Facile Synthesis of Size-controlled Rh Nanoparticles via Microwave-assisted Alcohol Reduction and Their Catalysis of CO Oxidation

Abstract

Size-controlled Rh nanoparticles stabilized by poly(vinylpyrrolidone) were quickly synthesized via alcohol reduction. Microwave-assisted synthesis in closed vessels allowed alcohols with low-to-high boiling points to be used as reductants under the same preparation conditions. Pure ethanol has not been used previously because its boiling point is lower than the temperature required for Rh 3+ reduction. Alcohols with relatively strong reduction ability were found to lead to smaller Rh nanoparticles. The ability to oxidize CO was enhanced as the Rh particle size decreased. additives, 10 pH, 11 and preparation temperature. 12 In this method, high-boiling-point alcohols such as polyols are often used to reduce metal cations in the presence of polymers that inhibit aggregation of the nanoparticles and stabilize metals in colloids because the boiling points of the polyols are higher than the temperatures required to reduce the metal cations. In contrast, the boiling points of monovalent alcohol including a small number of carbon such as ethanol are lower than the temperatures required to reduce metal cations such as Ru 3+ , Rh 3+, and Pd 2+ . To enable the use of low-boiling-point alcohols, the alcohols are mixed with water to increase the boiling point, and reduction is performed under reflux 13 or solvothermal 6 conditions. On the other hand, heating the alcohols with a conventional electric heater is slow and produces heterogeneous temperatures; thus, it takes a long time to prepare nanoparticles, and nanometals with a wide particle-size distribution are obtained. 14 Furthermore, because of differences in the equipment and physicochemical properties of the alcohol, the influence of the reduction ability of low-and high-boiling-point alcohols on the synthesis of nanoparticles has not been investigated under the same preparation conditions.In this study, we prepared Rh nanoparticles using different kinds of alcohols, including low-and high-boiling-point alcohols, as reductants under the same preparation conditions. The experimental design was enabled by using a microwaveassisted alcohol reduction method in a closed vessel, in which rapid and homogeneous heating and solvothermal conditions were achieved. We were thereby able to easily synthesize sizecontrolled Rh nanoparticles within 20min under the same preparation conditions. The average diameters of the nanoparticles, stabilized in poly(vinylpyrrolidone) (PVP), were 3.3 10.9 nm. The amount of PVP, a crucial determinant of catalytic activity, varied over a small range (72.384.1 wt %). 15 We discovered that the Rh particle size was dependent on the reduction ability of the alcohol. We also studied the particle size dependence of the CO oxidation ability of the Rh nanoparticles, because Rh is known to be an excellent catalyst for the oxidation of CO in car exhaust gas.Rh nanoparticles with different sizes were prepared by microwave-assisted alcohol reduction. Initially, RhCl 3 ¢3H 2 O as the metal precursor and PVP as the stabilizer were dissolved in either ethanol, e...

Nanocatalysis by noble metal nanoparticles: controlled synthesis for the optimization and understanding of activities

“…5F) as reducing agents and PVP as the stabilizer. 90 Polyalcohols with higher reduction potentials led to the formation of smaller Rh nanomaterials because of faster precursor reduction rate. 17 Aer incorporation of the obtained Rh nanomaterials (1 wt% Rh basis) onto g-Al 2 O 3 support by a wetimpregnation method, their catalytic activities were investigated in the CO oxidation reaction as a function of size.…”

Preparation of Noble-metal Nanoparticles by Microwave-assisted Chemical Reduction and Evaluation as Catalysts for Nitrile Hydrogenation under Ambient Conditions

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“…The present study investigated five Rh samples with different particle sizes to elucidate the effect of particle size in more detail. Rh samples with different particle sizes were obtained simply by changing the alcohol reductant 11) . The use of stronger reductants (i.e., alcohols that are readily oxidized at low potential in linear sweep voltammetry, Fig.…”

“…Recently, we reported a method for simple, rapid preparation of Rh nanoparticles with controlled size via microwave-assisted chemical reduction with alcohol 11) . The alcohol acts as both reductant and solvent, and is very important in modifying the Rh particle size.…”

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