Leaching homogeneous

A third technique that has been used to study colloidal nanocatalysis is the Colhnan test or the 3-Phase Test [16]. One reactant is chemically bound to a solid support (Phase 1) and the catalyst is chemically bound to a second solid support (Phase 2). Phases 1 and 2 are suspended in solution (Phase 3), into which a second reactant is also dissolved (not substrate bound). Direct contact between Phase 1 and Phase 2 is restricted due to the fact they are both substrate bound. If the heterogeneous catalyst in Phase 2 is required for the reaction to proceed there will not be any product formation. If the heterogeneous catalyst (Phase 2) leaches homogeneous complexes into solution (Phase 3), the reaction will proceed and in this way the nature of the active catalyst can be investigated. However, there are limitations to this experimental setup since the formation of products does not rule out heterogeneous catalysis. The formation of secondary particles from leached species is possible, so at best, this test supplies evidence for atomic leaching. 

Reaction experiments were performed at the substrate to catalyst ratios between 250 and 5000 (Table 1). The immobilized catalyst showed a rather constant values of TOP and enantioselectivity in spite of the increase in the S/C ratio, even though these values were slightly lower than those of the homogeneous Ru-BINAP catalyst. After the reaction, the Ru content in the reaction mixture was measured by ICP-AES and was found to be under 2 ppm, the detecting limit of the instrument, indicating the at Ru metal didn t leach significantly during the reaction. These results show that the immobilized Ru-BINAP catalyst had stable activity and enantioselectivity and that the Ru metal complex formed a stable species on the alumina support. 

Particular attention was given to the question of whether the catalysis with these systems is homogeneous or heterogeneous. It was found that the nature of the functional groups bound to the polymer backbone affects the rate and the extent of metal leaching, which also... 

Fig. 2.43. Graphical illustration of sulfur isotope values of HiS (left axis and. solid line) produced during basalt-seawater interaction at various water/rock ratios. Calculations assume that seawater sulfate is mostly removed as anhydrite, that any residual sulfate is reduced by iron oxidation in reacting basalt, and that there is quantitative leaching of basaltic sulfide and homogeneous mixing of both sulfides. Dashed line...

Waters Seawater (National Research Council Canada 1992) was collected in the North Atlantic Ocean at a depth of 10 m, 35 km southeast of Hahfax, Nova Scotia, Canada. The water was peristaltically pumped through cleaned polyethylene-hned ethyl vinyl acetate tubing and 0.45-pm acrylic copolymer filters. It was acidified to pH 1.6 with ultrapure nitric acid during its immediate transfer to 50-L acid-leached polypropylene carboys, previously conditioned with ultrapure water acidified to pH 1.6. The seawater was later homogenized in two linked 800-L polyethylene tanks in a clean room and immediately bottled in cleaned 2-L polyethylene bottles. Randomly selected bottles were used for analytical measurements. 

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