RESUMO
Lateral (adsorbate-adsorbate) interactions between adsorbed molecules affect various physical and chemical properties of microporous adsorbents and catalysts, influencing their functional properties. In this work, we studied the hydration of microporous AlPO4-11 aluminophosphate, which has an unusually ordered structure upon adsorption of water vapor, and according to 27Al NMR data, only tetrahedrally or octahedrally coordinated Al sites are present in the AlPO4-11. These 27Al NMR data are consistent with the results of density functional theory (DFT) calculations of hydrated AlPO4-11, which revealed the presence of a strong repulsive lateral interaction at the initial stage of adsorption, suppressing the adsorption of water on neighboring (separated by one -O-P-O- bridge) Al crystallographic sites. As a result, of all the different aluminum sites, only half of the Al1 sites adsorb two water molecules and acquire octahedral coordination.
RESUMO
Investigating the size distributions of Co nanoparticle ensembles is an important problem, which has no straightforward solution. In this work, we use the combination of 59Co internal field nuclear magnetic resonance (59Co IF NMR) and ferromagnetic resonance (FMR) spectroscopies on a metallic Co nanoparticle sample with a narrow Co nanoparticle size distribution due to encapsulation within the inner channels of carbon nanotubes. High-resolution transmission electron microscopy (TEM) images showed that the nanoparticles can be represented as prolate spheroids, with the majority of particles having an aspect ratio between 1 and 2. This observation has increased the accuracy of superparamagnetic blocking size calculations from Néel relaxation model by introducing the actual volume of the ellipsoids taken from the image processing. 59Co IF NMR and FMR experiments conducted under different temperatures allowed us to observe the thermal blocking of superparamagnetic particles in full accordance with the TEM particle volume distribution. This proved that these magnetic resonance techniques can be used jointly for characterization of Co nanoparticles in the bulk of the sample.
RESUMO
Enhanced activity in low-temperature water-gas shift (LT-WGS) reaction of some ceramometal catalysts compared to conventional Cu-Zn-Al oxide catalyst was demonstrated. Porous ceramometals were synthesized from powdered CuAl alloys prepared by mechanical alloying with the addition of either CuAlexp powders produced by current spark explosion of Cu+Al wires or CuZnAl oxide obtained by coprecipitation. Their structural, microstructural, and textural characteristics were examined by means of X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectrometry, NMR, and adsorption methods, and catalytic properties were studied in the LT-WGS reaction. CuAlO/CuAl ceramometals were found to have mostly the egg-shell microstructure with the metallic cores (Al x Cu1-x , Al2Cu, and Al4Cu9) and the oxide shell containing copper oxides and/or mixed oxides of copper and aluminum and, at same time, CuAlO/CuAl ceramometal with incorporated additives was found to create a more complicated microstructure. A large amount of X-ray amorphous oxides of copper and aluminum is typical for all composites. CuAl ceramometal was shown to be more active than the CuZnAl oxide catalyst in spite of a much lower specific surface area. The CuAl+CuZnAl catalyst consisting of prismatic granules showed a higher activity in comparison with CuZnAl oxide consisting of cylindrical granules. The activity of the composite granulated catalyst referred to its unit weight was more than 6-fold higher as compared to the oxide catalyst, while the activity per the surface area was found to be more than an order of magnitude higher due to much higher specific activity of small fraction and additively much lower diffusion limitation of granules.