Oxidation of Cyclohexene Catalyzed by Nanoporous Au(Ag) in Liquid Phase
Nanoporous gold with minor silver content has been identified as a new type of gold based catalyst for selective oxidation of cyclohexene with molecular oxygen in liquid. By oxidation of the leached nanoporous gold foils in ozone, the minor silver content was oxidized to form silver oxide nanoclusters on the surface of nanoporous gold. With further treatment in methanol, the surface silver oxide was reduced and surface alloy was formed on gold ligaments. Both nanoporous gold treated with ozone only and the one with ozone and then methanol are very active for selective oxidation of cyclohexene with molecular oxygen in liquid of cyclohexene with a turn-over-frequency (TOF) of 0.55–0.99 molecules per surface Au atom per second under a solvent-free and initiator- free condition. The total selectivity for production of 2-cyclohexene-1-one, 2-cyclohexene-1-ol, and cyclohexene oxide was increased from 57.5 % to 80.8 % by an additional treatment of nanoporous gold in methanol after activation in zone. The correlation of catalytic selectivity for the production of the three products and corresponding surface chemistry of ligament suggests that (1) the formed Au–Ag alloy surface is favorable for the formation of 2-cyclohexen-1-one, 2-cyclohexene-1-ol, and cyclohexene oxide and (2) the surface silver oxide is favorable for the production of cyclohexenyl hydroperoxide.
KeywordsOxidation processes and reactions Cyclohexene Catalysis Gold Liquid phase
The authors gratefully acknowledge the financial support provided by the Integrated Mesoscale Architectures for Sustainable Catalysis (IMASC), Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award No. DE-SC0012573. JD appreciates the help from B. Zugic and M. Personick in preparing the nanoporous Au–Ag samples.
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