Synthetically Tuned Atomic Ordering in PdCu Nanoparticles with Enhanced Catalytic Activity toward Solvent-Free Benzylamine Oxidation Vijaykumar S. Marakatti, † Saurav Ch. Sarma, † Boby Joseph, ‡ Dipanjan Banerjee, § and Sebastian C. Peter* ,† † New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560064, India ‡ Elettra Sincrotrone Trieste SCpA, SS14 Km 163.5, Trieste, Basovizza 34149, Italy § Dutch-Belgian Beamline, The European Synchrotron Radiation Facility, CS 40220, 38043 Grenoble, France * S Supporting Information ABSTRACT: Synthesis of ordered compounds with nano size is of particular interest for tuning the surface properties with enhanced activity and selectivity toward various important industrial catalytic processes. In this work, we synthesized ordered PdCu nanoparticles as highly efficient catalyst for the solvent-free aerobic oxidation of benzylamine. The Pd x Cu 1-x catalysts with different chemical compositions (x = 0, 0.25, 0.4, 0.5, 0.6, 0.75, 1) were prepared by polyol method using NaBH 4 as a reducing agent and were well-characterized by X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy (TEM) energy-dispersive analysis of X-rays, and X-ray absorption fine structure. The effect of different metal concentrations of Pd and Cu on the formation of Pd x Cu 1-x nanoparticles was investigated. The XRD and TEM confirmed the formation of ordered PdCu intermetallic phase with body-centered cubic (BCC) structure for the synthetic composition of Pd/Cu = 1:1. For compositions x = 0, 0.25, 0.75, and 1, Pd x Cu 1-x alloy with face-centered cubic (FCC) struc- ture was observed, whereas mixed phase of BCC and FCC was observed for x = 0.4 and 0.6. The use of strong reducing agent (NaBH 4 ) was essential to synthesize PdCu ordered phase compared to weak reducing agents such as oleylamine and ascorbic acid. The PdCu nanocatalyst with ordered structure (BCC) showed excellent catalytic activity compared to Pd x Cu 1-x alloy nanoparticles with FCC structure. The atomic ordering in the PdCu intermetallic was the driving force for the enhancement in the catalytic activity with high benzylamine conversion of 94.0% and dibenzylimine selectivity of 92.2% compared to its monometallic and alloy counterparts. Moreover, ordered PdCu alloy showed good recyclability and activity toward the oxidation of different amines. KEYWORDS: ordered structures, nanoparticles, intermetallics, catalysis, PdCu, alloy, benzylamine, oxidation 1. INTRODUCTION Nowadays, in the field of heterogeneous catalysis, much more interest has been dedicated to the systems such as bimetallic, alloy, and intermetallic compounds (IMCs) than to the mono- metallic systems due to the better control on electronic changes and surface properties like active site isolation. Bimetallics are usually formed by the phase segregation of two elements in which each of two elements shows individual phase, whereas, in case of alloys, nonuniform distribution of atoms within its solubility limit form a range of mixed phases with range of composition. Unlike alloys, intermetallics (IMs) contain two or more metals arranged in well-ordered periodic structure; hence, they are termed as “ordered alloys”. 1,2 The nature of bonding in all these com- pounds differs; bimetallics have metallic bonding, whereas alloys and IMs pose nondirectional and directional covalent bonding, respectively. The structurally ordered IM phases provide a site isolation of the active metal and electronic changes. The active site isolation affords the geometrical changes directing toward the noticeable enhancement of the catalytic activity. The modified electronic structures of IMCs make them attractive catalytic materials, as they tend to alter the binding energy of the surface adsorbents such as reactant, intermediate, and products. 3 Another interesting property of IMCs is their structural sta- bility arising from highly favorable formation of enthalpies. It is observed that the IMCs could maintain their surface structure under reaction conditions, whereas surface composition and structure of alloys changes during different reaction condi- tions. 4,5 All these features in combination make IMs to be poten- tial and attractive heterogeneous catalysts with improved acti- vity and selectivity compared to their monometallic and alloy counterparts. 6-8 In the literature a few IMCs have been applied as catalysts for the different organic reactions. The following Received: September 26, 2016 Accepted: January 9, 2017 Published: January 9, 2017 Research Article www.acsami.org © 2017 American Chemical Society 3602 DOI: 10.1021/acsami.6b12253 ACS Appl. Mater. Interfaces 2017, 9, 3602-3615