Abstract
A series of mixed Mn-Zr oxides with different molar ratios Mn/Zr (0.1-9) have been prepared by coprecipitation of manganese and zirconium nitrates and characterized by X-ray diffraction (XRD) and BET methods. It has been found that at concentrations of Mn below 30 at%, the samples are single-phase solid solutions (MnxZr1-xO2-δ) based on a ZrO2 structure. X-ray photoelectron spectroscopy (XPS) measurements showed that manganese in these solutions exists mainly in the Mn(4+) state on the surface. An increase in Mn content mostly leads to an increase in the number of Mn cations in the structure of solid solutions; however, a part of the manganese cations form Mn2O3 and Mn3O4 in the crystalline and amorphous states. The reduction of these oxides with hydrogen was studied by a temperature-programmed reduction technique, in situ XRD, and near ambient pressure XPS in the temperature range from 100 to 650 °C. It was shown that the reduction of the solid solutions MnxZr1-xO2-δ proceeds via two stages. During the first stage, at temperatures between 100 and 500 °C, the Mn cations incorporated into the solid solutions MnxZr1-xO2-δ undergo partial reduction. During the second stage, at temperatures between 500 and 700 °C, Mn cations segregate on the surface of the solid solution. In the samples with more than 30 at% Mn, the reduction of manganese oxides was observed: Mn2O3 → Mn3O4 → MnO.
Highlights
Materials based on zirconium dioxide (ZrO2) demonstrate unique properties and find wide applications in various industrial fields
The results of the study of freshly synthesized samples indicate that the concentration of Mn in the samples xMn(1 − x)Zr significantly affects their phase composition, unit cell parameters of the solid solution and the size of the coherently scattering domain (CSD)
At x = 0, the sample xMn(1 − x)Zr is ZrO2 with the lattice parameter of 5.115 Å. This modification of ZrO2 cannot be considered strictly cubic, its lattice parameter was calculated in the cubic approximation because of the low calcination temperature (650 °C) and because of the small size of the obtained particles that led to the broadening of diffraction peaks
Summary
Materials based on zirconium dioxide (ZrO2) demonstrate unique properties and find wide applications in various industrial fields. Their high durability, corrosion resistance, and low thermal conductivity allow the application of ZrO2 in the production of coatings for various toolware.[1,2] The high stability and ionic conductivity of ZrO2-based materials allow their use as electrochemical oxygen sensors, solid electrolytes in fuel cells, etc.[3,4,5] In heterogeneous catalysis, ZrO2 is widely used as a support with high thermal resistance.[6,7,8] solid solutions based on ZrO2 exhibit high catalytic activity in a number of practically important reactions. Recently it has been shown that Mn–Zn mixed oxides can effectively catalyze the gas-phase oxidation of hydrocarbons or chlorocarbons.[9,10,11] there is agreement that the catalytic performance of these catalysts is determined by their redox properties, the exact mechanism of these
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.