The Catalytic Performance of CO Oxidation over MnOx-ZrO₂ Catalysts: The Role of Synthetic Routes

MnOx-ZrO2 catalysts prepared by co-precipitation and vacuum impregnation were calcined at 400–800 °C and characterized by powder X-ray diffraction, textural studies, high-resolution transmission electron microscopy, temperature-programmed reduction, X-ray absorption near edge structure, and X-ray photoelectron spectroscopy. The catalytic activity was tested in the CO oxidation reaction. The activity of the co-precipitated samples exceeds that of the catalysts prepared by vacuum impregnation. The characterization studies showed that the nature of the active component for the catalysts obtained by co-precipitation differs from that of the catalysts obtained by impregnation. In the impregnation series, the most active catalyst was obtained at a temperature of 400 °C; its increased activity is due to the formation of MnO2 oxide nanoparticles containing Mn4+ and low-temperature reducibility. An increase in the synthesis temperature leads to the formation of less active Mn2O3, catalyst sintering, and, accordingly, deterioration of the catalytic properties. In the case of co-precipitation, the most active CO oxidation catalysts are formed by calcination at 650–700 °C in air. In this temperature interval, on the one hand, a MnyZr1−yO2−x solid solution is formed, and on the other hand, a partial separation of mixed oxide begins with the formation of highly dispersed and active MnOx. A further increase in temperature to 800 °C leads to complete decomposition of the solid solution, the release of manganese cations into Mn3O4, and a drop in catalytic activity

The Formation of Mn-Ce-Zr Oxide Catalysts for CO and Propane Oxidation: The Role of Element Content Ratio

The MnOх-ZrO2-CeO2 oxide catalysts were synthesized by co-precipitation method with varying (1) Zr/Zr + Ce molar ratio at constant manganese content of 0.3; (2) manganese content at constant Zr/Ce molar ratio of 1; (3) Mn/Mn + Zr molar ratio at constant Ce content of 0.5. Catalysts are characterized by XRD, N2 adsorption, TPR, and XPS. The catalytic activity of all the series was tested in the CO and propane oxidation reactions. In contrast to the variation of the manganese content, the Zr/Zr + Ce molar ratio does not significantly affect the catalytic properties. The dependence of the catalytic activity in CO oxidation on the manganese content has a «volcano» shape, and the best catalytic performance is exhibited by the catalyst with Mn/(Zr + Ce) = 1. In the case of propane oxidation reaction, there is «sigma» like dependence, activity increases with increase of Mn/(Mn + Zr + Ce) molar ratio up to 0.3, stabilizing with a further increase in the manganese content. XRD and XPS have shown that with an increase of the Mn concentration in the MnOx-ZrO2-CeO2 catalysts, the amount of crystalline manganese oxides such as Mn2O3 and Mn3O4, as well as the surface concentration of Mn cations, increases. While the content of MnxZryCe1-x-yO2 solid solution decreases, the concentration of manganese cations (x) in volume of MnxZryCe1-x-yO2 mixed oxide grows. The maximum activity in CO oxidation corresponds to the balance between the amount of the solid solution and the concentration of manganese cations in the volume of mixed oxide. The propane oxidation reaction is less sensitive to the state of manganese ion rather than to its amount. In this case, a decrease in the content of the MnxZryCe1-x-yO2 solid solution with increase in manganese amount in catalyst is compensated by an increase in content of crystalline manganese oxides and the surface concentration of manganese

Local Flexibility of a New Single-Ring Chaperonin Encoded by Bacteriophage AR9 Bacillus subtilis

Chaperonins, a family of molecular chaperones, assist protein folding in all domains of life. They are classified into two groups: bacterial variants and those present in endosymbiotic organelles of eukaryotes belong to group I, while group II includes chaperonins from the cytosol of archaea and eukaryotes. Recently, chaperonins of a prospective new group were discovered in giant bacteriophages; however, structures have been determined for only two of them. Here, using cryo-EM, we resolved a structure of a new chaperonin encoded by gene 228 of phage AR9 B. subtilis. This structure has similarities and differences with members of both groups, as well as with other known phage chaperonins, which further proves their diversity