Selective oxidation of methyl α-d-glucoside on carbon supported platinum

Abstract

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Graphite-Supported Platinum Catalysts: Effects of Gas and Aqueous Phase Treatments

“…Four deactivation mechanisms can be distinguished: (i) Deactivation by over-oxidation or oxygen poisoning has received the most attention. It has been reported for the oxidation of primary alcohols (5-10), secondary alcohols (8,(10)(11)(12), and carbohydrates (10,(13)(14)(15)(16)(17)(18)(19). It is generally accepted that over-oxidation is caused by the strong adsorption of oxygen or oxygen-containing species at the platinum surface (16-18, 20, 21).…”

On-line characterization of platinum/graphite catalysts during liquid phase oxidations using cyclic voltammetry

“…As can be seen, the reaction rate rapidly decreases during reaction. This was shown previously to be the result of over-oxidation [6]. The reactivity of methyl-c~-D-glucopyranoside is too low to keep the catalyst in the reduced state in an oxygen saturated solution.…”

“…This phenomenon is reported to be more pronounced when the catalyst is prereduced by the organic reactant [5,7]. When the oxidation is performed in the kinetic regime, strong chemisorption of oxygen can take place on the active metal leading to what is referred to as over-oxidation [6,8,11]. It was found recently [12] that during the oxidation of ethanol up to three steady-states can occur at the same reaction conditions, depending on the start-up procedure.…”

“…Possible causes of deactivation during liquid phase oxidations are: oxidation of the active metal [4], loss of active surface area due to site coverage by either reaction components or poisons [5], particle growth [6] and corrosion of the metal [5,6]. The actual cause of activity loss depends on the type of reaction and the conditions applied.…”

“…This explains why over-oxidation is observed in the oxidation of methyl-a-D-glucopyranoside ((2R)-2r, hydroxy-methyl-6t-methoxy-tetrahydropyran-3t,4c,5t-triol), leading to a low steady-state, and not in the oxidation for ethanol, while in both cases a reductive start-up is used [11]. Additionally, the oxidized platinum can be subject to dissolution and redeposition so that the already low activity becomes even lower and a steady-state is never reached [6].…”