Applied Surface Science 398 (2017) 19–32 Contents lists available at ScienceDirect Applied Surface Science jou rn al h om ep age: www.elsevier.com/locate/apsusc Full Length Article Selective liquid phase oxidation of benzyl alcohol to benzaldehyde by tert-butyl hydroperoxide over -Al 2 O 3 supported copper and gold nanoparticles Matumuene Joe Ndolomingo, Reinout Meijboom ∗ Department of Chemistry, University of Johannesburg, PO Box 256, Auckland Park 2006, Johannesburg, South Africa a r t i c l e i n f o Article history: Received 19 September 2016 Received in revised form 21 November 2016 Accepted 4 December 2016 Available online 5 December 2016 Keywords: Oxidation Benzyl alcohol Benzaldehyde Copper and gold nanoparticle Kinetics a b s t r a c t Benzyl alcohol oxidation to benzaldehyde was performed by tert-butyl hydroperoxide (TBHP) in the absence of any solvent using -Al 2 O 3 supported copper and gold nanoparticles. Li 2 O and ionic liquids were used as additive and stabilizers for the synthesis of the catalysts. The physico-chemical prop- erties of the catalysts were characterized by atomic absorption spectroscopy (AAS), X-ray diffraction spectroscopy (XRD), N 2 absorption/desorption (BET), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and temperature programmed reduction (TPR), whereas, the oxidation reaction was followed by gas chromatography with a flame ionization detector (GC-FID). The as prepared catalysts exhibited good catalytic performance in terms of conver- sion and selectivity towards benzaldehyde. The performance of the Au-based catalysts is significantly higher than that of the Cu-based catalysts. For both Cu and Au catalysts, the conversion of benzyl alcohol increased as the reaction proceeds, while the selectivity for benzaldehyde decreased. Moreover, the cat- alysts can be easily recycled and reused with neither significant loss of activity nor selectivity. A kinetic study for the Cu and Au-catalyzed oxidation of benzyl alcohol to benzyldehyde is reported. The rate at which the oxidation of benzyl alcohol is occurring as a function of catalyst and oxidant amounts was investigated, with the apparent rate constant, k app being proportional to the amount of nano catalyst and oxygen present in the system. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Selective oxidation of primary alcohols to the corresponding aldehydes is a fundamentally important laboratory and commercial procedure [1–8]. Aldehydes are valuable as both intermediates and high value components for the perfume, pharmaceutical, and agro- chemical industries [1,9–11]. After vanillin, benzaldehyde is the second most important aromatic molecule used in the perfumeries and food industries [12]. In this perspective, catalytic methods leading to high quality grade benzaldehyde are particularly attrac- tive for application in cosmetic and flavoring industries. To date, benzyldehyde is mainly commercially produced via hydrolysis of benzyl chloride, and as a byproduct during the oxidation of toluene to benzoic acid [13]. However, organic chlorine or benzoic acid contaminations are limiting factors of these two processes. Dur- ∗ Corresponding author. E-mail addresses: rmeijboom@uj.ac.za, reinout.meijboom@gmail.com (R. Meijboom). ing the last two decades, many studies have been reported on the catalytic vapor-phase oxidation of benzyl alcohol to benzalde- hyde [12,14–19]. However, in the vapor-phase oxidation process, a significant carbon loss, resulting from the formation of car- bon oxides, is a major problem. Catalytic liquid-phase oxidation of benzyl alcohol to benzaldehyde [11,20–29] is a prominently investigated reaction as it provides chlorine-free benzaldehyde required in perfumery and pharmaceutical industries, and avoids the formation of carbon oxides. The liquid- phase oxidation of ben- zyl alcohol to benzyldehyde can be performed in the presence [30] or absence [11,20–25] of the solvent using molecular oxygen [20–23,26], hydrogen peroxide [31] or tert-butyl hydroperoxide (TBHP) [11,24,25] as oxidizing agents. Benzyl alcohol was reported to be subjected to different reactions depending on the catalyst used and the reaction conditions. Indeed, in addition to the oxi- dation of benzyl alcohol to form benzaldehyde, benzoic acid and benzoate, reactions such as disproportionation to form toluene, benzaldehyde and H 2 O and dehydration to form dibenzyl ether have been reported (Fig. S1) [32]. http://dx.doi.org/10.1016/j.apsusc.2016.12.020 0169-4332/© 2016 Elsevier B.V. All rights reserved.