Aerobic oxidation of benzyl alcohol in methanol solutions over Au nanoparticles: Mg(OH)2 vs MgO as the support

Magnesium oxide and magnesium hydroxide materials containing supported gold nanoparticies (NPs), Au/Mg(OH)(2) and Au/MgO, were prepared from the commercial MgO through the deposition precipitation (DP) method and characterized by XRD, XPS, HRTEM, FTIR spectroscopy and N-2 adsorption techniques. It was found that the starting MgO support was fully transformed into the Mg(OH)(2) phase during the DP procedure. A nearly complete dehydration of the magnesium hydroxide and formation of Au/Mg was achieved through the reductive treatment at 500 degrees C, whereas the treatment at 350 degrees C still resulted in the Au/Mg(OH)(2) material. The FTIR analysis showed a much higher ability of the Au/MgO surface to adsorb both benzyl alcohol and benzaldehyde (ca. 10 and 3 times, respectively), as compared to Au/Mg(OH)(2). Probably for this reason, the Au/MgO catalyst exhibited ca. 50% higher catalytic activity in the aerobic oxidation/oxidative methoxylation of benzyl alcohol in the methanol solutions with respect to the amount of surface gold atoms as compared to the Au/Mg(OH)(2) catalyst, in spite of a larger size of the Au NPs. In addition, the thermal treatment of the catalyst at 500 degrees C to dehydrate the support allowed to suppress the undesired side reaction between benzyl alcohol and primarily formed benzaldehyde to give benzyl benzoate. (C) 2014 Elsevier B.V. All rights reserved.