Fabrication of a form- and size-variable microcellular-polymer-stabilized metal nanocomposite using supercritical foamin

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Fabrication of a form- and size-variable microcellular-polymer-stabilized metal nanocomposite using supercritical foaming and impregnation for catalytic hydrogenation Weisheng Liao1, Ben-Zen Wu1, Hungchi Nian1, Hsiang-Yu Chen2, Jya-Jyun Yu3 and KongHwa Chiu1*

Abstract This article presents the fabrication of size-controllable and shape-flexible microcellular high-density polyethylenestabilized palladium nanoparticles (Pd/m-HDPE) using supercritical foaming, followed by supercritical impregnation. These nanomaterials are investigated for use as heterogeneous hydrogenation catalysts of biphenyls in supercritical carbon dioxide with no significant surface and inner mass transfer resistance. The morphology of the Pd/m-HDPE is examined using scanning electron microscopy images of the pores inside Pd/m-HDPE catalysts and transmission electron microscopy images of the Pd particles confined in an HDPE structure. This nanocomposite simplifies industrial design and operation. These Pd/m-HDPE catalysts can be recycled easily and reused without complex recovery and cleaning procedures. Keywords: Nanoparticle, Heterogeneous catalysis, Supercritical fluids, Foaming, Impregnation

Background Nanotechnology has resulted in research that examines a scale of matter typically between 1 and 100 nm wherein properties are dependent on the size and form. The greater surface area per mass compared with larger particles with identical chemical composition makes nanomaterials an excellent catalyst and also makes them more biologically active. When examining possible exposure routes for manufactured nanoparticles or during their production and inhalation, oral and dermal exposure are the most obvious, depending on the type of product in which nanoparticles are used. Hence, the development of green methods for the fabrication of nanomaterials has become increasingly relevant as chemists look to shape a more sustainable future. Heterogeneous catalytic hydrogenation in supercritical fluids, especially in supercritical carbon dioxide (scCO2), has recently become an active research area because of its advantages over conventional organic* Correspondence: [email protected] 1 Department of Chemistry, National DongHwa University, Shoufeng, Hualien 97401, Taiwan Full list of author information is available at the end of the article

solvent-based systems. Sc-CO2 has proven to be an effective solvent for a wide range of homogeneous transition-metal-catalyzed reactions. The readily achievable critical point of sc-CO2 (Tc = 31.1 °C, Pc = 73.7 bar) is one of its many advantages, which also include its low cost, low toxicity, no flammability, and the ability to tune the reactive properties by small variations, i.e., variation in temperature or pressure in the sc-CO2 density [1]. Their advantages also include enhanced mass and heat transfer, adjustable salvation ability, total H2 miscibility, elimination of the gas/liquid interface, extended catalyst lifetime, ease of separation from products, and minimal organic solvent wast