Continuous Enantioselective Hydrogenation with a Molecular Catalyst in Supported Ionic Liquid Phase under Supercritical CO2 Flow
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Highly efficient continuous-flow asymmetric catalysis was achieved by combination of supported ionic liquid phase (SILP) catalysts with supercritical CO2 (scCO2) as the mobile phase, as demonstrated for enantioselective hydrogenation in the presence of a molecular rhodium–QUINAPHOS complex. The integrated reaction and separation process yielded chemically and enantiomerically pure products without the need for organic solvents. Detailed facts of importance to specialist readers are published as "Supporting Information". Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.The infrared spectra of the CO/Rh/Al2O3 system have been examined following several different means of preparing the supported rhodium catalyst. Rhodium precursor materials including RhCl3 ⋅ 3H2O, Rh(NO3)3 ⋅ 2H2O, Rh6(CO)16, [Rh(OCOCH3)2]2, and Rh2(SO4)3 have been compared as to their tendencies to produce upon reduction the various CO/Rh/Al2O3 species generally attributed to this catalytic system. The nitrate and carbonyl precursors are most easily reduced to rhodium metal. The acetate and sulfate anions poison the Rh/Al2O3 surface through decomposition during reduction leading to very minimal CO adsorption. The catalytic properties of Rh/Al2O3 could be quite dependent upon the nature of rhodium precursor chosen.
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Rhodium has been known for the good catalytic capability due to its unique electronic structure, and rhodium-based catalysts are used in the fields of environmental protection, petrochemical processing, fine chemical industry, biopharmaceutical, etc. The catalytic efficiency of rhodium catalysts is affected directly by rhodium content. As a result, accurate determination of the rhodium content is especially important. Methods for the determination of rhodium in rhodium catalysts of different types and varied contents are reviewed in the present paper.
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The influence of the support type and the metal precursor on the dispersion of rhodium after calcination and reduction was determined. The combination of electron microscopy and X-ray absorption analysis allowed the quantification of the amount of atomically dispersed rhodium in the samples. Higher amounts of atomically dispersed rhodium atoms are obtained when metal impregnation is performed with a rhodium acetate precursor in comparison to a rhodium chloride precursor over supports of the same composition. The stability of rhodium is improved with the addition of promoters; the co-presence of samaria and ceria in the support and metal impregnation with a rhodium acetate precursor leads to the highest amount of atomically dispersed rhodium remaining after reductive treatment at 773 K.
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Rhodium is one of the most insoluble platinum group metals,but rhodium dissolution is an indispensable key link in the extraction and application of rhodium.Research shows that rhodium particle size has a direct effect on rhodium dissolution.The effect of rhodium powder particle size and surface state on the dissolution of rhodium was studied.The experimental results show that,the dissolution rate of rhodium powders is negatively correlated with the particle size,rhodium powders of ≥ 100 μm are substantially insoluble,the rhodium powders of ≤ 10 μm have very high dissolution rate.EDX analysis results show that there is no oxidation formation on the surface of the dissolved rhodium powders by aqua regia,the slightly soluble phenomenon occurred at rhodium powder dissolved,due to small particles rhodium is firstly dissolved in rhodium powder,when the small particles rhodium powder has dissolved,the remaining large particles of rhodium powder insoluble.
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Abstract Der quadratisch‐planare Titelkomplex wurde mit 50% Ausb. durch Reaktion von Dichloro‐tetracarbonyldirhodium mit dem Liganden in EtOH dargestellt.
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