Approaches to the design of efficient and stable catalysts for biofuel reforming into syngas: doping the mesoporous MgAl2O4 support with transition metal cations.

The mesoporous MgAl2O4 support is promising for the design of efficient and stable to coking catalysts for natural gas and biofuel reforming into syngas. This work aims at doping this support with transition metal cations (Fe, Cr, Ti) to prevent the incorporation of Ni and rare-earth cations (Pr, Ce, Zr), loaded by impregnation, into its lattice along with providing additional sites for CO2 activation required to prevent coking. Doped MgAl1.9Me0.1O4 (Me = Fe, Ti, Cr) mesoporous supports prepared by the one-pot evaporation-induced self-assembly method with Pluronic P123 triblock copolymers were single-phase spinels. Their specific surface area varies in the range of 115-200 m2 g-1, decreasing to 90-110 m2 g-1 after successive addition of the supporting nanocomposite active component 10 wt% Pr0.3Ce0.35Zr0.35O2 + (5 wt% Ni + 1% Ru) by impregnation. Mössbauer spectroscopy for iron-doped spinels confirmed the spatially uniform distribution of Fe3+ cations in the lattice without clustering being mainly located at the octahedral positions. Fourier-transform infrared spectroscopy of the adsorbed CO molecules was performed to estimate the surface density of metal sites. In methane dry reforming, the positive effect of MgAl2O4 support doping was observed from both a higher turn-over frequency as compared with the catalyst on the undoped support as well as the highest efficient first-order rate constant for the Cr-doped catalyst as compared with published data for a variety of Ni-containing catalysts based on the alumina support. In the reaction of ethanol steam reforming, the efficiency of catalysts on the doped supports is comparable, while exceeding that of Ni-containing supported catalysts reported in the literature. Coking stability was provided by a high oxygen mobility in the surface layers estimated by the oxygen isotope heteroexchange with C18O2. A high efficiency and coking stability were demonstrated in the reactions of methane dry reforming and ethanol dry and steam reforming in concentrated feeds for the honeycomb catalyst with a nanocomposite active component on the Fe-doped MgAl2O4 support loaded on the FeCrAl-alloy foil substrate.

Nucleophilic versus Electrophilic Activation of Hydrogen Peroxide over Zr-Based Metal-Organic Frameworks.

Zr-based metal-organic frameworks (Zr-MOF) UiO-66 and UiO-67 catalyze thioether oxidation in nonprotic solvents with unprecedentedly high selectivity toward corresponding sulfones (96-99% at ca. 50% sulfide conversion with only 1 equiv of H2O2). The reaction mechanism has been investigated using test substrates, kinetic, adsorption, isotopic (18O) labeling, and spectroscopic tools. The following facts point out a nucleophilic character of the peroxo species responsible for the superior formation of sulfones: (1) nucleophilic parameter XNu = 0.92 in the oxidation of thianthrene 5-oxide and its decrease upon addition of acid; (2) sulfone to sulfoxide ratio of 24 in the competitive oxidation of methyl phenyl sulfoxide and p-Br-methyl phenyl sulfide; (3) significantly lower initial rates of methyl phenyl sulfide oxidation relative to methyl phenyl sulfoxide (kS/kSO = 0.05); and (4) positive slope ρ = +0.42 of the Hammett plot for competitive oxidation of p-substituted aryl methyl sulfoxides. Nucleophilic activation of H2O2 on Zr-MOF is also manifested by their capability of catalyzing epoxidation of electron-deficient C═C bonds in α,ß-unsaturated ketones accompanied by oxidation of acetonitrile solvent. Kinetic modeling on methyl phenyl sulfoxide oxidation coupled with adsorption studies supports a mechanism that involves the interaction of H2O2 with Zr sites with the formation of a nucleophilic oxidizing species and release of water followed by oxygen atom transfer from the nucleophilic oxidant to sulfoxide that competes with water for Zr sites. The nucleophilic peroxo species coexists with an electrophilic one, ZrOOH, capable of oxygen atom transfer to nucleophilic sulfides. The predominance of nucleophilic activation of H2O2 over electrophilic one is, most likely, ensured by the presence of weak basic sites in Zr-MOFs identified by FTIR spectroscopy of adsorbed CDCl3 and quantified by adsorption of isobutyric acid.

The properties of capillary columns with sorbents based on poly-(1-trimethylsilyl-1-propyne) modified with nitrous oxide.

In this work, we report the study of properties of capillary columns with a porous layer of the functionalized polymer prepared via oxidation of poly-(1-trimethylsilyl-1-propyne) (PTMSP) by nitrous oxide. It was shown that the double CC bonds of polymer reacted with nitrous oxide with formation of ketone, carbonyl and hydroxyl groups. The increase in number of those groups in polymer changed a polarity of PTMSP. The change in polarity of polymer led to the selectivity of separations, including oxygen-containing substances. The polarity values were calculated for the prepared columns. It was shown that the total polarity according to McReynolds (ΔI) was lower than that for known porous polymers. The examples of separations of aliphatic and aromatic hydrocarbons, oxygen- and halogen-containing substances were presented.