Physicochemical and catalytic properties of nanosized Au/CeO 2 catalysts for eco-friendly oxidation of benzyl alcohol Putla Sudarsanam, Baithy Mallesham, D. Naga Durgasri, Benjaram M. Reddy * Inorganic and Physical Chemistry Division, CSIR – Indian Institute of Chemical Technology, Uppal Road, Hyderabad 500 607, India 1. Introduction The selective oxidation of alcohols to carbonyl compounds represents one of the crucial functional group transformations in both laboratory and industry [1]. The resultant carbonyl com- pounds are vital intermediates in the production of drugs, vitamins, fragrances, agrochemicals, and fine chemicals [2,3]. Most of the oxidation reactions are conventionally performed by means of various toxic and expensive stoichiometric oxidants, such as chromates, permanganates, and peroxides with hazardous organic solvents [2,4,5]. Besides, such processes are atom inefficient due to poor selectivity, and/or requirement of additional separation and waste treatment steps to isolate the products [4]. From the viewpoint of green chemistry, the development of eco- friendly processes that use safe and inexpensive oxidants is of great research interest in modern organic chemistry. Recently, oxidation of alcohols using oxygen (O 2 ) as the oxidizing agent has attracted significant attention because O 2 is a green, economical, and abundant oxidant that produces water as the only byproduct [6]. As well, the selection of a promising catalyst and avoiding the use of hazardous solvents and/or bases will be an additional highly desirable option. Due to the potential advantages of heterogeneous catalysts over homogeneous counterparts, for example, favorable structural properties, high chemical stability, and prolonged reusability, they are more preferred in oxidation reactions [7,8]. The activity of heterogeneous catalysts can be further improved at nanoscale range, where quite remarkable physicochemical properties are expected in comparison to bulk materials [9]. Hence, a lot of research efforts have been undertaken to develop numerous promising nanosized heterogeneous catalysts for oxidation reac- tions. Among the various studied catalysts, gold nanoparticles (Au NPs) deposited on metal oxides have gained much attention in the aerobic oxidation of alcohols because of their high chemical stability to oxygen, excellent catalytic activity, and better product selectivity [10–13]. To stabilize the Au NPs, different metal oxide supports have been employed, such as CuO [13], CeO 2 [14], TiO 2 [15], MgO [16], MnO 2 [17], and other transition- and rare earth- metal oxides [18]. Amongst, CeO 2 is of immense interest in oxidation processes owing to facile redox properties and abundant oxygen vacancy defects [14,19]. Several factors have been examined to know the origin of the catalytic performance of Au/CeO 2 in the alcohol oxidation, including the Au particle size, its oxidation state, CeO 2 unique properties, preparation method, etc. Especially, the choice of an appropriate preparation method is of vital importance because different synthesis procedures result in diverse physicochemical properties, which significantly influence the catalytic activity of the resulting catalysts. For example, the presence of oxygen vacancies and ionic Au species on the Au/CeO 2 surface, prepared by means of NaOH as the precipitant at pH  10, are reported to be the key factors for the oxidation of various alcohols [14]. In contrast, it was showed that the activity of Au/CeO 2 , synthesized by reduction of gold precursor, strongly depends on the Au particle size [20]. An Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx * Corresponding author. Tel.: +91 40 2719 1714; fax: +91 40 2716 0921. E-mail addresses: mreddyb@yahoo.com, bmreddy@iict.res.in (B.M. Reddy). A R T I C L E I N F O Article history: Received 12 August 2013 Accepted 17 November 2013 Available online xxx Keywords: Aerobic oxidation Nano-gold Ceria Preparation method Oxygen vacancies A B S T R A C T In this work, benzyl alcohol oxidation was investigated over Au/CeO 2 -homogeneous deposition– precipitation (ACH) and Au/CeO 2 -direct anionic-exchange (ACD) catalysts. Various characterization techniques were employed to study their physicochemical properties. TEM images revealed presence of 5.3 and 7.4 nm Au nanoparticles in ACH and ACD catalysts, respectively. Raman studies showed that only ACH sample exhibits oxygen deficiency (0.0574). Amongst, the ACH catalyst exhibited better catalytic performance owing to smaller gold nanoparticles and abundant oxygen vacancies. The alcohol conversion and product selectivity were strongly dependent on temperature and time-on-stream conditions. The catalytic activity decreased after repeated use due to aggregation of Au nanoparticles. ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. G Model JIEC-1715; No. of Pages 7 Please cite this article in press as: P. Sudarsanam, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.11.053 Contents lists available at ScienceDirect Journal of Industrial and Engineering Chemistry jou r n al h o mep ag e: w ww .elsevier .co m /loc ate/jiec 1226-086X/$ – see front matter ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2013.11.053