The development of enantioselective catalytic processes that make use of sunlight as the energy source and nontoxic, affordable materials as catalysts represents one of the new and rapidly evolving areas in chemical research. The direct asymmetric α-alkylation of aldehydes with α-bromocarbonyl compounds can be successfully achieved by combining bismuth-based materials as low-band-gap photocatalysts with the second-generation MacMillan imidazolidinone as the chiral catalyst and simulated sunlight as a low-cost and clean energy source. This reaction also proceeded with high efficiency when the reaction vial was exposed to the morning sunlight on a clear September day in Tarragona, Spain.
The fabrication of highly luminescent, chemically stable and biocompatible small optical probes is of key interest in bioimaging. Herein we develop a multistep synthesis of hybrid superstructures that comprise quantum dot cores and dense layers of gold nanoparticles separated by a silica shell. This architecture allows for the versatile control of the QD-metal interactions by controlling the thickness of the dielectric spacer. The shell
The development of enantioselective catalytic processes that make use of sunlight as the energy source and nontoxic, affordable materials as catalysts represents one of the new and rapidly evolving areas in chemical research. The direct asymmetric a-alkylation of aldehydes with a-bromocarbonyl compounds can be successfully achieved by combining bismuth-based materials as low-band-gap photocatalysts with the second-generation MacMillan imidazolidinone as the chiral catalyst and simulated sunlight as a low-cost and clean energy source. This reaction also proceeded with high efficiency when the reaction vial was exposed to the morning sunlight on a clear September day in Tarragona, Spain.Chemical transformations that are promoted by sunlight are currently the subject of intense research. [1] Photocatalytic methods have shown promising potential for bulk production and are widely accepted and popular as convenient strategies in the area of asymmetric catalysis. [2] In a pioneering effort, MacMillan and co-workers merged organo-and photoredox catalysis to promote the direct asymmetric a-alkylation of aldehydes [3] through a process catalyzed by [Ru(bpy) 3 ] 2+ . [4] Since then, much effort has been devoted to the development of more convenient reaction conditions and to the extension of this combined approach to other key asymmetric organic transformations. [5] In view of the future, substantial use of such reactions, the "Achilles heel" of these methods is their dependence on ruthenium. This is a scarce and expensive metal with rather low production (ca. twelve tons of ruthenium are mined every year) and very limited estimated world reserves (5000 tons). Furthermore, ruthenium compounds are highly toxic and suspected carcinogens. For these reasons, the identification of more convenient visible-light photocatalysts that are suitable for singly occupied molecular orbital (SOMO) activation [6] has become an area of intense
This paper reports the characteristics of ferrochrome slag and its feasibility as aggregate in refractories aiming to substitute virgin refractory raw materials. Refractory castable specimens were formulated with ferrochrome slag as an aggregate and commercial calcium aluminate cement as a binder. Objective was to prepare refractory specimens with a maximum slag utilization but simultaneously to sustain good properties, comparable to those of virgin raw material refractory products. Mechanical and thermo-physical properties of the cured, dried and sintered specimens were characterized. Cold crushing strengths of best performing ferrochrome slag containing specimens were higher than 90 MPa and compressive strength values measured at 1200 °C were over 9 MPa. Thermal insulation properties were even better than those of commercial refractory reference, showing thermal conductivity values as low as λRT−1000 °C = 1.3 − 0.9 W/m K. The liquid phase formation above 1200 °C limits the ferrochrome slag use for refractory applications. Results suggest ferrochrome slag’s feasibility as an aggregate raw material for refractory materials up to temperatures of 1200 °C in air and up to temperatures of 700 °C in acidic gaseous atmosphere. Possible applications for this kind of novel refractory materials are, e.g., insulating secondary layers or bottom zones in metallurgical processes to substitute virgin refractories. A direct contact to molten metal must be avoided, but they are applicable as, e.g. floorings when exposed only to occasional melt droplets.
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