Aluminas, active, synthesis precipitation

In a case of synthesis of PBA homopolymer, the polymerization was carried out at 70 °C. DMDBrHD (56.6 pL, 0.26 mmol), PMDETA (54.4 pL, 0.26 mmol), BA (11 mL, 78 mmol), and anisole (1.1 rtiL) were added to a 25-mL Schlenk flask eqtripped with a magnetic stir bar. The flask was sealed, and the resulting solution was subjected to three freeze-pump-thaw cycles. After equilibration at room temperatrrre, CuBr (37.3 mg, 0.26 mmol) was added to the solution tmder nitrogen flow and the flask was placed in preheated oil bath. Aliquots were removed by syringe in order to monitor molectrlar weight evolution. After a predetermined time, the flask was removed from the oil bath and opened to expose the catalyst to air. The polymerization solution was diluted with CHCI3 and passed over an alumina (activated neutral) coltrrrm to remove the catalyst. Solvent was removed by rotary evaporation, and the polymer was isolated by precipitation into cold methanol. 

Besides supported (transition) metal catalysts, structure sensitivity can also be observed with bare (oxidic) support materials, too. In 2003, Hinrichsen et al. [39] investigated methanol synthesis at 30 bar and 300 °C over differently prepared zinc oxides, namely by precipitation, coprecipitation with alumina, and thermolysis of zinc siloxide precursor. Particle sizes, as determined by N2 physisorpt-ion and XRD, varied from 261 nm for a commercial material to 7.0 nm for the thermolytically obtained material. Plotting the areal rates against BET surface areas (Figure 3) reveals enhanced activity for the low surface area zinc... 

A parameter that determines the performances, as outlined also in patents, is the mean diameter of Pd or doped-Pd particles. This is also one of the claims in Headwaters Nanokinetix Inc. patents. It seems that a maximum in the activity/ selectivity as a function of the particle size is present. Figure 8.11 reports the effect of the Pd-particle size (Pd supported on alumina, prepared by deposition-precipitation method) in the direct synthesis of H202 in water at atmospheric pressure [77]. Low... 

Advances in pore structure control of the porous active aluminas have resulted in major improvements in commercial adsorbents. Zeolites have their pore structures determined simultaneously with the precipitation process and are constrained in size by the configuration of the sodalite cage. In contrast, active alumina porosity is relatively independent of the bulk phase formation process and is usually engineered following material synthesis. Microporosity is controlled via kinetics of the dehydroxylation process, whereas macroporosity is usually developed in the agglomeration process. 

Synthesis of DNP-Alanyl Diazoketone. DNP-Alanyl acid chloride (40 mg) is made up to 100 ml with anhydrous diethyl ether at 0° and added slowly to 10 ml of dry ether containing 0.01 mole of diazomethane at 0°. (For preparation of ethereal diazomethane, see deBoer and Backer. ) The resulting mixture is stored in a moisture-proof container in the dark at 4° for 12 hr. During large-scale preparations, the DNP-AD is precipitated from the ether solution and washed with ether at 4°. For small-scale synthesis of [ H]DNP-AD, the product is purified on a basic alumina (Brockman activity I) column, 1 X 15 cm, which is eluted with dry dioxane. Ultraviolet absorption Xmax was at 255 and 342 nm IR spectra gave a 2115 cm diazo stretch band. Mass spectroscopy gave no molecular ion, but two major peaks at m/e 210 and 69 were consistent with the two halves (DNP-NH CH CHs) and (0=CCH=N=N) ... 

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