Preparation And Catalysis Of Supported Nano-platinum Catalysts

MgAl₂O₄, Al₂O₃ and CeO₂ were synthesized and used as carriers for preparing a series of supported nano-platinum catalysts. Then the catalysts were applied in hydrogenation of benzaldehydes. Some corresponding researches were done as follows:(1) Platinum nanoparticles, synthesized via ethanol reduction of hexachloroplatinic acid in the presence of poly-(N-vinyl-2-pyrrolidone), were anchored on magnesium aluminate spinel using a colloidal deposition method. The samples were characterized using the following methods: transmission electron microscopy, powder X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The results revealed that platinum nanoparticles, with an average diameter of 2.8 nm, are homogenously dispersed on the surface of the carrier. Under very mild conditions, supported Pt/MgAl₂O₄ catalysts demonstrated excellent catalytic activity and high selectivity in the hydrogenation reaction of benzaldehydes to benzyl alcohols. The reaction kinetics for the catalytic hydrogenation of 3-phenoxybenzaldehyde to 3-phenoxybenzyl alcohol on a Pt/MgAl₂O₄ catalyst can be described by equation r = k. c. pH, and the apparent activation energy is 35.6 kJ mol-1.(2) Rare earths (La, Ce, Pr, Nd, Sm, Eu and Gd) promoted Pt/Al₂O₃ catalysts were synthesized by two methods. The in?uence of the preparation method and the dopants on the activity and stability of the catalysts were investigated. Transmission electron microscopy, powder X-ray diffraction and X-ray photoelectron spectroscopy were used to observe the characteristics of the prepared catalysts. The results reveal the beneficial role of La, Ce, Pr, Nd and Sm doping in increasing catalytic activity of hydrogenation of 3-phenoxybenzaldehyde, while the addition of Gd and Eu exhibited a negative effect. The main reason for the differences in 3-phenoxybenzaldehyde hydrogenation activity of these platinum catalysts depends on the nature of the modifier.(3) Cerium oxide nanoparticles and nanosized rod-shaped CeO₂ and microsized spherical CeO₂ structures have been synthesized by a one-pot, template-free hydrothermal method. The samples were characterized using the following methods: scanning electron microscopy, powder X-ray diffraction, and nitrogen adsorption-desorption measurements. CeO₂ products of different morphologies and specific surface area can be selectively produced. Furthermore, the applications of the CeO₂ as carriers were explored. 0.5 wt% Pt nanoparticles loaded on CeO₂(I) exhibited highest catalytic activity on hydrogenation of 3-phenoxybenzaldehyde.