A statistical Plackett-Burman design of the thermal process in the synthesis of the Bi-2223 HTSC

In this study, the most significant parameters in the thermal process for the preparation of high-quality Bi-2223 HTSCs are determined using a statistical Plackett-Burman screening design. This enabled us to obtain a quick and objective evaluation, where the significant parameters could be unambiguously defined, accounting for interactions with other parameters. Using the optimal conditions of the thermal process and starting from a spray dried nitrate solution with nominal composition Bi:Pb:Sr:Ca:Cu = 1.5:0.5:2:3:4, a more than 96% pure Bi-2223 phase (relative to the Bi-2212 phase) could be synthesized in a minimal thermal process of 5 h calcination at 650 degrees C and 60 h sintering at 855 degrees C

Generation of singlet molecular oxygen from H2O2 with molybdate-exchanged layered double hydroxides: effects of catalyst composition and reactions conditions

(Mg, Al)-layered double hydroxides (LDHs) with different Mg/Al ratios in the octahedral layer were prepared via the coprecipitation method and were exchanged with varying amounts of molybdate. The composition of the LDH supports and the state of the molybdate in these materials were studied with X-ray diffractometry, X-ray photoelectron spectroscopy and Raman. As was proven by NIR luminescence, aqueous H2O2 is converted at the surface of these catalysts into excited, singlet molecular dioxygen (1O2). The singlet dioxygen diffuses away from the 1O2 generating centers and can perform selective oxygenations, such as endoperoxidations of dienes, or hydroperoxidations of olefins. Catalyst composition and reaction conditions (temperature, solvent) have major effects on the catalyzed 1O2 generation and the subsequent substrate oxygenation. In order to maximize the efficiency of the H2O2 use and to limit the epoxidation side reaction, it is advisable to limit the amount of exchanged molybdate to 0.2 mmol per g and to use an LDH with Mg0.9Al0.1 composition in the octahedral layer. The latter material provides the optimum basicity for the catalytic activity of the exchanged molybdate.SCOPUS: ar.jinfo:eu-repo/semantics/publishe