In this study, the effect of the gibbsite content in bayerite on the properties of the CrO x /Al2O3 catalyst based on a support prepared from this bayerite was investigated. Two bayerites with gibbsite impurities were used for the preparation of granulated supports and CrO x /Al2O3 catalysts. The amounts of Cr in the catalysts were 5.5 +/- 0.5 and 13.1 +/- 0.5 wt %, respectively. Pure gibbsite and pseudoboehmite (binding agent) were used to prepare the reference samples. The gibbsite content in the supports was 20 wt %, 30, 80, and 100 wt %. Thermal analysis, laser diffraction method, 1H MAS NMR, low-temperature nitrogen adsorption-desorption, TPD-NH3, XRD, potentiometric titration of Cr6+, ESR, Raman spectroscopy, and XPS were used to study the initial powders of alumina precursors, Al2O3 supports, and CrO x /Al2O3 catalysts. The catalysts were tested in the isobutane and butane dehydrogenation processes. The gibbsite content in bayerite powder correlates with the content of the chi-Al2O3 phase in the support. The presence of the chi-Al2O3 phase in the support promotes a higher proportion of Cr5+ and a lower proportion of Cr3+ in the Cr2O3 species of catalysts containing 5.5 +/- 0.5 wt % Cr. It further leads to a decrease in the number of active sites and a decrease in the activity in isobutane conversion and isobutene yield while selectivity remains unchanged. As the content of the chi-Al2O3 phase in the support increased, the total Cr6+ content and the water-insoluble Cr6+ content also increased in catalysts containing 13.1 +/- 0.5 wt % Cr. Increasing the chi-Al2O3 content in the support also led to decreased n-butane conversion and butadiene yield.

A new nonredox reaction of petroleum vanadyl porphyrins with sulfur-containing compounds has been identified in heavy oil. The experimental data obtained using in situ EPR spectroscopy revealed that high-temperature treatment of heavy oil results in the reversible conversion of native petroleum vanadyl porphyrins (VPs) to thiovanadyl porphyrin complexes (TVPs) whose fraction can reach more than 25% under certain conditions. The content of TVPs and the extent of reversibility of the VO2+ -><- VS2+ reaction is controlled by sulfur compounds in the reduced form of S2-. Conversely, the presence of dioxygen and water impedes the formation of TVPs, ultimately leading to complete obstruction. This newly revealed reaction pathway demonstrates that VPs are capable of capturing chemically active sulfur compounds in crude oils and petroleum feedstock under conditions similar to those of the conventional refining process. The reversible chemical reaction discovered and identified here has the potential to impede the desulfurization of heavy oil, particularly under reaction conditions in which reduced sulfur species are present or may appear in the treated heavy oil. This reaction can significantly extend the turnover time of reduced sulfur species and prevent deep desulfurization of heavy oil.

The EPR method and vanadyl tetraphenylporphyrin complex (VOTPP) as a spin probe were employed to study the transformation of the γ-Al2O3 surface during temperature treatment. It has been shown that VOTPP complex is stable at least up to a temperature of 450 °C and P_O_2 ≲ 3 Pa. Four distinct forms of vanadyl complex were identified on the γ-Al2O3 surface, depending on the annealing temperature. The intensity ratio between these forms, exhibiting significantly different spin-Hamiltonian parameters, depend on the degree of surface hydration, which in turn determines the ratio between sites with different acidity on the γ-Al2O3 surface. It has been shown that VOTPP complex demonstrate reversible transitions between different adsorption forms on the alumina surface during dehydration/hydration cycles. The observed phenomenon can be explained by the coordination vanadyl spin probe along the axial axis to the surface centers of different polarity/acidity.

The work demonstrates the great potentialof using a vanadyl porphyrinprobe to study resin-paraffin aggregation processes in oils.The dynamics and polarity of the local environment of vanadyl octaethylporphine(VOOEP), used as a spin probe, specially introduced into oil witha high content of paraffins and resins, have been studied. It hasbeen found that VOOEP does not enter into paraffin crystallites evenat temperatures 25 K below the wax appearance temperature but formsaggregates composed of resin molecules that can be adsorbed onto thesurface of paraffins. The proposed approach to the precise simulationof experimental ESR spectra based on the Monte Carlo method in thetemperature range in which partial averaging of anisotropic interactionsis observed showed that as the temperature decreases from 320 to 200K, the fraction of aggregates that capture the spin probe increasesfrom 10 to 80%. It has been found that the incorporation of VOOEPinto the aggregates is accompanied by an increase in the polarityof the local environment of the spin probe, which is consistent withthe proposed mechanism of resin-paraffin aggregation processesin waxy oils.

The work demonstrates the results of the first experimental PFG NMR study in situ of the complex phase behavior of asphaltenes in the presence of high-pressure CO2. To perform the experiments, a series of sealed, thick-walled quartz capillaries were prepared with a mixture of CO2 and asphaltenes dissolved either in chloroform or benzene at different initial concentrations. Then, the temperature dependence of the diffusion coefficients of the asphaltene aggregates was measured for each sample after the mixture reached its equilibrium state, at which, in accordance with the solubility limit, only part of the initial asphaltenes remained dissolved. Despite quite low residual asphaltene concentrations in solution, experimental data clearly demonstrated the presence of aggregated structures (up to 70-80 wt %) attributed solely to nanoaggregates, with no signs of the presence of macroaggregates in the samples. Temperature dependencies of aggregate diffusivity clearly showed that the scenario, according to which the evolution of the asphaltene aggregates will develop, strongly depends on the initial asphaltene concentration, mass fraction of CO2 loaded into the system, and chemical nature of the solvent used. In particular, the most diluted asphaltene solution, expected to be the most resistive to the aggregation processes in a high-pressure CO(2 )environment, revealed the most pronounced aggregation-dependent translational dynamics as compared to those with a moderate initial asphaltene concentration. Contrarily, the concentrated asphaltene solution may not show drastic aggregation processes if the mass fraction of the CO2 loaded will not appear to be so high. Finally, the experimental results provide evidence that the temperature-triggered structural transformation of asphaltene aggregates due to the noncovalent bond breakup is not hindered under high-pressure CO2, but instead becomes more emphasized. The results obtained shed new light on asphaltene aggregate dynamics and brought new knowledge about the fundamental behavior of asphaltene in high-pressure CO2 conditions.

It has been shown for the first time that the high-temperature treatment of heavy oil with a high content of asphaltenes at 350–450 °C without a catalyst or H 2 leads to the formation of new vanadium(IV) porphyrin complexes detected by ESR spectroscopy. In anisotropic spectra of treated oil samples recorded at 130 K, together with the signals of the porphyrin complex of the vanadyl ion, VO 2+ , another component with distinct g and A spin Hamiltonian parameters was observed. A comparative analysis of the resonance parameters of the revealed complexes allowed us to unambiguously identify them as the thiovanadyl (VS 2+ ) porphyrins formed during the thermal treatment. Thus, the formation of thiovanadyl porphyrins from vanadyl porphyrins in asphaltene-containing heavy oils at high-temperature processing has been experimentally proven for the first time.

An original method to study the local environment of vanadyl-containing components of heavy oils based on fine-tuning simulation of their electron spin resonance (ESR) spectra in situ is developed. The approach is backgrounded on precise computation of anisotropic ESR spectra of individual porphyrin complexes in specific solvents modeling a particular local environment of certain polarity using specific g and A tensor components, their dispersion, and linewidth determined by unresolved super-hyperfine interaction with the closest nitrogen. The high level of simulation accuracy allowed us to differentiate the values of the g and A tensor components related to individual vanadyl complexes in different solvents with certain polarity in reference systems and attribute the observed variation to the interaction of the vanadyl complex with surrounding molecules located in its axial direction. The method developed for the model systems is successfully applied to the real oil-based systems where different vanadyl complexes with different local environments are presented, forming the experimentally observed ESR spectrum. The Monte Carlo procedure was suggested to define the relative contribution (weight) of the individual spectra having tiny peculiarities related to vanadyl fragments in different local environments and finally mapping the g and A tensor components distribution which is characteristic for the particular oil-based sample. Extraordinary sensitivity to the localization and interaction with surrounding molecules of vanadyl-containing complexes which are present in heavy oil as a natural spin probe or can be specially introduced give us a unique opportunity to in situ study the local environment of asphaltenes and their intermolecular interactions with other oil components.

A new ring opening reaction was found while attempting to isolate the imines from ortho-heteroatom substituted anilines and camphor-like bicyclic ketones. The benzoazoles containing a cyclopentanemethyl group at position 2 of the heterocycle were isolated instead of the expected imines. The detailed study of the transformation, including EPR experiments, revealed the most probable radical mechanism. The proposed reaction pathways were confirmed by quantum chemical calculations. The dichotomy of 1–2 and 2–3 bonds cleavage is discussed together with the evaluation of the stereochemical outcome of the reactions. The benzoazoles obtained via the new reaction are of particular interest for the medicinal chemistry.

In this work, a series of the chromia/alumina catalysts with the same surface Cr concentration of 4.4 +/- 0.2 at. Cr/ nm(2) and different K loadings (0-3.9 wt.%) has been investigated to evaluate the effect of K on the effective activation energy of isobutane dehydrogenation at 520-550 degrees C. The results of the study show that at K loadings up to 2.0 wt.%, K preferably interacts with alumina and modifies an average dispersion of Cr(3+)Ox species in the reduced catalysts, thus leading to a growth of conversion and selectivity, but the number of direct contacts of K with active sites is too low to affect the effective activation energy of dehydrogenation. When K loading is higher than 2.0 wt.%, the alumina capacity for K is reached and K interacts directly with Cr(3+)Ox species. This causes an enlargement of effective activation energy with K loading. One possible explanation relies on the formation of a new type of active sites in Cr3+-O(H)-K+ with modified energetics of the reaction pathway or even with other reaction pathway. Another explanation is that potassium ions, being in contact with active sites, induce strong chemisorption of water, which poisons active sites, especially at low temperatures of the reaction.

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.

In this work, the effect of surface properties of different alumina supports for CrOx/Al2O3-catalysts on Crspeciation and dehydrogenation activity was studied. For this purpose, a series of CrOx/Al2O3-catalysts with a monolayer coverage of CrOx (ca. 4.4 at. Cr/nm(2)) was prepared with gamma-, delta-, (delta + theta)-, eta-, theta-Al2O3 as supports. Systematic investigation of fresh catalysts with a set of techniques (chemical analysis, N-2 adsorption, XRD, Raman and ESR spectroscopy) showed that (i) chemical state distribution of Cr (Cr6+, Cr5+, Cr3+) was the same for all of the catalysts; (ii) CrOx-species were in X-ray amorphous state; (iii) surface chromate species were virtually of the same oligomerization degree. However, aggregation of Cr3+ ions both in calcined and reduced catalysts is support-dependent. ESR data and infrared spectroscopic results of adsorbed CO showed that increase of Lewis acid sites (LAS) surface density on bare aluminas promotes the growth of the relative amount of Cr3+ ions in a relatively large Cr2O3-like clusters in the fresh catalysts. Catalytic testing in a cycling dehydrogenation-regeneration mode leads to catalyst deactivation. Investigation of spent catalysts revealed that deactivation is accompanied with sintering of Cr3+Ox-species with partial migration of Cr3+ ions inside alumina. It was observed that increase of LAS surface density on aluminas promotes the growth of both the initial dehydrogenation activity and stability upon cycling. On the basis of experimental results, it was concluded that (i) Cr3+ ions on the surface of relatively large Cr2O3-like clusters are more active than isolated and poorly agglomerated Cr3+ ions; (ii) increase in LAS concentration on alumina induces growth of surface coverage by Cr2O3-like clusters with concomitant modification of intrinsic activity of active sites through their interaction with support. (C) 2020 Elsevier Inc. All rights reserved.

The effect of transition alumina (γ‐, η‐, χ‐Al2O3) on the activity and stability of model chromia/alumina catalysts with 4 wt% Cr in isobutane dehydrogenation is studied. It is shown that a fresh catalyst with η‐Al2O3 as a support has the highest activity, while with χ‐Al2O3 has the lowest one. The characterization of the catalysts by N2 adsorption, X‐ray diffraction (XRD), electron spin resonance (ESR) spectroscopy, and X‐ray photoelectron spectroscopy (XPS) is used to describe changes in the catalysts induced by high‐temperature treatment at 800, 1000, and 1200 °C in air. It is shown that sintering of the alumina support and formation of chromia‐alumina solid solutions are the reasons of irreversible decline in the catalytic activity. Cr/γ‐Al2O3 is found to be the most stable to sintering and phase transformation, whereas Cr/χ‐Al2O3 is found to be the least stable. Due to its highest initial activity, the η‐Al2O3‐supported catalyst loses its dehydrogenation activity most rapidly as the calcination temperature is raised. The segregation of sodium impurities is observed in the course of heat treatment, which may be an additional cause of deactivation.

The approach for quantitative estimation of asphaltene sizes in crude oils in situ via precise simulation of electron spin resonance (ESR) spectra of the slowly rotating VO2+-containing fragments was developed. The method is based on the correlation between the size of the paramagnetic particles and their characteristic rotational time that can be determined by ESR in situ while incomplete averaging of anisotropic hyperfine interactions is observed. The precise simulation of the ESR spectra of heavy molecules, labeled naturally with vanadyl ions, allows one to find their size distribution in crude oils. In particular, the Method is demonstrated, to be an effective tool for the quantitative determination- of the asphaltene sizes in different oil fractions in situ:

The potential of physical methods for in situ studies of the phase stability and physicochemical evolution of heavy oils is analyzed. The basic principles of in situ application of the methods are outlined; the scope and limitations of each approach are discussed. Particular attention is paid to the visualization of the asphaltene aggregation process using attenuated total reflection Fourier transform IR spectroscopy and magnetic resonance imaging, as well as small-angle X-ray and neutron scattering, electron spin resonance and electron and optical microscopy. These methods provide complementary information on the properties and behaviour of oil disperse systems on various spatial and temporal scales ranging from the rotational mobility of asphaltene molecules and the dynamics of their local environment with a characteristic time of ∼ 10−10 s and evolution of the size characteristics and shape of asphaltene aggregates to visualization of asphaltene aggregation and formation of precipitates in crude oils and their blends with spatial resolution from a few to thousands of micrometres with a characteristic time from seconds to hundreds of hours. The approaches described can be efficiently applied in a wide range of temperatures and pressures, as well as in the presence of chemicals that affect the stability of heavy oils. The bibliography includes 241 references.

Experimentally, in the range of 300–700 K, the temperature dependences of secondary ion emission (SIE) for iron-nickel alloys with nickel content of 30.2 % and 36 % are studied by secondary ion mass spectrometry. The observable changes in SIE for iron and nickel ions in the neighborhood of the Curie point are due to magnetic transition, which we hold to be a first-order phase transition. The influence of carbon contained in the alloys manifests itself in the form of SIE peaks at 530–630 K.

A comparison of the behavior of asphaltene molecules extracted from crude oil and dissolved in aromatic solvent as a model system with the behavior of vanadium-containing molecules in real crude oils via electron spin resonance in situ technique showed that the changes of rotational mobility of asphaltene molecules can be related to the changes of the local viscosity and environment of the asphaltenes as well as the characteristic sizes of vanadyl-containing fragments because of aggregation/disaggregation processes in crude oils. The information about the mobility of asphaltene molecules in different local environments at different temperatures and pressures is an important step in understanding both the aggregation of the asphaltenes and crude oil fouling processes in addition to the conditions required for the deposits to be formed.

The electron nuclear dipolar interactions responsible for some dynamic nuclear polarization (DNP) mechanisms also are responsible for the presence formally in CW EPR spectra of forbidden satellite lines in which both the electron spin and a nuclear spin flip. Such lines arising from 1H nuclei are easily resolved in CW EPR measurements of trityl radicals, a popular family of DNP reagents. The satellite lines overlap some of the hyperfine features from 13C in natural abundance in the trityl radical, but their intensity can be easily determined by simple simulations of the EPR spectra using the hyperfine parameters of the trityl radical. Isotopic substitution of 2H for 1H among the hydrogens of the trityl radical and/or the solvent allows the dipolar interactions from the 1H on the trityl radical and from the solvent to be determined. The intensity of the dipolar interactions, integrated over all the 1H in the system, is characterized by the traditional parameter called reff. For the so-called Finland trityl in methanol, the reff values indicate that collectively the 1H in the unlabeled solvent have a stronger integrated dipolar interaction with the unpaired electron spin of the Finland trityl than do the 1H in the radical and consequently will be a more important DNP route. Although reff has the dimensions of distance, it does not correspond to any simple physical dimension in the trityl radical because the details of the unpaired electron spin distribution and the hydrogen distribution are important in the case of trityls.

Temperature variations of the EPR spectra of VO2+ ions in sub- and supercritical water under isothermal and temperature gradient conditions are investigated using an in situ EPR. Broadening of the hyperfine structure at increasing temperature and the appearance of an unresolved broad low-intensity line (ΔH pp ≈ 300 Oe) in the supercritical state are observed in the absence of temperature gradients, indicating an increase of exchange interaction between VO2+ ions in supercritical water. An exchange-narrowed anisotropic absorption line is observed under the temperature-gradient conditions in the subcritical water near the transition to a supercritical state. The shape of this line is close to that observed in the solid salt VOSO4 · 3H2O. It is shown that in situ EPR allows us to investigate the effects of changing the local environment of paramagnetic ions, which precedes the well-known process of clustering and formation of amorphous oxide particles in sub- and supercritical conditions.

We have experimentally studied optical and magneto-optical spectra of solutions of crude oils of different origin and their heavy fractions in the visible spectral range. Magnetic circular dichroism of oil in the wavelength range ∼550 nm has been revealed. We show that the shape of the spectra of this dichroism depends on the origin of crude oil, with the magnetic dichroism magnitude being proportional to the concentration of the oil in the solution. A comparison of the data of magneto-optical spectroscopy with electron paramagnetic resonance spectra and chemical composition of samples has allowed us to conclude that the observed magneto-optical activity is determined by the occurrence of VO 2+ complexes in the oil samples. The revealed magneto-optical activity of crude oil can form the basis of a unique method of analysis of the composition and properties of oils of different origin and heavy fractions thereof.