Properties of chromatographic columns prepared on the basis of poly(1-trimethylsilyl-1-propyne) modified with organic bases

This article describes the effect of modification with organic bases such as uracil (U) and polyethyleneimine (PEI) on the adsorption and chromatographic properties of poly(1-trimethylsilyl-1-propyne) (PTMSP) used as a stationary phase (SP) in packed and capillary columns. It was shown that the sorbents prepared on the basis of diatomite Chromosorb P NAW support and successively modified with 9 wt.% PTMSP and 1 wt.% U (or PEI) (PC-U and PC-PEI samples, respectively), have a mesoporous structure. The IR spectrum shows the presence of carbonyl groups in the sorbent modified with uracil. The impregnation of the Chromosorb P NAW + (9/1) wt.% PTMSP sorbent with a polyethyleneimine solution leads to the appearance in the spectrum of bands characterizing NH stretching and bending vibrations, as well as a band at 1310 cm-1 which can be attributed to CN bond vibrations. The chromatographic properties of the studied sorbents differ significantly from the properties of the initial PTMSP. Packed columns PC-U and PC-PEI, as well as capillary columns with a polyethyleneimine-modified PTMSP layer, allow one to selectively separate mixtures of polar and non-polar compounds and structural isomers of hydrocarbons. Methanol on these columns is eluted in the form of a symmetrical peak separately from propane, propylene and other associated hydrocarbon impurities in commercial (technical, target) n-butane.

Heterogeneous H2O2-based selective oxidations over zirconium tungstate α-ZrW2O8

Catalytic properties of a crystalline zirconium tungstate, ZrW2O8, the material known mainly for its isotropic negative coefficient of thermal expansion, have been assessed for the liquid-phase selective oxidation of a range of organic substrates comprising CC, OH, S and other functional groups using aqueous hydrogen peroxide as the green oxidant. Samples of ZrW2O8 were prepared by hydrothermal synthesis and characterised by N2 adsorption, PXRD, SEM, EDX, FTIR and Raman spectroscopic techniques. Studies by IR spectroscopy of adsorbed probe molecules (CO and CDCl3) revealed the presence of Brønsted acidic and basic sites on the surface of ZrW2O8. It was demonstrated that ZrW2O8 is able to activate H2O2 under mild conditions and accomplish the epoxidation of CC bonds in alkenes and unsaturated ketones, oxidation of thioethers to sulfoxides and sulfones, along with the oxidation of alcoholic functions to produce ketones and aldehydes. The oxidation of tetramethylethylene and α-terpinene over ZrW2O8 revealed the formation of peroxidation products, 2,3-dimethyl-3-butene-2-hydroperoxide and endoperoxide ascaridole, respectively, indicating the involvement of singlet oxygen in the oxidation process. The ZrW2O8 catalyst preserves its structure and morphology under the turnover conditions and does not suffer from metal leaching. It can be easily recovered, regenerated by calcination, and reused without the loss of activity and selectivity.

State of Formic Acid Dissolved in Tar According to Infrared Spectroscopy

Formic acid is considered as a promising hydrogen carrier and can be used as a source of hydrogen in the processing of heavy oil fractions such as tar. The interaction of formic acid with tar was studied by infrared Fourier transform spectroscopy via special technique using a mirror substrate. The infrared (IR) spectra were interpreted considering density functional theory (DFT) calculations. It was shown that formic acid dissolved in tar in three forms, as dimers, monomers of cis- and trans-configurations, hydrogen-bonded to the aromatic rings of the tar compounds, and as free-rotating gas molecules (microbubbles in the tar bulk). The research performed provides an opportunity and methodological base for studying the process of tar conversion in the presence of formic acid into gasoline fractions at temperatures up to 300 ^oC.

New DRIFT spectroscopic methodology for acquiring infrared spectra of fiberglass materials

We report a new approach for infrared spectroscopic analysis of fiberglass materials using a mirror substrate, which allowed the specular reflection from the sample surface to be minimized and detect the light passing through the sample. The application of this technique for platinum-containing fiberglass catalysts made it possible for the first time to identify sulfate compounds formed in glass fibers during the oxidation reaction of sulfur dioxide. The developed technique can be applied for a number of research samples that are difficult to analyze by conventional IR spectroscopic methods.

Catalytic Performance of Zr-Based Metal-Organic Frameworks Zr-abtc and MIP-200 in Selective Oxidations with H2 O2

The catalytic performance of Zr-abtc and MIP-200 metal-organic frameworks consisting of 8-connected Zr₆ clusters and tetratopic linkers was investigated in H₂ O₂ -based selective oxidations and compared with that of 12-coordinated UiO-66 and UiO-67. Zr-abtc demonstrated advantages in both substrate conversion and product selectivity for epoxidation of electron-deficient C=C bonds in α,β-unsaturated ketones. The significant predominance of 1,2-epoxide in carvone epoxidation, coupled with high sulfone selectivity in thioether oxidation, points to a nucleophilic oxidation mechanism over Zr-abtc. The superior catalytic performance in the epoxidation of unsaturated ketones correlates with a larger amount of weak basic sites in Zr-abtc. Electrophilic activation of H₂ O₂ can also be realized, as evidenced by the high activity of Zr-abtc in epoxidation of the electron-rich C=C bond in caryophyllene. XRD and FTIR studies confirmed the retention of the Zr-abtc structure after the catalysis. The low activity of MIP-200 in H₂ O₂ -based oxidations is most likely related to its specific hydrophilicity, which disfavors adsorption of organic substrates and H₂ O₂ .

New Insight into Titanium-Magnesium Ziegler-Natta Catalysts Using Photoluminescence Spectroscopy

This paper presents the results of study of titanium-magnesium catalysts often used in polymerization processes, by photoluminescence spectroscopy (PL) in combination with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The interaction of dibutyl phthalate (DBP) with MgCl₂ was studied at DBP_added/Mg = 0-1 (mol/mol). The luminescence spectra with excitation at 278 nm and the excitation spectra for main emission bands were recorded. It was shown that DBP adsorbed on magnesium chloride, both in the form of donor-acceptor complexes (D⁺A^-) and in the form of molecular complexes. At DBP_added/Mg <0.15, the formation of D⁺A^- complexes occur predominantly; with an increase in DBP_added/Mg, the fraction of molecular complexes increases. Molecular complexes are destroyed during the treatment of the support by TiCl₄. In this case, the structure of magnesium chloride is disordered and new coordination-unsaturated sites are formed. This work is a first attempt to apply PL spectroscopy in combination with DRIFTS spectroscopy to study titanium-magnesium Ziegler-Natta catalysts. The application of PL spectroscopy to such systems made it possible to detect interactions within and between donor molecules, which would be particularly challenging to achieve using other spectroscopic methods. Both spectroscopic methods provided crucial information about the existence of two types of complexes on the sample surface which is important for tuning the synthesis procedure of the titanium-magnesium catalysts for olefin polymerization.

Ni-loaded nanocrystalline ceria-zirconia solid solutions prepared via modified Pechini route as stable to coking catalysts of CH4 dry reforming

Mixed nanocrystalline Ce-Zr-O oxides (Ce/Zr = 1 or 7/3) were prepared by modified Pechini route using ethylene glycol solutions of metal salts. Detailed characterization of their real structure and surface properties by X-ray diffraction on synchrotron radiation with the full-profile Rietveld analysis, high resolution electron microscopy with elemental analysis, Raman spectroscopy, UV-Vis and X-ray photoelectron spectroscopy revealed a high homogeneity of cations distribution in nanodomains resulting in stabilization of disordered cubic phase. This provides a high dispersion of NiO loaded on these mixed oxides by wet impregnation, a high reactivity and mobility of oxygen in these catalysts and strong interaction of Ni with support in the reduced state. This helps to achieve a high activity and coking stability of developed catalysts in CH4 dry reforming in feeds with CH4 concentration up to 15% and CH4/CO2 ratio =1.