Spinel Iron Oxide by the Co-Precipitation Method: Effect of the Reaction Atmosphere

Synthesis atmosphere (i.e., air and nitrogen) effects on the physical properties and formation mechanism of spinel iron oxide nanoparticles prepared via the co-precipitation method have been investigated using a multi-technique approach. The obtained magnetic nanoparticles (MNPs) were characterized using the X-ray diffraction, transmission electron microscopy (TEM), SQUID magnetometry, Mössbauer spectroscopy and X-ray absorption near-edge Structure spectroscopy techniques. The synthesis procedure leads to the formation of a spinel structure with an average crystallite size of 9.0(9) nm. The morphology of the particles synthetized under an inert atmosphere was quasi-spherical, while the nanoparticles prepared in air present a faceted shape. The small differences observed in morphological properties are explained by the influence of the reaction atmosphere on the formation mechanism of the MNPs. The magnetic characterization indicates that both samples exhibit superparamagnetic behavior at 300 K. The investigation by means of the Langevin approach at 300 K also leads to equal values for the mean size of the magnetic cores (Dm). Additionally, the analysis of the Mössbauer spectra revealed the lack of spin disorder for both samples, resulting in a high saturation magnetization. The fit of XANES spectrum suggests that about 2/3 of the iron ions reside in a local environment close to that of γ-Fe2O3 and about 1/3 close to that of Fe3O4 for the sample synthetized in inert atmosphere.

AN IR AND FLOW REACTOR STUDY OF CHLOROFORM OXIDATION OVER MANGANESE OXIDES

A series of manganese base oxides (MnCe, MnZr and MnCeZr) obtained by co-precipitation, were characterized by SBET, XRD, TPR, XPS and studiedby FTIR in the oxidation reaction of a typical Cl-VOC such as chloroform, CHCl3. The oxides were compared with a manganeseoxide obtained from the recycling of spent batteries (MnOx). In addition, the catalytic combustion of CHCl3 in a fixed-bed reactor was analyzed and the CHCl3 conversion decreased in the order: MnZr > MnOx = MnCeZr >MnCe. In all cases, the conversion is higher than that obtained without a catalyst. The surface Mn4+/Mn3+ ratio would favor the decomposition of Cl-VOC. The study of CHCl3 reaction atmosphere by in situ IR reveals that in the absence of catalysts, CCl4, COCl2, C2Cl4 and CH2Cl2 were observed. On the other hand, C2Cl4 is not formed in the presence of catalysts, although CCl4 and CH2Cl2 were observed and must be avoided

CO2-tuned highly selective reduction of formamides to the corresponding methylamines

An efficient, CO2-tuned and highly selective C–O bond cleavage of N-methylated formanilides with NaBH4 has been achieved. Notably, when using N2 as reaction atmosphere, the reaction gave N-methylaniline as major product via C–N bond hydrogenolysis.

Controllable chemoselectivity in the reaction of 2H-indazoles with alcohols under visible-light irradiation: Synthesis of C3-alkoxylated 2H-indazoles and ortho-alkoxycarbonylated azobenzenes

A high chemoselectivity of visible-light-induced reaction of 2H-indazoles with alcohols controlled by the reaction atmosphere (N2 or O2) was developed. Under N2 atmosphere, an alkoxylation of 2H-indazoles with alcohols in...

Comparison of novel Ni doped exsolution perovskites as methane dry reforming catalysts

Three perovskite-type materials with a different amount of B-site Ni doping have been tested for their catalytic performance during me-thane dry reforming (MDR) followed by characterization with X-ray dif-fraction (XRD) and scanning electron microscopy (SEM). They could be activated via a reductive treatment (either during a pre-reduction step or di-rectly in reducing reaction atmosphere), the main activating mechanism be-ing the formation of Ni nanoparticles on the surface by exsolution. The catalytic activity increased with the particle size and density. The particle distribution properties could be improved by increasing the amount of Ni doping from 3 % to 10 %, by using an A-site sub-stoichiometric perovskite and by choosing a higher annealing temperature during material prepara-tion. A deactivation over time was observed, due to segregation of CaCO3 on the surface, but no coking or particle sintering occurred