoparticles (Pt NPs) and sum-frequency generation (SFG) vibrational spectroscopy techniques.…”

Catalysing sustainable fuel and chemical synthesis

“…The scientific, technological and commercial importance of green chemistry presents a significant challenge to traditional selox methods, which previously employed hazardous and toxic stoichiometric oxidants including permanganates, chromates and peroxides, with concomitant poor atom efficiencies and requiring energy-intensive separation steps to obtain the desired carbonyl or acid product. Alternative heterogeneous catalysts utilising oxygen or air as the oxidant offer vastly improved activity, selectivity and overall atom efficiency in alcohol selox (Scheme 3), but are particularly demanding due to the requirement to activate molecular oxygen and C-O bonds in close proximity at a surface in a solid-liquid-gas environment [39][40][41], and must also be scalable in terms of both catalyst synthesis and implementation. For example, continuous flow microreactors have been implemented in both homogeneous and heterogeneous aerobic selox, providing facile catalyst recovery from feedstreams for the latter [42,43], but their scale-up/out requires complex manifolding to ensure adequate oxygen dissolution uniform reactant mixing and delivery [44,45].…”