Selective oxidation of fatty alcohol ethoxylates with H2O2 over Au catalysts for the synthesis of alkyl ether carboxylic acids in alkaline solution

In this paper, we report a green and selective route for the direct oxidation of alcohol ethoxylates (AEOs) into alkyl ether carboxylic acids over supported noble metal catalysts using H2O2 as an oxidant in the presence of a base. The catalytic performance of supported Au, Pt and Pd was assessed in the oxidation of AEO7 consisting of C-12-C-14-alcohol polyethyleneglycol ether with average 7 EO units. Among the different catalysts tested, Au/Al2O3 and Au/TiO2 displayed a yield up to 88% to polyoxyethylene(7) lauryl ether carboxylic acid (AECA6) at 80 degrees C. The effect of Au particle size, reaction temperature, reaction time, catalyst loading and base amount on the activity, selectivity and stability of Au/Al2O3 was explored in detail. Hydroxyl radicals were generated during the reaction as suggested by a series of poisoning tests using 2,2,6,6-tetramethylpiperidinoxyl and 1,4-benzoquinone as radical scavengers. Au/Al2O3 and Au/TiO2 could only be reused in two consecutive runs, showing a strong deactivation in the third run and beyond due to Au leaching and partial nanoparticle sintering as inferred by combined TEM and ICPAES analysis. The Au stability could be highly promoted over a bimetallic AuPt/TiO2 formulation, showing a good recyclability and reuse for at least 10 consecutive catalytic cycles. (C) 2016 Elsevier Inc. All rights reserved.