Annealing-Induced Structural Behavior of Mn Dopant Ions in Calcium Orthovanadate Ca3(VO4)2Single Crystals

The crystal and local structures of Czochralski-grown calcium orthovanadate (Ca3(VO4)2) single crystals doped with over-stoichiometric 0.05 wt % Mn2O3 (CVO:0.05Mn) and annealed under different conditions are studied by single-crystal conventional and synchrotron X-ray diffraction, X-ray absorption spectroscopy, and electron paramagnetic resonance for the first time. Bottom (annealing in air) and top (annealing in air and in vacuum) parts of the CVO:0.05Mn crystal differ in the manganese content (higher in the bottom part), formal charge (Mn4+ and Mn(3+)+, respectively), and color (orange bottom part; light orange and yellow top parts annealed in air and vacuum, respectively). Manganese ions are located in one (Ca3, distorted two-capped trigonal prism) of five crystallographic Ca sites and have octahedral coordination, which is consistent with crystal-chemical properties of transition-metal ions. The presence of vacancies in one of three V sites is revealed. Formal charge 5+ for vanadium ions is confirmed by X-ray photoelectron spectroscopy. Different colors of CVO:Mn crystals and different formal charges of manganese are explained depending on the growth and post-growth treatment conditions. © 2022 American Chemical Society

Acid Properties of Cesium-Nickel-Zirconium Complex Phosphates: Effect on Isobutanol Dehydration

Abstract: The physicochemical and catalytic properties of Cs1 – 2xNixZr2(PO4)3 (x = 0, 0.15, 0.25, 0.50) systems are studied. Double and triple nickel-containing phosphates with the NASICON structure are obtained by the sol–gel method. It is shown that these phosphates are active and stable isobutanol dehydration catalysts. The relationship between the catalytic activity in the dehydration reaction over triple cesium-zirconium phosphates and their crystallographic characteristics and surface acidity is established. It is shown that upon partial or complete replacement of cesium ions with nickel ions an increase in dehydration activity correlates with an increase in the number of acid sites determined by the pyridine adsorption titration method. © 2020, Pleiades Publishing, Ltd

Crystallochemical design of metal–organic polymer CuBTC and activated carbon composite

Metal–organic polymer CuBTC and composite with CuBTC and activated carbon (CuBTC/C) were prepared by hydrothermal method (BTC3− is a linker 1,3,5-benzenetricarboxylate ion, hydrolysis temperature 130 °C, ethanol + H2O in equal proportion as a solvent) and detailed characterized by a set of methods (X-ray diffraction—XRD, X-ray absorption spectroscopy—XAS, differential scanning calorimetry—DSC, scanning electron microscopy—SEM, low-temperature sorption capacity of samples to nitrogen—BET, X-ray photoelectron spectroscopy—XPS, FTIR-spectroscopy). According to XRD and XAS data, it was found that the composition of main phase CuBTC is [Cu3BTC2(H2O)3] × (nH2O + mC2H5OH) in both samples. The catalytic properties of CuBTC and CuBTC/C samples in the reaction of ethanol dehydrogenation were studied for the first time and the selectivity to acetaldehyde (AcH) was 100% in both cases. It was shown that on the CuBTC/C catalysis, the AcH yield is two times higher than on the CuBTC sample in the reaction of ethanol (Lewis base) dehydrogenation to acetaldehyde. This fact can be explained by the higher content of main phase CuBTC in composite CuBTC/C (~ 97.5 wt%) and the Cu2+ ions (Lewis acid sites) in bulk, the higher water and Cu2+ ions content on the particle surface in CuBTC/C (DSC, FTIR, XPS), the larger pore radii in CuBTC framework of the composite CuBTC/C (according to crystallochemical calculations) and the larger hydrogenation degree of CuBTC/C (XRD, DSC, FTIR) and the smaller specific surface area of CuBTC/C (SBET = 44.4 m2/g for CuBTC/C sample and SBET = 551.3 m2/g for CuBTC). It was found that in the reaction of propane conversion to ethylene C2H4 and methane CH4, the conversion degree on the samples CuBTC and CuBTC/C was the same from 100 °C up to 340 °C, which is caused by the absence of the Bronsted acid sites on the samples with CuBTC. Graphical abstract: [Figure not available: see fulltext.]. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature