Preparation of mesoporous palladium nanoclusters supported over hematite (a-Fe 2 O 3 ) for selective catalytic hydrogenation of a,b- unsaturated aldehydes Mostafa Farrag Chemistry Department, Faculty of Science, Assiut University, 71516, Assiut, Egypt article info Article history: Received 5 April 2017 Received in revised form 24 July 2017 Accepted 13 August 2017 Available online 15 August 2017 Keywords: Palladium nanoclusters Mesoporous materials Reduction of cinnamaldehyde 100% chemoselectivity Microwave-assisted synthesis abstract Atomically precise monodisperse palladium nanoclusters protected by N-acetyl-L-cysteine (Pd n (NALC) m ) ligand were synthesized. Protected nanoclusters block the mesoporous pores of supports and decrease their specific surface area after loading with 1 wt % as found in our previous work. The new synthesized palladium clusters with special crystal structure did not block the mesoporous pores of iron oxide support (a-Fe 2 O 3 ). Moreover, the pore volume and pore diameter of the support was increased by synthesizing palladium clusters with 1 wt % dopant. The doped catalyst was irradiated by microwave synthesis labstation 1 h at 80  C and 500 W to gently remove of the protected N-acetyl-L-cysteine ligands and produce bare palladium clusters supported on iron oxide. The particles size of the synthesized palladium clusters was investigated by high resolution transmission electron microscope (HRTEM). The spectroscopic properties and chemical composition of Pd n (NALC) m clusters were studied by UV-vis spectroscopy and thermogravimetric analysis (TGA), elemental analysis and atomic absorption spec- troscopy. FTIR was used for the free ligand (NALC) and the protected palladium cluster, where the disappearance of the SeH vibrational band at 2535e2570 cm 1 in the palladium clusters spectrum confirmed the ligand is anchored to the cluster surface through the sulfur atom. The crystallinity of the bare iron oxide and the doped palladium clusters (1%Pd n (NALC) m /a-Fe 2 O 3 ) and the microwave treated catalyst (1% Pd n /a-Fe 2 O 3 ) were determined by powder X-ray diffraction analysis. BET surface area, pore volume and average pore diameter were investigated via nitrogen adsorption at 196  C. The catalytic properties of atomically precise palladium nanoclusters supported on iron oxide were investigated for reduction of cinnamaldehyde as example for a,b-unsaturated aldehydes. The catalytic activity of syn- thesized catalysts increased in this order 1% Pd n /a-Fe 2 O 3 > 1% Pd n (NALC) m /a-Fe 2 O 3 > Pd n (NALC) m . The catalytic reduction reaction in toluene was performed at temperature 20e80  C. The aforementioned synthesized catalysts showed 100% chemoselectivity in the reduction of cinnamaldehyde at room temperature. © 2017 Published by Elsevier Inc. 1. Introduction Palladium based catalysts have gained much attention in the last decades due to their wide range of applications [1e3]. For example, Pd(0) or its compounds are used for carbon-carbon bond forming reactions like Suzuki, Heck, and Stille coupling [4,5] and supported PdO x has been recognized as one of the best catalysts for catalytic CH 4 oxidation [6]. In terms of catalytic hydrogenation, metal complexes such as Wilkinson's [7] or Crabtree's [8] catalysts and various Pd complexes [9,10] are very efficient for regioselective or chemoselective hydrogenation [9,10]. However, the ligand dissoci- ation mechanism and the risk of residue metal toxicity limit their modern synthetic utility [11,12] especially in pharmaceutical applications. Recently, the use of nanomaterials as catalysts gained significant attention because of their enhanced catalytic activity and recycla- bility [13e15]. Many groups have taken advantage of functionalized supports and ligands or designer surfactants to tune the properties of various nanomaterials [16,17]. Shon demonstrated that the cat- alytic activity and recyclability of palladium nanoparticles (PdNP) can be controlled with thiolate-capping agents by selectively E-mail address: mostafafarrag@aun.edu.eg. Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso http://dx.doi.org/10.1016/j.micromeso.2017.08.022 1387-1811/© 2017 Published by Elsevier Inc. Microporous and Mesoporous Materials 257 (2018) 110e117