Rhodium and Iridium Nanoparticles Entrapped in Aluminum Oxyhydroxide Nanofibers: Catalysts for Hydrogenations of Arenes and Ketones at Room Temperature with Hydrogen Balloon

Abstract

Abstract:The recyclable metal nanoparticle catalysts, rhodium in aluminum oxyhydroxide [Rh/ AlO(OH)] and iridium in aluminum oxyhydroxide [Ir/AlO(OH)], were simply prepared from readily available reagents. The catalysts showed high activities in the hydrogenation of various arenes and ketones under mild conditions. Selective hydrogenation was possible for bicyclic and tricyclic arenes in high yields. The catalysts were active at room temperature even with a hydrogen balloon. Also, the catalysts showed high turnover frequency (TOF) values under solventless conditions at 75 8C under 4 atm hydrogen pressure: ca. 1700 h À1 in the hydrogenation of benzene. Furthermore, Rh/AlO(OH) can be reused for at least 10 times without activity loss. The catalysts were characterized by the transmission electron microscopy (TEM), powder X-ray diffraction (XRD), inductively coupled plasma (ICP), energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption and hydrogen chemisorption experiments. The sizes of rhodium and iridium particles were estimated to be 3-4 nm and 2-3 nm, respectively. Aluminum oxyhydroxide nanofibers of these catalysts have surface areas of 500-600 m 2 g À1 .

Highly monodisperse cubic and octahedral rhodium nanocrystals: Their evolutions from sharp polyhedrons into branched nanostructures and surface-enhanced Raman scattering

“…Clearly, their morphologies affect not only the catalytic reactivity, but also the catalytic selectivity [15]. Thus, the issues of controlling their size and shape were considered in catalysis [1] and the structure sensitivity to a larger surface area [16,17]. Here, an effort is made to prepare cubic and octahedral Rh nanoparticles by polyol method using AgNO 3 and RhCl 3 .…”

Sustainable Preparation of Supported Metal Nanoparticles and Their Applications in Catalysis

“…Catalytically active supported metallic Rh nanoparticles have mostly been employed in hydrogenations including the reduction of 1-alkenes, [174] arenes, [45b, 175] and ketones [175] (Figure 26), CO hydrogenation, [176] and in the reduction of various a,b-unsaturated compounds. [177,178] Savastenko et al reported the lean NO x reduction using supported metallic Rh nanoparticles on SiO 2 in the 100-400 8C temperature range and employing a representative test gas mixture of oxygen-rich diesel engine exhaust gas.…”

“…TEM images and particle size distribution of Rh metal nanoparticles on aluminum oxyhydroxide nanofibers, used in the hydrogenation of arenes at room temperature with a hydrogen balloon. [175] Reproduced with permission. Figure 25.…”

Facile Hydrogenation of Ketones Catalyzed by Platinum on Carbon under Ordinary Pressures and Temperatures

“…[1] Boron-and aluminum-based hydride reagents have been widely used for the reduction of ketones to secondary alcohols, but such methods require the use of more than stoichiometric amounts of reductants and generate vast amounts of inorganic waste. [2] Improved methods using recyclable Ir nanoparticles [4] under 0.4 MPa of H 2 at 75 8C or Rh nanoparticles [5] under atmospheric H 2 pressure at room temperature have recently been reported. Hydrogenation using heterogeneous catalysts possessing a transition metal, such as Ru, Rh, Pd, and Pt, has been used for both the industrial and laboratory scale reduction of ketones because of the advantages of easy separation from the reaction mixture, recyclability, and low cost performance.…”

“…Aliphatic ketones are quite stable under the hydrogenation conditions, and the reduction often requires strong conditions, such as acid or base treatment, elevated temperature and/or high H 2 pressure, to obtain the hydrogenated secondary alcohols. [2] Improved methods using recyclable Ir nanoparticles [4] under 0.4 MPa of H 2 at 75 8C or Rh nanoparticles [5] under atmospheric H 2 pressure at room temperature have recently been reported. The use of supported silica heterogeneous catalysts, such as Ru-Sn-B/SiO 2 , [6] Si-S-Pt, [7] and silica-SMAP-[Rh(cod)(OMe)] [8] (SMAP = silicon-constrained monodentate trialkylphosphine, COD = 1,5-cyclooctadiene, OMe = methoxy), as well as sodium hydride containing a nickel salt [NaH-NaOtAm-Ni(OAc) 2 ] (NaOtAm = sodium 2-methyl-2-butoxide, OAc = acetate), [9] afforded an efficient hydrogenation under atmospheric H 2 pressure at room temperature.…”