P. Petrova

Gold catalysts on ceria doped with MeOx (Me = Fe, Mn, Co and Sn) for complete benzene oxidation: effect of composition and structure of the mixed supports

Gold catalysts supported on ceria doped with different metal oxides (Fe, Mn, Co and Sn) were synthesized using two techniques: CP and mechanochemical activation. The catalytic activity in complete benzene oxidation (CBO) was studied. The samples were characterized by means of XRD and high resolution transmission electron microscopy, and non-significant differences in the average size and the distribution of gold particles were observed. This means that the main reason for the different catalytic behavior in CBO has to be searched in the composition and structure of the supports. In spite of the higher hydrogen consumption (e.g., higher oxygen mobility) estimated by means of TPR, the gold catalysts on ceria doped with transition metal oxides generally are less active than gold/ceria catalyst. This observation could be explained taking into consideration that the key factor for the high oxidation activity is not the oxygen supplying but the activation of the very stable benzene molecule. The higher catalytic activity in comparison with that of the gold/ceria catalyst was observed only using a mixed ceria–CoOx support mechanochemically prepared. Very high and stable catalytic activity in CBO was obtained over this sample.

Effect of the preparation method on the reduction behavior of gold catalysts supported on ceria doped with FeOx: assignment and kinetic parameters of the individual reduction processes

Gold catalysts supported on ceria doped with FeOx were studied. The mixed supports were synthesized by two methods: co-precipitation (CP) or mechanochemical activation (MA). Depending on the preparation method, the structure of the mixed supports was different: using CP, only a Fe-modified ceria phase exists, while supplementary to ceria, a second hematite phase presents in the case of MA preparation. The reduction behavior of the gold catalysts and the initial supports was commented on the basis of hydrogen consumption and kinetic parameters of the individual reduction process. Their assignment was proposed using also the data of Mössbauer measurements. It was established that the existing separate Fe-containing phase could participate in a redox process at relatively low temperatures (LTs) and it could be promising for improvement of the catalytic performance of the mechanochemically prepared gold catalyst.

Discussion on Practical Elimination of Early or Large Releases for WWER-1000/V320

The paper presents a brief summary of the introduction of the term “practical elimination” as prevention of the conditions that could lead to early or large radioactive releases. The concept of “practical elimination” is defined as part of the Defence in Depth (DiD) of Nuclear Power Plant (NPP) in the International Atomic Energy Agency (IAEA) document INSAG-12 in 1999. But, the special attention to it was paid after the accident in Fukushima NPP in 2011. The mechanisms of the containment failure of reactor WWER-1000/V320 are presented. As an example, the summarized design features and preventing and mitigation measures already implemented at Kozloduy NPP to extend the design basis and beyond design basis envelop are presented. Issues related to external steam explosion are underlined for further study.