Andrey S. Andreev

Understanding silicate hydration from quantitative analyses of hydrating tricalcium silicates

Silicate hydration is prevalent in natural and technological processes, such as, mineral weathering, glass alteration, zeolite syntheses and cement hydration. Tricalcium silicate (Ca3SiO5), the main constituent of Portland cement, is amongst the most reactive silicates in water. Despite its widespread industrial use, the reaction of Ca3SiO5 with water to form calcium-silicate-hydrates (C-S-H) still hosts many open questions. Here, we show that solid-state nuclear magnetic resonance measurements of 29Si-enriched triclinic Ca3SiO5 enable the quantitative monitoring of the hydration process in terms of transient local molecular composition, extent of silicate hydration and polymerization. This provides insights on the relative influence of surface hydroxylation and hydrate precipitation on the hydration rate. When the rate drops, the amount of hydroxylated Ca3SiO5 decreases, thus demonstrating the partial passivation of the surface during the deceleration stage. Moreover, the relative quantities of monomers, dimers, pentamers and octamers in the C-S-H structure are measured.

EFfect of alumina modification on the structure of cobalt-containing Fischer-Tropsch synthesis catalysts according to internal-field 59Co NMR data

An internal-field 59Co NMR study of cobalt-containing Fischer-Tropsch synthesis catalysts supported on different alumina modifications was reported. The Co/δ-Al2O3 sample was shown to contain single-domain fcc packing and stacking faults, whereas Co/γ-Al2O3 gave signals from the fcc domain walls, hcp and stacking faults, thus indicating differences in the particle size of the studied samples. T2 relaxation times were measured; their distribution in a spectrum is non-uniform, which allows signals to be distinguished by their relaxation times. Quantitative measurements of the relative atoms content in different packings revealed that the catalysts have mostly a defect structure. A brief historical background was presented to characterize the internal-field 59Co NMR technique, the related problems, and different approaches to acquired data interpretation.

Design of Al2O3/CoAlO/CoAl Porous Ceramometal for Multiple Applications as Catalytic Supports

Porous ceramometal Al2O3/CoAlO/CoAl was studied by set of physicochemical techniques such as XRD, SEM, internal field 59Co and 27Al MAS NMR, and porosity measurements. They revealed the cermet containing three parts. First, cobalt-free large porous alumina particles which surrounded by the second oxide part representing spinel CoxAl3-xO4 (x=1,2,3) oxides. And third, oxygen-free metallic part consists of cobalt metal particles covered by Co-Al oxide protecting the metallic part from oxidation. Porosity measurements ascertained high porosity (60%) and good SSA (122 m2/g). Also the enhanced adsorption of microwaves due to metallic particles randomly distributed in oxides was found.

Effect of precursor on the catalytic properties of Ni2P/SiO2 in methyl palmitate hydrodeoxygenation

The effect of phosphorus precursor on the physicochemical and catalytic properties of silica-supported nickel phosphide catalysts in the hydrodeoxygenation (HDO) of aliphatic model compound methyl palmitate (C15H31COOCH3) has been considered. Nickel acetate (Ni(OAc)2) and diammonium hydrogen phosphate ((NH4)2HPO4) (phosphate precursor) or nickel hydroxide (Ni(OH)2) and phosphorous acid (H3PO3) (phosphite precursor) have been used for the catalyst preparation by incipient wetness impregnation of SiO2 with an aqueous solution of the precursors, followed by temperature-programmed reduction in hydrogen flow. Chemical analysis (ICP-AES), H2-TPR, NH3-TPD, 31P MAS NMR, XRD, and TEM have been employed for the characterization of the catalysts. The optimal reduction parameters of the silica-supported nickel phosphide catalysts have been found for the phosphate and phosphite precursors in terms of their activity in methyl palmitate HDO. The Ni2P/SiO2 catalysts prepared by the phosphite method have shown higher catalytic activity in comparison with the Ni2P/SiO2 catalysts prepared by the phosphate method. The activity has been shown to depend on the catalyst handling after reduction: in situ reduced catalysts demonstrate higher conversion of methyl palmitate than the samples exposed to the reduction, passivation and re-reduction steps.

Surface Hydroxyl OH Defects of η-Al2O3 and χ-Al2O3 by Solid State NMR, XRD, and DFT Calculations

Abstract For the first time, the detailed structure of χ-Al2O3 and η-Al2O3 surface has been established by implementing the NMR crystallography approach. The surface of η-Al2O3 has been demonstrated to be formed primarily by the (111) facets, while the χ-Al2O3 surface is a combination of (111) and (110) facets. This observation supports the block model of aluminum oxides previously proposed by Tsybulya and Kryukova [S. V. Tsybulya, G. N. Kryukova, Phys. Rev. B 77 (2008) 024112.]. The additional terminal OH groups, observed experimentally and not contributing to (111) and (110) theoretical calculations, are considered to be bonded to the tetrahedral aluminum sites. Their origin is related to the junctions of crystallographic faces of spinel building blocks, being a part of discussed model. Higher content of these terminal OH groups in χ-Al2O3 is a result of more junctions in the case of its more mosaic structure compared to η-Al2O3.

Design of micro-shell Cu–Al porous ceramometals as catalysts for the water–gas shift reaction

XRD, NMR, SEM with mapping, and XPS were used to examine the structure and microstructure of porous ceramometals, CuAlO/CuAl, synthesized by mechanochemical alloying of a mixture of Cu + Al (Cu : Al = 87 : 13 wt%) followed by hydrothermal treatment and heat treatment in air. The egg-shell nature of the microstructure was revealed: the metallic cores consisting of copper and aluminum alloys are surrounded by the oxide matrix containing copper oxides and X-ray amorphous mixed oxides of copper and aluminum. Catalytic activity of ceramometals in the water–gas shift reaction (WGSR) estimated for their fine fractions at 240 °C and expressed as efficient first-order rate constants is lower than that of a CuZnAl oxide catalyst due to the lower (approximately by an order of magnitude) specific surface area of the ceramometals. The specific activity of ceramometals expressed as the specific rate constant related to the unit surface area of metallic copper exceeds that for the CuZnAl oxide catalyst and correlates with the content of crystallized intermetallics. Mechanical, textural and thermophysical properties of ceramometals were assessed. The presence of ultramacropores with sizes up to tens of microns was shown to be typical for ceramometals. As a result, the activity of granulated ceramometal catalysts in the WGSR, due to a high diffusion permeability, is comparable with that of granulated CuZnAl oxide. A mild leaching substantially increases the activity of cermet granules.