Shaken, not stirred: CO oxidation was carried out continuously in a shaker ball mill. During milling, the reaction rate increases dramatically, but drops rapidly to zero when the mill is stopped. Compared to a conventional experiment in a plug‐flow reactor, the rate of a ball‐mill reaction catalyzed by Cr2O3 is three orders of magnitude higher at room temperature and one order of magnitude higher at 100°C.
Supported catalysts are among the most important classes of catalysts.T hey are typically prepared by wetchemical methods,s uch as impregnation or co-precipitation. Here we disclose that dry ball milling of macroscopic metal powder in the presence of asupport oxide leads in many cases to supported catalysts with particles in the nanometer size range.V arious supports,i ncluding TiO 2 ,A l 2 O 3 ,F e 2 O 3 ,a nd Co 3 O 4 ,a nd different metals,s uch as Au,P t, Ag,C u, and Ni, were studied, and for eacho ft he supports and the metals, highly dispersed nanoparticles on supports could be prepared. The supported catalysts were tested in CO oxidation, where they showed activities in the same range as conventionally prepared catalysts.T he method thus provides as imple and cost-effective alternative to the conventionally used impregnation methods.
Mechanochemical activation of solids can lead to a strong increase in their activity as catalysts in heterogeneously catalyzed reactions. In the following, we report on the effects of solid catalyst activation during ball milling that lead to oscillatory behavior in CO and CO 2 formation during propene oxidation. The oscillations arise under in situ ball milling conditions over chromium(III) oxide (Cr 2 O 3 ) and cerium(IV) oxide (CeO 2 ), respectively. The experiments were conducted under continuous gas flow at ambient pressure and temperature, using both a modified steel and a tungsten carbide milling vessel. Abrasion of particles from the steel milling vessel could be eliminated as the sole cause for the oscillations through substitution by a tungsten carbide milling vessel. The intensity and frequency of oscillations are shown to be dependent on the propene-to-oxygen ratio, the milling frequency, milling ball size and metal oxide used. Overall, Cr 2 O 3 shows higher activity for oscillatory propene combustion under in situ mechanical activation than CeO 2 .
This article describes the development of an effective thermomorphic multicomponent solvent (TMS) system for the production of branched polyamide monomers. In this system, methyl oleate, a renewable from fats and oils, and a functionalized amine are used as starting materials in a tandem catalytic reaction, which merges different reaction steps into a single preparative step. This particular TMS system consisted of a heptane/acetonitrile solvent mixture and made reusing the precious rhodium catalyst possible in three recycle runs. A constant yield of 61–65% was obtained for each run due to low‐catalyst leaching. Fortunately, the catalyst system does not require any additional phosphorous ligands and allows high yields. A scale‐up for the production of 10–11 g of the desired product in each run was realized. Subsequent hydrogenation of the product directly provided an amine ester, which is a valuable polyamide monomer.
Practical applications: A method was developed to enable access to primary amines via hydroaminomethylation and hydrogenation. The product, a nitrile ester, is a valuable intermediate for polyamide monomers. This nitrile ester was successfully hydrogenated to an amine ester, which features a potential polyamide monomer directly. A catalyst recycle of the homogeneous rhodium complex within the hydroaminomethylation of methyl oleate and an amino nitrile was successfully carried out, enabling constant homogeneous catalyst activity over the course of three recycle runs. A scale‐up to obtain 10–11 g of the hydroaminomethylation product was realized.
A general method is described for the conversion of methyl oleate within a hydroaminomethylation reaction. The catalyst can be recovered and reused. Valuable polyamide intermediates were obtained.
Geschüttelt, nicht gerührt: Kohlenmonoxid wurde in einer Kugelmühle kontinuierlich oxidiert. Beim Mahlen wird die Reaktionsgeschwindigkeit deutlich erhöht, diese sinkt jedoch schnell gegen null, wenn der Mahlvorgang gestoppt wird. Die Reaktionsgeschwindigkeit der Cr2O3‐katalysierten Reaktion in der Kugelmühle ist bei Raumtemperatur drei Größenordnungen und bei 100 °C eine Größenordnung höher als bei vergleichbaren Experimenten in einem Plug‐Flow‐Reaktor.
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