Soot Combustion over Niobium-Doped Cryptomelane (K-OMS-2) Nanorods—Redox State of Manganese and the Lattice Strain Control the Catalysts Performance

A series of Nb-doped (0–23 wt%) cryptomelane catalyst (Nb-K-OMS-2) was synthesized and thoroughly characterized by XRD, TEM/EDX, XRF, XPS, XAS, UV-Vis, and Raman techniques corroborated by the work function measurements. The obtained catalysts were tested for soot oxidation (Printex U) in model tight and loose contact modes. It was shown that the catalytic properties of the Nb-K-OMS-2 are controlled by the amount of Nb dopant in a strongly non-monotonous way. The introduction of niobium gives rise to the strain in the cryptomelane lattice, accompanied by significant Mn+3/Mn+4 ratio variations and concomitant work function changes. The isotopic exchange experiments revealed that the catalytic activity of the Nb-OMS-2 catalysts in soot combustion proceeds via the pathways, where both the activated suprafacial 18O and the surface 16O2− species participate together in the reaction. The niobium doping level controls the non-monotonous changes of the catalyst work function and the lattice strain, and variations of these parameters correlate well with the observed deSoot activity. To our best knowledge, the role of the lattice strain of the cryptomelane catalysts was documented for the first time in this study.

Designable Phase Transition Temperature of VO2 Co-Doped with Nb and W Elements for Smart Window Application

Monoclinic vanadium dioxide (VO2 (M)) particles co-doped with niobium and tungsten, with potential application in smart windows, were synthesized by hydrolysis and subsequent thermal decomposition of vanadyl sulfate. All the doped VO2 particles exhibited a monoclinic crystalline phase and the critical phase transition temperature (Tc) of VO2 (M) was adjusted by Nb and W co-doping. The Tc of Nb-doped VO2 (M) decreased at a rate of approximately 10 °C/at% Nb dopant, and the transition temperature could also be accurately controlled to room temperature (about 27 °C) by co-doping with Nb and W. A film prepared using co-doped VO2 (M) particles showed a solar modulation ability of ~18% and a luminous transmittance of 40%, indicating that the co-doped VO2 (M) particles represent suitable candidates for smart window applications.

Influence of Niobium Dopant on the Corrosion Resistance of a-C:N and a-C:N:H Coatings

Amorphous carbonitride coatings (a-C:N and a-C:N:H) with dopant of niobium (Nb) were deposited on substrates of JIS SKH51 high speed steel (HSS) by a four-target close-field unbalance magnetron sputtering system. Subsequently, they were characterized by GDOS, XRD and XPS, and their corrosion resistance was comparatively evaluated. An electro-chemical tester was used to evaluate the corrosive behavior. An SEM was used to examine the test surface. The results revealed that the Nb dopant provided improvements in the corrosive performance to both the a-C:N and a-C:N:H coatings.